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Title: The Philosophy of the Weather
And a Guide to Its Changes
Author: Thomas Belden Butler
Release Date: August 14, 2010 [EBook #33429]
Language: English
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THE PHILOSOPHY OF THE WEATHER.
AND A GUIDE TO ITS CHANGES.
BY T. B. BUTLER.
NEW YORK:
D. APPLETON & COMPANY,
NOS. 346 & 348 BROADWAY.
1856.
Entered according to Act of Congress, in the year 1856, by
T. B. BUTLER,
In the Clerks Office of the District Court of the District of
Connecticut.
ELECTROTYPED BY
THOMAS B. SMITH,
82 & 84 Beekman Street.
PRINTED BY
J. F. TROW,
379 Broadway.
INTRODUCTION.
The atmospheric conditions and phenomena which constitute "The Weather"
are of surpassing interest. Now, we rejoice in the genial air and warm
rains of spring, which clothe the earth with verdure; in the alternating
heat and showers of summer, which insure the bountiful harvest; in the
milder, ripening sunshine of autumn; or the mantle of snow and the
invigorating air of a moderate winter's-day. Now, again, we suffer from
drenching rains and, devastating floods, or excessive and debilitating
heat and parching drought, or sudden and unseasonable frost, or extreme
cold. And now, death and destruction come upon us or our property, at any
season, in the gale, the hurricane, or the tornado; or a succession of
sudden or peculiar changes blight our expected crops, and plant in our
systems the seeds of epidemic disease and death. These, and other normal
conditions, and varied changes, and violent extremes, potent for good or
evil, are continually alternating above and around us. They affect our
health and personal comfort, and, through those with whom we are
connected, our social and domestic enjoyments. They influence our business
prosperity directly, or indirectly, through our near or remote dependence
upon others. They limit our pleasures and amusements--they control the
realities of to-day, and the anticipations of to-morrow. None can
prudently disregard them; few can withhold from them a constant attention.
Scientific men, and others, devote to them daily hours of careful
observation and registration. Devout Christians regard them as the
special agencies of an over-ruling Providence. The prudent, fear their
sudden, or silent and mysterious changes; the timid, their awful
manifestations of power; and they are, to each and all of us, ever present
objects of unfailing interest.
This _interest_ finds constant expression in our intercourse with each
other. A recent English writer has said: "The germ of meteorology is, as
it were, innate in the mind of every Englishman--the weather is his first
thought after every salutation." In the qualified sense in which this was
probably intended, it is, doubtless, equally true of us. Indeed, it is
often not only a "first thought" _after_ a salutation, but a part of the
salutation itself--an offspring of the same friendly feeling, or a part of
the same habit, which dictates the salutation--an expression of sympathy
in a subject of common and absorbing interest--a sorrowing or rejoicing
with those who sorrow or rejoice in the frowns and smiles of an
ever-changing, ever-influential atmosphere.
If consistent with our purpose, it would be exceedingly interesting to
trace the varied forms of expression in use among different classes and
callings, and see how indicative they are of character and employment.
The sailor deals mainly with the winds of the hour, and to him all the
other phases of the weather are comparatively indifferent. He speaks of
airs, and breezes, and squalls, and gales, and hurricanes; or of such
appearances of the sky as prognosticate them. The citizens, whose lives
are a succession of _days_, deal in such adjectives as characterize the
weather of _the day_, according to their class, or temperament, or
business; and it is pleasant, or fine, or _very_ pleasant or fine;
beautiful, delightful, splendid, or glorious; or unpleasant, rainy,
stormy, dismal, dreadful or horrible. The farmer deals with the weather
of considerable periods; with forward or backward _seasons_, with "cold
snaps" or "hot spells," and "wet spells" or "dry spells." And there are
many intermediate varieties. The acute observer will find much in them to
instruct and amuse him, and will probably be surprised to find how much
they have to do with his "first impressions" of others.
But I have a more important object in view. I propose to deal with "The
PHILOSOPHY _of the Weather_"--to examine the nature and operation of the
arrangements from which the phenomena result; to strip the subject, if
possible, of some of the complication and mystery in which traditionary
axioms and false theories continue to envelop it; to endeavor to grasp
_its principles_, and unfold them in a plain, concise, and systematic
manner, to the comprehension of "_the many_," who are equal partners with
the scientific in its practical, if not in its philosophic interest; and
to deduce a few general rules by which its changes may be understood, and,
ultimately, to a considerable extent, foreseen.
This is not an easy, perhaps not a prudent undertaking. Nor is my position
exactly that of a volunteer. A few words seem necessary, therefore, by way
of apology and explanation.
In the fall of 1853, in the evening of a fair autumnal day, I started for
Hartford, in the express train. Just above Meriden, an acquaintance
sitting beside me, who had been felicitating himself on the prospect of
fine weather for a journey to the north, called my attention to several
small patches of scud--clouds he called them--to the eastward of us,
between us and the full clear moon, which seemed to be enlarging and
traveling south--and asked what they meant.
"Ah!" said I, "they are scud, forming over the central and northern
portions of Connecticut, induced and attracted by the influence of a
storm which is passing from the westward to the eastward, over the
northern parts of New England, and are traveling toward it in a southerly
surface wind, which we have run into. They seem to go south, because we
are running north faster than they. You see them at the eastward because
they are forming successively as the storm and its influence passes in
that direction, and are most readily seen in the range of the moon; but
when we reach Hartford you will see them in every direction, more numerous
and dense, running north to underlie that storm."
I had seen such appearances too many times to be deceived. It was so. When
we arrived at Hartford they were visible in all directions, running to the
northward at the rate of twenty-five miles an hour. In the space of forty
minutes we had passed from a clear, calm atmosphere (and which still
remained so), into a cloudy, damp air, and brisk wind blowing in the same
direction we were traveling, and toward a heavy storm. My friend passed
on, and met the southern edge of the rain at Deerfield, and had a most
unpleasant journey during the forenoon of the next day. Taking the cars
soon afterwards, in the afternoon, for the south, I found him on his
return.
"Shall I have fair weather now till I get home?" said he.
"There are no indications of a storm here, or at present," I replied, "but
we may observe them elsewhere, and at nightfall."
He kept a sharp look-out, and, as we neared New Haven, discovered faint
lines of cirrus cloud low down in the west, extending in parallel bars,
contracting into threads, up from the western horizon, in an E. N. E.
direction toward the zenith.
"Now, what is that?" said he.
"The eastern outlying edge of a N. E. storm, approaching from the W. S. W.
It is now raining from 150 to 200 miles to the westward of the eastern
extremity of those bars of cirrus-condensation; perhaps more, perhaps
less; and under those bars of condensation the wind is attracted, and is
blowing from the N. E. toward the body of the storm, and where the
condensation is sufficiently dense to drop rain. That dense portion will
reach here, and it will rain from twelve to fifteen hours hence. As we
pass along the shore, and run under that out-lying advance
cirrus-condensation, we shall see that the vessels in the Sound have the
wind from the N. E., freshening, but we shall continue to have this light
and scarcely-perceptible air from the northward for a time--_the N. E.
wind always setting in toward an approaching storm, out on the Sound, much
sooner than upon the land_."
As we approached the storm, and the storm us, the evidence of denser
condensation at the west, and of wind from the east, blowing toward it,
became more apparent. The fore and aft vessels were running "up Sound"
with "sheet out and boom off," before a fresh N. E. breeze, and my friend
was astonished.
"I must understand this," said he; "how is it?"
"All very simple. The page of nature spread out above us is intelligible
to him who will attentively study it. The laws which produce the
impressions and changes upon that page, are few and comprehensible.
Although there is great variety, even upon the limited portion which is
bounded by our horizon, there is also substantial uniformity; and,
although the changes are always extensive, often covering an area of one
thousand miles or more, and our vision can not extend in any direction
more than from thirty to fifty, yet those changes are always, to a
considerable extent, intelligible, and may often be foreseen."
"Has meteorology made such progress?"
"By no means. It has, indeed, been raised to the dignity of a science, and
professorships endowed for its advancement. Some books have been written,
and many theories broached in relation to it; and innumerable observations
of the states of the barometer and thermometer, of the clouds, and the
quantity of fallen rain, and the direction and force of the wind--made and
recorded simultaneously in different countries--have been published and
compared; and a great many important facts established, and tables of
'_means_' constructed, and just inferences drawn, yet the _few and simple
arrangements_ upon which all the phenomena depend, and _their philosophy_,
have not yet been clearly elicited or understood."
"Have not the 'American Association for the Advancement of Science'
arrived at some definite and sound conclusion upon the subject?"
"No; it has been with them, for many years, an interesting subject for
papers and debate. Some very valuable articles, upon particular topics, or
branches of the subject, have been read and published. But the
_Cyclonologists_, as they term themselves, and who seem to think the great
question is, '_Are storms whirlwinds?_' appear with new editions and
phases of their favorite views as regularly as the annual meeting recurs;
and, though they have not convinced, they seem to have silenced their
opponents. The only conclusion, however, judging from their debates, to
which the Association appear to have come with any considerable unanimity,
is, that they are yet without sufficient _authentic observations_ and
well-established facts, to authorize the adoption of the Huttonian,
Daltonian, Gyratory, or Aspiratory, or any of the other numerous theories
which abound. And they are right. The subject is mystified by these
theories and speculations of the study, founded on barometrical and
thermometrical records, and the direction and force of the surface winds.
"The qualities of heat were among the earlier discoveries of science, and
all the phenomena of the weather were forthwith attributed to its
influence. Hastily-formed and erroneous views of its power, and the manner
of its action in particular localities, and under particular
circumstances, have retained the credence accorded to them when first
announced, although subsequent discoveries have shown their fallacy; some
new theory of _modification_ having been invented to reconcile the
discrepancies as soon as they appeared. Perhaps it is not too much to say
(however it may seem to one not thoroughly acquainted with the subject,
who does not know that the _primary_ and secondary modifying hypotheses
found in Kämtz, may be counted by hundreds) that there is not remaining in
any other science, and possibly in all others, an equal amount of false
and absurd theory, and of forced and unnatural grouping of admitted facts
to sustain it, as in meteorology as at present taught and received.
Astronomy, as a science, is almost perfected--the nature, and size, and
orbits, of the distant worlds around us are known--while constant changes
and alternating atmospheric conditions, which all occur _within less than
six miles of us_, affecting all our important interests, and obvious to
our senses, although much talked off, and made the objects of many
theories, are but little understood."
"How, then, did you acquire the information you seem to possess?"
"By studying '_the countenance of the sky_,' for in no other way has such
information ever been, or can it ever be, acquired. By a long-continued,
daily, and sometimes hourly observation of the clouds and currents of the
atmosphere, in connection with such reports of the then state of the
weather elsewhere, as have fallen under my notice, and the effect of its
changes upon the animal creation--for very much can be learned from them.
Yonder flock of black ducks that sit on that inshore rock, above the
tide--the wildest and most suspicious of all their tribe--although the
air is calm about them, know well that a storm is at hand. They probably
both see and feel it. As twilight approaches they will fly away inland,
forty or fifty miles perhaps, and settle among the lilies or grass which
surround some fresh-water pond, certain of remaining while the storm
lasts, and for one day at least, out of danger, and undisturbed. Many a
time, in my boyhood, have I heard, in the stillness of evening, the
whistling of their wings, as they swept up the Connecticut valley, to
seek, on the borders of the coves, and in the creeks of the meadows, a
concealed and safe feeding-place during a coming storm. And many a time in
the autumn, after they had all passed down for the season, when the
indications of an approaching storm were clearly visible at nightfall,
have I waited for them to return, on the eastern margin of a bend in the
cove, on the eastern side of a creek, to shoot them, though invisible, by
shooting across the head of the wake, which they made upon the water in
alighting, and from which the few remaining rays of twilight that came
from the western sky were reflected.
"But I am far from being singular in this. That page is more extensively
read than is generally supposed. Many plain, unassuming men--farmers,
shipmasters, and others within the circle of my acquaintance--know more,
practically, of the weather than the most learned closet-theorist, or the
most indefatigable recorder of its changes. Every one, by studying the
page of nature above him, as he would the page of any other science, and
testing, by observation, the numerous theories invented to account for the
varied phenomena, may learn much, very much, that will be useful and
interesting to him, and which he can never learn from books, or
instruments, or theories alone."
"Well," said my friend, "I am too far advanced in life, as are many
others, to commence such observations, and you must publish."
I demurred, and he insisted.
"It is difficult to spare the time; and I can not neglect my profession,"
I urged.
"Where there is a will there is a way," he replied.
"It is difficult to make one's self understood without many
illustrations."
"Very well, they are easily obtained."
"But they cost money, and it is said 'science will not pay its way' like
fiction and humbug."
"That," said he, "is a libel--such science will. Every one is interested
in the weather--all talk about it--and thousands would carefully observe
it, if they could be correctly guided in their observations."
"I may get into unpleasant controversy."
"Suppose you do; you can yield your position if wrong, and maintain it if
right, and _magna est veritas_."
"But I may be mistaken in some of the views to which it will be necessary
to advert, if I attempt to systematize the subject."
"Be it so--your mistakes may lead others to the discovery of the truth.
Besides, the weather is _common property_, and every one has a right to
theorize about it, or to talk about it, as they please--even to call a
stormy day a pleasant one, or make any other mistaken remark concerning
it; and every other person is entitled to a like latitude of reply. And
further," said he, with some emphasis, "no important observation, in
relation to a subject of such interest, should be lost; and, if you have
observed one new fact, or drawn one new and just inference from those
which have been observed by others; and especially if, from observation
and reading, you can deduce from the phenomena an intelligible,
_observable, general system_, it is not only your right, but duty, to make
it known. Such a knowledge of the true system is greatly desired by every
considerate man."
To my friend's last argument I was compelled to yield. I could make no
reply consistent with the great principles of fraternity, which I shall
ever recognize. The promise was given. My friend went on his way, and I
went to the daguerreotypist to procure a copy of the then appearance of
the sky, as the first step toward its fulfillment. The fulfillment of that
promise, reader, you will find in the following work. It was commenced as
an article for a magazine, but it has grown on my hands to a volume.
Justice could not well be done to the subject in less space. It has been
written during occasional and distant intervals of relaxation from
professional avocations, or during convalescence from sickness, and it is,
for these reasons, somewhat imperfect in style and arrangement. But I have
no time to rewrite. There is much in it which will be old to those who
read journals of science, but new to those who do not. There is more which
will be new to all classes of readers, and may, perhaps, be deemed
heretical and revolutionary by conservative meteorologists; yet I feel
assured that the work is a step in the right direction--that it contains a
substantially accurate exposition of the Philosophy of the Weather, and
valuable suggestions for the practical observer.
I have inserted my name in the title-page, contrary to my original
intention, and at the suggestion of others; for I have no scientific
reputation which will aid the publisher to sell a copy. Nor do I desire to
acquire such reputation. It can never form any part of my "capital in
life." Nor has it influenced me at all in preparing the work. I have aimed
to fulfill a promise, too hastily given, perhaps--to put on record the
observations I have made, and the inferences I have drawn from those of
others--to induce and assist further observations, and, if possible, of a
_general_ and _connected character_--and to impress those who may read
what I have written with the belief, that _they will derive a degree of
pleasure from a daily familiarity with, and intelligent understanding of,
the "countenance of the sky," not exceeded by that which any other science
can afford them_.
I have examined, with entire freedom and fearlessness (but I trust in a
manner which will not be deemed censurable or in bad taste) the theories
and supposed erroneous views of others, for, in my judgment, the
advancement of the science requires it. Says Sir George Harvey, in his
able article on Meteorology, written for the Encyclopædia Metropolitana:
"It is humiliating to those who have been most occupied in
cultivating the science of meteorology, to see an agriculturist or a
waterman, who has neither instruments nor theory, foretell the future
changes of the weather many days before they happen, with a precision
which the philosopher, aided by all the resources of science, would
be unable to attain."
The admissions contained in this paragraph, in relation to the comparative
uselessness of instruments and theories, and the value of practical
observation, are both in a good measure true. And the time has come, or
should speedily come, when "_pride of opinion_," and "_esprit du corps_,"
among theorists and philosophers, should neither be indulged in, nor
respected; and when their theories should be freely discussed, and rigidly
tested by the observations of practical men. Such measure, therefore, as I
have meted, I invite in return. Let whatever I have advanced, that is new,
or adopted that is old, be _as_ rigidly tested, and _as_ freely discussed.
Let the errors, if there be any--and doubtless there are--be detected and
exposed. Let the TRUTH be sought by all; and meteorology, as a PRACTICAL
SCIENCE, advance to that full measure of perfection and usefulness, of
which it is unquestionably susceptible.
TABLE OF CONTENTS.
PAGE
CHAPTER I.
Heat and moisture are indispensable to the fertillity of the
earth--Arrangements exist for their diffusion and distribution,
and all the phenomena of the weather result from their
operation--Heat furnished or produced mainly by the direct
action of the sun's rays--Manner in which it is diffused over
the earth--Other causes operate besides the sun's rays--The
earth intensely heated in its interior--Heat derived from the
great Oceanic currents, and the aerial currents which flow
from the tropics to the poles, and from magnetism and
electricity--Water distributed by an atmospheric machinery as
extensive as the globe--Evidences of this--Its distribution over
the continents of North America--Explanation of it--Source from
whence our supply of water is derived, and from which our rivers
return 1
CHAPTER II.
Our rivers return in the form of clouds, and in storms and
showers--Definition and character of storms--Differences in
the character of the clouds which constitute them--Nomenclature
of Howard--Its imperfections--New order of description--Low
fog--High fog--Storm fog--Storm scud--N. W. scud--Cumulus--
Stratus--Cirrus--Compounds of the two latter--recapitulation in
tabular form 24
CHAPTER III.
Our rivers do not return from the North Atlantic--All storms and
showers move from the westward to the eastward--Seeming clouds
seen moving from the eastward to the westward are scud--They are
incidents of the storm, and not a necessary part of it--The
storm clouds are above them, moving to the eastward--Occasions
when this may be seen--Admitted facts prove it--Investigations
prove it--May be known from analogy--From the fact that there is
an aerial current pursuing the same course in which the storms
originate--Character of this current--Its influence upon our
country--Importance of a knowledge of its origin, cause, and the
reciprocal action between it and the earth--To this end necessary
to go down "to the chambers of the South" 43
CHAPTER IV.
The trade wind region--Its extent and arrangements--Its belt of
daily rains and movable character--The trade winds--The extra
tropical belt of rains--Connection between them and their annual
movements--The counter-trades--Their origin and situation--One
of them constitutes our aerial current--It originates in the
South Atlantic as a surface-trade--Anomalies of the trade wind
region--Dry seasons--Humboldt's description of them--Exist where
the surface trades are situated--The rainless countries--
Concentrated counter-trade--Monsoons--Received theory in relation
to them a fallacy--Cause of the great central phenomena--
Calorific theory a fallacy--Land not hotter under the belt of
rains, nor sea materially so--Theory should be abandoned 52
CHAPTER V.
The agent, magnetism--Its character and currents--Oxygen
magnetic--Precipitation at the belt of rains occasioned by
depolarization--Storms originate in this central belt, and move
toward the poles 82
CHAPTER VI.
Course and functions of the counter-trade--Ours come from the
South Atlantic--Reason why it can not come from the Pacific--
Mistake of Mr. Redfield and Lieutenant Maury in regard to it--
All our storms originate in it--Proofs of this--State of the
weather, whether hot or cold affected by it--Proofs of this--All
our surface winds are incidents of it, and due to its conditions
and attractions--Proofs of this--Character of the different
winds--Anomalies of Mr. Blodgett accounted for--Received theory
in regard to sea and land breezes a mistaken one--Proofs of
this--Peculiar character of the N. W. wind--Identity with the
winter Mexican northers--Character of the West India hurricanes--
Of the thunder-gust--Of the tornado--Sundry particulars in
relation to the latter--Due to currents of electricity--
Proportions of winds in different localities--Examination of the
work of Professor Coffin upon that subject--Examination of
Lieutenant Maury's theory of the monsoons 92
CHAPTER VII.
Height of the counter-trade in different latitudes--Cause of the
Calms of Cancer--Influence of mountains upon the counter-trade--
Reports of Herndon and Gibbon--Focus of precipitation in the
extra-tropical belt north of its southern line--Evidences of
this--The elevation of the counter-trade above the earth varies
in the same latitude with the variations in the phenomena of the
weather--Temperature of the counter-trade--Rain dust, its origin
and indications--Volcanic ashes--How far they indicate its course
of progression--Question whether there is an eastern progression
of the body of the atmosphere above the machinery of distribution 179
CHAPTER VIII.
Important to understand the precise character of the reciprocal
action between the earth and the counter-trade--Connection
between the width and movements of the belt of inter-tropical
rains and the volume of the trades--Its peculiarities over
Africa, the Atlantic, and South America--The magnetic equator--
Character of the storms which originate in the inter-tropical
belt indicate local magnetic action--Supposed influence of
volcanic action--Gulf Stream changes its position--This the
result of magnetic action--Alternating contrasts of heat and
cold, and rain and drought--Dr. Webster's history of the
weather--Spots upon the sun--Their character and influence--Cold
or warm periods during the same decade, and during different
decades--Connection between the spots and magnetic disturbances
and variations--Influence of the moon upon the weather--No
decisive inference to be drawn from these facts, and a more
critical examination necessary 204
CHAPTER IX.
Examination of existing theories--Calorific theory the prevailing
one--Lateral overflow of Professor Dove--Absurdity of his views
in relation to them--His theory of hurricanes--Its absurdity--A
new theory by Mr. Dobson--Three theories advanced by
meteorologists of this country--Professor Espy's theory--Mr.
Bassnett's theory--Mr. Redfield's theory--Extended examination of
the latter--His theory in relation to the fall of the barometer
contradictory in its character--Philosophy of the barometric
change--No aid to be derived from these theories 232
CHAPTER X.
Further inquiry in relation to the reciprocal action between the
earth and the counter-trade--Terrestrial magnetism, and what we
know of it--Its elements, and their variations--Their connection
with the variations of atmospheric condition--Magnetism acts
through its connection with electricity--Character of the latter
and its variations--Their connection with atmospheric conditions--
Electricity as well as magnetism in excess over this country--
Effects of it upon our climate--Closer consideration of the
atmospheric phenomena--Their diurnal changes and connections
compared with those of magnetism and electricity--Grouping of all
the diurnal variations--Particular and separate examination of
them--Classification of storms--Examination in detail of the
several classes and the primary influence of the earth or
counter-trade in relation to each 285
CHAPTER XI.
Prognostics 340
THE PHILOSOPHY OF THE WEATHER.
CHAPTER I.
Heat and moisture are indispensable to the fertility of the earth. Without
suitable arrangements for their diffusion and distribution, and within the
limits of certain minima and maxima, it would not have been habitable, or
the design of its Creator perfected. These arrangements therefore exist,
and "while the earth remaineth seed time and harvest shall not cease." Few
and simple in their character, though necessarily somewhat complicated and
irregular in their operation, the ultimate result is always attained. A
beautiful system of compensations supplies the losses of every apparent
irregularity in one section or crop, by the abundance of others.
From the operation of these few, simple, connected, and intelligible
arrangements for the diffusion of heat and the distribution of moisture
over the earth, result all the phenomena which constitute the weather; and
by studying them, and their operation, we may acquire an accurate
knowledge of its "_Philosophy_."
The necessary heat is furnished, or produced, mainly by the direct action
of the sun's rays; and the most obvious feature in the arrangements for
its diffusion is that by which the sun is made to shine successively and
alternately upon different portions of the earth. Nothing animate or
organic could endure his burning rays, if they shone continuously or
vertically upon one point, or could exist without their occasional
presence. Hence the provision for a diurnal rotation, to prevent the
exposure of any portion of the globe to the action of those rays for
twenty-four consecutive hours, except for a limited period, and at a
considerable angle, in the polar regions. But the earth is spheroidal, and
a diurnal revolution would still leave that portion which lies under the
equator too much, and the other too little, exposed to the action of the
sun. This is obviated by an annual revolution of the earth around the sun,
and an obliquity of its axis, by reason of which the northern and southern
portions are alternately and, as far as the tropics vertically, exposed to
the sun; and it is made to travel (so to speak) from tropic to tropic,
producing summer and winter, and other important phenomena.
This obliquity and consequent change of exposure are in degree precisely
what the wants of the earth would seem to require. If it was greater, the
sun would travel further north and south, but the alternate winters would
be longer and more severe. If it was less, the end would not be as
perfectly attained.
The direct action of the sun's rays upon the earth, particularly those
portions which lie north and south of the tropics, is not the only source
from which the supply of heat is derived. Although there is a general
increase of heat in spring and summer when the sun travels north, and of
cold when he travels south in winter, yet there are frequent
irregularities attending both. Very sudden and great changes occur in each
of them. Frost sometimes, cool weather often, occurs in midsummer, and
considerable heat and tornadoes in midwinter. And ordinarily the maxima
and minima of each month and, indeed, of each week are widely apart. Even
in the polar regions, in midwinter, _where the sun does not shine at all_,
the same moderating changes with which we are conversant occur in degree.
An extract or two from the register found in Dr. Kane's narrative of the
"Grinnell Expedition" will illustrate this.
JANUARY 1851, (LATITUDE ABOUT 74°, LONGITUDE ABOUT 70°).
Date. Wind. Force. Ther. Bar. Sky and Weather.
Jan. 3 calm -26.1 29.62 blue sky, m.
" 4 W. gent breeze -21.3 29.53 blue sky,
detached clouds, m.
" 5 W. by N. gent breeze -3.9 29.59 blue sky, m.,
clouded over.
" 6 W. by S. light breeze -0.8 29.67 clouded over, m.,
snow.
" 7 W. gent breeze -14.4 29.96 blue sky, detached
clouds, m.
" 8 W.S.W. light air -21.2 30.14 blue sky, m.
" 29 W.N.W. light air -18.9 30.19 blue sky.
" 30 NW. by W. light air -13.5 30.17 clouded over, m.
" 31 NW. by W. gent breeze -4.4 29.35 clouded over, snow.
Feb. 1 W. light breeze -11.7 29.27 cloudy, blue sky, m.
" 2 W. light air -25.1 29.62 blue sky, detached
clouds, m.
These extracts are instructive. It will be seen that on the 3d of
January, when the sun had been absent some weeks, it was calm, the
thermometer stood at 26° below zero (the - or minus mark before the
figures indicates that), and the barometer at 29.62, with blue sky,
somewhat misty or hazy--(the letter "m." standing for misty or hazy)--a
state of the air which existed most of the time when it did not snow or
rain, and therefore is of no importance in this connection. The next day
the thermometer began to rise, and the barometer to fall. On the 5th it
clouded over, and the thermometer rose rapidly, and on the 6th it had
risen more than 25°, and snow fell. On the 7th it cleared off, the
thermometer fell rapidly, and the barometer rose. On the 8th the
thermometer had fallen to 21° below zero, and the barometer had risen to
30.14. Another instance, in all respects similar, occurred the latter part
of the month. We shall see hereafter that these changes are precisely like
those which occur with us, and every where. That, as in the polar regions,
and whether the sun be present or absent, or obscured by clouds, and by
night as well as by day, the changes from warm to cold and from cold to
warm are sudden and great, and that the latter are connected with the fall
of rain and snow--that every where in winter it _moderates to storm_.
Many other instructive instances, especially in relation to the great
difference in the seasons in our own country, and upon the same parallels
elsewhere, might be cited if it were necessary. But they will more
appropriately appear in the sequel.
[Illustration: Fig. 1.
In the above cut the isothermal lines are Centigrade. The zero of the
Centigrade thermometer is the freezing point of water, or 32° of
Fahrenheit. The boiling point of water is 100° Centigrade, or 212°
Fahrenheit. A degree of Centigrade is equal to one degree and four-fifths,
Fahrenheit. The 0° line of the cut, therefore, is 32° of Fahrenheit--the
line of 5° above is 41° Fahrenheit--the line of 5° below is 23°
Fahrenheit, and so on. The reader, who is not familiar with the difference
in the scale of the thermometer, is desired to remember this; for we shall
make occasional extracts in which the temperature is given in the
Centigrade scale.]
The cause of those irregularities, especially in the same seasons of
different years, and when very great, is often sought and supposed to be
found in the presence or absence of spots on the sun, ice floes and bergs
in the Atlantic, etc., etc. But neither the spots, nor ice, nor other
local causes produce them. The cause will be found in the character of the
arrangements we are considering, and the irregular action of the power
which controls them.
Nor is the temperature of the northern hemisphere, north of the tropics,
equal in the same latitudes. Very great diversities exist in the "annual
mean" as well as the "mean" of the different seasons. Accurate
observations at many points have enabled men of science to demonstrate
this by drawing isothermal lines (_i. e._, lines of equal average annual
heat) from point to point around the earth, which show at a glance these
differences. The annexed cut is a polar projection of the isothermal lines
of the northern hemisphere, as far down as the tropic, copied from
Kaemtz's Meteorology. The dotted lines show the parallels of latitude, the
dark lines the isothermal lines, or lines of equal annual average
temperature. The reader is desired to observe how rarely they correspond
with the parallels of latitude, and how they fall below in a few
instances, and in others with great uniformity rise almost to the pole.
Take, for example, the isothermal line of 0 or zero--that is, the line
where the mean or _average_ height of the thermometer _for the year_ is at
zero. At Behring's Straits this line is a little below the Arctic circle,
or the parallel of 66.30 north latitude. Passing east over North America,
it descends into Canada, almost to Lake Superior, and to about the 50th
parallel: that is to say, it is on an average during the year as cold on
our continent at the 50th parallel as it is near Behring's Straits at the
65th parallel. Passing east, the line of zero rises again over the
Atlantic Ocean until, in the meridian of Spitzbergen, it reaches, within
the Arctic circle, up almost to the 75th parallel. So, too, the isothermal
of 5° below zero, which is below the 60th parallel in Siberia, rises in
the North Sea, above Behring's Straits, to the parallel of 75°, descending
on the continent in North America to the 55th parallel, and rising again
almost to the pole at Spitzbergen, to descend again in Siberia, while the
isothermals of 10° and 15° below zero, which in North America are but just
above the latitude of 60° and 75° respectively, ascend abruptly
_surrounding the magnetic pole_, and _falling short of the geographical
one_. Let this projection of the lines of equal temperature, and
particularly the situation of the magnetic poles, be studied well, for we
shall recur to it hereafter in illustration of many important portions of
our subject.
It is apparent from these facts, and were it necessary might be rendered
still more so by referring to others, that other causes operate in the
distribution of heat over the earth besides the direct action of the sun's
rays upon it. Doubtless very considerable allowance is to be made for the
difference of seasons, and difference during the same season upon the
land and upon the ocean; in mountainous countries and level ones. But
making every allowance for them, the fact that other causes have a
_controlling_ influence in producing the deviations still remains most
obvious. Neither the difference of temperature between the land and the
ocean, or land surfaces of unequal elevations, will account for the
elevation of the isothermal lines on different portions of the ocean, or
their extension around the magnetic poles.
Returning to a consideration of the arrangements for the diffusion of
heat, we observe: First, that the earth itself is intensely heated in its
interior. This is inferred, and justly, from the fact that the thermometer
is found to rise about one degree for every fifty-five feet of
descent--whether in boring artesian wells, exploring caves, or sinking
shafts in mines. It is demonstrated, also, by the existence of hot springs
and the action of volcanoes. Heat is supposed to be conducted from the
center toward the surface every where, but with difficulty and slowly. It
is also supposed to be conducted from the tropical regions toward the
poles. Such is the opinion of Humboldt. (Cosmos, vol. i. p. 167.)
Probably it reaches the surface and exerts an influence, also, upon the
weather through the ocean, and by heating it in its greatest depths.
Little attention has been paid, so far as I am informed, to the question
how far the ocean is thus heated in _tropical latitudes_. Doubtless a
portion of the warmth of the ocean there is derived from that source, and
it has its influence in changing the temperature of the deep-seated cold
polar currents of, the great oceans. Perhaps it may yet be found that the
icebergs are detached by it in the polar seas--the observations of Dr.
Kane point to such a result. (Grinnell Expedition, p. 113, and also chap.
48.)
Little need be said of the inconsiderable quantities of heat supposed to
be derived by radiation from the stars, the planets, and from space. If
any such are derived they are too inconsiderable to be of importance in
this inquiry.
Heat is also carried, and in quantities which exert very considerable
influence upon the weather, from the tropics to the poles by the great
oceanic currents which flow unceasingly from one to the other.
The most important of these with which we are acquainted is the Gulf
Stream of the Atlantic. Gathering in the South Atlantic, and passing north
through the Caribbean Sea and the Gulf of Mexico, it issues out through
the Bahama Channel, and flows north along the eastern coast of the United
States, but some distance from it, to Newfoundland, and from thence
continuing to the north-east and spreading out over the surface of the
ocean--a portion of it mingling with the waters of the North Atlantic in
passing--it flows up on the western coast of Europe, around the Faroe
Islands, and Spitzbergen, to the polar sea; passing around Greenland, and
perhaps through its Fiords, it descends again through the sounds and
channels of the Arctic regions into Baffin's Bay, and through Davis's
Straits, burdened with the icebergs and floes of the polar waters, to
return again to the South Atlantic. For reasons which will appear in the
sequel, it has comparatively little influence upon the weather of the
United States. Western Europe, however, Greenland, the islands which lie
in its course, and the polar seas, are most materially influenced.
Although not the only cause, it has very much to do with the remarkable
elevation of the isothermal lines over the Northern Atlantic, and upon
Western Europe, as seen upon the map.
A like oceanic current exists in the Pacific Ocean, the influence of which
may also be traced upon the map by the elevation of the isothermal lines
at the northern extremity of that ocean, and upon the north-west coast of
North America. A vast amount of heat is transported from the tropical to
the temperate and frozen regions of the earth by these great oceanic
currents.
Another supply is derived from aerial currents which flow from the tropics
toward the poles. These currents exist every where over the entire surface
of the earth, but in more concentrated volumes along the great "lines of
no variation," and greater magnetic intensity, on the western side of the
great oceans, over the eastern portions of the two continents of North
America and Asia. Not, as meteorological writers suppose, in the upper
portions of the atmosphere, having risen in the trade-wind region and run
off at the top toward the poles by force of gravity, but near, and
sometimes in contact with the earth. The influence of these aerial
currents upon the temperature of the atmosphere, and in producing the
phenomena we are to consider, is exceedingly important. We shall have
occasion to examine them with great care and minuteness under another
head, for upon them, more than any other portion of the arrangements,
depend not only the diffusion of heat, but also the distribution of
moisture.
Still another supply of heat, during the sudden changes, at least, is
produced by the action of terrestrial magnetism and electricity. Very
great progress has been made within a short period, in the investigation
of the nature of these agents. The identity, or at least intimate
association or connection of heat, light, electricity, and magnetism,
always suspected, has been in various ways, and by a variety of
experiments demonstrated. The influence of magnetism if distinct from
gravitation, is second only to that; and its agency in producing the
phenomena we are considering is primary and controlling. We will only, in
this connection, ask the reader to note the situation of the north
magnetic poles (for there are two of them); the manner in which the
isothermal lines _surround_ them; the fact that they are _poles of cold_,
_i. e._, that it is colder there than even to the north of them. We shall
recur to this part of the subject again.
Such, briefly considered, are the principal arrangements by which heat is
diffused over the earth.
Equally marked by infinite wisdom, and equally interesting and important,
are the arrangements by which moisture is distributed. Doubtless the
general belief is that this is a simple process; that water evaporates
and rises till it meets a colder stratum of atmosphere, and then condenses
and falls again; or that, according to the Huttonian theory, currents of
air of different temperatures mingle and equalize their heat, and the
aggregate mass when equalized in temperature is cooler, and therefore is
unable to hold as much moisture in solution as the most heated portion
had, and the excess falls in rain. But the process is by no means so
simple, nor is heat the sole or most powerful agent concerned in it.
Currents of air do not mingle, but stratify. Evaporation from the surface
of any given portion of the earth outside of the tropics does not alone
supply that portion with rain. _Vast and wonderful, coextensive with the
globe itself, and perfectly connected, is the machinery by which that
supply is furnished even to the most inconsiderable portion of its
surface._
Take your map of North America and note, in this respect, its
peculiarities. It extends from the Isthmus of Darien to the Arctic
regions, and from the 65th to the 160th meridian of west longitude from
Greenwich, and has upon its surface a type of every climate in the world.
For the purpose of simplifying and illustrating the matter in hand, let us
divide it into five sections. Let the first section embrace Central
America and Southern Mexico, south of 28°; the second, Northern Mexico and
Southern New Mexico, California, etc., between the parallels of 28° and
32°; the third, Northern California, Utah, Southern Oregon, and Western
New Mexico, north of the parallel of 32°; the fourth, the entire
continent north of 42°; and the fifth, the eastern United States, east of
the meridian of 100°. These divisions are not intended to be entirely
accurate in their separation, but substantially so for the purpose of
illustrating the differences which exist in each.
The accompanying diagram shows approximately, by dotted lines, the
divisions.
[Illustration: Fig. 2.]
Now let us see in what a diverse manner, and to what a different extent,
they are severally supplied with moisture.
Central America and Southern Mexico lie within the tropics--their rains
are tropical rains. The season is divided into wet and dry, as are the
seasons of all tropical countries which are not rainless. During the rainy
season it rains a portion of nearly every day, and during the dry season
the sky is clear, the air is pure, and rain seldom falls.
All around the earth within the tropics, over the land and over the sea,
there is a belt of almost daily rains, varying in width, north and south,
in different sections, but averaging about five hundred miles. This belt
of daily rains is formed at and by the meeting of N. E. and S. E. trades,
and travels north and south with them, as they do with the sun,
_encircling the globe_. By this narrow belt a portion of the earth's
surface, an average of some 35° of latitude, is supplied with moisture.
Wherever it is situated at any given period, the tropical rainy season
exists; and when it is absent in its northern or southern transit, the dry
season prevails. Southern Mexico is within the range of this moving belt,
and in its course to the northward with the sun, in our summer from May to
October, it arrives over, and covers that country with a rainy season.
When the sun returns to the south, taking with it the trades and this belt
of tropical rains, that portion of Mexico is without rain, and dry, and so
continues until the rainy belt returns in the following year. While the
belt is over Southern Mexico it is nearly all _precipitation_, and there
is little _evaporation_; while that belt is _absent_ it is all
_evaporation_, with little or no _rain_. Surely this is not consistent
with the prevailing belief of simple evaporation, ascent to a colder
stratum, commingling, and condensation, and rain. Southern Mexico at least
is not supplied by mere evaporation from its surface, and must therefore
form an exception to that belief, and to the Huttonian theory.
But we shall recur again to the peculiarity of distribution within the
tropics.
Turn now for a brief space to Northern Mexico, Southern New Mexico, and
Southern California. In Northern Mexico, Southern New Mexico, Utah, and
California, between the parallels of 28° and 32°, and particularly west of
the mountain ranges, we find an almost rainless region, sterile and
worthless, resembling that which is found upon nearly the same parallels
of north latitude in Northern Africa, Egypt, Arabia, Beloochistan,
Afghanistan, and North-western India; and in corresponding latitudes south
of the Equator, in Peru, a portion of Southern Africa, and the northern
and middle portions of New Holland. Why Northern Mexico and the other
countries named are thus sterile and comparatively rainless, we shall see
hereafter, when we examine critically the machinery of distribution as it
operates within the tropics. It is the fact that it is thus sterile and
rainless to which we desire to call attention in this place.
Mr. Bartlett thus describes it:
"On leaving the head waters of the Concho, nature assumes a new
aspect. Here shrubs and trees disappear, except the thorny chaparral
of the deserts; the water-courses all cease, nor does any stream
intervene until the Rio Grande is reached, three hundred and fifty
miles distant, except the muddy Pecos, which, rising in the Rocky
Mountains, near Santa Fé, crosses the great desert plain west of the
Llano Estacado, or Staked Plain.
"From the Rio Grande to the waters of the Pacific, pursuing a
westerly course along the 32d parallel, near El Paso Del Norte, there
is no stream of a higher grade than a small creek. I know of none but
the San Pedro and the Santa Cruz--the latter but a rivulet, losing
itself in the sands near the Gila--the other but a diminutive stream,
scarcely reaching that river. At the head-waters of the Concho,
therefore, begins that great desert region, which, with no
interruption save a limited valley or bottom-land along the Rio
Grande, and lesser ones near the small courses mentioned, extends
over a district embracing sixteen degrees of longitude, or about a
thousand miles, and is wholly unfit for agriculture. It is a
desolate, barren waste, which can never be rendered useful for man or
beast, save for a public highway."--_Bartlett's Personal Narrative_,
vol. i. p. 138.
Turning now to Central and Upper California, and Utah, and Southern
Oregon, we find still another peculiarity. Like Southern Mexico, they have
a rainy and dry season, but at a different period, and for a different
reason. The dry season of California, etc., is the summer of the northern
hemisphere, and her rainy season the winter. _California_ is, therefore,
_dry_ when Southern _Mexico_ is _wet_, and _vice versâ_. The belt of rains
which supplies California with moisture during her rainy seasons is the
belt of _extra-tropical_ rains, which extends from the northern limit of
the north-east trades to the poles, encircling the earth. The southern
edge of this extra-tropical belt is _carried up_ on the western coast of
America, and in that portion of the continent in _summer_, when the sun
and trades, and the inter-tropical rainy belt travel to the north, and
uncover California, etc., leaving them without rain for a period of about
six months.
[Illustration: Fig. 3. IN SUMMER.]
As the sun, with the trades, travels south, the southern edge of the belt
of extra-tropical rain follows, and covers California, etc., again
extending gradually from the north to the south, and thus their wet
season returns. The annexed diagrams by the shading will show the
situation of the rainy belts which cover Mexico, Utah, New Mexico, and
California in summer and winter, and that the belts of rains are entirely
distinct and different in character.
[Illustration: Fig. 4. IN WINTER.]
Here again in this section of the continent, as in Mexico, evaporation is
going on for six months of the year, and were it not for the return of the
belt of rains from the north, in the fall, would go on for the entire year
without precipitation; and for the other six months precipitation is
vastly in excess. Nor can this be reconciled with, or explained by, the
Huttonian or any other received theory of rain. Here again it is obvious
that evaporation alone, however great or long continued, will not furnish
the evaporating section with rain.
The northern portion of the continent lies beneath the zone of
extra-tropical rains, and north of the northern limit of the N. E.
trades--is never uncovered from it, and has no distinct rainy or dry
season, although more rain falls at certain periods, and in certain
localities, than at others. The climate of that part of Oregon which lies
upon the Pacific, and the character of its rains, resemble those of
North-western Europe, and will be further explained hereafter.
Coming to the portion of the continent which we occupy, the 5th section,
we find it different still--a most favored region. Portions of it--Eastern
Texas, for instance--are upon the same parallels of latitude as the
rainless regions of Northern Mexico, etc. Eastern Texas, however, is not
rainless. Other portions are upon the same parallels as California, etc.,
yet have no distinct rainy and dry season. We repeat, this section is a
most favored region--without a parallel upon any portion of the earth's
surface, except, in degree, in China and some other portions of Eastern
Asia.
It is not only without a distinct rainy and dry season, but it is watered
by an average, annually, of more than forty inches of rain, while Europe,
although bounded on three sides by seas and oceans, and apparently much
more favorably situated, receives annually an average of only about
twenty-five--if we except Norway, and one or two other places, where the
fall is excessive. The distribution of this supply of moisture over the
United States is, in other respects, wonderful. Iowa, in the interior of
the continent, far away from the great oceans, on the east or west, or the
Gulf of Mexico on the south, receives fifty inches; some ten or fifteen
inches more than fall upon the slope east of the Alleghanies, and
contiguous to the great Atlantic (from which all our storms are,
erroneously, supposed to be derived), and the average over the entire
great interior valley is about forty-five inches, falling at all seasons
of the year.
Observe, then, by way of recapitulation: Southern Mexico has a rainy
season furnished by the belt of _inter_-tropical rains, which _travels up
over it from the south_ in summer. California has a rainy season, which is
furnished by the _extra_-tropical belt of rains, which travels _down from
the north_, and covers it in winter. Northern Mexico and the adjoining
regions west of the 100th meridian are between the limits of the two, and
neither travels far enough to reach them, except for brief and uncertain
periods; they are comparatively rainless; while the eastern portion of
the continent, _in all latitudes_, unlike the others, is without a
distinctly marked dry season, or a rainless region, and with the exception
of occasional droughts, is abundantly supplied with rain at all seasons of
the year.
And now, what is the explanation of all this? What produces the
extra-tropical belt of regular rains surrounding the earth, north of the
parallel of 30° north, in some places, and 35° in others, extending to the
pole, with its southern edge traveling up ten or more degrees in summer,
leaving large portions of the earth subject to a dry season; and back
again in the winter to give them a rainy one? What produces the narrow
belt of inter-tropical rains, encircling the earth; traveling up and down
every year over an average of 35° of latitude, supplying every portion of
it alternately with rain? And what connects the two together over the
eastern portion of North America, so as to leave no distinctly marked wet
and dry season, and no rainless and sterile portion there? Are all these
the result of simple evaporation, ascent to a colder region, condensation,
and descent again? Demonstrably not. Of the forty inches which fall
annually upon the middle and eastern portions of the United States, an
average probably of one-half or twenty inches, runs off by the rivers to
the ocean, or is carried away eastward by the westerly and north-westerly
evaporating winds. The same is true, in degree, of the rain which falls
upon the other portions. Evaporation, therefore, could not keep up the
supply. From whence, then, does it come? this twenty inches, thus lost by
the rivers and winds, and with such wonderful regularity every year.
"All the rivers run into the sea, yet the sea is not full. _Note the place
whence the rivers come, hither they return again._"
But how is it that they thus return with such wonderful regularity, in a
narrow traveling belt of daily rains within the tropics, and a movable
belt of irregular rains without the tropics, extending to the poles,
leaving a space on each side of the equator encircling the earth in like
manner (except at two points, _viz._, Eastern Asia and Eastern North
America), from which they do not go, and to which they do not return, and
which is almost entirely unfurnished with rain? And all this without any
relation, whatever, to the contiguity of the oceans? Obviously this is not
the work of mere evaporation, or of the accidental or irregular
commingling of winds with different dew points, or quantities of moisture
in solution, or accidental, irregular changes of barometric pressure. _It
is one vast, wonderful, connected, and regular system--co-extensive with
the globe--necessary to the return of moisture from the oceans upon the
most inconsiderable portion of it, and to the condensation of the local
moisture of evaporation; and by it the waters are returned from the oceans
as regularly and bountifully upon the far interior of the great continents
in the same latitudes, as upon the "isles which rest in their bosoms."_
CHAPTER II.
Before proceeding to an examination of this connected atmospheric
machinery, and an investigation of the particular ocean from which our
rivers return, it may be well to look at the form in which they appear to
return, that we may have a clear understanding of terms.
They seem to return in the form of clouds, and in storms and showers,
although, in truth, they return in regular, uniform, ordinarily invisible
currents, and the storms and showers are but condensations in, and
discharges from portions of those currents, aided by the local moisture of
evaporation.
The term _storms_, seems to be used by European meteorologists to denote
what we term thunder showers or gusts, and tornados; while what we call
storms are denominated by them regular rains. As the terms are extensively
in use in this country, we must adhere to the meaning attached to them
_here_ rather than _there_.
Storms with us, then, are regular rains of from six to forty-eight or more
hours' continuance: generally without lightning, or thunder, or gusts, and
usually with wind of more or less force, from some easterly point. They
are called north-east storms, or south-east storms, according to the
point from which the surface winds blow. Practically we shall find that
this distinction is of some importance, for the north-east storms are the
longest, lasting generally twenty-four hours, or more, while the
south-east ones seldom, if ever, continue as long.
These storms extend over a considerable surface, rarely less than one
hundred miles in one direction or another, and sometimes fifteen hundred,
or more. Distinct showers cover but a small surface, sometimes not more
than forty to one hundred rods, as in the tornado, and rarely more than
ten miles. Belts of showers, each new one forming a little more to the
south, often, in summer, pass across the country, following each other in
succession; and these belts may be of considerable width, say thirty to
one hundred and fifty miles.
The clouds which constitute the storms and showers differ in appearance
and character, as well in the active as in the forming state. Clouds are
of distinct characters, alike, substantially, every where under like
circumstances; and a distinct nomenclature has been applied to them by Dr.
Howard, of London. He notes three kinds of primary clouds: _viz._, cirrus,
stratus, and cumulus; and inasmuch as the boundary line between them is
not very distinct, certain compounds of the three, _viz._: cirro-stratus,
cirro-cumulus, and cumulo-stratus. This nomenclature is every where
received, and portions of it are of great practical importance.
The three principal descriptions of cloud, _viz._: the cirrus, the
stratus, and the cumulus, we have very much as they have in Europe, and
doubtless as they exist every where outside of the tropics. The nimbus,
another cloud described by him, is not distinct from the cumulus or
stratus. An isolated, limited thunder-shower in a clear sky, presents the
appearance of a nimbus, as shown in the cuts, but the basis of it is a
cumulus, and it differs from an ordinary fair-weather cumulus merely in
the dark and fringe-like appearance of the rain as it is falling from its
lower surface, and sometimes in the existence of a stratus above and in
connection with it. A similar form is often assumed by the peculiar clouds
of the N. W. winds in March or November, when they assume the form of
_squalls_, and drop flurries of snow. The nimbus, therefore, is not a
distinct cloud, but an appearance which the cumulus, stratus, or
cirro-stratus has in a stormy or showery state, and does not deserve a
distinct name. It is but a cumulus, or a stratus, or cirro-stratus
dissolving in snow or rain. It is important that this term should be
abandoned. It tends to confuse and prevent a clear understanding of the
difference in the character of the clouds, and in relation to which
precision is both difficult and desirable.
The figures on pages 27 and 29, show the different kinds of clouds as
designated by Howard. They are copied from the engravings in the sixth
edition of Maury's "Sailing Directions."
[Illustration: Fig. 5.]
[Illustration: Fig. 6.]
Figure 5.
The cirrus is indicated by 1 bird.
The cirro-cumulus by 2 "
The cirro-stratus by 3 "
The cumulo-stratus by 4 "
Figure 6.
The cirrus by 1 "
The cumulus by 3 "
The stratus by 2 "
The nimbus by 4 "
How far these representations correspond with the actual appearance of the
different compound forms in England, I can not say. But although they
convey a _general_ idea, _they are not sufficiently accurate for practical
illustration or observation here_. Indeed Howard himself has omitted from
his last edition his plate of the clouds, assigning as a reason, "that the
real student will acquire his knowledge in a more solid manner by the
observation of nature, without the aid of drawings, and that the _more
superficial are liable to be led into error by them_." The collection of
forms in the cuts _does not contain some very important ones_, and
contains some which are not distinct forms; but they may aid us somewhat
in this inquiry, and, therefore, I have copied them. It is well, also, for
the reader to have the generally received description before him.
But for the purpose of _practical_ illustration hereafter, and greater
precision, I shall follow a somewhat different order in describing them,
and introduce two forms of _scud_ quite as important, practically, as any
other.
First, then, commencing at the earth, we have what may be properly termed
_fog_, or low fog. This forms, in still clear weather, in the valleys, and
over the surface of the rivers and other bodies of water, during the
night, and most frequently the latter part of it, and is at its acmé at
sunrise, or soon after, limiting vision horizontally and perpendicularly,
and dissolving away during the forenoon. It is rarely more than from two
to four hundred feet in height at its upper surface, and often much less,
and is composed of vesicular condensed vapor, sometimes sufficiently dense
to fall in mist, and is doubtless in composition substantially what the
clouds are in the other strata of the atmosphere, as observed by us, or
passed through by aeronauts. I have never seen it carried up to any
considerable height into the other strata by any of the supposed ascending
currents, to form permanent clouds, and shall have occasion to allude to
the fact in another connection. It disappears usually before mid-day, and
has, when thus formed, no connection with any clouds which furnish rain.
To this Dr. Howard originally gave the name of stratus, and so it is
represented upon the cut; but the latter term may be with greater
propriety applied to the smooth uniform cloud in the superior strata from
which the rain or snow is known to fall, and I shall retain and so apply
it.
The next in order, ascending, is high fog. This is usually from one to
two thousand feet in height at its lower surface. It forms, like low fog,
during the night and in still weather; and is rarely, if ever, connected
with clouds which furnish rain. It breaks away and disappears between ten
and twelve in the forenoon, usually passing off to the eastward. This fog
is most commonly seen in summer and autumn, particularly the latter, and
unless distinguished from cloud will deceive the weather-watcher. It is
readily distinguishable. Although often very dense, obscuring the light of
the sun as perfectly as the clouds of a north-east storm, it differs from
them. It forms in still clear weather, is present only in the morning, is
perfectly uniform, and, before its dissolution commences, without breaks,
or light and shade, or apparent motion, and unaccompanied by scud or
surface wind. The storm clouds are never entirely uniform, or without
spots of light and shade, by which their nature can be discerned, and
rarely, when as dense as high fog, without scud running under them and
surface winds.
There is another fog still, connected with rain storms, but it does not
often precede them; occurring at all seasons, but most commonly in
connection with the warm S. E. thaws and rains of winter and spring; and
which usually comes on _after_ the rain has commenced and continued for
awhile, and the easterly wind has abated; occupying probably the entire
space from the earth to the inferior surface of the rain clouds or
stratus. Practically this does not require any further notice. It is an
_incident_ of the storm. When formed it remains while the storm clouds
remain, and passes off with them. It is sometimes exceedingly dense in
February and March, when it accompanies a thaw, and if there is a
considerable depth of snow, it has the credit of aiding essentially in its
dissolution.
Mingled with the smoke of London, it produced there the memorable _dark
day_ of the 24th of February, 1832, and at various other times has
produced others of like character. (See Howard's Climate of London, vol.
iii. pp. 36, 207, 303.) These fogs have been so dense there that every
kind of locomotion was dangerous, even _with lanterns, at mid-day_.
The next in order, ascending, are the storm scud, which float in the
north-east or easterly, south-east or southerly wind, before and during
storms.
These, as the reader will hereafter see, are, _practically_, very
important forms of cloud condensation--although they have found no place
in any practical or scientific description given of the clouds, and are
not upon the cuts. They are patches of foggy seeming clouds of all sizes,
more or less connected together by thin portions of similar condensation,
often passing to the westward, south-westward, north-westward, or
northward with great rapidity. Their average height is about half a mile,
but they often run much lower. They are usually of an "ashy gray" color.
The annexed cut shows one phase of them, from among many taken by
daguerreotype. The arrows pointing to the west show the scud distinguished
from the smooth partially formed stratus above. This view was taken a few
hours prior to the setting in of a heavy S. E. rain storm. It is a
northerly view.
[Illustration: Fig. 7.]
At about the same height, but in a _different state of the atmosphere_,
float the peculiar fair-weather clouds of the N. W. wind. They usually
form in a clear sky, and pass with considerable rapidity to the S. E.
Sometimes they are quite large, approaching the cumulus in form, and
white, with dark under surfaces, and at others, in the month of November
particularly, are entirely dark, and assume the character of squalls and
drop flurries of snow; and then resemble the nimbus of Howard. They assume
at different times and in different seasons, different shapes like those
of the scud, the cumulus, or the stratus.
[Illustration: Fig. 8.]
They form and float in the peculiar N. W. current which is usually a
fair-weather wind, and are never connected with storms. In mild weather
they are usually white, and in cold weather sometimes very black, and at
all times differ _in color_ from the ashy gray scud of the storm. This
variety is not represented upon the general cuts. The annexed diagram
shows one phase of them, but they are readily observable at all seasons of
the year, when the N. W. wind is prevailing; differing in appearance
according to the season. Let these, as well as the storm scud, be
carefully observed and studied by the reader, and let no opportunity to
familiarize himself with their appearance be lost. A brief glance at
each recurrence of easterly or north-westerly wind will suffice.
[Illustration: SUMMER CUMULI.]
The _cumuli_ appear in isolated clouds of every size, or in vast clouds
composed of aggregated masses, as the peculiar cloud of the thunder
shower. They form as low down as the scud or fair-weather cloud of the N.
W. wind, which, for convenience, I will call N. W. _scud_; and often in
violent showers, and particularly in hail storms, extend up as far as the
density of the atmosphere will permit them to form. Professor Espy thinks
he has measured their tops at an altitude of ten miles. Others have
estimated their height, when most largely developed, at twelve miles; but
it is very doubtful whether the atmosphere can contain the moisture
necessary to form so dense a cloud at that elevation. It is their immense
height, however, whether it be six, or eight, or ten miles, together with
the sudden and violent electric action, condensing suddenly all the
moisture contained in the atmosphere within the space occupied by the
cloud, which produces such sudden and heavy falls of rain or hail. As the
rain drops or hail, when formed at such an elevation, in falling through
the partially condensed vapor of the cloud must necessarily enlarge by
accretion from the particles with which they come in contact, and probably
also by attraction, their size when they reach the earth, though
frequently very considerable, is not a matter of astonishment. The cumulus
is represented in the general plate with sufficient accuracy to show its
peculiar character.
In summer, when the air is calm, the weather warm, and no storm is
approaching, there is always, in the day time, a tendency to the formation
of cumuli. This tendency exhibits itself about ten o'clock in the
forenoon, and they gradually form and enlarge until about two in the
afternoon; and after that, if they do not continue to enlarge and form
showers, they melt away and disappear before nightfall. Sometimes in July
and August the atmosphere will be studded with them at mid-day, floating
about three-quarters of a mile from the earth (in a level country), gently
and slowly away to the eastward. At times it may seem as if they must
coalesce and form showers, yet they frequently do not, but gradually melt
away, as before stated.
The cumulus is the principal cloud of the tropics, and is not often seen
with us except in summer, or when our weather is tropical in character.
The engraving on the preceding page, shows a phase of these fair-weather
summer cumuli.
The last in order occupying (with their compounds) the higher portions of
the atmosphere, are the cirrus and stratus. The cirrus is often the
skeleton of the other, and precedes it in formation.
These are the proper clouds of the storm, in our sense of the term. While,
however, the cirrus remains a cirrus, it furnishes no rain. When it
extends and expands, and its threads widen and coalesce into cirro-stratus
and stratus, or it induces a layer of stratus below it, the rain forms.
The following is Dr. Howard's description of cirrus: "Parallel, flexuous
or diverging fibers, extensible by increase in any or in all directions.
Clouds in this modification appear to have the least density, the greatest
elevation, and the greatest variety of extent and direction. They are the
earliest appearance after serene weather. They are first indicated by a
few threads penciled, as it were, on the sky. These increase in length,
and new ones are in the mean time added to them. Often the first-formed
threads serve as stems to support numerous branches, which in their turn,
give rise to others."
The illustrations in the general cut are imperfect, and do not represent
the delicate fibers of the cloud, for it is a difficult cloud to
daguerreotype or engrave, but the representation is sufficiently accurate
to give the reader a general idea of the different varieties, and enable
him to discover them readily by observation. They are the most elevated
forms, always of a light color, and often illuminated about sunset by the
rays of the sun shining upon their inferior surface; the sun, however,
often illuminates, in like manner, the dense forms of cirro-stratus, and
the latter, from their greater density, are susceptible of a brighter and
more vivid illumination.
The stratus is a smooth, uniform cloud--the true rain cloud of the storm;
often forming without much cirrus above, or connected with it. It may be
seen in its partially formed state in the bank in the west, at nightfall,
or in the circle around the moon in the night. When it becomes
sufficiently condensed, rain always falls from it, but in moderation. If
there be large masses of scud running beneath it for its drops to fall
through (especially as is sometimes the case, in two or more currents),
the rain may be very heavy. But more of this hereafter.
[Illustration: Fig. 10.]
The annexed cut shows the forming stratus, light and thin, passing to the
east, as indicated by the short arrows just before a storm, while the scud
beneath is running to the west.
It was copied from a daguerreotype view, facing northwardly.
Intermediate between the fibrous, tufted, cirrus, and the smooth uniform
stratus, there is a variety of forms partaking more or less of the
character of one or the other, and termed _cirro-stratus_. No single
correct representation of cirro-stratus as a distinct cloud, can be
given--but several varieties will be hereafter alluded to, under the head
of prognostics. Several modifications are represented with tolerable
accuracy upon the cuts.
The cirro-cumulus is a collection in patches of very small distinct heaps
of white clouds; they are called fleecy clouds, from their resemblance to
a collection of fleeces of wool, and are imperfectly represented on the
general cut. They do not appear often, and are usually _fair-weather
clouds_.
This form has none of the characteristics of the cumulus, and does not
appear in the same stratum. It was probably called cumulus because its
small masses are distinct, as are those of the ordinary cumulus. It occurs
in the same stratum as cirro-stratus, and properly belongs to that
modification. I retain the name inasmuch as the cloud is of some practical
importance.
The cumulo-stratus is seldom seen in our climate, as it is represented in
the cut. Stratus condensation _above_, and in connection with cumulus
condensation, is not uncommon, but that precise form is rare.
This, too, is practically of no consequence, and I shall take no further
notice of it.
Recapitulating, I give (in a tabular form) the three principal strata and
their modifications, located with sufficient accuracy for illustration.
The clouds which are found in an upper or lower portion of a stratum are
so represented by the location of their names; those which appear at all
heights in the stratum, with the names across. The elevation is the
average one--although there is no limit to the cirrus above, except the
absence of sufficient moisture. It was seen by Guy Lussac, and has been by
other aeronauts, at an elevation of five miles, or more, when too delicate
to be visible below.
+------------------------------------------------+
| | 3 miles.
|Cirrus. |
| Cirro-cumulus. |
| Cirro-stratus. |
| |
Primary | { Cumulus extending up |
stratum. | { in violent showers. |
| |
| |
|Stratus. |
|------------------------------------------------|
| | 1-1/2 miles.
Scud & |N. W. scud. { Cumulus Storm scud. |
cumulus |Fair-weather { ordinarily and |
stratum. | { its base always. |
| |
|------------------------------------------------|
| | 1/2 mile.
Fog |High fog. Storm fog. |
stratum. | |
| Low fog at the surface of the earth. |
| |
+------------------------------------------------+
With the assistance of this table of elevations, and a careful
observation, the reader can soon become familiar with the forms of clouds
and their relative situations.
CHAPTER III.
Having thus taken a brief view of the different clouds, let us return to
the inquiry, from what ocean, and by what machinery, _our_ "rivers
return."
Not wholly or mainly from the North Atlantic, although it lies adjacent to
us, and they often _seem_ to do so; for, first, all storms, showers, and
clouds, which furnish, _independently_, any appreciable quantity of rain
to the United States, and even adjacent to the Atlantic, or indeed to the
Atlantic itself, come from a westerly point, and pass to the eastward.
_This is a general, uniform, and invariable law, although there is in
different places, and in the same place at different times, some variation
in their direction; ranging in storms from W. by S. to S. S. W., and in
showers between S. W. and N. W., to the opposite easterly points of the
compass; the most general direction, east of the Alleghanies, being from
W. S. W. to E. N. E._
But do we not see, you inquire--at least those of us who live east of the
Alleghanies--that when it rains, the wind is from the eastward; and that
the _clouds_ follow the wind from the east to the west? You do indeed,
generally, in all considerable storms, observe that the wind blows from
some easterly point, and that _seeming_ clouds are blown by it to the
westward; but what you see, and call clouds, are not the clouds which
furnish the rain. Far above the seeming clouds you notice, directly over
your head when it rains or snows, are the rain or snow clouds, dense and
dark, passing to the eastward, how strong soever the wind may blow from
the quarter to which they tend, or any other quarter, between you and
them. What you see below them are _scud_. So the sailors call them, and so
I have termed them. It is a "dictionary name," and a good one, expressive
of a distinction between them and _clouds_. They are thin, and the sun
shines through them, although with some difficulty, when the rain clouds
above are absent or broken. _This east wind and the scud are not the
storm, or essential parts of it._ Storms occasionally exist, particularly
in April, without either. They are but _incidents_, _useful_, but not
_necessary incidents_, as all surface winds are.
If you could see a section of the storm, you would see the rain cloud
above, moving to the east, and the scud beneath running to the west, as
indicated by the arrows in the cut on page 40. Opportunities frequently
occur when these appearances may be seen. Storms are sometimes very long,
a thousand miles, perhaps, from W. S. W. to E. N. E., and not more than
one to three hundred miles wide from S. E. to N. W., and their sides,
particularly the northern ones, regular, and without extensive partial
condensation. Then the storm cloud above, moving to the eastward, and the
scud running under to the westward, may be seen as in the cut.
So they may be seen before, at the commencement, and at the conclusion of
easterly storms, in a majority of cases, and the reader is desired to
notice them particularly as opportunities occur.
The term _running_, too, is a very expressive one, used by sailors as
applicable to _scud_. For while the forming or formed storm clouds may be
moving moderately along, at the rate of twelve to fifteen or twenty miles
an hour, from about W. S. W. to E. N. E., the scud may be running under
them in a different direction--opposite, or diagonal, or both--at the rate
of twenty, fifty, sixty, and, in hurricanes, even ninety miles an hour.
You have doubtless seen these scud running from N. E. to S. W., and
without dropping any moisture, a day or sometimes two days, before the
storm coming from the S. W. reached the place where you were; and then,
sometimes the storm cloud slipped by to the southward, and the expected
storm at that point proved "a dry northeaster." Sometimes the
condensation, although sufficiently dense to influence and attract the
surface atmosphere, and create an easterly wind and scud, does not become
sufficiently dense to drop rain, and then, too, we have a dry northeaster,
which may melt away or increase to a storm after it has passed over us. _I
have never seen, except, perhaps, in a single instance, one of these
masses of scud, however dense, which had not a rain (stratus) cloud above
it, drop moisture enough to make the eaves run._ So you see it may be
true, and if you will examine carefully, you may satisfy yourself that it
is true, that the storms all move from a westerly point to the eastward,
notwithstanding the wind under them is blowing, and the scud under them
are running to the westward.
There are many other methods by which the reader may determine this matter
himself. He may catch an opportunity for a view, when there is a break in
the stratus cloud above, and the sun or moon, no longer obscured by the
_storm cloud_, shines through the scud beneath. Then he may see they are
moving in different directions. _The upper cloud, if there be any of it
left, always to the eastward._
Again, we may see the storm approach from the westward, as it often does,
before the wind commences to blow, and the scud to run from the eastward;
particularly snow storms in winter, and the gentle showers and storms of
spring.
Again, thunder storms, we know, come from the westward, and apparently
against an east wind. It is sometimes said they approach from the east,
but it is a mistake. During thirty years attentive observation in
different localities, I have never seen an instance. They sometimes _form_
over us, or just east of us, or one may form at the east and another at
the west, and as they _spread out in forming_, one may seem to be coming
from the east, or there may be an easterly current, with dense flocculent
scud at the under surface of the shower cloud running westward, but they
finally pass off to the eastward, and never to the westward. It is
possible that a _patch of scud_ may become sufficiently _dense_ and
_electrified_ to make a _shower_, but I have never observed one. Such an
_apparent_ instance may be found recorded in "Sillman's Journal," vol.
xxxix. page 57. I have seen the scud assume a distinct cumulus form, but
never to become sufficiently dense to make a thunder shower.
Thunder and lightning sometimes attend portions of regular storms in
spring and autumn, but the thunder is always heard first in the west, and
last in the east.
Again, there are admitted facts with which you are conversant, which prove
this proposition. When it has been raining all day, and just at night the
storm has nearly all passed over to the eastward, and the sun shines under
the western edge of it, and "_sets clear_," as it is termed--you say that
"_it will be clear the next day_." Why? Because the storm will not pass to
the westward, covering the sun and continuing, how strong soever the wind
may be from the east; and because it is passing, and will continue to pass
off to the eastward, leaving the sky clear. _The easterly wind will stop
as soon as the storm clouds have passed, and it will fall calm, or the
wind will "come out" from the westward._
So, too, when the clouds are dark in the west in the morning, and the sun
rises clear, but "_goes into a cloud_," as it is expressed, you say that
it will rain. And if the clouds are dense this generally proves true;
because there is a storm or shower approaching from the west, and passing
over to the east, the western edge of whose advance condensation has met
the sun in his coming, and obscured him from your vision.
When, too, it has been storming, and lights up in the N. W. you say it
will clear off; the N. W. wind will blow all the clouds away. It is,
indeed, generally true that when it so lights up it is about to clear off;
although it sometimes shuts down again, in consequence of the approach of
another storm from the westward, following closely behind the one which is
passing off. It is a great mistake, however, to suppose the N. W. wind
blows away the clouds. Watch the smooth stratus rain cloud at its lower
edge, where the clear sky is seen, and you will see that it is moving on
steadily to the N. E., in obedience to the laws of its current, and will
do so, even when its retreating edge has passed up to the zenith, and down
to the S. E.
The storm uncovers us from the N. W. by the contraction of its width, _or_
because it has a _southern lateral extension_ and _dissolution_, and not
by being blown away by the N. W. wind; although that wind, by its peculiar
fair-weather clouds, may be, perhaps, observed beneath, ready to follow
its retreating edge.
Again, when it has been clear all day, and the sun sets in a bank of
cloud, you say--"_it will rain to-morrow, the sun did not set clear_," and
unless that bank is a thunder cloud, merely, which will pass over or by
you, with or without rain, before morning, it is generally true that it
will. The bank will prove the eastern edge of an approaching storm.
From these generally admitted and understood facts, you may know that
storms pass from the west to the east.
This proposition is also proved by all the investigations of storms, which
have taken place since the settlement of this country. Storms of great
severity attract particular attention, and are said to "back up" against
the wind, because they are observed to commence storming first at the
westward, although the wind is from the eastward. Doubtless you recollect
many such instances recorded in the newspapers. No season occurs without
such notices.
Many storms have been investigated by Mr. Redfield, for the purpose of
sustaining his theory. Many others by Professor Espy, to sustain his. One
by Professor Loomis, with great research and ability--and some by others,
accounts of all which have been published; and every one yet investigated,
north of the parallel of 30°, has been shown to pass from a westerly to an
easterly point.
So, too, we may know it from analogy. The laws of nature are uniform.
There is a great end to be accomplished, _viz._: the distribution of forty
inches of water, at regular intervals, over a large extent of country. The
rivers are to return, and the clouds are to drop fatness, and seed time
and harvest are not to cease. It is to be done and is done, by means of
storms and showers, and pursuant to general laws, as immutable as the
result. Most of these storms and showers, it has been found, and may be
observed, move from the westward to the eastward. Then we may know, from
analogy, that they do so in obedience to a general, uniform law; and so I
might say with confidence, if our inquiry stopped here, it will ever be
found by those who may hereafter examine them.
But, 2d. There is a current in the atmosphere, all over the continent
north of the N. E. trades, but in great volume over the United States,
east of the meridian of 105° W. from Greenwich--varying in different
seasons, and upon different parallels, and flowing near the earth, when no
surface wind interposes between them. In the vicinity of New York, the
usual course of this current is from about W. S. W. to E. N. E. In the
western and south-western portion of the United States, it is, doubtless,
more southerly--varying somewhat according to the season--and in other
sections varies in obedience to the general law of its origin, and
progress.
I have observed its course in many places, between the parallels of 38°
and 44° N. _This current comes from the South Atlantic Ocean._ It is our
portion of the aerial current, which flows every where from the tropics
toward the poles, to which I have already alluded in connection with the
distribution of heat. _It brings to us the twenty inches of rain which we
lose by the rivers, and by the westerly winds, which carry off a portion
of the local moisture of evaporation, and its action precipitates the
remaining portion of that moisture. It spreads out over the face of our
country, with considerable, but not entire uniformity. All our great
storms originate in it, and all our showers originate in or are induced
and controlled by it._
_From the varied action, inherent or induced, of this current, most of our
meteorological phenomena, whether of wet or dry, or cold or warm weather,
result_; and a thorough knowledge of its origin, cause, and the reciprocal
action between it and the earth, is essential to a knowledge of the
"_Philosophy of the Weather_."
Let us then go down to the "chambers of the south," to the inter-tropical
regions, of which we have said something in connection with a notice of
Southern Mexico, and see where, and how this great aerial current
originates.
CHAPTER IV.
Between the parallels of 35° north latitude, and 35° south
latitude--changing its location within this limit at different seasons of
the year--encircling the earth, and covering about one-half of its
area--we find the trade-wind region. In this region are the simple and
uniform arrangements, which extend every where, and produce all the
atmospheric phenomena. In the center of it we find that movable belt of
continual or daily rains, and comparative calms, particularly _near its
center_, about four hundred and fifty miles in width upon the Atlantic,
and over Africa, and the eastern portions of the Pacific, and something
more over South America and the West Indies, the western portion of the
Pacific and the Indian Ocean, to which we have already alluded. This belt
of rains and calms follows the trades and sun, in their transit north and
south, from one tropic to the other--its width and extension depending
upon the volume of trade-winds existing on the sides of it. Its southern
edge, when the sun is at the southern solstice, extends to 7° south in the
Atlantic, to 10° south in the Indian Ocean, and still further, probably,
over South America: on this point I do not pretend to be accurate, for
accuracy is not essential. When the sun is at the northern solstice the
southern edge is carried up as far as 12° north, over the Atlantic, and
still further over the northern portions of South America, the West
Indies, and Mexico. It travels, therefore, from south to north, over from
twenty to forty degrees of latitude. The presence of this belt of rains
over any given portion of the inter-tropics, gives that portion its rainy
season, and its absence, as it moves to the north, or the south, gives the
portion from which it has moved, its dry season. It passes in its transit
twice each year over some portions of the country, Bogota, for instance,
and two corresponding rainy and dry seasons result. Its presence, and
character, and movements, are as fixed and regular, over from twenty-five
to forty degrees of the earth's surface, _and all around it_, as the
presence and movements of the sun over the same area.
At the northern edge of this movable belt of rain, and extending in some
places, particularly in the Pacific Ocean, north about 20°, or about one
thousand four hundred miles, and in other places a less distance, the N.
E. trade winds prevail, blowing toward and into it from N. N. E., N. E.,
and E. N. E., averaging about N. E. At the south line of this belt of
rains, extending south from twenty-five to thirty degrees, or from sixteen
hundred to two thousand miles, the S. E. trades blow toward and into it,
from the S. E., S. S. E., or E. S. E., averaging about S. E. Of course the
northern limit of the N. E. trades travels north and south with the belt
of rain, toward which it blows; and so the southern limit of the S. E.
trades travel in like manner with the rainy belt, or rather, to speak with
entire accuracy, the belt of rain moves with the trades, and the trades
follow the verticality of the sun. The following diagrams exhibit
approximately, and with sufficient accuracy for illustration, the
situations of the rainy belt and the trades, when at their northern and
southern limit, as well as the manner in which it must give certain
localities two rainy seasons each year, in its transit north and south.
At the northern and southern limits of the trade-winds, and extending from
them to the poles, are found the variable winds and irregular
extra-tropical rains, all over the earth, which are shown by the shading
on the maps. This line of extra-tropical rains descends to the south,
following the retreating trades as they descend in our winter, and recedes
north before the trades when they return in spring and summer, so that at
the outer limit of the trades respectively, toward the poles, the line of
extra-tropical rains will be found, receding or following that limit, as
the trades pass up and down with the sun. From the north pole to the
northern limit of the N. E. trade-winds, wherever found, whether at 38°
north latitude, as in some places in summer when the sun is at the tropic
of Cancer; or whether at 20° to 30° north latitude, as in our winter, when
the sun is at the tropic of Capricorn; the extra-tropical rains prevail. A
state of things precisely similar exists between the south pole and the
southern limit of the S. E. trades. Between this northern limit of the
N. E. trades and the northern line of the inter-tropical belt of
rains, wherever situated (with two exceptions, to which we have alluded
and shall allude again), there is, for the time being, a dry season; and a
like dry season between the southern line of the belt of rains and the
southern limit of the S. E. trades. We have, therefore, extending around
the earth, a belt of daily tropical rains, near the center,--two belts of
drought which are mainly trade-wind surfaces, one on each side of the
central rainy belt,--extending to the outward limits of the trades and the
line of extra-tropical rains; and these rainy and dry belts, moving up and
down after the sun, a distance of from twenty to forty degrees of
latitude, each year.
[Illustration: Fig. 10. IN SUMMER.]
[Illustration: Fig. 11. IN WINTER.]
Such are the _main_ phenomena, _at the surface_, in the trade-wind region.
Ascending a step higher in the atmosphere, we find, above the
surface-trades, a counter-trade, running, not in the opposite direction,
but at right angles, or nearly so. The counter-trade which issues from the
northern side of the rainy belt, running to the N. W. or W. N. W., and the
counter trade which issues from the southern side, running to the S. W. or
W. S. W., varying, as the trades do in direction in different localities.
These counter-trades are continuations of the surface trades, which,
ascending in their course, have threaded their way through the opposite
trade in the rainy belt, and are continuing on at the same angle, and in
the same direction at which they blew upon the surface, and in obedience
to the same law. This is apparent from several considerations.
1st. They issue at the same angle, and over the top of the surface trades.
In the West Indies and elsewhere, this has been ascertained and proved by
the course of the storms, and the rotation of their surface winds, and
observation.
2d. We can not suppose the N. E. trade to be reflected, and turn back over
itself at a right angle. That would be impossible, even if there were a
wall of solid material there for it to blow against. Air is a peculiar
fluid, and it stratifies with astonishing ease. He who supposes that a
current of air put in motion can be turned aside by another current, or by
the atmosphere at rest, or can be made to mingle, is mistaken. It will
stratify, and force itself onward through the adjacent and opposing
atmosphere, and in a right line. I have observed some remarkable instances
of this character.
3d. The cause which operates to produce the surface trades, still operates
upon the current to carry it over into the other hemisphere; a
counter-trade, as we shall see. It is impossible, therefore, to believe
that the surface-trades as they arrive at the belt of rains and calms,
turn at a right angle, or at any angle, and return: and impossible to
doubt that they pass through each other in this belt, and out at the
opposite side, as upper currents, at the same angle at which they entered.
Of course the N. E. trade of the Atlantic becomes the N. E. counter-trade
of South America, carrying their storms in a S. W. direction, and the S.
E. trade of the Atlantic the S. E. counter-trade of the West Indies,
carrying all their storms in a N. W. direction; and what is true of them
is true of the trade winds _every where, all over the globe, over the land
and over the sea_.
Doubtless here some one will say, our upper current is a S. W. current.
True, the S. E. trade which enters the belt of rains, and issues out on
the north, a S. E. upper current or counter-trade, keeps that course until
it arrives at the northern limit of the surface trade, when, in _obedience
to another law_, which we shall notice, it gradually _decends near the
surface, curves to the eastward_, and becomes _the S. W. current which
passes over us_. And so we have the S. E. trade-wind of the South
Atlantic, with its moisture, warmth, electricity, and polarity, over, and
perhaps sometimes around us, dropping the electric rain which makes glad
our fields; giving us, when not prevented by other conditions, the balmy
air of spring, the Indian summer of autumn, and the mild mitigating
changes of winter; and thus, _our rivers, which run into the sea, return
to us again_.
But let us go back to the trade-wind region--the region of regularity and
uniformity--and examine somewhat more attentively its features, that we
may more fully understand the character of this counter-trade.
Here are 60° at least of the 180° of the earth's surface, and at its
largest diameter, covered in the course of the year, and of their travels,
by the trade-winds at the surface, the counter-trades above, and the belt
of rains and comparative calms, formed by the action of the opposite
trades, as they thread their way through each other, to assume the
relation of counter-trades. Truly the magnitude, simplicity, and
regularity of this machinery are most wonderful.
There are, however, some _apparent_ anomalies which deserve attention.
Here are most distinctly marked the _rainy_ and _dry seasons_, existing
side by side. Here are the _rainless portions_ of the earth, already but
briefly alluded to; here the _monsoons_, and another peculiarity, _viz._:
the _gathering of the counter-trades_ upon the western sides of the two
great oceans, into two _aerial currents of greater volume_, _analogous_
somewhat to the two _gulf streams_ of those oceans. Let us examine these
anomalies.
The rainy and dry seasons depend, as we have seen, upon the transit north
and south of the rainy belt, or belt of comparative calms. Wherever this
belt may happen on any given day to be situated, each side of it the
trades prevail, it is dry, the earth is parched, and vegetation withers.
These changes are graphically described by Humboldt in his "Views of
Nature," as they occur on the northern portions of South America, as
follows: "When, beneath the vertical rays of the bright and cloudless sun
of the tropics, the parched sward crumbles into dust, then the indurated
soil cracks and bursts, as if rent asunder by some mighty earthquake. The
hot and dusty earth forms a cloudy vail, which shrouds the heavens from
view, and increases the stifling oppression of the atmosphere; while the
east wind (_i. e._ trade-wind), when it blows over the long heated soil,
instead of cooling, adds to the burning glow.
"Gradually, too, the pools of water, which had been protected from
evaporation by the now seared foliage of the fan-palm, disappear. As in
the icy north animals become torpid from cold, so here the crocodile and
the boa-constrictor lie wrapped in unbroken sleep, deeply buried in the
dried soil. Every where the drought announces death, yet every where the
thirsty wanderer is deluded by the phantom of a moving, undulating, watery
surface, created by the deceptive play of the reflected rays of light (the
mirage). A narrow stratum separates the ground from the distant
palm-trees, which seem to hover aloft, owing to the contact of currents of
air having different degrees of heat, and therefore of density. Shrouded
in dark clouds of dust, and tortured by hunger and burning thirst, oxen
and horses scour the plain, the one belowing dismally, the other with
outstretched necks snuffing the wind, in the endeavor to detect, by the
moisture in the air, the vicinity of some pool of water not yet wholly
evaporated.
"Even if the burning heat of day be succeeded by the cool freshness of the
night, here always of equal length, the wearied ox and horse enjoy no
repose. Huge bats now attack the animals during sleep, and vampyre-like
suck their blood; or, fastening on their backs, raise festering wounds, in
which mosquitos, hippobosces, and a host of other stinging insects, burrow
and nestle. Such is the miserable existence of these poor animals, when
the heat of the sun has absorbed the waters from the surface of the
earth.
"When, after a long drought, the genial season of rain arrives, the scene
suddenly changes. The deep azure of the hitherto cloudless sky assumes a
lighter hue. Scarcely can the dark space in the constellation of the
Southern Cross be distinguished at night. The mild phosphorescence of the
Magellanic clouds fades away. Even the vertical stars of the
constellations Aquila and Ophiuchus, shine with a flickering and less
planetary light. Like some distant mountain, a single cloud is seen rising
perpendicularly on the southern horizon. Misty vapors collect and
gradually overspread the heavens, while distant thunder proclaims the
approach of the vivifying rain. Scarcely is the surface of the earth
moistened, before the teeming steppe becomes covered with Killingiæ, with
the many-panicled Paspalum, and a variety of grasses. Excited by the power
of light, the herbaceous Mimosa unfolds its dormant, drooping leaves,
hailing, as it were, the rising sun in chorus with the matin song of the
birds, and the opening flowers of aquatics. Horses and oxen, buoyant with
life and enjoyment, roam over and crop the plains. The luxuriant grass
hides the beautiful and spotted jaguar, who, lurking in safe concealment,
and carefully measuring the extent of the leap, darts, like the Asiatic
tiger, with a cat-like bound on his passing prey."
Such is Humboldt's description of the dry season on the Orinoco, and the
return of the belt of rains from the south.
Again, within this trade-wind region are the _rainless countries_. These
are portions of the earth which the equatorial rainy belt does not ascend
far enough north in summer to cover, nor does the southern edge of the
extra-tropical regular rains descend, in winter, far enough south to cover
them, and where, of course, rain seldom, if ever, falls. Such are the
central parts of the Desert of Sahara, Egypt, Arabia, portions of
Affghanistan, Beloochistan, and the western parts of Hindoostan, to the
north of the inter-tropical belt, and a similar state of things exists
south of the equator in parts of South America, Africa, and New Holland,
although upon a comparatively small surface.
Again, another anomaly is the gathering of the trade winds into greater
volumes, on the westerly side of the great oceans, and the consequent
carrying of the equatorial rainy belt up to the region of extra-tropical
rains, on the eastern side of the great continents of Asia and North
America, and the peculiar liability of these aerial gulfs to hurricanes
and typhoons. Such an aerial gulf gathers over the Caribbean Sea, and the
West Indies. Passing across the Gulf of Mexico, it enters over Texas, and
Louisiana, and the other southern states; its western edge passing north
in autumn and winter, on the eastern side of the highlands of Western
Texas, New Mexico, and the Great Desert; curving, as all counter-trades
do, to the eastward as soon as it passes the limit of the N. E. trades,
and spreading out over our favored country, leaving the evidence of its
pathway in the greater quantities of rain, which fall annually upon its
surface. This gathering deprives a portion of the Atlantic, north of the
tropics, of its share of the counter trade, and there, as every where,
where the volume of counter-trade is small, storms and gales are
infrequent, and of less force, and comparative calms prevail. That portion
of the Atlantic has long been known as "the horse latitudes," a name given
to it by our Yankee sailors, because, there, in former times, the
old-fashioned, low-decked, flat-bottomed, horse-carrying craft of New
England, bound for the West Indies, often floundered about in the calms
and baffling winds, until their animals perished for want of water, and
were thrown overboard. Lieutenant Maury, in his most praiseworthy and
exceedingly useful investigation of "The Winds and Currents of the Ocean,"
has defined the situation of these calms and baffling winds at different
seasons--for they move up and down, of course, with the motion of the
whole machinery--and enabled navigators to avoid them, by running _east_
before they attempt to make _southing_; and very materially shortened the
voyages to the equator.
A like gathering, in volume, of the S. E. trade, on the western side of
the Pacific, enters over Asia, and covers China and Malaysia, extending,
in its western course, nearly as far as the western edge of Hindoostan. In
this concentrated volume of counter-trade, and owing to its concentrated
action, form and float the typhoons of the China Sea, and of the Bay of
Bengal; and to this anomalous aerial gulf stream, the S. E. portions of
Asia, from the western desert of Hindoostan, to the eastern portion of
China, north of the rainy belt, owe their great supply of moisture and
fertility, and their peculiar climate. The western line of this volume of
counter-trade is marked by the eastern portion of the rainless region of
Beloochistan, and the north-western deserts of India, as the western edge
of our concentrated volume of counter-trade, is marked by the arid plains
of northern Mexico, western Texas, and New Mexico. On the south of the
equatorial rainy belt, there is no corresponding aerial gulf of equal
volume, as there is no corresponding gulf stream of equal magnitude. On
the western side of the Indian Ocean we find a gathering of the N. E.
trades from the Bay of Bengal and the Indian Ocean, in which form and
travel the hurricanes which prevail--traveling to the southward and
westward--about the Isle of France or Mauritius; and the lagullus oceanic
current, which runs down to the S. W. toward the Cape of Good Hope. But
the extension of South America to the eastward, under, or just south of
the N. E. trades, does not permit the formation of such a concentrated
volume on the western side of the Atlantic, nor is the strength or
regularity of the N. E. trades, on that ocean, equal to those of the S. E.
Nor is the magnetic intensity on the eastern and middle portions of the
Pacific, sufficient to produce such a concentration, in large volume,
there. The trades over that ocean, therefore, curve without concentration,
except a partial one, over the western groups of Polynesia, which the
Asiatic line of magnetic intensity approaches and where hurricanes are
sometimes found, until we arrive near the eastern line of magnetic
intensity, on the eastern side of Asia. We shall, hereafter, have occasion
to follow the anomalous concentrated volumes of the S. E. counter-trade,
of the northern tropic, on the western side of the great oceans, in
explanation of some of the phenomena which we find north of the trade-wind
region. Suffice it here to add, that if it were not for the concentration
of these counter-trades, on the western side of the great oceans, the
rainless region between the parallels of 20° and 30° would encircle the
earth; and China and the Eastern United States would have a distinctly
marked rainy and dry season, as have California, the Barbary States,
Syria, Persia, and other countries which lie north of the rainless region,
within the summer range of the N. E. trades, but also within the winter
descending range of the belt of extra-tropical rains.
Another anomaly which we find in the trade-wind region, is the monsoon.
There are several of them, but they are found, in the greatest strength
and regularity, in the Indian Ocean. Another, defined by the
investigations of Maury, is found on the west coast of Africa, extending
out over the Atlantic. Another prevails on the western coast of South and
Central America. The etesian winds of the Mediterranean are but the N. E.
trades, whose northern limit is carried up in summer, by the transit of
the connected machinery, to the north, over that sea. The N. E. and S. E.
monsoons, so called, of the Indian Ocean, are but the regular trades,
blowing when the belt of rains is absent, as they do all over the globe.
The N. W. monsoon, south of the equator, in the vicinity of New Holland;
the S. W. monsoon which blows from the Arabian Sea, in upon Hindoostan;
the S. W. monsoon of the Atlantic, south of the Cape De Verde Islands; and
the variable west monsoon winds of the west coast of Southern and Central
America, and Southern Mexico (known under several different names, but
chiefly by that of Tapayaguas), are all that deserve attention as such.
At first sight they appear to be anomalies, but the facts declare their
character with perfect certainty. First, they are not continuous, like the
trades, but _prevailing_ winds, and are _storm winds_; _they always blow
toward a region_, _or portion of the ocean_, _covered at the time by
clouds and falling weather_.
Second, they do not blow upon, or toward, heated surfaces of land or
water--_i. e._, toward the dry and parched surfaces, where the dry season
prevails, or from adjoining cold waters on to warm surfaces, but toward
the land or water _situated under the rainy belt_. They are therefore
incident storm winds, (as our easterly winds are incident storm winds) of
the rain clouds of the tropics. They blow in upon the land, under the belt
of rains, while that belt with its daily cloud, and inducing electric
action, is over it, and follow that belt in its transit north and south.
They blow from the warm south polar current of the Atlantic, which flows
N. W. from the coast of Africa, toward the inshore north polar current,
which is there flowing south, but under the belt of rains. In the Indian
Ocean they blow from the center of that ocean, and the Arabian Sea, toward
the belt which hangs over Hindoostan, from the S. W.; and when the rainy
belt travels south they still blow toward, and under it, from the Indian
Ocean, but of course from the N. W. The heated character of the waters of
the Indian Ocean and Arabian Sea, which receive no polar currents, but
heated waters from the Persian Gulf, and from rivers which flow into the
Bay of Bengal over the heated plains of a tropical country, explain this.
So, too, the monsoon of the Atlantic Ocean, does not blow north of the
Cape De Verde Islands,--where the heated surface of Sahara, burning with
the rays of a vertical sun, has a temperature sometimes ranging from one
hundred and forty to one hundred and sixty degrees--but remains under the
rainy belt, drawn from the heated waters which flow up from the South
Atlantic, and travels north as the rainy belt travels north in summer, and
south to the Gulf of Guinea, as that travels south in winter. The same is
true of the Pacific monsoon, the Tapayaguas, the least marked of all,
which blows in during the rainy season upon the west coast of Southern
Mexico, and of Southern and Central America. They are all incident rain or
storm winds, blowing in upon the land, or on to a colder surface of
different polarity, _during the rainy season_; and if it were possible to
catch one of our north-easters, in its passage over our country to the
eastward, and anchor it to the Alleghanies, "paying out" so to have it
reach in part over the Atlantic, and keep it there in operation six
months, we should have a continual easterly wind under it; a _monsoon_
more strongly marked than the monsoons of the Indian, or Atlantic Oceans.
_The received theory in relation to them is a fallacy._
Recapitulating, then, all the phenomena, we have,--_Surface-trades_,
blowing toward the center, passing through each other, and continuing on
as upper or counter-trades; a _belt of rains_, with calms near the center,
formed by the trades where they meet and pass through each other, which
travels with them north and south following the sun; _two belts of
drought_, following the belt of rains and the trades, and followed by the
_extra_-tropical line of rains, as it travels with the trades and the
rainy belt, leaving a part of the earth which the equatorial rainy belt
does not travel far enough north, nor the extra-tropical line of rains far
enough south to cover, and which is consequently a _rainless region_; _the
monsoons_, which are but incidents of the rainy belt, and the _gathered
volumes_ of counter-trade, on the west of the two great oceans, which
usurp the place of the N. E. trades, carrying the rainy belt up to the
region of extra-tropical rain, and preventing the rainless region from
encircling the earth.
Upon _what cause_ do these great central phenomena, so vast, so regular,
so wonderful, depend? What is the _motive power_ of this connected
atmospheric machinery, whose action and influence extend over the entire
globe?
"_Heat, heat_," say the text books, the Professors, the votaries of
meteorology. "All these phenomena are owing to the heat of the sun. It
heats the ocean and the earth--the air is thereby heated and rises, the
cold air rushes in from below, then the ascended current rolls off each
way at the top toward the pole, acquiring a westerly motion from the
rotation of the earth, slipping away from under it, and a different,
_viz._: an easterly motion, after reaching the latitude of 30°, from the
_same rotation_; and all the winds and disturbances of the atmosphere are
produced in the same way. They are produced by the action of heated
surfaces upon the adjacent atmosphere."
This is the great theory of meteorologists, by which they attempt to
account for the various atmospherical disturbances, of both tropical and
extra-tropical regions.
The whole theory is a fallacy--it will not stand the test of a careful
examination. The bases of the theory, which are assumed to be facts, are
not so. The agent has not the power claimed for it. A heated surface,
alone, never caused any considerable ascending current, or if it did,
never produced a mile of wind. I repeat it, the theory and all incidental
ones--the thousand explanatory and modifying theories, and
hypotheses--_the whole system_--is without foundation in fact, and will
not bear a critical examination.
Let us see if this language is stronger than the facts will warrant.
The theory assumes that both the land and water, under this central belt,
where the air is supposed to be rising are _materially hotter_ than the
land and ocean are on _either side of it_. Now, how much hotter are the
air and the land under the belt of rains and calms, upon Hindoostan, or
Africa, or South America, where the former is supposed to be acquiring
heat and expansion so rapidly, and to be ascending, than under, and in the
dry belts on either side? None; it is cooler by the thermometer--_much
cooler_.
The central belt of rains in midsummer over Africa, extends up as far as
17° north latitude, and perhaps further. North of this line over the whole
surface of the desert, the Barbary States, a part of the Mediterranean,
and some portion of Italy, the dry season extends, and from the entire
surface the N. E. trade blow into the central belt.[1] Over the desert
they all pass. Now this desert is a sea of sand, under a vertical sun,
intensely heated, blistering the skin with which it comes in contact, and
often acquiring a temperature of 150° to 160° of Fahrenheit. Under the
central belt of rains neither the earth nor air exceed the temperature of
84°. And yet the hot air of the desert does not ascend, but blows into
this cooler central belt; and when it is felt as it blows off the western
coast by the mariner, or even in Guinea, when the belt of rains has gone
south in winter, as it often is as the _harmattan_, it is suffocating and
intolerable. There, then, not only is it untrue, that the land and the air
over it under the rainy belt are hotter, but it is true that intensely
heated air blows horizontally from the Desert of Sahara. Nay, as it will
appear in the sequel, this hottest of all surfaces not only can not have a
vortex, but it can not induce a monsoon, and scarcely a sea breeze. The
same is true in a great degree of the surface, and the air over it, on
either side of the supposed vortex of the rainy belt upon South America.
See the description of Humboldt, already given, where the thermometer
stood as high as 115° of Fahrenheit in the shade, while the N. E. winds,
the regular trades, were blowing over the land. And it is equally true of
Arabia, and indeed of every portion of the earth. There is not a spot upon
the globe where the land and the air are cooler _by the side_ of the
central belt of rains, than _under it_. _And the opposite is true every
where upon the land._
How much hotter is the ocean and air under this supposed vortex? But
little hotter than they are on the side where the sun is not vertical,
_and none on the other_. Let us be a little more particular. The
temperature of the Atlantic under the belt of rains in our winter, and on
the south of the belt at the latitude of 3° south, and down to 9° or more
south, is 82°. The air may range a degree, or possibly two, higher than
the water at either point. On the north this difference is from nothing at
the meeting of the trades and belt of rains, to about 4° at their northern
limit. This is too _trifling_ to be worth one moment's consideration. It
is less, far less than the difference between the water and air of the
Gulf Stream which runs along our coast, and the adjoining waters and air
over them. While on the south side of the belt of rains the _difference is
actually against the theory_--and the same state of things is reversed in
summer, when the sun is vertical at the north.
From the log of an intelligent shipmaster, found in the wind and current
charts of Lieutenant Maury, I abridge the following, which will illustrate
this. Captain Young in February, found the N. E. trades at about 17° north
latitude, with the water at 75° and air at 76°, trade-wind N. E.
At 12° 16' the water was 75° the air 76° wind N. E.
Feb. 22d. 9° 49' " 76-1/2° " 77° " N. E.
" 23d. 7° 13' " 78° " 78° " N. E.
" 24th. no obs. " 79-1/2° " 79° " N. E.,
E. S. E. rain.
" 25th. 3° 10' " 81° " 83° " E. S. E. rain.
" 26th. no obs. " 82° " 82° " S. E. to
E. S. E. hazy,
rain & sqs.
" 27th. 2° 24' " 82° " 82° " calm,
with rain.
" 28th. no obs. " 82° " 82° " calm rain.
March 1st. 0° 29' " 82° " 82° " E. S. E.
sqs. rain.
" 2d. 1° 27' S. L. " 82° " 82° " S. E. sqs.
rain.
" 3d. 2° 44' " 82° " 83° " S. E. &
S. S. E.
weather
settled.
" 4th. 4° 17' " 82° " 83° " S. S. E. &
S. E. fair
weather.
" 5th. 6° 08' " 82° " 84° " S. E. fair
wthr.
" 6th. 8° 08' " 82° " 84° " S. E. &
E. S. E. fair
weather.
Here the air was seven degrees colder at the extreme limit of the N. E.
trades than in the _center_ of the belt of rains, as it is, usually, in
mid-winter, but not in summer. On the other hand, _after he left the
region of calms and rains_, where the water and air stood with almost
entire uniformity at 82°, on the 3d of March, and for three days
thereafter, during which he was in the S. E. trades with fair weather,
the water was the same as under the supposed vortex, _viz._, 82°, _and the
air rose to 83° and 84°_! _This is demonstration._
I also take from a letter of Lieutenant Walsh to Lieutenant Maury,
relative to the cruise of the "Taney" the following, showing the warmth of
the Gulf Stream compared with the adjacent ocean.
"We first crossed the Gulf Stream on the 31st of October; we struck
it in latitude 37° 22', longitude 71° 26' as indicated by the
temperature of the water, which was as follows:
8 A.M. water at surface 66°
9 " " " 73°
10 " " " 76°
11 " " " 77°
77° was the highest temperature found in crossing at this time.
Re-crossing it in May, in latitude 35° 30', longitude 72° 35', he
found the water as follows:
8 A.M. water at surface 71° 8'
9 " " " 73°
10 " " " 75° 5'
11 " " " 78° 5'
12 M. " " 78° 5'
79° being the highest temperature found."
The average difference between the temperature of the water of the Gulf
Stream and the adjoining ocean, at the line of division, is about ten
degrees, increasing to more than twenty on approaching the coast, and
within one hundred miles--a far greater difference than is ever found on
the winter side of the inter-tropical rainy belt.
It is not only not so, then, that the surface of the ocean is materially
warmer under the belt of rains than the adjoining surface under the
trades, especially on the summer side, but if it were so, the trades would
not be created thereby, any more than upon the Gulf Stream. And the
opposite is true of the land where the line of calms, and rains, and
drought meet, all around the globe. The fact assumed is therefore untrue.
The hottest surfaces, even at the rainless portion, where there is no
vortex, no storm, and no wind but the continual uniform N. E. horizontal
trade-wind, _never_ created, by reason of the heat alone, a mile of wind,
a storm or shower.
But, again, the belt of calms, where the air is supposed to rise and
create a suction which draws the trades on either side a distance of from
one thousand to two thousand miles, an average of three thousand miles in
all, at least, is not itself, on an average, over five hundred miles in
breadth from north to south. What a wonder of meteorology is here!
With a breadth of five hundred miles, the rising of the atmosphere is
supposed to be so rapid and of such immense volume that it draws the
surface atmosphere, one thousand to fifteen hundred miles on one side and
two thousand on the other, with a uniform steady velocity of twenty miles
per hour. Is this vast suction found by the unlucky mariner who may be
drawn within the vortex? _Not at all._ He finds no rapid suction there,
but _horizontal currents_, not steady, indeed, like the trades, and
sometimes calms _at the center_, but still the _currents are there_, and,
_except near the center, there as squalls, showers, and baffling winds
and as monsoons_.
Again, is there at the mouth of this vortex, or as you approach it, an
increased rapidity in the trade corresponding to the magnitude of its
influence? Does the trade become a hurricane as it approaches the spot
where it is to supply the place of that which has suddenly "expanded by
heat, and been forced to rise, boil over, and run off at the top in turn?"
Not at all. It blows gently, even up to the very line of the rainy belt,
and becomes squally and baffling, falls gradually calm near the center, or
changes to a monsoon.
But, again, the belt of rains is so far from being a belt of calms
strictly, that its monsoons in the Indian, Atlantic, and Pacific Oceans,
at times, extend hundreds of miles out over the ocean. That of the
Atlantic, triangular, with its base resting on Africa, according to
Lieutenant Maury, extends sometimes almost to the coast of South America,
a distance of one thousand miles, and thus under the supposed ascending
vortex. Where is the great uprising suction during the prevalence of this
extensive surface horizontal monsoon beneath it? Manifestly it does not
exist. Nay, that monsoon is blowing from the warm current which sets up
from the Cape of Good Hope toward the Caribbean Sea, and over the cold
north polar current, which runs down between the continent and the Cape de
Verdes. Equally untrue is the presumption that the air rises over heated
portions of the earth elsewhere, and by reason of such heating.
_Perpendicular currents of the atmosphere are rarely seen, never
extensive, or attaining any considerable altitude._ I have watched for
them thirty years. I have seen currents of air ascend, with their moisture
condensing as they ascended, and unite with the under surface of a highly
electrified cloud--the advance condensation of a thunder shower--but that
cloud was moving horizontally at a distance of from one to two thousand
feet above the surface of the earth, and did not rise. I have seen patches
of scud rising from the surface during the intervals of a showery and
highly electrified storm, toward, and uniting with, the clouds above, when
very low, as I have seen them approach and unite horizontally; and
doubtless there is a tendency upwards of the wind, created and attracted
by the summer shower, as may be seen in the ascending dust before the
rain, but I have never been able to detect an ascending current, except as
induced and attracted by a cloud above moving horizontally, in the hottest
day or dryest time. None of the clouds of our climate, even when the earth
is heated and parched by a two months' unbroken drought, can be detected
rising above the strata in which they form. I have watched the cumuli at
such periods when they filled the air, and can assert that they never
rise. The atmosphere moves, invariably, in horizontal strata, and the
whole theory of ascending currents is fallacious.
But let us look still further at the tropical currents. The true harmattan
of north-western Africa (for the term is sometimes misapplied), hot and
blistering, generated upon the sand of the desert--why does it blow from
Sahara horizontally, on or over cooler surfaces, following the belt of
rains as a N. E. trade? Why does it not ascend? The sirocco of north
Sahara, the kamsin or chamsin of eastern Sahara, and the simoon of Arabia,
which blow hot and suffocating from those deserts--why do they blow _from_
heated surfaces and _horizontally over_ cooler ones? Why do they not
ascend? Arabia is surrounded on three sides by seas and gulfs, from which
evaporation is rapid. Her interior deserts are extensive and intensely
hot--why are they rainless? Why do they not have a _vortex_, a _monsoon_,
or even a _shower_? Because there is no such law or action as this theory
supposes. Those winds blow horizontally in obedience to other laws, and
under the control of other and more powerful agents. But further still,
what heating and ascending process is it that makes the variable winds
north of the tropics? that brings in the warm air and fog of the Gulf
Stream upon our _snow-clad coast_, in mid-winter, to increase the January
thaw? Nay, what heating process is it that disturbs the calms of the polar
regions with fresh breezes and gales, sometimes of the force of 6, when
the _sun does not shine_, the thermometer is from 20° to 40° below zero,
the _earth and sea one frozen surface_, and the hardy explorer dressed in
furs, barely lives in his cabin covered by an embankment of snow, and
heated by a stove?
Gentlemen, meteorologists, it will not do. The theory is unsound; the
assumed facts do not exist. The whole universe has not an agent, organic
or inorganic, which can play such absurd and inconsistent pranks in the
face of its Creator, as your various and complicated theories assign to
caloric.
Away with the theory and all its incidental and complicated and mystified
hypotheses, they rest like a pall upon the science;--away with the whole
system, and let us seek some agent whose _power_ and _adaptation_
correspond with the _extent_, and _simplicity_, and _magnificence_ of the
phenomena, and, in some degree, with the _power_ and _wisdom of their
Author_.
CHAPTER V.
One, and the principal end attained by the power of the agent, is the
gathering of a volume of atmosphere from, or near, the _surface_ of the
land and sea, so as to ensure its possession of all the moisture of
evaporation which rises from the locality, and the highest degree of
temperature, and from a space ranging from one to two thousand miles in
width, in one hemisphere, and to carry it over into the other. Not over
the top, or upon the top, of the whole mass of atmosphere situated in the
opposite hemisphere--_out of reach of all influences from the earth_--but
through it, and curving gradually down near to, and within influential
distance of the surface of the earth, soon after it passes the outward
limit of its fellow trade; and to continue the current onward, leaving
portions of it and its heat and moisture on the way, but taking a
considerable volume up and around the magnetic poles--it being impossible
for the entire volume to be thus carried around the poles in consequence
of the diminished circumference of the earth. To this end it is obvious it
must possess _polarity_.
Another end to be attained is to combine the moisture of evaporation with
the air, so that the cold atmosphere through which, or the earth over
which it passes, may not be _continually condensing its moisture_, and
thereby _enveloping the earth in a perpetual mist_; but so that it may
part with it at _intervals_, making _cloudy_ and _clear days_; and part
with it in _portions_, so that a _regular_ and _necessary supply_ may be
furnished to the _entire hemisphere_, even up to the geographical poles.
Is there such an agent? There is, precisely and perfectly adapted to the
ends to be attained, ever there and ever active, and that agent is
_magnetism_.
[Illustration: Fig. 12.]
The earth is a magnet. It has its magnetic poles, and they are distinct
from its geographical ones; and there are two in each hemisphere. They are
situated from 17° to 19° distant from the geographical poles; and ours is
not far from longitude 97° W. from Greenwich, and 71° north latitude.
Navigators have gone north and north-west of it, and found its situation
by the declination of the needle. From these poles, lines of magnetic
intensity extend to the opposite and corresponding pole of the other
hemisphere, and upon or near those lines the needle points north without
variation; and toward these lines of no variation the needle every where,
on either side declines. The foregoing diagram shows the situation of our
magnetic pole and line of no variation, the dip of the needle by the
arrows, and the magnetic equator.
Recent discoveries have shown that the magnetic force is exerted in lines
and currents; that such currents, as physical lines of force, surround
magnets, and currents of electricity. Doubtless such lines of force exist
around the earth and the magnetic poles. There are also _longitudinal_
lines of force existing and active, between the poles, and extending from
one side of the center to the other, occupying nearly one third of the
magnet. If you take a large needle thoroughly magnetized, place it upon
paper and drop filings of iron upon it, they will become arranged about it
in circular and perpendicular, and also in _longitudinal lines_,
conforming to the currents.
[Illustration: Fig. 13.]
This experiment is illustrated in all our books on natural philosophy.
The foregoing diagram, copied from Olmstead's Philosophy, does not show as
accurately as Faraday's projection of the lines upon a globe-magnet the
comparative distance from the poles of the needle, at which the
longitudinal currents commence and terminate, and _where the filings will
not adhere_ to any considerable extent. The lines shown upon the needle
should bear the same proportion to its length as the trade-winds bear to
that of the earth, measured from pole to pole, and if the needle had a
globular form they would so appear.
These lines are made by currents arising from one side of the magnetic
equator, and passing over to the other. Doubtless, just such currents
rise, and pass over upon the earth.
Magnetic and electric currents carry the air with them. This is well
settled by experiment. _Oxygen_, too, is _magnetic_, and capable both of
receiving and retaining polarity and of combining with, or attracting and
retaining vapor, and of course the moisture of evaporation. Here then we
have a power existing, capable of producing the result--precisely, and
with evident wisdom adapted to its production--ever present and active;
and no other known agent can.
Is it not then the agent?
Let us look a little further. This result is affected by the action of the
sun: the trades with the central belts of rains travel north and south
after it; so does the sun affect the magnetic currents every where, even
the magnetic needle is daily affected by its action, as it increases the
intensity of the terrestrial magnetic currents, and hence its well
established diurnal oscillations.
Again, along the eastern lines of the continents which skirt the great
oceans on the west, run the northerly and southerly lines of no variation,
and of greatest magnetic intensity. Here are the trade currents gathered
into a volume, which curve and carry unusual fertility to South-eastern
Asia, and North America, and in those great aerial gulf streams we find
the _intense_ electric action which produces the typhoons of the former,
and the hurricanes of the latter. It may still be said that these
conditions and phenomena of the trade-wind region, are not produced by
magnetism or magneto-electricity, _but the objector can point to no other
adequate power_. That it must be heat, electricity, or magnetism, must be
admitted. There is no other power known. Heat demonstrably can not produce
them. Magnetism or electricity therefore must, and they are doubtless
states or phases of the same power, producing in their different states or
phases the different results. And even heat--atmospheric temperature, is
often, if not always the result of their action. In the present state of
science, it is enough for me that the _magnetic longitudinal currents are
there_; that they are _lines of force_ and _adequate_; that _oxygen is
magnetic_, and therefore the atmosphere must be affected by them--that so
far as we can reason from analogy, they ought to produce the effect upon
the atmosphere which we find produced, and until further light is thrown
upon the subject I shall presume that they do. Every step we take
hereafter in this investigation will confirm the presumption.
There is one peculiarity to be more particularly noticed before we leave
the trade-wind region, and we are now prepared to notice it.
The belt of rains, formed by the currents of the two trades, threading
their way through each other--how are they produced? Why should the place
where the currents thus pass through each other be a place of almost daily
precipitation? There is, in fact, no ascension, except that which the
currents have in their line of ascent to attain the elevation which the
magnetic law of the current requires.
The trades have passed over an evaporating surface and are charged with
moisture. This moisture they hold in magneto-electric combination.
_Evaporation_ does not depend upon _temperature_. Ice and snow evaporate
at all temperatures (Howard, vol. 1, p. 86). So the cold N. W. wind, full
of positive electricity, will lap up, as it were, the pools from the
earth, with astonishing quickness; and when this electricity is deranging
the action of the machinery and material of the manufacturer, he allays it
by a supply of moisture, with which the electricity can combine. Nor does
the air lose its moisture when below the freezing point. In all parts of
the atmosphere, as at the surface of the earth in winter, moisture is held
in large quantities in the coldest and severest weather; and it is not
till it moderates, and a perceptible _electric_ change takes place, that
it is precipitated as rain or snow. Doubtless there is an exposure of
considerable surfaces, of opposite currents, charged with opposite
polarity, and a constant depolarization where their surfaces meet. May
there not be a consequent dissolution of the electro-magnetic combination
between the air and moisture, or the excitation of that electric action
which attends or produces like rains every where? and hence the constant
precipitation. This is rendered probable, by the fact that precipitation,
at the meeting of the trades, takes place in level countries in the
day-time, between 10 A. M. and sunset, in showers, with thunder and
lightning, as with us in summer, although among the mountains the rain
sometimes falls in the night also. The precipitation in the heat of the
day is obviously induced by the action of the sun, although it is by no
means certain that the friction of the opposing surfaces does not assist
in the operation.
I am well aware that the lines of magnetic force curve upward and carry
the trades with them, and that, therefore, precipitation by condensation
from the mere cold of the upper stratum of the atmosphere is possible.
But, there are three reasons why I do not believe such to be the fact.
1st. Precipitation takes place in the day time mainly, and in sudden,
isolated, heavy showers and not in steady continuous rain. Nor is there
condensation or continual mist at other hours of the day.
2d. They occur at a time of day when the sun is affecting the magnetic
currents most powerfully, _viz._, between ten o'clock A. M. and sunset,
and mainly at the time of greatest heat.
3d. The counter-trades _do not precipitate_ after they leave the rainy
belt, although at a great elevation, until they reach the outward limits
of the trades; and they _do precipitate again_, although they gradually
descend _nearer the earth_, as soon as they become subject to the action
of the currents of an opposite magnetism. Their precipitation is partial
too, even then, and they carry a portion of their moisture through an
atmosphere of the coldest temperature up to the geographical poles.
A similar result attends the action of the sun in the extra-tropical
regions. Cumuli commence forming in the counter-trade, or at the line
between that and the surface current, at the same time of day that the
diurnal motion of the magnetic needle commences, or the rain clouds form
in the tropics; they continue to enlarge here as there, till about the
same hour of the day that the _needle_ obtains its maximum diurnal
variations; and when the influence of the sun upon the needle ceases, and
it returns to its original status, the cumuli disappear. Hail storms too,
it is said, always, or generally occur in the day time.
In like manner the sea-breezes and other fair-weather surface winds, rise
in the forenoon with the influence of the sun upon the magnetic currents
and the needle, and die away at nightfall when the influence ceases.
There are other electro-magnetic, or to speak more correctly,
magneto-electric, effects of the sun's action equally illustrative, which
tend to show that the precipitation at the passing of the trades, is the
result of their action upon each other, aided by the sun, to which we
shall allude when we come to speak of the causes and character of the
surface winds of the extra-tropical regions.
As, however, this takes place only, or mainly, where the threading
surfaces meet, it is but partial, and the body of the respective polarized
currents pursue their way unaffected, toward the opposite magnetic
pole--and there for the present we leave them.
Storms sometimes originate in these currents, when concentrated, as in the
West Indies, the China Sea, the Bay of Bengal, and Indian Ocean, while
passing through the rainy belt, and move with the current to the
north-west if issuing on the north side of it, and to the south-west if
issuing on the south side of it, until they respectively get beyond the
extreme limits of the trades, and then they curve to the eastward,
imbedded in and following their current. The peculiar extension of the
land to the east on the northern portions of South America, prevents the
gathering of an aerial gulf similar to the one which we have described to
the north-west, entering upon our division of the continent over the Gulf
of Mexico. It is otherwise in the Indian Ocean, and there the storms are
found issuing from the rainy belt on the southern side, sweeping over the
Mauritius and other islands of that ocean, and _often simultaneously_ with
storms issuing on the north over the Bay of Bengal. Colonel Reid mentions
instances and gives a diagram.[2]
These storms in milder forms issue from the rain belt at other points, and
may issue any where, but will always be found most extensive and most
violent, that is to say, as hurricanes and typhoons, in the concentrated
volumes of counter-trade on the western side of the great oceans, within a
few hundred miles of the lines of magnetic intensity and no variation, and
when they form in the rainy belt they are highly electric. Most
frequently, however, as we shall see, they form in these currents after
they have issued from the rainy belt, and after they have passed the
extreme limits of the trades and become subject to the circular and
perpendicular magnetic currents which exist north and south of the
longitudinal ones, and which when seen upon the magnetic needle, attract
the filings and cause them to adhere--although but slight attraction or
adhesion takes place where the longitudinal currents exist.
Such, then, are the atmospheric arrangements and phenomena of the
trade-wind region, and the cause that produces them; such is the character
and cause of the enlarged volume of counter-trade, which spreads out and
blows over our country as permanently as the S. E. trades blow on the
South Atlantic and South America, returning to us the rivers which had run
from us to the sea.
CHAPTER VI.
Coming back now, to a consideration of the course and functions of the
counter-trade after it leaves the northern limit of the surface-trades, we
find it curves to the eastward and gradually assumes about an E. N. E.
course, and becomes a W. S. W. current where it crosses the line of no
variation, and continues on until it passes off over the Atlantic; and
this course and curve is analogous to what may be found true of the
counter-trades every where. It is best illustrated by the course of all
the storms (in the American sense of the word, as distinguished from
thunder showers and other brief rains), which have been traced north or
south of the limits of the trades. It was found by Mr. Redfield in most of
the storms investigated by him, which originated within, or north of the
tropics.
Doubtless it was the actual course of the others, and that the
investigation was imperfect. All the great autumnal, winter, or spring
storms which have traversed the whole or any considerable portion of the
territory of the United States, east of New Mexico, which have been
investigated by Professors Espy, Loomis, Redfield, or others, have been
found to follow this course. A storm which passed over Madeira, appears
from the investigations of Colonel Reid to have followed the same law of
curvature.
And so, doubtless, did another which he has described as passing over the
Levant. The storms which supply the winter rains of California and Utah,
reach them by this law of curvature and progress, after the northern
limits of the trades have descended to the south with the sun, so that the
counter-trades of the Pacific may descend to the surface and curve in upon
them. But the absence of a concentration of the counter-trade, and its
deficient action because of its passage over mountain ranges, and their
location so near the northern limit of the trades that their storms can
not expand and become extensive, as well as their weaker magnetic
intensity, prevent their storms from becoming violent, and their supply of
rain is not large and much of it falls in showers. The same is true of the
Barbary States, of Syria, and Persia, and of Southern Europe; and indeed
of all the countries of the globe which lie between the winter and summer
extreme limits of the surface-trades, and without the limits of the two
concentrated counter-trades. Enough appears in the writings of the
meteorologists of Europe to show, that their long continued rains, which
are analogous to our storms and are _preceded by the formation of the true
cirrus of the counter-trade_, follow the same great law of curvature and
progress; although the presence of the Gulf Stream with its mass of south
polar waters on the western side of the British Islands, Denmark, and
Norway supplies them with showers, and fogs, and cumuli from the west and
north-west, and makes the mean of the surface winds of their storms
somewhat variant from ours. A like law reversed prevails in the southern
hemisphere. The storms of New Holland and the Indian Ocean, south of the
limits of the trade, curve to the eastward and travel about south-east,
their _south-west_ being a _clearing off wind_ as our _north-west_ is, and
_precisely similar in all its other characteristics_, where the relation
of magnetic intensity is the same.
The storms of the Pacific on the S. W. coast of South America, in like
manner travel to the S. E., flooding the western slopes of the mountain
ranges with rain, and aggravated by the intensity of the magnetic currents
at the extremity of the continent in a high latitude, meet the mariner in
the face as he emerges from under the lee of the land and attempts to pass
the Horn. It will ultimately be shown that the precipitation which takes
place, as the storms and counter-trades pass north and east in the
northern hemisphere and south and east in the southern hemisphere, is
owing less to cold than increased magnetic intensity. And all this is the
result of one great uniform law, existing every where, varying in its
phenomena only in consequence of the difference in volume, and
magneto-electric intensity of the portions of the counter-trade, as of the
surface-trade at different places, and the different magnetic intensity of
the local perpendicular and circular currents of the earth over which they
pass, at different periods and at different points.
Mr. Redfield and Lieutenant Maury have assumed that our S. W. current
comes from the Pacific Ocean. Aside from the adverse evidence which the
investigations of the former in relation to the course of the West Indian
storms, and their curving over the continent, furnish to the contrary, and
that which has herein before been stated in relation to the law of
curvature, it is obvious they are mistaken, for another and conclusive
reason.
In order to reach us from the Pacific in a direction from S. W. to N. E.,
it must pass the table lands and mountain ranges of Mexico and New Mexico,
and it would supply them bountifully, even if it did not thereby leave us
comparatively rainless and sterile. Every where currents passing from the
ocean _over mountain ranges_ part with a large share of their moisture.
Thus the counter-trade which curves over the Andes and over Peru, is
deprived of its moisture and leaves the western coast rainless. So in
degree of the counter-trade which curves over the Himalaya and Kuenlon
Mountains, and from there passes over the Desert of Cobi, to the north and
east--it is deprived by those elevated ranges of its moisture. So the
mountains on the south-western coast of South America are drenched with
rain, while Patagonia, which lies on the east of them is comparatively
dry. And so of every other country similarly situated.
Now the mountain ranges and table lands of Mexico are not thus supplied
with moisture. For the space of four months in Southern and less in
Northern Mexico, and in summer, and while the belt of the tropics is
extended up over them, they have rain and in daily showers which _travel
up from the south_, indicating the course of the counter-trade. (See
Bartlett's Personal Narrative, vol. ii. p. 286.) At other seasons, and
while we are bountifully supplied, they are dry. In short, there are no
two portions of the earth that differ more widely in regard to their
supply of moisture, and all their climatic characteristics and relations.
It is therefore, according to all analogy, impossible that our
counter-trade should come from the South Pacific across the continent and
below 35°, and in this also those gentlemen are mistaken.
Messrs. Espy and Redfield recognizing the existence of "a prevailing" S.
W. current, but considering the surface-winds beneath it as the principal
actors in producing the atmospherical conditions and changes, have
attributed no office to that current, except that of giving direction and
progression to our storms. This is their great mistake. It plays no such
unimportant part in the philosophy of the weather, as we have already
incidentally seen, and will proceed still further to consider.
_All our storms originate in it._ This we may know from analogy.
_Where there is no counter-trade, outside of the equatorial belt of rains,
and within influential distance of the earth, there are neither storms nor
rain._ So, when, as we have seen, the concentration of the volume of
northern counter-trade in the West Indies, gathered by the hauling of the
S. E. trades more from the east, as they approach the central belt,
diminishing the volume of the counter-trade over the North Atlantic, the
calms and drought of the horse-latitudes are found. And when the
counter-trade is small in volume and weak in intensity, by reason of the
fact that the surface-trades from the opposite hemisphere which constitute
it, formed upon land where evaporation was small, as upon Southern Africa
and New Holland, or formed where the magnetic intensity was weak, or
passed over mountain ranges in their course, the annual supply of rain,
the ranges of the barometer, and the alternations of atmospheres
conditions are remarkably less.
We have already seen where the rainless portions of the earth are, and why
they are so; because those lying north of the northern limit of the
equatorial rainy belt were yet too far south to be covered by the line of
extra-tropical rains; or in other words, too far south to be uncovered by
the surface N. E. trades and the longitudinal magnetic currents, and to be
covered by the counter-trades in contact, or nearly so with the earth, and
influenced by the perpendicular north polar magnetic currents. Thus we
have seen that the rains of Southern Mexico were summer rains, due to the
northern extension of the equatorial rainy belt; those of California were
winter rains, due to the southern extension of the extra-tropical rains
following the N. E. surface trades. We have also briefly alluded to the
fact that either side of the equatorial rainy belt, evaporation is going
on for months under a vertical sun, without precipitation--unless it be
from an occasional brief storm of great intensity which originates in that
belt at the line of it, and passing on in the counter-trade, reverses, for
the time being, by its concentrated and powerful action, like a magnetic
body introduced into the field of another magnet, the surface-trades. Mere
evaporation then, does not produce the storm, or shower, or rain, where
most active in the dry torrid zone. It may be said that those dry portions
are, for the time being (as the rainless portions of the earth are
continually), within the operation of the surface-trades, and that
therefore the evaporated moisture is carried away by them toward the
equatorial rainy belt. Precisely so; but why carried away? Why should it
not condense, occasionally, at least, and drop the rain as it passes
along, if a great supply of moisture from excessive evaporation could
furnish rain. Perhaps it may still be said it is going from a cold to a
warm section. This is not true, as we have shown.
But, it may be said that the rainless regions at any rate receive no
moisture, and therefore can not supply any by evaporation. This would not
meet the case, as it would still be true that when the rainy belt has left
a given spot, the dry weather sets in with excessive evaporation, and the
north-east trades in summer, blowing from the countries lying north of the
rainless regions, and which have been supplied during the interval by the
extra-tropical rains, and are loaded with evaporation, are passing over
the rainless regions on their way to enter the central belt. So blow the
N. E. trades from the Mediterranean, and the Barbary States _over the
Desert of Sahara_ and into the rainy belt south of it; but drop no
moisture on their way, because exposed to no magnetic currents of an
opposite polarity.
But it is not true that all the rainless regions are without evaporation.
Egypt is an exception. The annual freshets of the Nile saturate its
central valley, and vast reservoirs of water are saved from it and let out
over its surface, and it all evaporates, but produces no rain. And so are
large quantities turned aside and scattered over the bottom lands of
Northern Mexico, and other countries, during the dry season, and their
evaporation furnishes no rain. Hygrometers and dew points are of no
consequence there--nor are they of any, on either side of the rainy belt,
where six perpendicular feet of moisture is evaporated in six months.
Again we have alluded to a strip of coast on the Pacific west of the
mountain ranges of South America, lying partly in Peru, partly in Bolivia,
and partly in Northern Chili, which, although long and narrow, washed by
the broad Pacific Ocean, is without rain. South America has no other
_wholly_ rainless region, so far as is known. A part of this region would
lie between the equatorial belt of rain, and the southern extra-tropical
one, and never be covered by either; but the volume of N. E. trades from
the Atlantic, although from the make of the land not concentrated to so
great an extent as the volume of S. E. trade on the north, and therefore
not so liable to hurricanes and other violent storms, is yet sufficiently
so to carry the southern line of the equinoctial rainy belt down in winter
to the summer line of extra-tropical rains, and give a supply of rain to
all the continent--leaving no strictly rainless region south of the
equatorial rainy belt and east of the Andes. Those mountains, however,
present a barrier to its south-western progress which it doubtless passes
to some extent, but deprived of its moisture, and unable to supply the
rainless coast region of Peru, Bolivia, and Northern Chili. There is,
therefore, a portion of this rainless line of coast which is within the
region of extra-tropical rains, over which a portion of the N. E. trades
of the Atlantic, as a counter-trade, should or do, curve, and where there
should therefore be extra-tropical rains. It is washed by the Pacific, an
evaporating surface, and westerly and south-west breezes are drawn in from
that ocean over it. Why then is it rainless? The only reason which can be
assigned why rain does not fall there is that the high mountain ranges of
the Andes intercept and perhaps in part divert the counter-trade, and
deprive that portion of it which passes them, of its moisture, by that
reciprocal action of opposite polarities which takes place whenever and
wherever the trade approaches so near the earth; and it curves over the
narrow line of coast with the feeble condensation, and imperfect forms,
and varied coloring which mark so peculiarly the rainless clouds of that
region. (See Stewart's Journal of a Voyage to the Sandwich Islands, page
72.)
Again, it is estimated, and on reliable data, that twelve perpendicular
feet of water are annually evaporated from the surface of the Red Sea,
between Nubia on one side, and Arabia on the other; yet they are both
rainless countries, except so far as the inter-tropical belt of rains
extends up on to a small portion of them. The moisture of evaporation,
floated up from a surface covered by the surface-trade is invariably so
combined as to remain uncondensed till it has passed south into the
equatorial rainy belt, and over to the opposite hemisphere, and been
exposed to the currents of an opposite magnetism.
Again, the N. E. trades extended up in summer over the Mediterranean Sea,
an evaporating surface, blow over the Barbary States in June and July, but
furnish no rain. And so of the S. E. or N. E. trades which blow over
Brazil and other countries in the absence north or south of the tropical
belt of rains.
It is obvious from these facts--and more like them might be cited--that
mere evaporation, however copious or long continued, does not make the
storm or shower in the locality where it takes place, and _without the
existence and influential agency_ of a counter-trade; and that _reciprocal
action_, whatever it may be, that takes place _between it and the earth_.
Again, our own experience is conclusive of this. We have no surface-trade
north of 30°, and yet a long drought and great evaporation may follow a
wet spring. Belts of droughts and frequent rains occur every year in
different portions of the country side by side, and _the dividing line
follows the course of the counter-trade_, and is sometimes distinctly
marked for weeks. When a change occurs in the counter-trade, whether from
causes existing there or the influence of terrestrial magnetism (in
relation to which we shall inquire hereafter), showers form or storms come
on: until it does they will not. Efforts at condensation will occasionally
appear, but they will be feeble and ineffectual, and occasion a repetition
of the axiom that "all signs fail in a drought." And we may know it from
direct observation.
The first indications of a storm, and of most if not all showers, are
observable in the counter-trade. These indications, so far as they are
visible, are of course to be looked for in the west; although the
direction and character of the surface-winds are often indicative of these
changes when not visible at the west as we shall see.
The indications are those of condensation, and vary very much in different
seasons of the year. It is not my purpose in this place to examine them
particularly. They will be alluded to hereafter under the head of
prognostics. Suffice it now to say, then, that whether it be the long
threads or lines of cirrus which occur in the trade in the winter after a
period of severe cold, following the interposition of a large volume of N.
W. cold air and the elevation of the counter-trade; or the forms of cirrus
which occur at other times and other seasons; or whether it be the
ordinary bank at night-fall, or the evening condensation which makes the
"circle" around the moon, or the morning cirro-stratus haze which
gradually thickens, passes over and obscures the sun, all which may be
followed by the easterly scud and winds: they are alike condensation in
the trade, the advance or forming condensation of a storm or showers.
The state of the weather, whether hot or cold, is extensively affected by
this trade current. As we have already suggested, the mere presence of the
sun in its summer solstice, or its absence in winter, is not an adequate
cause of all the sudden and various changes to which we are subject. The
state of the counter-trade, which is always over, or _within influential
distance of us_, and sometimes probably in contact with us--the nature of
the surface-winds which it is at any given time creating and attracting
around us, and the electric condition of the surface-atmosphere _induced_
by it, or by the immediate action of the earth's magnetism, produce those
sudden changes which mark our climate. When no intervening surface-winds
elevate it above us, and there is no storm or other condensation within
influential distance, it induces the gentle balmy S. W. wind of
spring--the cooling S. W. wind of summer--the peculiar Indian summer air
of autumn, or the comparatively moderate, although cold, open weather of
winter. If there be a partial tendency to condensation in it, the cumuli
form under the magnetic influence excited by the sunbeams from ten to
three o'clock in the day, and float gently away to the eastward,
disappearing before night-fall. If the disposition to condensation is
stronger, whether inherent or induced by an increased local activity of
terrestrial magnetism, these cumuli will increase toward night-fall, or
earlier, and terminate me showers; and if it is in a highly electrical
state, the still oppressive sultriness which precedes the tornado, and
that devastating scourge may appear. If this disposition to condensation
becomes extensive, cirri form and run into cirro-stratus, or they extend,
coalesce, and form stratus; the surface-wind will be attracted under them,
the thermometer fall in summer or rise in winter, and a storm begin.
Intense action and sudden cold may exist in and under this counter-trade
over the southern portion of the country, while all is calm, warm, and
balmy at the north. Heavy snow storms sometimes pass at the south when
there are none at the north, and a corresponding state of the weather
follows. If a large body of snow fall at the north, the winter is cold,
regular, and "old fashioned;" if little snow falls at the north and more
at the south, the winter at the north is open and broken. I have known the
ice make several inches thick at Baltimore and Washington, when none could
be obtained for the ice-houses on the Connecticut shore of Long Island
Sound. In short, although heat and cold are mainly dependent upon the
altitude of the sun, aided by the other arrangements we have alluded to,
yet the counter-trade, and the reciprocal action which takes place between
it and the earth, are most powerful agents, mitigating the rigors of
winter, bringing about the changes from cold to warm weather which the
sun is too far south to produce. And on the other hand, by this reciprocal
action, producing the electrical phenomena, the gusts, the tornadoes, the
hail storms, and the cool seasons of summer, and the period of intense
cold in winter.
_All our surface-winds, except the light, peculiar W. S. W. wind which is
felt where the counter-trade is in contact with the earth, and which is a
part of it, and perhaps the genuine N. W. wind which is very peculiar, are
incidents of the trade, and are due to its conditions and attractions._ We
have already said this was true of the easterly wind and scud of a
storm--it is alike true of all. The storm winds east of the Alleghanies
are usually, though not always, from the eastward. They are sometimes from
the southward, as they doubtless are still more frequently in the interior
of the continent.
There is occasionally a southerly afternoon wind, followed by short rains
in spring and fall, or a succession of showers in summer, which is rather
a precedent wind than a storm wind; blowing toward and under an advance
portion of the storm at the north, and hauling to the eastward when the
rain sets in, or to the westward when the showers reach us.
When there are no storms, or showers, or inducing electric action in the
counter-trade, within influential distance to disturb the surface
atmosphere, it is calm. If a storm approaches, or forms within inducing
distance, the surface atmosphere is _affected_ and _attracted toward the
storm_, from one or more points, and "blows," as we say, toward and under
it. It commences blowing first nearest the storm, and extends as the
storm travels, or becomes more intense and extends its inducing influence.
I have repeatedly noticed this in traveling on steamboats and railroads
running _toward_ or _from_, and in several instances _through_ a storm,
and telegraphic notices and other investigations prove it. The point from
which the surface atmosphere is attracted and blows, depends very much
upon the position of the storm in relation to bodies of water and the
point of observation, and its shape; and the force with which it may blow
will depend much upon its intensity.
Let us take an instance or two by way of illustration of all these points;
and as I have given instances of summer in the introduction, we will take
those of winter. It is January of an "old fashioned winter;" the snow is
about three feet deep in Canada, about one foot in Southern New York, and
a few inches in Philadelphia, and so extends west to the Alleghanies at
least. For several days the sky has been clear, the thermometer rising in
the day-time, in the vicinity of New York to about 25° Fahrenheit, falling
at night to about 6°, with light airs from the N. W. during the middle and
latter part of the day; the counter-trade and the barometer both running
high; cold but pleasant, steady, winter weather. There is a warm
south-east rain and thaw coming, as one or more such almost invariably
occur in January. How coming? The sun is far south, and shines aslant, but
through a pure and windless atmosphere; he has tried for several days to
melt the snow from the roof; a few icicles are pendant from the eaves;
but the body of the snow is still there. How can a thaw come? not from the
sun, surely. No, indeed, not from the action of the sun directly, upon our
country, nor from the Atlantic or the Gulf Stream which is off our coast.
But a portion of the current of counter-trade is coming, heated by his
rays and the warm water in the South Atlantic, in an intense
magneto-electric state, capable of inducing an electro-thermal change in
the surface atmosphere which it approaches, and of being reciprocally
acted upon by the north polar terrestrial magnetism. It is now over
Northern Texas and Western Louisiana, it will be here day after tomorrow.
The day passes as the day previous had passed; the sleigh-bells jingle
merrily in the evening; the moon shines clear all night; the storm is
coming steadily on, but its influence has not reached us, and the morning
and midday are like those which preceded it. As nightfall approaches,
however, the thermometer does not fall as rapidly as on the day previous;
the sun shines dimly and through lines of whitish cirrus cloud extending
from the horizon at the west, appearing darker as the sun descends and
shines more _horizontally_ through them--perhaps mainly in the N. W.--and
which extend up and over toward the E. N. E. The air next the earth begins
to feel raw; it is changing, not from warm to cold, but _electrically_
from positive to negative; and dampening, from a tendency to condensation
by induction, as we shall see--the same condensation which in warm
weather may be seen on flagging stones, and walls, and vessels containing
cold water. The advance cirrus condensation of the storm is over us and
affecting us; the earth too is affecting the adjacent atmosphere by action
extended from beneath the storm. Still there is no wind, although sounds
seem to be heard a little more distinctly from the east, and so ends the
day. Evening comes, and the moon wades in a smooth bank of cirro-stratus
haze, with a very large circle around her; the cirrus bands of haze have
coalesced and formed a thin stratus. The storm is coming steadily on, its
condensation is seen to be thicker as it approaches, it is now raining
from one hundred to one hundred and fifty miles to the west, but we do not
know it.
That it is about to storm all believe, for all are conscious of a change.
The candle if extinguished will not relight as readily, if at all, on
being blown; there is a crackling almost too faint for snow in the fire;
the sun did not set clear; the old rheumatic joints complain, and the
venerable corns ache.
Morning comes, and the storm is on. The wind is blowing from the S. E.,
the scud are running rapidly from the same quarter to the N. W., the
thermometer continues rising, and it rains. The storm has reached us and
the thaw has commenced. Gradually, as the densest portion of the storm
cloud reaches us, it darkens; the scud are nearer the earth, and run with
more rapidity; the rain falls more heavily and continuously, and by the
middle of the day a thick fog has enveloped the earth; the wind is dying
away, and the trade itself, with its southern tendency to fog, has settled
near us; the barometer has fallen, the thermometer is up to fifty degrees,
the water is running down the hills, the snow is saturated with water and
is disappearing under the influence of the fog, the rain, and the warm
air. Evening comes; the south-east wind and the rain have ceased; the rain
clouds have passed off to the eastward; the fog has followed on and
disappeared; there is a light trade air from the S. W.; the moon shines
out, and a few patches of stratus, broken up into fragments and melting
away, are following on in the trade: the storm is past.
Hark! to the tones of Boreas as he bursts forth from the N. W., and
rushing, whistling, howling, dashes on between the trade and the earth,
following the storm. Now the barometer rises rapidly, the thermometer
falls, and in an incredibly short time all is congealed, and cold and
wintery as before. The cold N. W. wind has again interposed between the
trade and the earth; the trade is elevated a mile or more above it and is
entirely free from its influence and from condensation; the deep blue of a
sky "as pure as the spirit that made it" is over us, and steady winter
reigns again.
It is obvious that there was nothing in the action of the sun upon our
snow-clad country, to induce the thaw or the storm. It began, continued,
approached, and passed off to the N. E. in the counter-trade. The S. E.
wind which existed every where within its influence: in the interior
States, Missouri, Illinois, Indiana, Ohio, Michigan, and in Canada, as
well as upon the Atlantic coast, commencing in the former earlier than
upon the last, was the result of its induction and attraction. Of the N.
W. wind that followed we shall speak hereafter. If any one doubts whether
this be a true sketch let him examine the investigation of a storm
published by Professor Loomis, or observe for himself hereafter. If,
however, the storm of Professor Loomis is referred to, it should be
remembered that his notes show the occurrence of a slight distinct snow
storm at the N. W. stations one day in advance of the principal storm. The
latter appears first as rain at Fort Towson, on the nineteenth, moving
north and curving to the east--its center passing near St. Louis, and
south of Quebec, and the whole storm enlarging as it advanced.
Take another instance. Since the thaw it has not been quite as cold as
before; but the rain-soaked snow is hard and solid, the ground, where the
snow was blown or worn off, icy and slippery--the thermometer falls during
the night to about 12°, and rises to about 30°; the sun makes no
impression upon the snow; the firmament is of the deepest blue, the
borealis at night vivid. "O, for a storm of some kind, to mitigate the
still severe cold;" for the thaw has made us more sensitive, and storm
winds do blow warm in their season. But patience, it will come. Another
day, or two, perhaps, pass: the sun rises as usual, the thermometer has
the same range still. "Long cold snap," we exclaim; "how long will it
last?"
A change is coming, but this time it will snow. About an hour or two after
sunrise the cirrus threads are discoverable again in the west, but now
they are most numerous in the S. W. As the day passes on they thicken and
advance toward the E. N. E., the sun begins to be obscured, the
thermometer rises, and it slowly "_moderates_." There is a snow storm
approaching from the S. W.
But the thermometer rises slowly; it must get up to 26° or 28° before it
can snow much. I have known in one instance, at Norwalk, a considerable
fall of snow, although much mingled with hail, when the thermometer stood
at 13° above zero, and one, a moderate fall, some two inches, with it at
24°, but these were exceptions. The snow range of the thermometer on the
parallel of 41° north latitude, and south of it, is from 26° to 30° above
0°; when colder or warmer it may snow to whiten the ground, or perhaps
barely cover it, but usually rains or hails. We have seen that in the
polar regions, according to Dr. Kane, it is about zero, but the rise of
the thermometer there, previous to the snow, was about the same as here,
_i. e._, from 15° to 25°. This fact is instructive. Since the foregoing
was written, and on the 7th of February, 1855, a snow-storm of
considerable length set in, with the thermometer at 5°, and continued more
than twenty-four hours, the thermometer gradually rising. The snow was
very fine, like that described by Arctic voyagers as falling in extreme
cold weather.
As the dense and darker portions of the storm approach, and although the
sun is obscured, and the ground frozen, it continues to moderate, and at
evening, when the thermometer is up to 28°, and the dense portion of the
storm has reached us, gently and in calmness the snow begins to fall.
Perhaps a light air following the storm, or the presence of the trade near
the earth, at first inclines the snow-flakes to the eastward. This is
frequently so at the commencement of snow storms. Ere long, however, the
wind rises from the N. E., and the snow is driven against the windows,
rounded and hardened by the attrition of its flakes upon each other, in
their descent through the eddying and opposite currents. The next day we
rise to witness a heavy fall of snow, perhaps, and a continued driving N.
E. storm, in full blast; the snow whirling and settling in drifts under
the lee of every fence or building.
Can it be, you ask, that this driving wind is but an _incident_ of the
storm? the result of _attraction_, while the storm clouds are sailing
quietly and undisturbed on in the counter-trade above, directly over the
gale which is blowing below? It is even so. Nor has it "backed up," as it
is termed by those who have ascertained that it has commenced snowing
first, and cleared off first, at a point west of them. You saw, or might
have seen, the cirro-stratus cloud passing to the E. N. E. in the
afternoon, and until the snow-flakes filled the air, and the clouds became
invisible. You may still see that the wind will die away before the storm
breaks, and "come out" gently from the S. W., unless it should back into
the northward and westward, and in either event you may see the last of
the storm clouds, as you did see, or might have seen the first of them,
pass to the eastward. Toward night the wind dies away, and the storm
passes off abruptly, or the sky becomes clear in the N. W. Now you may see
the smooth stratus storm cloud, continuous, or breaking up into fragments
and passing off to the east, even at the edge which borders the clear sky
in the west or north-west, to be followed that evening or the next day, by
the north-west wind and its peculiar fair-weather scud.
I have given these as instances illustrating the manner in which rain and
snow storms originate the surface easterly winds in winter.
But it must not be supposed that they commence with precisely the same
appearances in every case in winter; much less in summer. There is very
great diversity in this respect, in different seasons, and in different
storms during the same season. A great many different and accurate
descriptions might be given, if time and space would permit, which all
would recognize as truthful. Very frequently in summer, and sometimes in
winter, the wind will set in from the eastward, and blow fresh toward a
storm, before the condensation in the trade, which forms the eastern and
approaching edge of the storm, has assumed the form of a distinct cloud.
Not unfrequently, when it is calm next the surface, a narrow stratum of
easterly wind, a half a mile or a mile above the earth, may be seen with a
continuous fog, condensing, but not in considerable patches like the
usual scud, running with great rapidity toward the storm. Such a stream of
fog blew with great rapidity for thirty-six hours toward the storm which
inundated Virginia and Pennsylvania, in 1852, and carried away the Potomac
bridge at Washington. Such a stream of fog was visible the evening before
the great flood of 1854, which inundated Connecticut, and curried away so
many railroad and other bridges. I have also seen such a stream of fog
running at about the same height, when it was calm at the surface, from
the S. W. toward a violent storm which formed over central New
England--and from the north toward a heavy storm passing south of us. Such
strata form, as far as I have been able to discover, the _middle current_
of storms which are accompanied with very heavy falls of rain. These
double currents are much more common than is supposed. East of the
Alleghanies, short and heavy rain storms, which commence north-east,
hauling to the south and lighting up about mid-day _after a very rainy
forenoon_, frequently have a S. E. or S. S. E. middle current of this
character, which involves the whole surface atmosphere when the storm has
nearly passed, and the N. E. wind dies away, and the wind seems to haul to
the S. S. E. and S.; so that it is rather the prevalence of a _different_
and _coexisting current_, than a hauling of the _same wind_, which marks
the period of lighting up in the south.
Sometimes the easterly wind will set in and blow a day or two before the
border of the storm reaches us. Sometimes the storm is passing, or will
pass, in its lateral southern extension, south of us, and the
condensation in the trade extends over us sufficiently dense to induce an
easterly current beneath it, but not dense enough to drop rain, and then
we have a dry north-easter. I can not, within the limits I have
prescribed, allude to all the peculiarities attending the induction and
attraction of an easterly wind, by the storm in the counter-trade. They
are readily noticeable by the attentive and discriminating observer, and
their existence and cause is all with which I have to do at present.
Winds from the north, or any point from N. N. E. to N. N. W., are
comparatively infrequent in the United States, east of the
Alleghanies--though it is otherwise in the vicinity of the great lakes.
Sometimes the wind "backs," as sailors term it, during a N. E. storm, from
the N. E. through the N. N. E., N., and N. N. W. to N. W. When this takes
place, it is toward the close of the storm. Occasionally, though very
rarely, it continues to storm after the wind has passed the point of N. N.
E., and until it gets N. W. I have known a few instances in the course of
thirty years, and but a few. They are exceptions--rare exceptions. When
the wind thus backs from the N. E. to the N. W. through the N., you may be
very certain that the body of the storm, or at least the point of greatest
intensity and greatest attraction, is at the time passing to the southward
of you. This is most commonly the course of the wind when the storm
extends far south and lasts several days, and does not extend north far,
or if so, with much intensity, beyond the point of observation. The
change of the wind is explained by the situation of the focus of intensity
and attraction, to the south of the observer, and its passage by on that
side.
Probably in locations further north and (as I think I have observed) south
of the lakes, it may be more frequent than upon the parallel of 44° east
of the Alleghanies (which is as far north as I have observed), inasmuch as
the further north the locality, the more likely storms and other
disturbances in the counter-trade will be to pass to the southward of it.
Between the N. E. and S. E. the wind may blow from any point, before and
during storms, and in a clear day in the morning, as a light variable
breeze, or, after mid-day, toward approaching showers. I have known it
blow all day during a storm from due east; to change back and forth
between south-east and north-east, and to blow for hours from any
intermediate point--as different portions of the storm were of different
intensity, and exerted a more or less powerful inducing influence; and
doubtless this often takes place at sea. It depends upon the situation of
the focus of attraction of the storm, its shape relative to the particular
locality, and with reference to the atmosphere east of it, and peculiar
local magnetic action; or, as is sometimes the case in low latitudes, is
owing to the fact that the storm is made up of many imperfectly connected
showers, which have different force, and induce changeable and baffling
winds.
The inducing and attracting influence of the approaching storm is exerted
sooner, and with most force, upon the surface atmosphere, over bodies of
water like the ocean and the lakes. Thus, the wind will set from the
eastward toward an approaching storm out upon Long Island Sound, for hours
before it is felt upon either shore; and when all is calm in the evening
on land, and often before the moon forms a halo or circle in the milky
condensation of the approaching storm, or any sign of condensation is
visible, the breaking of the waves upon the shores may be heard. Doubtless
this may be observed on the shores of the Atlantic at other points.
This power of attracting the surface atmosphere from bodies of water like
the ocean and the great lakes, will account for two apparent anomalies,
mentioned by Mr. Blodget in a valuable and instructive article read to the
Scientific Convention, in 1853, regarding the annual fall of rain over the
United States.
First--the influence of mountains in extracting the water from the
atmospheric currents which pass over them, is well known and readily
explainable. Mr. Blodget, however, found that the source of our rains,
whatever it might be, when it reached the Alleghanies, was so far
exhausted of its moisture that those mountains extracted less from it than
fell to the westward, by some five to ten inches annually; and that the
fall of rain upon them was less than upon the Atlantic slope eastward of
them, to the ocean. This does not accord with observation elsewhere, but
is easily explained. As the storm approaches the ocean, it attracts in
under it the surface atmosphere of the ocean, loaded with vapor,
condensing in the form of fog and scud, as it becomes subject to the
increasing influence of the storm. Although the scud and fog would not of
itself make rain, it aids materially in increasing the quantity of that
which falls through it. The drops, by attraction and contact, enlarge
themselves as they pass through, in the same manner as a drop of water
will do in running down a pane of glass which is covered with moisture.
The small drop which starts from the upper portion of a fifteen-inch pane,
will sometimes more than double its size before it reaches the bottom. _It
is by this power of attracting the surface atmosphere, which contains the
moisture of evaporation, under it, and inducing condensation in it, that
the moisture of evaporation which rarely rises very far in the atmosphere
is made to fall again during storms and showers._ This attraction of a
moist atmosphere from the ocean accounts for the excess of rain on the
east of the Alleghanies, compared with its fall upon them. So the great
valley of the Mississippi is comparatively level, and less of its water
runs off than of that which falls upon the Alleghanies. There is,
therefore, more moisture of evaporation in the atmosphere of the former to
be thus precipitated and add to the annual supply of rain upon that
valley, and it exceeds that which falls upon the Alleghanies. Those
mountains, too, are elevated but about 1,500 feet above the table-lands at
their base, and exert little influence on the counter-trade. If they, were
6,000 or 8,000 feet high, a different state of things would exist.
Second--Mr. Blodget found the quantity of rain which fell in Iowa, and to
the south and west of the lake region, to be greater than fell over the
lake region itself. This is doubtless in part owing to the same cause. The
counter-trade, in a stormy state, attracts the surface atmosphere from the
lake region, with its evaporated moisture, before it arrives over it, and
therefore more rain falls S. W. of the lake region than upon it. This
power of attracting the surface wind of the ocean in under it, produces
the heavy gales which affect our coast, and which are rarely felt west of
the Alleghanies to any considerable degree; and a storm coming from the W.
S. W., extending a thousand miles or more from S. S. E. to N. N. W., may
have the wind set in violently at S. E. on the _southern coast first_, and
at later periods, successively, at points further north, and thus induce
the belief that the storm traveled from south to north.
Mr. Redfield finding that some of the gales which he investigated,
particularly that of September 3d, 1821, did not extend far inland, and
commenced at later periods regularly, at more northern points, concluded
that the gale traveled along the line of the coast to the northward. In
this, and in relation to the storm of 1821 (and perhaps some others), he
has been deceived. My recollections of that storm are accurate and
distinct. But I shall recur to this again when I come to speak of his
theory.
Toward storms, or belts of showers which would be storms if it were not
summer and the tropical tendency to showers active in the trade, which
pass mainly to the north of us, or commence north and pass over us,
condensing south while progressing east, the wind may commence blowing
before the body of the storm reaches us, from any point between south by
west and south east, particularly in the summer season and in the
afternoon. When the rain in a storm of this character sets in, in the
night, it will sometimes haul into the S. E., if the focus of attraction
be situated north of us, and so remain until just before the storm is to
break.
There are, however, a class of southerly summer winds which deserve more
particular notice. For two or three months in the year--say from the
middle of June to the 20th of August--storms on the eastern part of the
continent, except in wet seasons, are rare, and most of our rain is
derived from showers. During these periods belts of drought are frequent,
sometimes in one locality, and sometimes in another, extending with
considerable regularity from W. S. W. to E. N. E. in the course of the
counter-trade, while rain falls in frequent and almost daily showers to
the northward or southward of them. If the daily rains are at the north,
over the belt of drought, S. S. W. and S. W. by S. winds blow, sometimes
with cumuli or scud, during the middle of the day and afternoon, to
underlie the showery counter-trade on the north of the line of drought.
Thus, sometimes nearly every day for several days, the evaporated moisture
of the dry belt will be carried over to increase the store of those who
have a sufficient supply without. During the latter part of the afternoon
the clouds in the west may look very much like a gathering shower, but the
attractions of the counter-trade fifty or one or two hundred miles to the
north, will absorb them all, and at nightfall the wind will haul to the S.
W. on a line with the counter-trade, and die away.
If there be a drought on any given line of latitude, and frequent showers
or heavy rains at the south of it, although there may not be a like
surface-wind, with cumuli and fog, blowing from the north toward it, yet a
general, gentle set of the atmosphere, from the N. N. W., or N. W., or
other northerly point, toward the belt of rains, some distance above the
earth, will often be observable, with a barometer continually depressed,
and perhaps a cool atmosphere.
During set fair weather, when the attracting belt of rains is far north,
on the north shore of Long Island Sound, the wind, like a sea breeze, will
set in gently from about S. S. E. or S. by E. in the forenoon, blowing a
gentle breeze through the day, and hauling to W. S. W. on a line with the
trade at nightfall, and dying away. During a drought I have known this to
happen for seventeen successive days. It is obvious to an attentive
observer that this is the result of the influence of the sun in exciting
the magnetic influence of the earth, and producing a state of the trade
not unlike that which induces the formation of cumuli, and which attracts
the surface atmosphere from the Sound in over the land: for the _tendency
to cumulus condensation precedes the breeze_, and the breeze is often
wanting in the hottest days where no such tendency to the formation of
cumuli exists. The same is true of sea breezes elsewhere. They do not blow
in upon some of the hottest surfaces. Where they do exist, they do not
always blow, but are wanting during the hottest days; and careful
observers have identified their appearance with the formation of cumuli,
or other condensation, upon the hills inland. They are not, therefore, the
result of ascending currents of heated air.
The received theory regarding sea and land breezes is a mistaken one in
another respect. There is no such thing as a land wind corresponding in
force to, and the opposite of, the sea breeze--occasioned by the
comparative warmth of the ocean. These breezes blow mainly within the
trade-wind region. Of course they are either beneath the belt of rains or
the adjoining trades. They are said to be, and doubtless are, most active
and strongly marked on lines of coast, particularly the Malabar coast, and
where the trade-winds are drawing usually from them. In the day-time, when
the action of the sun increases the action of the magnetic currents upon
the land, or there are _elevations inland_ which approach the
counter-trade, and especially if it is elevated near the coast, as the
Malabar coast is by the Ghauts, the attraction of this atmosphere over it
_reverses the trade_, or inclines it in upon the land, and it blows in
obliquely or perpendicularly, according to the relative trending of the
coast and the direction of the surface-trade. Thus, where islands are
situated within the range of the trades, the latter will be _reversed_
during the day on the _leeward_ side, but continue to blow as land winds
during the night. So they are sometimes deflected in upon the land on the
sides, during the day, and in like manner return to their course in the
night. So, too, the north-east trades of Northern Africa, are occasionally
(though feebly where the coast is flat) deflected during the day-time, and
blow in as N. W. winds. Upon the southern coast of Africa the S. E. trade
is deflected, and blows in as a S. W. wind. Upon the south-western coast
of North America, the N. E. trades are deflected in like manner, and so
are the S. E. trades upon the western coast of South America. Where the
coast mountain ranges are very elevated, as upon the western coast of the
American continent, this attracting influence and consequent deflection
extends to a considerable distance seaward, and hence the westerly winds
of California, etc. It must be understood that we are now speaking of the
winds which blow within the range and during the existence of the
trade-winds or the presence of the dry belt--for the trades are not always
perceptible on the land. Captain Fitzroy thus describes the sea breezes of
the western coast of Peru, at 23° south latitude. "The tops of the hills
on the coast of Peru are frequently covered with heavy clouds. The
prevailing winds are from S. S. E. to S. W., seldom stronger than a fresh
breeze, and often very slight. _Sometimes during the summer, for three or
four successive days, there is not a breath of wind, the sky is
beautifully clear, with a nearly vertical sun._ On the days that a sea
breeze sets in, it generally commences about ten in the morning, then
light and variable, but gradually increasing till one or two in the
afternoon. From that time a steady breeze prevails till near sunset, when
it begins to die away, and soon after the sun is down there is a calm.
About eight or nine in the evening _light winds_ come off the land, and
continue till sun-rise, when it again becomes calm until the sea breeze
sets in as before."
To illustrate this further, I take the following letter from Professor
Espy's Philosophy of Storms:
CLINTON HOTEL, N. Y., Dec. 20, 1839.
TO PROFESSOR ESPY,
DEAR SIR,--Understanding you are desirous of collecting curious
meteorological facts, I take the liberty of communicating to you what
I saw in the month of December, 1815, at the Island of Owhyhee. I lay
at that island in the Cavrico Bay,[3] in which Captain Cook was
killed, three weeks, and every day during that time, very soon after
the sea breeze set in, say about nine o'clock, a cloud began to form
round the lofty conical mountain in that island, in the form of a
ring, as the wooden horizon surrounds the terrestrial artificial
globe, and it soon began to rain in torrents, and continued through
the day. In the evening the sea breeze died away and the rain ceased,
and the cloud soon disappeared, and it remained entirely clear till
after the sea breeze set in next morning. The land breeze prevailed
during the night, and was so cool as to render fires pleasant to the
natives, which I observed they constantly kindled in the evening. I
was particularly struck with the phenomena of the cloud surrounding
the mountain, when none was ever seen in any other part of the sky,
and none then till after the sea breeze set in, in the morning, which
it did with wonderful regularity. The mountain stood in bold relief,
and its top could always be seen from where the ship lay, above the
cloud, even when it was the densest and blackest, with the lightning
flashing and the thunder rolling, as it did every day. I passed up
through the cloud once, and I know, therefore, how violently it
rains, especially at the lower side of the cloud. This rain never
extends beyond the base of the mountain;[4] and all round the horizon
there is eternally a cloudless sky. The dews, however, are very
heavy, and there seems to be no suffering for want of rain. That this
state of things continues all the year, I have no doubt, from what an
American, by name Sears, who had spent four years there, told me; he
had seen no change in regard to the rain.
CALEB WILLIAMS.
Providence, R. I.
Similar citations might be made to show that the sea breeze is induced by
the same cause which forms the clouds over the land--that it is frequently
wanting for three or four days under a vertical sun, and that the land
breeze blows gently and not with corresponding force where there is no
surface trade, or where it is deflected, not reversed.
A succession of showers passing across the country to the north, within
one hundred to one hundred and fifty miles, almost always produces a
southerly wind to the southward of them. There is more that is peculiar
about these belts of showers. Although they consist of large
highly-electrified cumuli, there is a strong tendency to cirro-stratus
condensation in the lower part of the trade over them; and it is that
condensation rather than the cumuli, which attracts the surface atmosphere
from the south. They would be storms, if the atmosphere had not a
summer-tropical tendency to showers. There is, too, a tendency in these
belts to extend to the south, and it is generally, as far as I have
observed, the extension southerly of those belts, by the formation of new
showers which terminate the "hot spells" or "heated terms" of mid-summer.
The very oppressive and fatal one of the summer of 1853, was, in
character, a type of all--although exceeding them in severity. The first
three or four days were calm, hot, and smoky--an appearance which attends
all similar periods more or less, refracting the red ray of the light, and
giving the sun a peculiar dry-weather, red appearance. (This smoky haze is
usually atmospheric, and occasionally seen even in March, although not
unfrequently fires in the woods fill the air with actual smoke, and very
much increase it, and when this is so, the odor of the smoke is often
perceptible.) Then we began to have a fresh south-west by south breeze in
the day-time, hauling to the south-west, and dying away at nightfall. The
next day, the tendency to condensation and consequent belt of showers
having extended further south and approached nearer to us, the S. S. W.
wind blew _fresher_ toward it, and _did not die away at nightfall_. During
the evening the reflection of the lightning playing upon the tops of the
thunder clouds, just visible at the north (heat-lightning, it is termed,
because supposed to be unaccompanied by thunder, but in reality lightning
reflected from clouds at too great a distance for the thunder to be
heard), and the continuance of the southerly wind after nightfall, gave
sure evidence of the coming showers the next day, and an end of the
excessive heat for that time. So ended both of those long-to-be-remembered
"heated terms" of 1853.
The same is probably true of the interior of the country every where.
Lieutenant Maury, in the course of his investigations, and in order to
ascertain the direction of the winds in the Mississippi valley during
rain, addressed a number of gentlemen, and received their replies, which
are published with his wind and current charts. Several answered, among
other things, that, "whenever the lightning appears to linger at the north
at eventide, rain almost invariably follows speedily; not so in the
south." Thus it frequently is with us. If, during a hot, dry time, of a
few days continuance, the lightning so lingers in the evening, and the
wind continues to blow _fresh_ from the southward _after nightfall_,
showers will generally follow within forty-eight hours, most commonly the
next day, and a cool N. N. W. or N. W. wind with a favorable change ensue.
Such, at least, has been the result of my observation for many years.
Indeed this seems to be the general law in summer in the Mississippi
valley, where the easterly winds are not so common as with us. To
illustrate this further, I copy from a recent work by T. Bassnett,
entitled the "Mechanical Theory of Storms," two short extracts, showing
the manner in which belts of showers extend southerly, while progressing
north-eastwardly, at Ottawa. The first occurred in August, 1853; the last,
December, 1852. The first was a belt of showers; the latter would have
been in August, but the lateness of the season changed its character
somewhat, though not entirely, to a more regular rain, especially toward
the close.
"AUGUST 6th.--Very fine and clear all day: wind from S. W.; a light
breeze; 8 P.M. frequent flashes of lightning in the northern sky; 10
P.M., a _low bank of dense clouds in north_, fringed with cirri,
visible during the flash of the lightning; 12 P.M., same continues.
"7th.--very fine and clear morning; wind S. W. moderate; noon, clouds
accumulating in the northern half of the sky; _wind fresher_, _S.
W._; 3 P.M., a clap of thunder over head, and black cumuli in west,
north, and east; 4 P.M., much thunder and scattered showers; six
miles west rained very heavily; 6 P.M., the heavy clouds passing over
to the south; 10 P.M., clear again in north.
"8th.--Clear all day; wind the same (S. W.); a hazy bank visible all
along on _southern horizon_.
"DECEMBER 21st, 1852.--Wind N. E., fine weather.
"22d.--Thick, hazy morning, wind east, much lighter in S. E. than in
N. W.; 8 A.M., a clear arch in S. E. getting more to south; noon,
_very black in W. N. W._; above, a broken layer of cirro-cumulus, the
sun visible sometimes through the waves; wind around to S. E., and
fresher; getting thicker all day; 10 P.M., _wind south, strong_;
thunder, lightning, and heavy rain all night, with strong squalls
from south.
"23d.--Wind S. W., moderate, drizzly day; 10 P.M., wind west, and
getting clearer."
It is obvious that the showers at the north passed east on the evening of
the 6th of August; that new showers, taking the same course, originated in
the north, but more southerly next day, with S. W. wind, and that they
passed east, and others formed successively further south, which passed
over the place of observation late in the afternoon, and that others
formed south and passed east during the night and next day, visible in a
bank on the southern horizon.
Later or earlier in the spring and autumn, these brisk afternoon
southerly winds continuing after nightfall, indicate moderate rains from a
rainy belt extending in a similar manner, without the cumuli and thunder
which attend those of mid-summer. I shall recur to this class of showers
and storms when we come to their classification.
Light surface winds from south-west to west are not often storm-winds, and
are usually those which the trade near the earth draws after it. Sometimes
the trade seems to draw the surface wind from the S. W. and W. S. W. with
considerable rapidity, and some scud a little distance above the earth.
When this is so, it will be found that a storm has passed to the north of
us, or a belt of rains is passing north, which may or may not have
sufficient southern extension to reach us. When there have been heavy
storms at the south in the spring, especially if of snow, the S. W. wind
which the trade draws after it, and which comes from the snowy or chilled
surface, is exceedingly "raw"--that is, damp and chilly, although not
thermometrically very cold. Probably every one has noticed these "_raw_"
S. W. winds of spring.
Usually, when storms and showers, which have not a southern lateral
extension, pass off, the trade is very near the earth, and a light S. W.
wind or calm follows for a longer or shorter period. Not unfrequently,
however, our N. E. storms terminate with a S. W. wind, shifting suddenly,
perhaps, just at the close of the storm, during what is sometimes called a
"clearing-off-shower," or, more frequently, dying gradually away as a N.
E. wind, and coming out gently from the S. W., following the retreating
cloud of the storm. In such cases it is said to "clear off warm."
With us the wind rarely blows from the west, except while slowly hauling
from some southerly point to the N. W. It is probably otherwise east of
the lakes and in some other localities to the north-west.
Occasionally, and most frequently in March, a W. to W. N. W. wind follows
storms, and blows with considerable severity, with large irregular,
squally masses of scud, and sometimes a gale. Such was the character of
the dry gale which crossed the country, particularly Northern New York, in
March, 1854, doing great damage. These westerly winds are always
accompanied by a continued depression of the barometer, and peculiar,
foggy, scuddy, condensation, and should be distinguished with care from
the regular and peculiar N. W. wind, as they may be, by the continued
depression of the barometer, and the character of the scud. They are
doubtless magnetic storms.
The remaining surface wind, the N. W., the genuine Boreas of our climate,
the invariable fair-weather wind, is one of great interest. It is unique
and peculiar. It is not the left-hand wind of a rotary gale, and has no
immediate connection with the storm. I have known it blow moderately,
fifteen successive days in winter; rising about ten A.M., and dying away
at nightfall. Occasionally, but very rarely indeed, a light wind exists
from the N. W. during a storm, owing probably to a focus of intensity in
relation to some surface the storm covers, like the focus which exhibits
itself as a clearing-off shower near the close of a storm; but the real
fair-weather Boreas is a different affair altogether. Let us observe with
care its peculiarities; they are instructive.
1st. It rarely blows with any considerable force beneath the trade while
there are storm clouds, or any considerable condensation in it. It does
not interfere with that reciprocal action which takes place between the
trade and the earth, during approaching or existing storms. I have
frequently seen it with its peculiar scud clouds in the N. W., waiting for
the storm condensation of the trade to pass by, that full of positive
electricity it might commence its sports; rushing and eddying along the
surface, licking up the warm, south polar, electric rain, which stood in
pools upon the ground, or rose in steamy vapor from the surface, and with
its cool breath dry up the muddy roads as no degree of heat can dry them.
The annexed figure (14) shows the appearance of the northern edge of a
stratus storm cloud, passing off E. N. E. at the close of the storm, which
was "_clearing off from the north-west_." It is from a daguerreotype view,
looking W. N. W., taken at eight o'clock in the morning, in the fall of
the year. Near the horizon maybe seen the N. W. scud, forming in the N. W.
wind, which is about to follow the retreating edge of the storm cloud.
Figure 15 is from a daguerreotype view, taken at eleven o'clock the same
day, when the storm cloud had passed off and its edge remained visible
only south of the zenith, and the north-east scud had risen up and covered
the northern half of the sky, and the wind was blowing a gale from that
quarter.
[Illustration: Fig. 14.]
Another view was taken about two P.M. of the same day, when the scud had a
very dark, gloomy appearance--as _dark_ and _gloomy_ as those of a Mexican
norther--too dark to represent by a cut.
Not unfrequently in a moist summer season, after a day of showers or rain,
which have had an extending formation or lateral extension from north to
south, it will commence blowing in the morning, and encourage the
hay-maker with the hope of fine weather. But often before noon, the milky
stratus condensation above with cumuli below, will appear in the trade;
the N. W. wind die away and variable airs from the east or south appear,
to be followed toward night by an enlargement of the cumuli and showers.
It rarely, if ever, blows fresh till the storm condensation of the trade
has passed; or continues to blow after that condensation reappears. When
it commences blowing after a storm, and the northern edge of the storm is
not over us, we may frequently see the latter low down in the S. E.
passing eastward.
[Illustration: Fig. 15. NORTH VIEW.]
2d. Its scud are peculiar. Every one, probably, has noticed them. They are
distinct, more or less disconnected, irregular, with every form between
those of the easterly scud, cumulus, and stratus, according to the season.
If large, with _dark under surfaces_; forming _rapidly_ and as _rapidly
dissolving_; rarely dropping any rain, sometimes dropping a flurry of
snow, in November or March, oftener than at any other period; sailing away
to the S. E., and casting a traveling shadow as they pass on over the
surface of the earth. Their electricity, particularly when white, is
probably always positive, as that of all whitish clouds is supposed to be.
3d. _It is emphatically a surface wind._ The incident storm winds, the N.
E. and S. E., frequently _commence blowing_ under the storm, toward its
point of greatest intensity, _up near the line of cirro-stratus
condensation_, evidenced by the running scud; or blow there with most
rapidity, and so continue for hours before the whole surface atmosphere
from thence to the earth becomes involved in the movement; and sometimes
without being felt below at all. Not so with the N. W. wind; it _begins at
the surface_ and blows there with more rapidity than above; it seems to be
attracted by the earth; it interposes between the earth and the trade,
wedging the trade up and occupying its place. It blows under at all
seasons of the year, but most readily and strongly from a surface of snow
whose electricity is always positive. Hence it blows most strongly and
_continuously_ when snow has fallen at the north, and prevails during
winter very much in proportion to the extent and continuance of the
covering of snow which invests the earth in that direction. It follows
after storms, and particularly warm rains, during the autumn, winter, and
spring months, which have a lateral southern extension. Whether it is
increased by the snow from the surface from which it blows, or is caused
by the same magnetic action which causes the great fall of snow, is a
question we shall consider hereafter.
4th. It does not connect or mingle with the trade current in any way, or
change or divert the course of that current; but interposes between it and
the earth, elevating the trade in proportion to its own volume, above the
influences of the earth (when the trade becomes free from condensation,
and singularly, clear); and raising _proportionately_ the barometer. An
experienced observer can frequently estimate, with considerable accuracy,
the rise of the barometer, by measuring with his eye, (when the clouds
will enable him to do so,) the depth of this interposed N. W. current. The
barometer rarely rises after a storm, for twenty-four or forty-eight hours
if the wind continues at any point from S. W. to W. N. W., but always
rapidly as soon as the genuine N. W. current with any considerable depth
interposes and elevates the trade.
It will be obvious to every one, I think, certainly, if they will
hereafter study the subject and observe for themselves, that the N. W.
wind does not blow away the storm; and that it follows after it, blowing
over the surface which is uncovered by the storm; rarely, if ever, with
any force when the body of the storm passed south of us; and that it is a
purely surface wind, seemingly attracted by the peculiar magneto-electric
state in which the surface of the earth is left, compared with a snow-clad
surface to the north, by a recent storm, or that peculiar state of the
trade which is left by the action of the storm. It seems to follow that
magnetic wave which, passing from north to south, acts in its course upon
the counter-trade, producing the storm, or belt of showers, and giving
them their southern lateral extension, and will well repay future
telegraphic investigation. Its electricity is intensely positive--that of
the earth by the action of the storm as intensely negative.
5th. This N. W. wind occurs in all parts of the northern hemisphere, so
far as we have data to determine, and its corresponding wind from the S.
W. occurs in the southern hemisphere. It is identical with a class of the
northers of the Gulf of Mexico, as a brief analysis of the character of
the latter will show.
1st. The fall and winter _norther_ is a dry wind without rain or falling
weather--so is our N. W. wind.
2d. It is preceded by a falling barometer; S. E. scud and rain at the
point where it blows, or to the eastward of it. So is ours when it blows a
gale in the fall and spring months, which bear the nearest resemblance in
climatic character to the periods when the northers blow. With this
distinction, however, that our precedent rains either pass over us or to
the southward, the direction of storms being E. N. E.; their precedent
storms passing over or to the eastward of them as they move more to the
northward.
3d. It is often preceded by a copious dew; so is ours--such dews often
following light fall rains in our climate, and preceding N. W. wind.
4th. The most peculiar characteristic, however, is that the barometer
rises rapidly and invariably while the norther prevails, and very much in
proportion to its violence. The same is true of our genuine N. W. wind,
and is not true _of any other wind_ on this continent which I have
observed or read of.
5th. While they are thus alike in these respects, they are unlike in no
respect.
Mr. Redfield has traced them in _supposed_ connection with storms which
continue from that vicinity across the United States to the E. N. E., and
endeavored to connect them with those storms, as the left-hand winds of a
rotary gale. Obviously, I think, they are identical with our N. W. winds
which also _follow_, indeed, but _are distinct from the storms_.
There are a class of northers in the Gulf of Mexico--the "Nortes del Muero
Colorado"--sometimes occurring in the summer months, beginning at N. E.,
veering about and settling at N. N. W., and as they decline hauling round
by the west to the southward. These winds correspond precisely with the
hurricane winds of the West Indies, and are doubtless the incident winds
of a storm traveling thence to the N. N. W. precisely as our N. E. or E.
N. E gales are incident storm winds to the N. E. storms of our latitude.
In this connection we will look at the peculiarities of a West India
hurricane.
"It is not a little remarkable," says Mr. Espy, speaking of the storms and
hurricanes of the West Indies, "that all these storms, and _all others
which have been traced to the West Indies_, traveled N. W. almost at right
angles to the direction of the trade-wind in those latitudes, but very
nearly, if not exactly, in the direction of an upper current of the air
known to exist there toward the N. W." Substantially the same facts have
been repeated by Mr. Redfield, and demonstrated by his able
investigations, both there and in the Eastern Pacific, and are confirmed
by the observations of Edwards, Lawson, and others, while residents there.
It is a matter of surprise that gentlemen like Messrs. Redfield and Espy,
who have certainly displayed great ability in the investigations of
meteorological phenomena, should fail to recognize a more intimate
relation between this upper current and the storms they were
investigating, and to detect the general laws which govern both. The
storms and hurricanes of the West Indies are comparatively of small
diameter, and have little advance condensation. When they pass on to the
south-western portion of North America and curve to the N. E., as they
frequently do, they enlarge in front and at the sides, and their advance
condensation, which is not dense enough to drop rain, extends in some
cases from one to three hundred miles; and the storm itself, by the time
it reaches the Alleghanies, may extend one thousand to fifteen hundred
miles, and perhaps in certain magnetic states of the surface, and
occasionally, may cover the entire portion of the continent, from north to
south. Such, probably, was very nearly the extension of the storm
investigated by Professor Loomis. In the West Indies, however, at the
commencement, they vary from twenty to one hundred miles, or possibly
more, in width.
First, they are preceded by a hot, sultry and oppressive atmosphere--_as
are electric storms every where_--a peculiar electric state of the earth
and adjacent air.
Second, the black clouds and lightning which indicate the approaching
hurricane are seen to the S., S. E., and E. S. E., according to the season
of the year, as we see them at the westward. During the rainy season, and
when the storm, as is usual at that period, is small, and the S. E. trade
blows more eastwardly, the wind at the Windward Islands, possibly, may set
in at the north, and back round by the east as it progresses. So Colonel
Reid thinks it sometimes does, at Barbadoes. But when the belt of rains is
south, and the hurricane comes from the south-east, and is larger and more
violent in its action, and the north-east winds prevail, the first effect
is an increase of these trades. Soon, however, the wind hauls to the north
and north-west, in opposition to its course, bearing the same relation to
it that our east and north-east winds bear to storms in the United States;
and the wind hauls around during the passage of the storm to the west,
south-west, and south-east, and at the latter point it clears off. Mr.
Edwards in his History of Jamaica says--and as a resident, his authority
should be decisive as to this Island--"_that all hurricanes begin from the
north_, veer back to the W. N. W., W., and S. S. W., and when they get
around to the S. E. the foul weather breaks up." Doubtless the same is
true of the class of northers of which we are speaking on the Gulf of
Mexico. _But with this class the barometer does not rise during the gale,
and in proportion to its length and violence._ With the other class of N.
W. winds--the northers of winter--it does.
The following description of two winter northers, copied from Colonel
Reid's valuable work, will illustrate what has been said. _Precisely such
changes from S. E. rains to N. W. winds, with blue sky and detached dark
clouds--fair-weather N. W. scud--occur every autumn in October and
November_, and the falling of the thermometer and rising of the barometer,
after rain, and a change of the wind, are perfectly characteristic.
------------------------------------------------------------------------
1843. | Wind. |Force.|Weather.| Bar.|Ther.|
------------------------------------------------------------------------
Jan. 30.| | | | | |
A.M. 4. |S. S. W. | 2 |b. c. |29.90| 77 |Off Tampico.
Noon. |South. | 5 |b. c. r.|29.86| 76 | {Lat. 23° 41' N.,
P.M. 8. |South. | 6 |b. c. r.|29.84| 76 | {Long. 94° 50' W.
Jan. 31.| | | | | |
A.M. 4. |S. Easterly.| 3 |b. c. |29.90| 74 | {Between 6 and 10
| | | | | | {A.M., wind was
| | | | | | {variable.
Noon. |N. by W. | 9 |c. q. w.|29.96| 76 |Norther commenced at
| | | | | | 10 A. M.
P.M. 8. |N. N. W. | 9 |c. |30.09| 73 |Lat. 22° 36' N.,
| | | | | | Long. 95° 48' W.
Feb. 1. | | | | | |
A.M. 4. |N. N. W. | 7 |c. g. |30.29| 63 |Lat. 22° 9' N.,
| | | | | | Long. 94° 50' W.
Noon. |Westerly. | 6 |c. |30.30| 67 |
P.M. 8. |Calm. | 0 |c. |30.26| 67 |
------------------------------------------------------------------------
Feb. 14.| | | | | |
A.M. 4. |S. E. | 3 |b. c. r.|29.66| 73 |At Sacraficios.
Noon. |S. W. | 4 |b. c. |29.62| |Norther comc'd at 5.30
| | | | | | P.M.
P.M. 8. |N. W. by N. | 10 |c. q. u.|29.72| 65 |
Feb. 15.| | | | | |
A.M. 4. |N. W. by N. | 10 |c. q. u.|30.10| 61 | {Gale moderated and
| | | | | | {again freshened
| | | | | | {about 8 A.M.
Noon. |N. W. by N. | 10 |c. g. q.|30.19| 61 |
P.M. 8. |N. W. | 4 |c. g. |30.20| 65 |
Feb. 16.| | | | | |
A.M. 4. |N. W. | 3 |q. |30.18| 62 |
P.M. 8. | N. N. W. | 2 | c. g. |30.21| 66 |
------------------------------------------------------------------------
b. indicates blue sky--c. detached clouds--r. rain--v. visibility of
objects--q. squalls--w. wet dew--u. ugly threatening appearance--g.
gloomy weather.
The exact counterpart of the first norther may be observed with us every
fall. On the 30th January, with a rising thermometer and falling
barometer, there was rain at midday. The night following was moist--the
next day, about ten A.M., the wind came out N. W., with squalls and gloomy
weather, a falling thermometer, and rising barometer.
The norther of Feb. 14th differed from the other only in regard to the
time of the day when it commenced; the order of events was the same. The
rain fell in the night--it cleared off early in the day, and the norther
followed in the afternoon. This also is frequently the case with us, as
every one may observe.
This brief notice of the surface winds of our climate would be incomplete
without a description of those of the thunder-gust and tornado.
The former is exceedingly simple. The showers, which are accompanied with
much wind, form suddenly in hot weather, and have a considerable advance
condensation (frequently with obvious lateral internal action), extending
eastwardly from the line of smooth cloud from which the rain is falling,
or rather where the falling rain obscures the inequalities of the cloud.
_The gust is never felt until the advancing condensation has passed over
us_, when it takes the place of the gentle easterly breeze which
previously set toward the shower. _The gust ceases as soon as the cloud
has passed._ It is obviously the result of the inducing and attracting
influence of the cloud upon the atmosphere near the surface of the earth
as it passes over it. Let the reader watch attentively this advance
condensation, from its eastern edge to the line of smooth cloud and
falling rain, and he will understand at a glance this internal action of
gust-clouds. The whole phenomena are simple and intelligible. A cloud
approaching from a westerly point, dark and irregular from its eastern
edge to the line of falling rain, where it appears smooth and of a light
color; wind from the east blowing gently toward it, till the condensation
is over us; then the gust following the cloud; then the rain, and in a few
minutes the cloud, and wind, and rain have passed on to the east, and
"sunshine" returns.
The tornado, as it is termed when it occurs upon land, "spout," if on the
water, is sometimes of a different character, and as it undoubtedly had
great influence in inducing the gyrating theory of Mr. Redfield, and the
aspiratory theory of Mr. Espy, and has been cited by both in support of
their respective theories, it deserves a more particular notice. There are
several marked peculiarities attending it which determine its character.
1st. It occurs during a _peculiarly sultry and electric_ state of the
trade and surface atmosphere, and at a time when thunder showers are
prevailing in and around the locality, and at every period of the year
when such a state of the atmosphere exists. One recently occurred in
Brandon, Ohio, in midwinter.
2d. There is always a cloud above, but very near the earth, between which
and the earth the tornado forms and rages. It is usually described as a
black cloud, ranging about 1000 feet or less above the earth, often with
a whitish shaped cone projecting from it, and forming a connection with
the earth; at intervals rising and breaking the connection, and again
descending and renewing it with devastating energy. Its width at the
surface varies from forty to one hundred and eighty rods--the most usual
width being from sixty to ninety rods. Sometimes when still wider, they
have more the character of thunder-gusts, and are brightly luminous.
3d. Two motions are usually visible, one ascending one near the earth and
in the middle, and a gyratory one around the other. The latter is rarely
felt, or its effects observed, near the earth. Occasionally, and at
intervals, objects are thrown obliquely backward by it.
4th. It is composed, at the surface of the earth, of _two lateral
currents_, a northerly and southerly one, varying in direction, but
normally at right angles in most cases, although not always, with its
course of progression, extending from the extreme limits of its track to
the axis; which currents are most distinctly defined toward the center,
and upward. These currents prostrate trees, or elevate and remove every
thing in their way which is detached and movable. There does not seem to
be any current in advance of these lateral ones tending toward the
tornado, save in rare and excepted cases, and then owing to the make of
the ground or the irregular action of the currents; nor any following,
except that made by the curving of the lateral currents toward the center
of the spout as it moves on, and perhaps a tendency of the air to follow
and supply the place of that which has been carried upward and forward,
like that of water following the stern of a vessel. The south current is
always the strongest, and often a little in advance of the other, and
covers the greatest area. The proportion of the two currents to each other
is much the same that the S. E. trades bear to the N. E. This excess in
volume and strength of the southerly current will explain the
irregularities in most cases, and the fact that objects are so often
_taken up and carried from the south to the north side_, and so rarely
from the north and carried south of the axis. These irregularities are
such as attend all violent forces, and something can be found which will
favor almost any theory; but the two lateral currents appear always to be
the principal actors, except, perhaps, when it widens out and assumes more
the character of a straightforward gust. See a collection by Professor
Loomis, American Journal of Science, vol. xliii. p. 278.
The following diagram is a section of the New Haven tornado, from
Professor Olmstead's map accompanying his article in the "American Journal
of Science and Art," vol. 37. p. 340.
The manner in which the main currents flow is shown by their early and
unresisted effect in a cornfield, as represented by the dotted lines. The
direction in which the fragments of buildings were carried by the greater
power of the southerly currents is shown also. And so is this irregular
action, where a part of the southerly current broke through the northerly
one, and prostrated two or three trees backward on the north side of the
axis.
[Illustration: Fig. 16.]
5th. This cloud, and its spout, move generally with the course of the
counter-trade in the locality--_i. e._, from some point between S. W. and
W., to the eastward, but occasionally a little south of east, deflected by
the magnetic wave beneath the belt of showers.
6th. Several exceedingly instructive particulars have been observed and
recorded.
_a_. _No wind is felt outside of the track_, as those assert who have
stood very near it, and its effects show.
_b_. The track is often as distinctly marked, where it passed through a
wood, as if the grubbers had been there with their axes to open a path for
a rail-road. The branches of the trees, projecting within its limits, are
found twisted and broken off, or stripped of their leaves, while not a
leaf is disturbed at the distance of a foot or two on the opposite side of
the tree, and outside of the track.
_c_. As the spout passes over water, the latter seems to _boil up_ and
_rise to meet it_, and _flow up_ its trunk in a _continued stream_.
_d_. As it passes over the land, and over buildings, fences, and other
movable things, they appear to _shoot up_, instantaneously, as it were,
into the air, and into fragments. If buildings are not destroyed or
removed, the doors may be burst open _on the leeward side_, and gable ends
_snatched out_, and roofs taken off on the _same side_, while that portion
of the building which is to the windward remains unaffected.
_e_. Articles of clothing, and other light articles, have been carried out
of buildings through open doors, or chimneys, or holes made in the roofs,
and to a great distance, without _any opening_ being made for the air to
_blow_ in.
_f_. If there be a discharge of electricity up the spout from the earth,
like that of lightning, the intense action ceases for a time or entirely.
_g_. Vegetation in the track is often scorched and killed, and so of the
leaves on one side of a tree, which is within the track, while those on
the other side, and without the track remain unaffected. (Espy's
Philosophy of Storms, 359, cited from Peltier.)
_h_. The active agent whatever it is, has been known to _seize hold of a
chain attached to a plow_ and _draw the plow about, turning the stiff sod
for a considerable distance_. (See Loomis on the tornado at Stow, Ohio,
American Journal of Science, vol. xxxiii. p. 368.)
_i_. In passing over ponds, the spout has taken up all the water and fish,
and scattered them in every direction, and to a great distance.
_j_. The barometer falls very little during the passage of the spout. (See
the Natchez hurricane of 1827, Espy page 337.) Not more than it
_frequently_ does during gentle showers.
_k_. Persons have been taken up, carried some distance, and if not
projected against some object in the way, or some object against them,
have usually been _set down gently and uninjured_.
_l_. Buildings which stood upon posts, with a free passage for the air
under them, although in the path of the tornado, escaped undisturbed.
(Olmstead's account of the New Haven tornado, American Journal of Science,
vol. xxxvii. p 340.)
_m_. A chisel taken from a chest of tools, and stuck fast in the wall of
the house. (Ibid.)
_n_. Fowls have had all their feathers stripped from them in an instant
and run about naked but uninjured.[5]
_o_. Articles of furniture, etc., have been found torn in pieces by
antagonistic forces.
_p_. Frames taken from looking-glasses without breaking the glass. Nails
drawn from the roofs of houses without disturbing the tiles.
_q_. Hinges taken from doors--_mud taken from the bed of a stream_ (the
water being first removed), and let down on a house covering it
completely--a farmer taken up from his wagon and carried thirty rods, his
horses carried an equal distance in another direction, _the harness
stripped from them_, and the wagon carried off also, _one wheel not found
at all_. (American Journal of Science, vol. xxxvii. p. 93.)
Pieces of timber, boards, and clapboard, driven into the side of a hill,
_as no force of powder could drive them, etc., etc._
Now to my mind, these circumstances indicate clearly, that it is not wind,
_i. e._, mere currents of air, which produces the effect, but that a
_continuous current_ or _stream of electricity_ from the earth to the
cloud exists, and carries with it from near the earth, such articles as
are movable: That this stream collects from the _northerly_ and
_southerly_ side upon the _magnetic meridian_, in _two currents_ with
_polarity_, which meet in their passage up at the center; curving toward
the center in the posterior part as the spout moves on, when acting in a
normal manner, and making the "_law of curvature_" observed: That no
conceivable movement of the air alone in such limited spaces could produce
such effects; or if so, that no agent but electricity could so move the
air: That the air in a building could not shoot the roof upward, and into
fragments; much less could the air in a cellar by any conceivable force,
be made to elevate _or shoot up_ the entire house, and its inmates, and
contents--effects so totally unlike what takes place in gales,
hurricanes, and typhoons: That elastic free air never did nor could take
hold of the plow chain, and plow up the ground; or scorch and kill the
vegetation; or twist the _limbs_ from one side of a tree, while the most
delicate leaves on the other, and within two or three feet, remained
unaffected and undisturbed; or pick the chickens: That even if the
expansion of the air could produce these effects--if a sudden vacuum were
produced--_nothing but currents of electricity could produce the sudden
vacuum_, by removing the air above.
It is well settled that atmospheric electricity can and does flow in
currents with light, by experiments in relation to the brush discharge,
etc. That it may do so without light or disruptive discharge, and in a
stream, or as it is termed, by convection, with the force and effect seen
in the tornado, is perfectly consistent with what we know of it--and it
is, I think clearly evinced that such is the character of the phenomena,
by the fact that a sudden powerful _disruptive_ discharge, _with light, up
the spout_, produces an instantaneous partial or total suspension of its
action; to be renewed as the cloud passes over _another_ and more highly
charged _portion_ of the _earth's surface_. Peltier gives instances where
the spout has been entirely and instantaneously destroyed by such a sudden
and powerful discharge of electricity; marking the spot where it was so
destroyed by a large hole in the earth, from which the discharge issued.
And in fact these tornados are often steadily luminous, and so much so,
when they occur in the night, as to enable persons to read without
difficulty.
The lateral inward and upward currents, are accompanied, after they meet
and unite, or seem to unite, by gyratory or circular ones. How are they
produced? This question can only be answered by analogy. No permanent
impressions are left by the circular currents, except to a limited extent,
and in occasional instances; and observation of them has been, and must
necessarily be limited and uncertain. I have witnessed one or two on a
moderate scale; but owing to the suddenness of their passage, and the
confusion of the objects taken up, it was difficult to determine what the
circular currents were. When the southerly current is much the strongest,
it appears sometimes to cross the axis, and curve round the northerly one.
Perhaps this may be all the curving that really takes place, except at the
posterior part of the axis, for evidence of a curving on the south of the
axis is rarely, if ever seen.
Assuming, however, that the main currents unite and form one from the
earth to the cloud, _induced_ circular currents would be in perfect
keeping with the known laws of electricity. Such currents, and with
magnetic properties, are always induced by powerful currents of voltaic
electricity passing through wires. And doubtless _in all cases_ powerful
currents of electricity _induce attendant circular currents_. This may
account for the external gyration of the spout.
Or it may be that the two lateral currents of air which attend the
currents of electricity, do not unite; having opposite polarity, but pass
by and around each other, in connection with the circular magnetic
currents. Future observation and perhaps experimental research will
determine this. But it may not be accomplished by the present generation;
for the belief that tornados are mere whirlwinds, produced by the action
of the sun in heating the land, is adhered to, notwithstanding they cross
the intense magnetic area of Ohio in mid-winter, and seems to be
ineradicable.
The proportions of different winds vary in different localities. For the
benefit of those who are curious, I copy a table from an able compilation
by Professor Coffin, published by the Smithsonian Institute, showing the
proportion of the winds at New Haven (the station nearest to me). It will
be noticed that during the year the N. W. winds blow the greatest number
of days; the S. W. next; the N. E. and S. E. less than either, and about
equal. It may be observed that the two latter bear about the same
proportion to the whole, that our number of cloudy and stormy days,
averaging about ninety, bear to the whole number of days in the year.
+------------------------------------------------+
|Course.| 1804. | 1811. | 1812. | 1813. | Total. |
|------------------------------------------------|
| N. | 143 | 105 | 90 | 111 | 449 |
| N. E. | 99 | 207 | 138 | 138 | 582 |
| E. | 33 | 18 | 22 | 23 | 96 |
| S. E. | 131 | 108 | 135 | 110 | 484 |
| S. | 58 | 69 | 113 | 80 | 320 |
| S. W. | 224 | 255 | 153 | 261 | 893 |
| W. | 81 | 69 | 102 | 57 | 309 |
| N. W. | 329 | 264 | 345 | 315 | 1253 |
+------------------------------------------------+
This work of Mr. Coffin has been brought to my notice since the foregoing
pages were written. The facts embodied in it will be found to comport with
what I have observed and stated. In relation to the proportionate number
of days in the year during which the wind blows from the different points
of the compass at the several stations it is very full and able.
But it has cardinal defects. It does not show the _main currents_ of the
atmosphere. It treats the surface-winds, which are incidental, as
principals. The direction of the main currents is indeed shown frequently
by the mean course of the surface winds, but not uniformly or
intelligibly. Nor does it distinguish between the fair weather and storm
winds; nor always between the trade winds during their northern transit,
and the variable winds north of the trade-wind region. Hence, the
deductions derived from it disclose no general system, and sustain no
theory, although many very important facts appear. Some of these,
Professor Coffin found it difficult to reconcile with received theories,
or satisfactorily explain. For instance, he found the prevailing winds of
the United States, in Louisiana and Texas, S. and S. E.; in western
Arkansas, and Missouri, southerly, and in Iowa and Wisconsin, S. W.,
forming a curve, and evidently connected together.
Thus, alluding to the winds west of the Mississippi, and between the
parallels of 36° and 60°, he says:
"On the American continent, west of the Mississippi, there appears to
be more diversity in the mean direction of the wind, yet here it is
westerly at sixteen stations out of twenty, from which observations
have been obtained. The most peculiar feature in this region, is the
_line_ of southerly winds on the western borders of Arkansas and
Missouri. It seems to form a connecting link between the winds of
this zone and the south-easterly ones that we find south of it; and,
in some degree, to favor an idea that has been advanced, that there
is a vast eddy, extending from the western shore of the Gulf of
Mexico, to the eastern shore of the Atlantic; that the easterly
trade-winds of the Atlantic Ocean, when they strike the American
continent, veer northwardly, and then N. E., and thus recross the
Atlantic, and follow down the coast of Portugal and Africa, till they
complete the circuit."
This mean prevalence of the curving winds indicates the course of the
western portion of the concentrated counter-trade, of which we have so
fully spoken, and to which that portion owes its rains and fertility.
Doubtless the curve would have been traced somewhat further west, if
observations had been obtained from more westerly stations.
The idea of an eddy, to which Professor Coffin alludes, is of course
unsound; that of a counter-trade, most fully confirmed; the curve
corresponding with that of the regular rains and fertility as they are
known to exist.
Professor Coffin is a believer in the generally-received theory of
rarefaction, as the cause of all winds. His work is published by the
Smithsonian Institution, and the theory is, so far forth, nationalized.
But he found it very difficult to reconcile all the facts he obtained,
with the theory, and, possessing a truth-loving mind, he frankly admits
it. Alluding to the prevalence of N. E. winds off the coast of Africa in
the summer months, as shown by certain numbered wind-roses, he says:
"Nos. 81, 83, 86, and 91, have caused me much perplexity. The arrows
for the warmer months evidently indicate a point of rarefaction
situated to the _south_ or _south-west_, and yet all the observations
from which they were computed were taken within a few hundred miles
of the African coast and desert of Sahara; a region, the annual range
of whose temperature must be exceedingly great. The only way in which
I can account for a fact so astonishing, is, by supposing the
deflecting forces at these numbers to be secondary to the influence
which we see so strongly marked in Nos. 88, 89, and 90. Let us, then,
first devote our attention to these."
(We have not space for the map of Professor Coffin, nor is it necessary to
insert it. The numbers 81, 83, 86, and 91, refer to respective portions of
the Atlantic, west of Africa, North of the Cape de Verdes, of 5° of
latitude each, where the N. E. trades are drawing off from the coast. The
Nos. 88, 89, and 90 refer to like portions _below_ the Cape de Verde,
where the S. W. monsoons are found under the rainy belt; and the
explanation of the distinguished author is an attempt to account for the
blowing of the trades _from_ Sahara, by supposing them connected with the
monsoons further south, which seem to blow toward it.)
"The intense heat of the Great Desert rarefies the air exceedingly
from June to October, inclusive, and hence the arrows of unparalleled
length (Plate XII.)," (showing the monsoon winds below the Cape de
Verdes,) "pointing toward it during those months, the longest being
longer than that which represents the most uniform of the
trade-winds, in the ratio of 104 to 89. The influence of this
rarefaction is sufficient to curve the powerful current of the
trade-winds in the manner exhibited on Plate VII. Nos. 89 and 90, and
to produce the not less remarkable change in No. 88, holding the
current back and retarding it, so that its progressive motion in the
_three_ months of July, August, and September united, hardly exceeds
that during any _one_ of the colder months of the year. But while
this is so, the trades on the western side of the Atlantic are
pursuing nearly their regular track, being but slightly affected by
these influences. As a consequence, the latter must leave, as it
were, a partial vacuum behind them, which is filled by air flowing in
from the north-east and south-east. This will account for the seeming
anomaly of having a somewhat strong deflecting force directed toward
mid-ocean, in the hottest part of the year, as in the numbers above
referred to. _And yet it may be very naturally asked, Why does not
the air from these parts supply the Great Desert directly, instead of
taking a circuitous route to supply the region that supplies it? A
question which, I confess, it seems difficult to answer._"
(The italicization in the foregoing extract is mine).
Here the worthy professor finds a fact inconsistent with the theory of
rarefaction--viz.: that the winds blow off shore, and toward mid-ocean,
opposite Sahara, and he is "perplexed and astonished." The theory,
however, must be maintained, and one of those modifying hypotheses which
have made meteorology such a complicated piece of patch-work, must be
invented; some "deflecting forces" found. There is the Great Desert,
bordering upon the ocean, north of the Cape de Verde Islands, for a
distance of six hundred miles, widening as it extends inland, whose
temperature, as he says, "_must be exceedingly great_;" and doubtless is
so, and yet the air, instead of blowing in upon it in a hurricane, is
actually drawing off from it, and blowing towards the S. W., where the
water and air do not rise above 84°. Well may he be "perplexed and
astonished."
Turning south, however, to the distance of five hundred miles or more, he
finds the S. W. monsoon winds, which in those months blow under the belt
of rains, toward the land, in the direction of, but at a great distance
from, Sahara. It is an easy matter to suppose that they reach the Great
Desert and supply its vortex of rarefaction, inasmuch as they blow in a
direction toward it, and distance is no impediment to supposition.
Then it is necessary to _suppose_ that the S. E. and N. E. trades, at the
south-west, draw so strongly to the westward as to create a partial vacuum
to the S. W. of Sahara, which is filled by the winds which draw off shore,
and then we have the supply brought from the distance of five hundred
miles or more, by an ascending vortex, which creates a vacuum, and the air
near the vortex taken away in _another_ direction by a _partial_ vacuum;
and so an ascending _vortex_, which creates a vacuum is supplied from a
distance, and a _partial vacuum_ at a distance is supplied by the air near
the perfect vacuum. Such an idea of a supply by a circuitous route, and
secondary influence, is not very philosophical, to say the least, and
Professor Coffin feels it; and to the question, Why is it so? which, he
says, may very naturally be asked, he confesses there is no answer. And
there would be none, even if his suppositions were based upon facts. But
other questions might be asked equally difficult to be answered, viz.:
1st. Is there any rarefaction which can draw the trades to the west, and
in that particular locality, in opposition to the supposed vortex of
Sahara, by creating a _partial vacuum_?
2d. Are they in fact so drawn?
3d. Do the S. W. winds, south of the Cape de Verdes, and _under the rainy
belt_, which in the summer months extend up to these islands, _reach the
desert at all_?
These are pertinent questions, _and every one of them must be answered in
the negative_. The hypothesis is without foundation, and Professor's
Coffin's perplexity and astonishment must remain, until he abandons the
theory of rarefaction entirely. The winds which so perplex him are nothing
but the regular N. E. trades, made to originate on the coast and continent
of Africa, in summer, by the northern transit of the whole machinery. They
not only draw off from the desert coast, but they _blow over the desert
itself_ on to the ocean, and into the rainy belt upon the land, as we have
already seen, and the supposed vortex of rarefaction does not exist.
That the monsoons do not reach the desert is demonstrated by the tables of
Professor Coffin, and to set it at rest we will make the necessary
extracts. Commencing with the region from the equator to 5° N., and from
10° to 55° W. longitude, we have the observed winds in proportion, as
follows, for July and August--the south-east trades prevailing, inasmuch
as the belt of rains is at this season situated further north.
LATITUDE 0° TO 5°, LONGITUDE FROM GREENWICH 10° TO 55°.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 0 | 0 | S. S. W.| 54 | 111 |
| N. N. E.| 8 | 2 | S. W. | 1 | 29 |
| N. E. | 6 | 2 | W. S. W.| 6 | 19 |
| E. N. E.| 27 | 16 | West. | 2 | 9 |
| East. | 31 | 20 | W. N. W.| 1 | 6 |
| E. S. E.| 120 | 96 | N. W. | 1 | 0 |
| S. E. | 216 | 276 | N. N. W.| 0 | 2 |
| S. S. E.| 218 | 443 | Calm. | 8 | 4 |
| South. | 69 | 279 |---------------------------|
| | | | Total | 768 | 1,314 |
+-------------------------------------------------------+
Here, it is evident that the S. E. trades are the prevailing winds, but
their course is variable.
Ascending to the region between 5° and 10° north latitude, and 10° to 55°
west longitude, the northern part of which at this season is covered by
the rainy belt; we find the monsoon, the S., S. S. W., and S. W. winds,
the prevailing ones in August, although the winds are variable, as usual
under the rainy belt.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 19 | 6 | S. S. W.| 188 | 368 |
| N. N. E.| 26 | 11 | S. W. | 63 | 94 |
| N. E. | 104 | 32 | W. S. W.| 73 | 93 |
| E. N. E.| 30 | 16 | West. | 33 | 48 |
| East. | 45 | 29 | W. N. W.| 30 | 18 |
| E. S. E.| 36 | 40 | N. W. | 21 | 9 |
| S. E. | 93 | 53 | N. N. W.| 17 | 13 |
| S. S. E.| 225 | 307 | Calm. | 109 | 74 |
| South. | 239 | 514 |---------|-------|---------|
| | | | Total | 1,351 | 1,725 |
+-------------------------------------------------------+
Ascending to the region of 10° to 15° north latitude, and 15° to 45° west
longitude, we find the winds exceedingly variable, and the monsoons
diminished remarkably. If Professor Coffin's theory was correct, they
should increase as they approach the desert; but they in fact, diminish,
and the N. E. trades are found at the north portion.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 17 | 55 | S. S. W.| 30 | 71 |
| N. N. E.| 64 | 74 | S. W. | 33 | 63 |
| N. E. | 155 | 149 | W. S. W.| 19 | 43 |
| E. N. E.| 91 | 71 | West. | 12 | 25 |
| East. | 83 | 60 | W. N. W.| 17 | 21 |
| E. S. E.| 25 | 26 | N. W. | 13 | 24 |
| S. E. | 17 | 26 | N. N. W.| 24 | 56 |
| S. S. E.| 13 | 33 | Calm. | 62 | 78 |
| South. | 9 | 44 |---------|-------|---------|
| | | | Total | 684 | 919 |
+-------------------------------------------------------+
Ascending to the region between 15° and 20° north latitude, and 15° to 45°
west longitude, we get north of the belt of rains _and lose the monsoons
entirely although still below the desert_; and find the regular N. E.
trades, with less variable winds than are found in almost any other part
of the ocean.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 39 | 20 | S. S. W.| 0 | 5 |
| N. N. E.| 210 | 185 | S. W. | 0 | 5 |
| N. E. | 112 | 87 | W. S. W.| 8 | 3 |
| E. N. E.| 114 | 104 | West. | 0 | 1 |
| East. | 20 | 36 | W. N. W.| 0 | 4 |
| E. S. E.| 21 | 17 | N. W. | 3 | 4 |
| S. E. | 0 | 2 | N. N. W.| 3 | 31 |
| S. S. E.| 2 | 11 | Calm | 20 | 8 |
| South. | 5 | 1 |---------|-------|---------|
| | | | Total, | 557 | 526 |
+-------------------------------------------------------+
Ascending still further to the region between 20° and 25° north latitude,
and 15° and 45° west longitude, which borders, in part, on the S. W.
corner of the desert, and we have not, during the month of August, a
single wind between S. S. E. and W. N. W., which blows in upon the land;
and _only twelve instances out of three hundred and ninety-four in this
hottest month in the year, and on the southern portion of the desert, when
the wind blows on shore from any quarter_. This is demonstration. The
monsoon winds are confined to the rainy belt; they do not reach the
desert, nor does the desert attract the winds from the ocean, or
reverse, hold back, or disturb the trades.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 25 | 20 | S. S. W.| 3 | 0 |
| N. N. E.| 210 | 153 | S. W. | 2 | 0 |
| N. E. | 129 | 77 | W. S. W.| 13 | 0 |
| E. N. E.| 110 | 86 | West. | 0 | 0 |
| East. | 8 | 20 | W. N. W.| 0 | 3 |
| E. S. E.| 4 | 11 | N. W. | 2 | 1 |
| S. E. | 0 | 3 | N. N. W.| 5 | 8 |
| S. S. E.| 1 | 7 | Calm. | 2 | 5 |
| South. | 1 | 0 |---------|-------|---------|
| | | | Total, | 515 | 394 |
+-------------------------------------------------------+
Ascending once more, to the region between the degrees of 25 and 30, north
latitude, and 15 and 45, west longitude, we find it bounded east entirely
on the center of the desert. Now here, certainly, there must be evidence
of the truth of the rarefaction theory, if any where on the face of the
earth. Yet here, in July and August, we find the trades as regular as any
where, and not more variable winds than are found in the trades toward
their northern limits every where, and in August, only forty out of four
hundred and twenty-nine winds, blowing directly or indirectly on shore.
+-------------------------------------------------------+
| Course. | July. | August. | Course. | July. | August. |
|-------------------------------------------------------|
| North. | 32 | 19 | S. S. W.| 9 | 6 |
| N. N. E.| 155 | 125 | S. W. | 3 | 9 |
| N. E. | 144 | 35 | W. S. W.| 13 | 14 |
| E. N. E.| 140 | 89 | West. | 12 | 3 |
| East. | 48 | 57 | W. N. W.| 7 | 7 |
| E. S. E.| 31 | 23 | N. W. | 11 | 1 |
| S. E. | 8 | 7 | N. N. W.| 36 | 6 |
| S. S. E.| 8 | 12 | Calm. | 18 | 12 |
| South. | 5 | 4 |---------|-------|---------|
| | | | Total, | 680 | 429 |
+-------------------------------------------------------+
It would seem to be impossible for any man to believe in the theory of
rarefaction, after an examination of these tables.
Professor Coffin discovers other anomalies, for which he finds it
difficult to account. Among these are the northerly tendency, in the
afternoon, of the winds in Ohio, south of Lake Erie; the winds of
south-western Asia, which, he says, "Are so irregular as to defy all
attempts to reduce them to system;" particularizing the N. W. at
Jerusalem, the westerly at Bagdad, the N. E. at Constantinople, the
northerly at Trebizond, etc., etc. Jerusalem has the Mediterranean at the
N. W., Bagdad has it at the west, Constantinople has the Black Sea at the
N. E., Trebizond N. N. W. and N. E., and the counter-trade, as it passes
over them, draws its storm-surface wind or sea-breeze, from the quarter
where evaporation is greatest, and the atmosphere is most susceptible of
electrical inductive influence. Precisely as it draws from the ocean and
the eastward, east of the Alleghanies, from the lake region, west of the
lakes, and from the northward, south of the lakes, and from the westward,
east of them.
This law of attraction will explain, too, the mean prevalence of easterly
winds north of the parallel of 60°, at the stations named in his work.
Great Bear Lake, Great Slave Lake, and Fort Enterprise, lie east of the
Rocky Mountain range which interposes between them and the Pacific, and
have Hudson's Bay and other large bodies of water on the east and north.
Hence, easterly winds prevail at these places. At Norway House, on
Nelson's River, near the north end of Lake Winnipeg, a large body of
water, which stretches off to the south, we find the south wind the
prevalent one, especially in December, when the northern and north-eastern
waters are frozen up, and the N. E. largely present at all seasons of the
year.
At New Hernhut, in winter, when Davis' Straits are covered with floes, the
prevailing wind is east, drawn from the warm, open sea east of Greenland,
where the Gulf Stream is evaporating. But in June and July, when
evaporation is going on over Davis' Straits and Baffin's Bay, the
prevailing winds are west and south, and the east winds fall off.
Other stations are equally instructive, but I must forbear.
In relation, however, to the easterly zone of wind, of which Professor
Coffin speaks, it should be added that the counter-trade, south of the
magnetic pole, in high latitudes, pursues an easterly course, is near the
earth, and attracts an opposite wind as it does on the east and north of
the pole, in localities where the surface atmosphere is not peculiarly
susceptible to its influence, and, therefore, the _winds are mainly
opposite to its course_. Thus, at Melville Island, they are almost all
westerly and north-westerly, for there the remnant of the counter-trade is
passing west around the magnetic pole. These westerly and north-westerly
winds are very light, and like the gentle easterly breeze which sets
toward the cumulus clouds and summer showers.
Since most of this work was written, I have procured, and read with great
pleasure, Lieutenant Maury's "Geography of the Sea." It is a work of
great interest, and should be in the hands of every one. The extent of
ground covered, however, made it necessary for Lieutenant Maury to
introduce much matter not derived from his own investigations. In doing
this, he has taken received opinions, and has thereby introduced much
heresy. The view he adopts in relation to the monsoons, although the
popular one with philosophers, is of that character. He says (page 222):
"Monsoons are, for the most part, formed of trade-winds. When a
trade-wind is turned back, or diverted, by over-heated districts,
from its regular course at stated seasons of the year, it is regarded
as a monsoon. Thus, the African monsoons of the Atlantic, the
monsoons of the Gulf of Mexico, and the Central American monsoons of
the Pacific, are, for the most part, formed of the north-east
trade-winds, which are turned back to restore the equilibrium which
the over-heated plains of Africa, Utah, Texas, and New Mexico have
disturbed. When the monsoons prevail for five months at a time--for
it takes about a month for them to change and become settled--then
both they and the trade-winds, of which they are formed, are called
monsoons."
Again (§ 476-7):
"The agents which produce monsoons reside on the land. These winds
are caused by the rarefaction of the air over large districts of
country situated on the polar edge, or near the polar edge, of the
trade-winds. Thus, the monsoons of the Indian Ocean are caused by the
intense heat which the rays of a cloudless sun produce, during the
summer time, upon the Desert of Cobi and the burning plains of
Central Asia. When the sun is north of the equator, the force of his
rays, beating down upon these wide and thirsty plains, is such as to
cause the vast superincumbent body of air to expand and ascend. There
is, consequently, a rush of air, especially from toward the equator,
to restore the equilibrium; and, in this case, the force which tends
to draw the north-east trade-winds back becomes greater than the
force which is acting to propel them forward. Consequently, they obey
the stronger power, turn back, and become the famous south-west
monsoons of the Indian Ocean, which blow from May to September
inclusive.
"Of course, the vast plains of Asia are not brought up to monsoon
heat _per saltum_, or in a day. They require time both to be heated
up to this point and to be cooled down again. Hence, there is a
conflict for a few weeks about the change of the monsoon, when
neither the trade wind nor the monsoon force has fairly lost or
gained the ascendency. This debatable period amounts to about a month
at each change. So that the monsoons of the Indian Ocean prevail
really for about five months each way, viz.: from May to September,
from the south-west, in obedience to the influence of the over-heated
plains, and from November to March inclusive from the north-east, in
obedience to the trade-wind force."
What the "trade-wind force" is, Lieutenant Maury tells us in another
paragraph, viz.: "Calorific action of the sun and diurnal rotation of the
earth"--the received calorific theory. I have already shown, I think,
conclusively, that there is no expansion and ascent in the supposed region
of calms, which induces, or can induce, the trades; and that, in point of
fact, the air on the land is cooler under the belt of rains. But as
Lieutenant Maury, whose reputation is national, adopts the theory, I shall
be pardoned for copying the following table, showing the difference of
temperature at two cities of India, before, after, and while the belt of
inter-tropical rains is over them. It will be seen that the temperature is
actually less when the belt is there, viz., in July and August, than in
April and May. _This should be conclusive upon that point._
+----------------------------------------------------+
| | Anjarakandy. | Calcutta. |
| Months. |--------------------|-------------------|
| | Rain. | Temp. | Rain. | Temp. |
|-----------|----------|---------|---------|---------|
| | M. M. | | M. M.| |
| January, | 2,26 | 26°,5 | 0,0 | 18°,4 |
| February, | 2,26 | 27°,7 | 67,68 | 21°,5 |
| March, | 6,77 | 28°,4 | 24,82 | 25°,6 |
| April, | 29,33 | 29°,8 | 130,84 | 28°,5 |
| May, | 175,96 | 28°,6 | 16,24 | 29°,7 |
| June, | 794,05 | 26°,6 | 575,24 | 29°,3 |
| July, | 807,59 | 25°,8 | 338,38 | 28,°1 |
| August, | 572,98 | 26°,0 | 311,31 | 28°,3 |
| September,| 311,31 | 26°,4 | 254,91 | 28°,0 |
| October, | 157,91 | 26°,8 | 42,86 | 27°,2 |
| November, | 65,42 | 26°,9 | 20,30 | 23°,0 |
| December, | 29,33 | 26°,5 | 0,0 | 19°,2 |
|-----------|----------|---------|---------|---------|
| Year, | 2955,14 | 27°,2 | 1928,74 | 26°,4 |
+----------------------------------------------------+
Anjarakandy is on the Malabar coast, between 12° and 13° north latitude.
Calcutta in an angle of the Bay of Bengal, at 22° 30' north latitude. The
former is in and near the focus of the monsoons, and has a temperature in
July (when 18 inches of rain fall), about as low as in December.
In the foregoing table from Kaemptz, the rain is in millimetres, about
twenty-five of which make an inch, and the temperature is centigrade,
which may be raised to Fahrenheit by adding four fifths of the quantity
and also 32°--thus, if the height of the centigrade thermometer be 25°,
add to this four fifths of 25°, which is 20°, and also 32°, the result is
77°. Twenty-five centigrade is therefore equal to seventy-seven
Fahrenheit.
Lieutenant Maury is not, and should not be a theorist. He occupies the
position, in some sort, of a national _investigator_, and, of course, of
national _instructor_. Opinions which emanate from him, or which are
endorsed by him, should be accurate. Sooner or later that which he has
adopted in relation to the monsoons, and some others, must be abandoned.
In addition to what has already been said, I wish to call his, and the
reader's attention, to several other facts and considerations in relation
to the monsoons, and particularly those of India.
1st. The deserts of Cobi and Bucharia, which constitute the "burning
plains" of _Central_ Asia, north-east of the Indian Ocean, lie between 38°
and 45° of north latitude, and under the zone of extra-tropical rains.
They are not wholly rainless. They partake of that saline character which
affects so much of Asia and the western part of this continent. South of
them, running nearly east and west, are the lofty ranges of the Himmalaya
and Kuenlun Mountains, and the table lands of Thibet. To their saline
character, in part, but mainly to the interposition of these mountain
ranges, depriving the counter-trade of moisture, they owe their
comparative sterility. _If bountifully supplied with rains, this salt
would doubtless ere this have been washed to the ocean, as it has been
from other countries, once as salt as they._ But they have some rain, and
more or less vegetation, and are not intensely hot. They lie too far
north, and are too elevated. Their temperature is not materially different
from that of the western, and comparatively desert portions of our own
country, and they are utterly incapable of creating a monsoon at the
Indian Ocean, and especially from the long line of Malabar coast, where
the south-west monsoons are found in most strength. The sterile portions
of Utah, New Mexico, and Texas are alike incapable of such effect upon the
atmosphere of Central America and Mexico. These monsoons commence in May,
and prevail until October, and the temperature of the air where they blow
ranges with considerable regularity between 76° at night, and 84° at
mid-day, on the Malabar coast, and a trifle lower in Central America.
At Fort Fillmore, El Paso, New Mexico, in latitude 32°03, the mean
temperature for
May is 68°
June " 78°, 5'
July " 80°, 1'
August " 83°, 8'
September " 77°, 9'
-------
And for the whole period, 77°, 1'
At Santa Fé, New Mexico, the mean for
May is 66°, 9'
June " 72°, 5'
July " 75°, 3'
August " 72°, 9'
September " 62°, 3'
-------
And for the whole period, 69°, 3'
Mean of the two united, 73°, 2'
The mean of Western Texas is about 2° higher than at Fort Fillmore, and of
Utah not materially different; and the mean of _Central_ Asia between 38°
and 45° does not materially vary from them.
Now, it is perfectly evident that during May and September the temperature
of Central Asia is far below that of the Indian Ocean and India, and never
materially exceeds it. Central Asia is hot, "burning," if you please,
compared with more elevated, fertile, or better watered territory _in the
same latitude_, and so it has been characterized; but not so, compared
with the Indian Ocean, or India, where the sun is vertical. During the
greater part of the time, therefore, that the monsoons are in full blast,
Utah, Texas, and New Mexico, and Cobi, and the burning plains of Asia, are
from 5° to 10° colder than the temperature of the place where the monsoons
are blowing. Would not such a fact be perfectly conclusive in any other
science except theory-swathed meteorology?
2d. The theory assumes that the heated air has an ascensive force, which
causes it to rise and create a vacuum, and this vacuum, by its suction,
draws in the adjoining air, which immediately ascends. The adjoining air,
drawn away from its locality, leaves a vacuum, and that is filled by
another rush from the S. W., and so on, till the Indian Ocean is reached,
and the monsoons are accounted for.
Now, look at the difficulties:
The highest temperature that can be assumed for the air over Cobi, at any
time, without disregarding facts and analogy, is 100°. What is the
ascensive power of an area of atmosphere of 100°? For this we have no
problem or formula, although problems and formulas abound in the science.
Professor Espy relied on heated air only to give the storm a _start_. His
main reliance was on the latent heat supposed to be given out during
condensation, for his ascensive storm power. But over these "burning
plains" there is, according to the theory, no storm or cloud, or
condensation on which that supposed reliance for expansion can be placed.
What, then, is the ascension force of air at 100°? _We ought to know, for
we sometimes have it as high, or within two or three degrees as high, in
all the eastern and middle States._
The monsoons blow at from twenty to twenty-five miles an hour, and
sometimes more. Is that the ascensive force of air at 100°? At 25 miles an
hour it would be 2,200 feet; at 20 miles, 1,760 feet; and at 10 miles, 880
feet per minute.
Does any man believe that either current exists? Why, then, do we not have
our hats taken off, or light objects carried up, or have a monsoon, or, at
least, have the clouds running up, when we have such elevated
temperatures. _Nothing of the kind occurs with us._ Our hottest days are
comparatively still days; and I have seen the cumulus sailing gently to
the east, horizontally, when the air was at 98°. Why should we be exempt?
Is not our air the same and our heat the same?
Again, suppose we grant that the ascensive force is equal to 20 or even 10
miles an hour, will not the adjoining air hold back somewhat to avoid
leaving behind an entire vacuum? or, will it all voluntarily rush in, and
leave a new complete vacuum? and, if so, why the preference of vacuums by
the air, and _when, where, and why_, should the _successive vacuums stop_?
Nay, would not gravity fill the second vacuum from _above_, rather than
from the south-west side? and will not the air incline to rush in, to some
or all these successive vacuums, from some other side than south-west? or,
have these deserts the power of selecting the quarter from which their
vacuum shall be filled, and of delegating it to succeeding vacuums? Would
it not incline to rush in from the east and west where there are no
elevations, rather than from the S. W. and over the Kuenlun Mountains, the
intervening ridges and valleys of Thibet, the lofty Himmalayas, the extent
of India, and the Ghaut Mountains, from three to four thousand feet high,
on its eastern coast? Would it not, at least, _leak in a little_, and
lessen the force with which the vacuums would draw from the far-off Indian
Ocean, so that the monsoon could not blow with equal force? or, if Cobi
and its fellow deserts _must_ and _can_ draw from an _ocean_, why not from
the head of the Arabian Sea, or Bay of Bengal, or the China Sea, which are
nearer, or from the Japan Sea, which is still nearer, or the Yellow Sea,
which is close by? Why draw only from under the central belt of rains?
Nay, what shall be done with Professor Dove? In a recent article,
republished in the American Journal of Science and Art, for January, 1855,
he says: "A greatly diminished atmospheric pressure taking place in summer
over the _whole continent_ of Asia must produce an influx from all
surrounding parts; and thus we have west winds in Europe, north winds in
the Icy Sea, east winds on the east coast of Asia, and south winds in
India. _The monsoon itself becomes, as we see, in this point of view, only
a secondary phenomena._" This looks very like _antagonism_. Who shall we
believe?
Again, suppose you get one atmosphere from the whole area, raised up by
the supposed ascensive force, and at the rate of twenty-five, twenty, or
even ten miles an hour, and a new volume drawn in from the south-west,
and _over the mountains_: will it not take a _little time_ for _that_ to
_heat up_? Does it heat so fast as to _keep up the ascensive force_
without intermission, at twenty-five, or twenty, or ten miles the hour?
What says Mr. Ericsson to this? Can he not arrange with a moderate lens,
to move his engine with the rays of the summer sun? Nay, Lieutenant Maury
says they can not heat up "_per saltum_, or in a day." But according to a
reasonable calculation, they must heat up the air from 80°, or less, to
100°, at the rate of 2,000 feet per minute. Heating 2,000 feet in depth,
in the proportion of 20° per minute, night and day, for five months, is
"_per saltum_" in a minute, and 1,440 "_saltums_" per day!
And further still, the Indian Ocean, from which the monsoons are drawn to
Cobi and Central Asia to the N. E., is during those months covered by the
belt of calms and rains, as heretofore stated; and the S. E. trades
blowing into it are attributed to the suction created by the ascent of
heated air _there_. So, then, the monsoons are blowing away from under the
rainy belt, from 500 to 1000 miles, to Cobi and the burning plains of
Asia, while the ascensive force of that belt is such as to draw the S. E.
trades toward the very spot, a distance of 1,200 or 1,500 miles, at 20
miles an hour! What must the ascensive force over Cobi, etc., be, if, as a
"stronger power," it can overcome an ascensive force over the Indian Ocean
sufficient to draw the S. E. trades 1,500 miles, at 20 miles an hour; and,
in addition to the force necessary to resist this central suction, not
only stop or hold back the N. E. trade, but reverse it and draw it back,
at 20 miles an hour, as a monsoon? Must it not be, at least, double that
of the belt of calms, or the "great region of expansion," as Professor
Dove calls it?
Now, I am irresistibly tempted to ask whether a meteorological theory can
be too absurd for credence, and whether it would not be as well to endow
the deserts with ribs and lungs, and a proboscis long enough to reach the
Indian Ocean, and the necessary power of inspiration and expiration? Such
a theory would avoid all difficulties, conflict with no more analogies,
and, in my judgment, be as much entitled to credit as the one to which
meteorologists adhere.
3d. North of the Malabar coast, in the north-west of India, lies an
extensive desert. West of that is Beloochistan, with its rainless deserts.
Further west are the rainless deserts of Arabia, and these three,
including the Persian deserts further north, cover _as much surface_ as
the deserts of Cobi and Bucharia--have the sun vertical in part, and
nearly so over the entire surface--_are more intensely hot_, and lie
within _one third of the distance_ which intervenes between that desert
and the Indian Ocean off the Malabar coast, with _an open sea and_ no
_mountains between_. Now, look at it. The north-west desert of India, and
the rainless deserts of Beloochistan and Arabia _reverse no trade_ and
_have no monsoon_, although the Arabian Sea heads right up among them.
They do not attract one from the Indian Ocean off the Malabar coast,
although not more than one third of the distance off, and without such
mountains and table lands intervening as separate that coast from Cobi. It
is said by Lieutenant Maury that the monsoons, "_obey the stronger
force_." But which is the stronger force? Cobi, not _wholly_ rainless,
lying north of 35°, under the zone of extra-tropical rains, with India and
the Ghauts, the Himmalaya Mountains, the table lands of Thibet, and the
Kuenlun Mountains between? or the deserts of India, Beloochistan, and
Arabia, _wholly rainless_, and _intensely hot, near by_, and in _open
view_. There can be but one answer to this question. Nothing in the way of
desert barrenness, or elevated temperature, unless it be those of Sahara,
can exceed the deserts about the head of the Arabian Sea and Persian Gulf.
Certainly those of Cobi can not compare with them; yet the trades blow
steadily over them, although more northerly there, as every where, near
their northern limits, especially on land. Says Hopkins, in his
atmospheric changes:
"If any one part of the broad expanse of the continent of Asia could
be heated so as to draw air from the Arabian Sea and the Indian Ocean
during the summer, it would be that part which lies between
Hindoostan and the Lake of Aral, including the region between the
Valley of the Oxus and Persia, and the land of this part, unlike
Hindoostan, is not screened from the sun by thick vapors. But what
says Burnes respecting the winds of this part? Why, that about the
latter end of June, though the thermometer was at 103° in the day,
'In this country a steady wind generally blows from the north.' And
on the 23d of August, after having passed the Oxus--'The heat of the
sand rose to 150°, and that of the atmosphere exceeded 100°, but the
wind blew steadily, nor do I believe that it would be possible to
traverse this tract in summer if it ceased to blow. The steady manner
in which it comes from one direction is remarkable in this inland
country.' Again--'The air itself was not disturbed but by the usual
north wind that blows steadily in this desert.' And he has many other
similar passages."
Here there is a vast tract of country south of 35° which has a temperature
often of 103°, and does not reverse the trade and create a monsoon. How
utterly unphilosophical, then, to attribute the monsoons to Cobi because
they "obey the stronger force!" or to attribute them to it at all.
4th. The monsoons can not be _traced from_ the Malabar coast _to Cobi_.
They do not exist on the south-west of Cobi and near it, where they should
in greatest force, and there is no connection, in fact, shown between
them. They do not often extend more than twenty-five miles inland, or to
the east of the Ghauts. There are no corresponding intervening monsoons
crossing India to the mountains--none over the mountains and table
lands--none under the northern lee of the mountains--nor, in short, on the
whole track, nor any S. W. winds except such as naturally belong to the
action of the curving counter-trade.
Finally, the investigations of Commodore Wilkes on Mauna Loa, a mountain
upon Hawaii, more than 13,000 feet high, and the observations of Professor
Wise and other aeronauts are sufficient to put this whole matter of heated
lands and ascent of the atmosphere as the cause of winds, at rest.
Commodore Wilkes was encamped for about _twenty days_ on Pendulum Peak, in
December and January 1840. Although not up to the elevation of the
counter-trade in that latitude, he was above the local clouds which form
over the island during the day, where the sea breezes blow in with as
great strength as any where. Indeed, he was on the top of the "lofty
conical mountain" to which Caleb Williams alludes in the letter to
Professor Espy I have quoted, and above the spot where Professor Espy
assumed that the clouds were rising with such force as to induce the
strong sea breezes of that island. During this time there were two
snow-storms on Mauna Loa, and they had the wind from the S. W. during the
storm, as might be expected, looking at the situation of the mountain on
the western side of the island. These storms moved to the N. W., and were
observed at the other islands in that direction as rain.
The local clouds lay over the island every day, as they do over active
volcanic islands which are very elevated, although it was the dry season.
_Nothing like an ascent of the clouds or of the currents of air from the
ocean was observed._ On the contrary, the clouds formed before the sea
breezes set in, and the latter blew from the different sides of the island
in under the clouds, and outward again, probably on the opposite side. The
whole interior of the island is elevated, and its temperature low; and
_there was no elevation of temperature on the high portions of the island
over which the clouds formed, and toward which the winds blew, which could
create an upward current_.
"During our stay on the summit, we took much pleasure and interest in
watching the various movements of the clouds; this day in particular,
they attracted our attention; the whole island beneath us was
covered with a dense white mass, in the center of which was the cloud
of the volcano rising like an immense dome. All was motionless until
the hour arrived when the sea-breeze set in from the different sides
of the island; a motion was then seen in the clouds, at the opposite
extremities, both of which seemed apparently moving toward the same
center, in undulations, until they became quite compact, and so
contracted in space as to enable us to see a well defined horizon; at
the same time there was a wind from the mountain, at right angles,
that was affecting the mass, and drawing it asunder in the opposite
direction. The play of these masses was at times in circular orbits,
as they became influenced alternately by the different forces, until
the whole was passing to and from the center in every direction,
assuming every variety of form, shape and motion.
"On other days clouds would approach us from the S. W. when we had a
strong N. E. trade-wind blowing, coming up with cumulus front,
reaching the height of about eight thousand feet, spreading
horizontally, and then dissipating. At times they would be seen lying
over the island in large horizontal sheets as white as the purest
snow, with a sky above of the deepest azure blue that fancy can
depict. I saw nothing in it approaching to blackness at any time."
(Exploring Expedition, vol iv. p. 155).
Here, in the last paragraph, we have the whole truth disclosed. The N. E.
trade was blowing on Mauna Loa, 13,000 feet above the sea, and the
sea-breeze blew in on the _leeward side_, its moisture condensing over the
volcanic island, but without rising _up the mountain_, or _through the
surface-trade_, or _above 8,000 feet_.
So, too, the celebrated aeronaut, Mr. Wise, in the course of more than a
hundred ascensions, some during high wind, and others during rain storms,
never met with an ascending current, except in a single instance, in the
body of a hail-cloud, and then there were descending currents also, the
usual intestine motion of hail-cloud with its opposite polarities.
I copy a description of his passage through the clouds of a rain-storm,
and his floating a long period above them; and there was no ascending
current which disturbed their horizontal repose or progression. The double
layer is not uncommon--condensation taking place at the connection of the
upper and lower portions of the trades, with the surrounding atmosphere;
or in the trade, and by _induction in the surface atmosphere_ at the same
time. Such instances are frequently visible, and if his ascensions had
been undertaken at other times in stormy weather he would have seen more
of them.
"Before I passed the limits of the borough, a parachute, containing
an animal, was dropped, which descended fast and steady, and, just as
it reached the earth, my ærial ship entered a dense black body of
clouds. Ten minutes were consumed in penetrating this dismal ocean of
rainy vapor, occasionally meeting with great chasms, ravines, and
defiles, of different shades of light and darkness. When I emerged
from this ocean of clouds, a new and wonderfully magnificent scene
greeted my eyes. A faint sunshine shed its warmth and luster over the
surface of this vast cloud sea. The balloon rose more rapidly after
it got above it. Viewing it from an elevation above the surface, I
discovered it to present the same shape of the earth beneath,
developing mountains and valleys, corresponding to those on the
earth's surface. The profile of the cloud-surface was more depressed
than that on the earth, and, in the distance of the cloud-valley a
magnificent sight presented itself. Pyramids and castles, rocks and
reefs, icebergs and ships, towers and domes--every thing belonging to
the grand and magnificent could be seen in this distant harbor; the
half-obscured sun shedding his mellow light upon it, gave it a rich
and dazzling luster. They were really "castles in the air," formed of
the clouds. Casting my eyes upward, I was astonished in beholding
another cloud-stratum, far above the lower one; it was what is
commonly termed a "mackerel sky," the sun faintly shining through it.
The balloon seemed to be stationary; the clouds above and below
appeared to be quiescent; the air castles, in the distance, stood to
their places; silence reigned supreme; it was solemnly sublime.
Solitary and alone in a mansion of the skies, my very soul swelled
with emotion; I had no companion to pour out my feelings to. Great
God, what a scene of grandeur! Such were my thoughts; a reverence for
the works of nature, an admiration indescribable. The solemn
grandeur--the very stillness that surrounded me--seemed to make a
sound of praise.
"This was a scene such that I never beheld one before or after
exactly like it. Two perfect layers of clouds, one not a mile above
the earth; the other, about a mile higher; and, between the two, a
clear atmosphere, in the midst of which the balloon stood quietly in
space. It was, indeed, a strange sight--a meteorological fact, which
we cannot possibly see or make ourselves acquainted with, without
soaring above the surface of the earth." (History and Practice of
Aeronautics, p. 209).
This is graphic. Perhaps in relation to the conformity of the upper
surface of the inferior layer of clouds, to the irregularities of the
earth's surface, he was misled during the enthusiasm of the moment. He is
certainly mistaken as to the possibility of observing these double layers
from the earth; I have seen them in hundreds of instances. But in relation
to the _quiescence_ of the clouds for an hour, and _the entire absence of
ascending currents_, he could not be mistaken.
And now, in the absence of all direct proof to sustain the hypothesis,
that the heating of the land produces ascending currents, and thereby the
winds, and especially the monsoons, and in view of all the adverse
evidence, I put it to Lieutenant Maury, and every sincere searcher after
meteorological truth, whether the theory should not be abandoned.
CHAPTER VII.
The counter-trade of the northern hemisphere ranges at different heights
in different latitudes, in the same latitude at different seasons, and
also upon different days of the same season; and, like the line of
perpetual snow, has its greatest elevation in the tropics, descending
gradually to the surface of the ocean at the poles. At the northern limit
of the N. E. trades, it does not, ordinarily, approach the earth
sufficiently near for decided reciprocal action. Hence, at that point,
storms do not often originate; the winds are lighter and more variable,
and calms are more frequent than at any point, except at the meeting and
elevation of the trades, or in the polar regions. Doubtless this state of
things is increased by the feebler action of north polar magnetism, and
the irregular action of the longitudinal magnetic currents, evinced by the
irregular, and often, feeble action of the trades, near their extreme
limits. They are not unfrequently wholly wanting, near the northern limit,
for several days in succession, and calms and baffling winds are found in
their place--another effect of the irregular action of terrestrial
magnetism, consequent upon the ever-changing transit of central activity
from south to north, and from north to south. Upon the islands, however,
and continents, which have elevated mountain peaks and ridges, especially
if of volcanic origin and activity, which approach more nearly the path of
the counter-trade, a different state of things exists. There, showers and
gusts are frequent. Thus, upon the Sandwich Island, Kauai, the most
northern one, which is within the region of the N. E. trade during ten
months of the year, and upon its volcanic peaks and elevated table-lands,
and north-easterly from them, over the district of Waioli, rain falls in
abundance during the year, while the coastlines upon other portions of the
island can not be cultivated without irrigation. (See Wilkes' Exploring
Expedition, vol. iv. pp. 61 and 71; and American Journal of Science and
Art, for May, 1847).
A like state of things, in degree, may be found upon the Canaries, and the
more elevated of the West India Islands. The Cape de Verdes are an
exception, and the Christian world are quite often called upon for
contributions of provisions, to save the inhabitants of these islands from
starvation. They lie at the northern limit of the equatorial belt, and for
a period of two months only (July and August), are supplied with rain. If,
from any cause, the belt does not move as far north as usual during any
season, unbroken drought and famine are sure to overtake them. The islands
contain some elevated peaks, and are of volcanic origin, but not of
present volcanic activity, and the counter-trades as they issue from the
equatorial belt at their highest elevation, are too far above them for
reciprocal, influential action. If the islands could be placed 10° further
north, we should hear no more of drought or famine from them, and their
quantity of rain and fertility would be not only more permanent, but much
increased. Superadded to this, is the fact, that at that point the belt of
rains precipitates feebly because the S. E. trade originates upon the
southern part of the continent of Africa, and the N. E. mainly, upon the
desert and the Barbary States--and both are sparingly supplied with
moisture.
The same state of things is strikingly obvious upon continents wherever
the mountains are sufficiently elevated, even within the trade-wind
region. Thus, in South America, the Andean ranges are of great elevation,
and spurs and table-lands extend from them a considerable distance to the
eastward. There, the S. E. and N. E. trades of the Atlantic meet in very
considerable volumes, and not only is the equatorial belt much wider than
upon the Atlantic and Pacific, but the counter-trades are met upon the
elevated peaks and mountain-ranges, and showers and storms on their
eastern slopes and summits are frequent during the dry season--down even
to the extra-tropical belt. I have already said that it was probable that
the great elevation of the Andes diverted and turned south a portion of
the N. E. counter-trade which would otherwise pass over the western coast
of Peru.
The report of Lieutenant Herndon, which has come to my notice since that
was written, states facts which strongly corroborate that opinion. It
seems that the trades and counter-trades actually _bank up_, in their
passage to the westward, against those mountains, and the true elevation
of their eastern slopes can not be barometrically ascertained. (See report
of the Exploration of the Amazon, p. 261). Lieutenant Herndon says:
"I was surprised to find the temperature of boiling water at Egas to
be but 208° 2', the same within 2' of a degree that it was at a point
one day's journey below Tingo Maria, which village is several hundred
miles above the last rapids of the Huallaga river; at Santa Cruz, two
days above the mouth of the Huallaga, it was 211° 2'; at Nauta, three
hundred and five miles below this, it was 211° 3'; at Pebas, one
hundred and seventy miles below Nauta, 211° 1'. I was so much
surprised at these results that I had put the apparatus away,
thinking that its indications were valueless; but I was still more
surprised, upon making the experiment at Egas, to find that the
temperature of the boiling water had fallen 3° below what it was at
Santa Cruz, thus giving to Egas an altitude of fifteen hundred feet
above that village, which is situated more than a thousand miles up
stream of it. I continued my observations from Egas downward, and
found a regular increase in the temperature of the boiling water
until our arrival at Pará, where it was 211° 5'.
"From an after-investigation, I am led to believe that the cause of
this phenomenon arises from the fact that the trade-winds are dammed
up by the Andes, and that the atmosphere in those parts is, from this
cause, compressed, and, consequently, heavier than it is further from
the mountains, though over a less elevated portion of the earth. The
discovery of this fact has led me to place little reliance in the
indications of the barometer for elevation, at the eastern foot of
the Andes. It is reasonable, however, to suppose that this cause
would no longer operate at Egas, nearly one thousand miles below the
mouth of the Huallaga."
The report of Lieutenant Gibbon, is also exceedingly instructive.
Separating from Lieutenant Herndon at Tarma, upon the Andes, he pursued a
southern course, along the eastern slopes of the chain from 11° 30'
south, almost to 18° south, at Ohuro, making a journey of about 7° 30' of
latitude.
A considerable portion of this journey was over eastern and less elevated
portions of the Andes; but little below, however, the line of perpetual
snow. Here, during the dry season, he met with frequent showers and fogs
from the eastward, but left them as he descended into the plains upon the
table-land. There he found the dry season more distinctly marked; but
occasional irregularities were found upon the table-lands, as every where
upon corresponding elevations. The S. E. trades, however, were there
obvious, during the dry season, notwithstanding the irregularities. The
rainy season, from December to May, he spent at Cochabamba, and at its
close he traveled north down the Madeira and its tributaries, to the
Amazon. Although scarcely consistent with my prescribed limits, I can not
forbear making a few extracts. Thus, when on the mountains, east of
Huanvelica, in the N. E. counter-trade, he says:
"Our course is to the eastward. The snow-capped mountains are in
sight to the west. Temperature of a spring 48°; air 44°. Lightning
flashes all around us; as the wind whirls from _north-east_ to
south-west, rain and snow-flakes become hail, half the size of peas.
Thunder roars and echoes through the mountains; the mules hang their
heads, and travel slowly; the thinly-clad aboriginal walks shivering
as he drives the train ahead; the dark cumulus cloud seems to wrap
itself around us."
Again, at the Bombam Post-house, in the focus of change from cirrus to
cumulus, and stratus, and storm:
"The winds are very gentle, and curl the cirrus or hairy clouds in
most graceful shapes about the hoary-headed Andes, in rich and
delicate clusters; when the peak is concealed, all but the blue tinge
below the snow, we see a natural bridal vail. An _easterly wind_
lifts and turns them to dark, cumulus clouds, settled on the frosty
crown, like an old man's winter cap; the physiognomical expression is
that of anger. The change is accompanied by thunder, and seems to
command all around to clothe themselves for storms. The cold rain
comes down in _fine drops_ upon us; the day grows darker, and the
_clouds press close upon the earth_."
During an excursion east of Cuzco--
"Turning from the river, we ascend a steep ridge of mountains--the
eastern range at last. A heavy mist _wafts upward as the winds drive
it against the side of the Andes_, so that our view is shortened to a
few hundred yards. We hope the curtain will rise that we may view the
productions of the tropical valley below; but the mist thickens, and
the day gets dark with heavy, heaped-up black clouds; a rain-storm
follows. The grasses are thrifty, and the top of the ridge covered
with a thick sod. By barometer, we stand eleven thousand one hundred
feet above the level of the sea."
In May following, having spent the rainy season in Cochabamba, he travels
north--
"Our route from Tarma to Oruro was south. We traveled ahead of the
sun. In December, when we arrived in Cochabamba, the sun had just
passed us. As soon as he did so, the rains descended heavily on this
side of the ridge; it was impossible to proceed. The roads were
flooded, the ravines impassable, and the arrieros put off their
journey until the dry season had commenced. After the sun passed the
zenith of Cochabamba, and had fairly moved the rain belt after him
toward the north, then we came out from under shelter, and are now
walking behind the rain belt in dry weather, while the inhabitants
are actively employed in tending their crops."
So on the north of the equatorial belt, along the whole line of the Andes,
up to the northern boundary of the desert valley of the Gila, rain falls
on the high mountain-ranges, owing to the contiguity of the counter-trade
and the diversion of showers to the north, along their eastern sides.
During the survey of the boundary line between Mexico and California,
etc., by the commission under Mr. Bartlett, it became necessary to find
some spot where water and grass were abundant, for the head quarters of
the commission. This was found, and _could only be found_, upon the
Mimbres Mountains, at an old abandoned Spanish copper mine, 7,000 or 8,000
feet above the level of the sea, surrounded with peaks of still greater
height. These elevated ranges were within influential distance of the
counter-trade, and here snow fell in the winter, from the extra-tropical
belt, and rain, in showers, in summer, at the period of the most northerly
extension of the tropical belt; when fifteen miles off, in the valley, it
was unbroken drought. Mr. Bartlett thus describes it in his Personal
Narrative:
"We reached this district on the 2d of May. Vegetation was then
forward, though there had been no rain. But it must be remembered
that during the winter there is snow, and hence a good deal of
moisture in the earth when the spring opens. The months of May and
June were moderately warm. On the third of July the first rain fell.
It then came in torrents, accompanied by hail, and lasted three or
four hours. Many of our adobe houses were deluged with water, and the
mountain-sides exhibited cataracts in every direction. The Arroyo,
which passes through the village, and which furnishes barely water
enough for our party and the animals, became so much swollen as to
render it difficult to cross; and, by the time it had received the
numerous mountain torrents, which fall into it within a mile from our
camp, it became impassable for wagons, or even mules. The dry gullies
became rapid streams, five or six feet deep, and sometimes fifty feet
or more across. On this day, a party, in coming to the copper mines,
from the plain below, _where there had been no rain_, found
themselves suddenly in a region overflowing with water, so that
their progress was arrested, and they were obliged to wait until the
flood had subsided. After this we had occasional showers, during the
months of July and August."
The location of this mountain station is near the thirty-third degree of
north latitude, while the northern limit of the equatorial belt, nowhere,
except upon the mountain ranges and table-lands of Mexico, extends above
25°.
There, for the reason we have been considering, it does extend further
north during July and August, in occasional showers, and in the vicinity
of Mount Picacho, Mr. Bartlett met one of its mountain thunder-storms on
the 13th of July, on his return south through Mexico, in latitude 32°, in
the following year. (Personal Narrative, vol. ii. p. 285). These showers
originated in strata of counter-trade, which had followed up along the
eastern side of the mountains and not from strata which had crossed them
and curved to the eastward, as is shown by the course of progression of
the showers.
Let us look, in this connection, at a fact or two of great interest,
though not directly connected with the point in hand. The southern limit
of the extra-tropical belt in winter, on the Pacific coast of North
America, is in the vicinity of San Diego, at about 32°. In summer, that
limit is carried up above Astoria, which is in latitude 46° 11'--about
14°--yet New Mexico receives little if any rain in winter in the vicinity
of Albuquerque, but does receive a limited supply of about seven inches in
summer and autumn, five and a half inches of which falls in June, July,
and August. Albuquerque is in latitude 35° 13', below the southern summer
limit of the extra-tropical belt, and north of the northern limit of the
equatorial belt. This anomaly is explained by the extension west over
northern New Mexico, of the extreme western edge of our concentrated
counter-trade, by reason of its issuing further west from the equatorial
belt in its northern extension in the summer months. This western edge, in
curving to the east, north-east of New Mexico, covers the north-western
States, Iowa, Minnesota, Wisconsin, etc., and furnishes them that great
excess of summer precipitation which is a peculiarity of their climate;
and its absence further east in winter, and the very great elevation of
the Rocky Mountains and other ranges over which their ordinary
counter-trade of that season curves, account for the absence of much
precipitation and snow there, or over the valley of the Rio Grande in New
Mexico, in winter.
We may now see, too, why the western coast and the Pacific region of the
continent, below 45°, are so deficient in moisture. The S. E. trades,
which arise from the western portion of the south Atlantic and the
continent of South America, which, if it were not for the Andes chain, in
their natural course, after passing the equatorial belt, would continue on
to the north-west until they passed the limits of the N. E. trades, and
curve in upon the western portion of our continent below 45°, and supply
it bountifully with rain, are, in part, perhaps, diverted along the
eastern side of those mountains to swell the volume of our counter-trade,
and in part pass them, almost exhausted of their supply of moisture by
their contiguous reciprocal action. Hence, too, the deficiency of
precipitation at the base of the Andes, on the western side, and the
peculiar and irregular character of the winds under the western lee of the
Andean range. Baffling airs and bands of calms prevail on this portion of
the Pacific, except where the mountains fall off, and then there is a
westerly or south-westerly monsoon under the equatorial belt. Says
Lieutenant Maury in his Charts, sixth edition, p. 731:
"The passage, under canvass, from Panama to California, as at present
made, is the most tedious, uncertain, and vexatious that is known to
navigators.
"My investigations have been carried far enough to show that at
certain seasons of the year a vessel bound from Panama to California,
must cross at least three, at some seasons four, such meetings of
winds or bands of calms, before she can enter the region of the N. E.
trades. Hence the tedious passage."
Such will ever be the state of things on this continent and upon the
eastern Pacific, so long as the S. E. counter-trades are compelled to pass
over the mountain chain of South and Central America.
Again, if we examine carefully the belt or zone of extra-tropical rains,
we shall find that the focus of greatest precipitation is considerably
north of its southern limit, and that, other things being equal, this
focus travels north in summer, and gives to higher latitudes their needed
summer rains. This is very apparent upon the north-western portion of our
continent, as the following table will show:
+-----------------------------------------------------------
| | Lat. |Jan.|Feb.|Mar.|Apr.|May.|June.|
| |-------|----|----|----|----|----|-----|
|San Diego, Cal. |32° 41'| 0.3| 1.7| 1.1| 0.9| 0.5| 0.0 |
|San Francisco. |37° 48'| 1.7| 0.5| 4.4| 2.1| 0.4| 0.0 |
|Cant., Far W., Cal.|39° 02'| 3.3| 0.6| 6.4| 2.2| 0.9| 0.0 |
|Astoria, Oregon. |46° 11'|27.0|10.9| 6.1| 4.4| 5.9| 2.6 |
|Puget's S'd, Ore. |47° 07'|11.8| 3.9| 4.7| 4.1| 0.8| 0.6 |
|Sitka, Russ. Am. |57° 3'| 2.5| 9.6| 3.5| 3.3| 1.9| 5.9 |
+-----------------------------------------------------------
---------------------------------------+
|July.|Aug.|Sept.|Oct.| Nov.|Dec.|Year.|
|-----|----|-----|----|-----|----|-----|
| 0.0 | 0.2| 0.0 | 0.1| 1.5 | 3.4| 9.6|
| 0.0 | 0.0| 0.4 | 0.6| 3.0 | 5.5| 18.8|
| 0.0 | 0.0| 0.3 | 0.1| 3.5 | 4.6| 21.9|
| 0.0 | 2.3| 1.9 | 6.7|13.2 | 6.2| 87.2|
| 0.5 | 1.3| 1.6 | 3.6| 5.9 | 6.1| 44.8|
| 3.7 |10.1|14.8 |12.7| 7.4 | 4.2| 79.5|
---------------------------------------+
The figures are for inches and tenths of an inch of rain.
Thus, it will be seen that in January, when the southern line is at San
Diego, at the south line of California, the focus of precipitation is over
Oregon; and that in August and September when the southern line is carried
up and over Oregon, the focus has traveled north to Sitka, and that it is
always at least 10° north of the southern line of the belt upon that
coast. The increased quantities of rain which fall at the focus of
precipitation there, from Oregon up, are doubtless much enhanced by the
equatorial oceanic current which flows over opposite that part of the
continent. A like effect, precisely, is produced in Europe. The quantity
of rain which falls at Bergen, in Norway, being 87-61/100 inches per year,
more than three times the average for that continent.
The difference shown in the foregoing table, between Astoria and Puget's
Sound, is owing to the fact that the latter lies in the interior and
within the coast range of mountains, while Astoria is situated at the
mouth of the Columbia River, with an open view of the ocean.
A like comparative increase of precipitation in northern latitudes, in
summer, is found every where varying according to the local influences
which operate in the particular case. Thus,
------------------------------------------------------------------------
There falls in |Winter.|Spring.|Summer.|Aut'mn.| Year.
---------------------------------|-------|-------|-------|-------|------
Burlington, Vt., lat. 44° 20' | 5.7 | 7.3 | 11.4 | 9.8 | 33.9
Albany, N. Y., lat. 42° 39' | 8.3 | 9.8 | 12.3 | 10.3 | 40.7
Minnesota, Iowa, lat. 41° 28' | 7.3 | 12.3 | 17.4 | 11.7 | 48.8
St. Peters'g, Russ., lat. 59° 56'| 3.89 | 3.20 | 5.70 | 4.71 | 17.51
Pekin, China, lat. 40° | .54 | 3.35 | 18.80 | 2.29 | 25.68
------------------------------------------------------------------------
Pekin lies in the northern part of China, and would have a much larger
fall of rain from a concentrated counter-trade, but for the numerous
mountain-ranges which intersect its path in winter, but over which it
passes at a greater elevation during the summer--a peculiarity from which
the eastern section of this country is most remarkably and happily free.
Thus, it is obvious that the focus of precipitation in the zone of extra
tropical rains, is some 8° to 12° north of its southern line, and travels
with the whole machinery in its annual transit north and south.
It is a question of some difficulty, perhaps, whether this focus is
increased by the increase of magnetic action at this point, for both the
line of descent of the counter-trade, and the focus of magnetic action,
are carried up in a like manner, and for a like cause, and, in all
probability, both concur in the result.
There is exceeding wisdom in this provision for the gradual subsidence of
the counter-trade, and gradual increase of magnetic intensity, and
consequent gradual precipitation. On the European continent, and over
western Asia, there are 50° of latitude to be supplied with moisture by
this polar belt of rains. If the focus of precipitation was at its
southern border, the counter-trade would be deprived of its moisture at
that point, and little would reach the more northern portions of the globe
which are to be supplied by it. But the movement of the whole machinery
carries up the southern line from the south boundaries of the Barbary
States on to the Mediterranean and portions of southern Europe, and the
focus of precipitation and of near approach of the counter-trade to the
earth, being situated far north of the southern line, is carried up
correspondingly, while the combination of the moisture with the atmosphere
by south polar magnetism and electricity, and the gradual descent of the
counter-trade, enable it to resist, to some extent, the influence of north
polar magnetism and cold, and thus retain portions of its moisture for
distribution in the polar regions.
_The elevation of the counter-trade above the earth varies in the same
latitude with the variations in the phenomena of the weather._ An
attentive observation of the clouds of our climate will soon satisfy any
one of this, after he has become familiar with them, so as to distinguish
with certainty the clouds of the trade. Its range, in this country, is
from 3,000 feet, or less, to 12,000 feet above the earth, and its depth
with us probably, from 6,000 to 8,000 feet. Gay-Lussac, in his scientific
experimental balloon ascension, the first of _that character_ ever made,
except an imperfect one just previous, by himself and Biot, found it at
about 12,000 feet over Paris, and about 4,000 feet in depth. It is
detected by the thermometer when much elevated.
The atmosphere grows cool as it is ascended on mountains, or by balloons.
The rate of cooling is ordinarily about 1° of Fahrenheit for every 300
feet. If it were not for the equatorial current, this progressive decrease
of temperature would doubtless be perfectly uniform. Of Gay-Lussac's
ascension, on this point it was said:
"At forty minutes after 9 o'clock, on the morning of the 15th
September, 1804, the scientific voyager ascended, as before, from the
garden of the repository of models. The barometer then stood at 30.66
English inches, the thermometer at 82° Fahrenheit, and the hygrometer
at 57-1/2°. The sky was unclouded, but misty.
"During the whole of this gradual ascent, he noticed, at short
intervals, the state of the barometer, the thermometer, and the
hygrometer. Of these observations, amounting in all to twenty-one, he
has given a tabular view. We regret, however, that he has neglected
to mark the times at which they were made, since the results appear
to have been very materially modified by the progress of the day. It
would likewise have been desirable to have compared them with a
register, noted every half hour, at the Observatory. From the surface
of the earth to the height of 12,125 feet, the temperature of the
atmosphere decreased regularly, from 82° to 47° 3' by Fahrenheit's
scale; _but afterward it increased again, and reached to 53° 6' at
the altitude of 14,000 feet_; evidently owing to the influence of the
warm currents of air which, as the day advanced, rose continually
from the heated ground. From that point the temperature diminished,
with only slight deviations from a perfect regularity. At the height
of 18,636 feet the thermometer subsided to 32° 9', on the verge of
congelation; but it sunk to 14° 9' at the enormous altitude of 22,912
feet above Paris, or 23,040 feet above the level of the sea, the
utmost limit of the balloon's ascent."
The high range of the barometer indicated a very considerable elevation
of the trade at the time Gay-Lussac made his ascension. I am not aware
that it has since been found at so great an elevation, in so high a
latitude, though it is undoubtedly elevated by the interposition of a
large volume of N. W. air, upon some occasions, to nearly the same
altitude with us.
In the extract in relation to the ascension of Gay-Lussac, we have another
of the thousand hastily-adopted and absurd hypotheses connected with the
caloric theory. It is obviously and utterly _impossible_ that in addition
to the ordinary accumulation of heat at the surface of the earth "_as the
day advanced_"--that is, _during the forenoon_, warm currents should
ascend, unobserved by Gay-Lussac during an ascent of 12,000 feet--not
_affecting in the least_ so large an intervening body of the atmosphere or
his thermometer, and in such immense volumes as to increase the warmth of
a stratum of 4,000 feet in depth, an average of 3° of Fahrenheit, and to
the extent of 6° at the center.
Very few balloon ascensions have been made with a view to scientific and
accurate observation. But other aeronauts have met the counter-trade at
different altitudes, and in both clear and stormy weather.
Recently, in 1852, four ascensions were made in England, under the
direction of the Kew Observatory Committee, of the British Association. I
copy from the August number of the "London, Edinburg, and Dublin
Magazine," for 1853, the following condensed amount of the result:
"The ascents took place on August 17th, August 26th, October 21st,
and November 10th, 1852, from the Vauxhall Gardens, with Mr. C.
Green's large balloon.
"The principal results of the observations may be briefly stated as
follows:
"Each of the four series of observations shows that the progress of
the temperature is not regular at all heights, but that at a certain
height (_varying on different days_) the regular diminution becomes
arrested, and for the space of about 2,000 feet the temperature
remains constant, or even increases by a small amount. It afterward
resumes its downward course, continuing, for the most part, to
diminish regularly throughout the remainder of the height observed.
There is thus, in the curves representing the progression of
temperature with height, an appearance of _dislocation_, always in
the same direction, but varying in amount from 7° to 12°.
"In the first two series, viz.: August 17th and 26th, this peculiar
interruption of the progress of temperature is strikingly coincident
with a _large_ and _rapid fall_ in the temperature of the
_dew-point_. The same is exhibited in a less marked manner on
November 10th. On October 21st a dense cloud existed at a height of
about 3,000 feet; the temperature decreased uniformly from the earth
up to the _lower_ surface of the cloud. When a slight rise commenced,
the rise continuing through the cloud, and to about 600 feet above
its upper surface, when the regular descending progression was
resumed. At a short distance above the cloud, the dew-point fell
considerably, but the rate of diminution of temperature does not
appear to have been affected in this instance in the same manner as
in the other series; the phenomenon so strikingly shown in the other
three cases being perhaps modified by the existence of moisture in a
_condensed_ or vesicular form.
"It would appear, on the whole, that about the principal plane of
condensation heat is developed in the atmosphere, which has the
effect of raising the temperature of the higher air above what it
would have been had the rate of decrease continued uniformly from the
earth upward."
These gentlemen do not adopt the absurd explanation of the French
philosophers; they account for the phenomenon by supposing heat to be
_developed_ at that particular part of the atmosphere; but they are
equally wide of the mark. They found the excess of heat there to the
extent of 7° to 12°, and on days when there was no condensation, or other
assignable cause for its _development_.
The temperature of the counter-trade partakes, doubtless, of the
temperature of the adjoining strata at its upper and lower portion, and
has never been found much, if any, higher than 60° at the center. Nor
could it be expected. The trade, in its upward curving course, within the
tropics, attains a considerable altitude where the atmosphere is
comparatively cold, and necessarily loses a portion of its heat there, and
during its northern flow. Probably its central summer range, in the
latitude of Paris, is not far from 55°, and with us 60°.
The contrast between the trade and the surrounding atmosphere, in winter,
is much more striking, and this has been observed particularly upon the
Brocken of the Alps, and in the polar regions.
"In all seasons the temperature is higher on the Brocken, on a serene,
than on a cloudy day, and, in the month of January, _the serene days were
warmer than at Berlin_." (Kämtz's Meteorology, by Walker, p. 217.--Note.)
As the portion of the counter-trade, which does not become depolarized--in
diminished volume--progresses toward the polar regions, it settles nearer
the earth, and within the Arctic circle is found but little way above it.
Thus, in December, 1821, Parry, at Winter Island, in latitude 66° 11',
flew a kite, with a thermometer attached, to the height of 379 feet, and
found that the temperature, instead of falling 1-1/4°, the usual ratio of
decrease, rose 3/4 of a degree.
The same thing was observed at Spitzbergen, in latitude 77° 30' north, and
at Bosekop, latitude 69° 58', by a scientific commission, and by means of
kites, confined balloons, and the ascent of elevations.
"In winter the temperature goes on increasing with the height, up to
a certain limit, which is variable, according to the different
atmospheric circumstances, the influence of which is not yet very
exactly known. The hour of the day appears to be indifferent, since
there exists no thermometric diurnal variation in the strata of the
surface. The mean of thirty-six experiments, made with kites, or with
captive balloons, at Bosekop, latitude 69° 58' north, has given a
mean rate of increase of 1° 6' for the first hundred meters.[6]
Beyond this limit, and even beyond the first 60 or 80 meters, the
temperature again becomes decreasing, at first very slowly, but
afterward the decrease is accelerated. The observations that have
been made on the flanks, or on the summits, of mountains, during the
same expeditions, entirely confirm these results. The cooling
influence of a soil, that radiates its own heat for several weeks,
without receiving any thing on the part of the sun, in compensation
of its losses, the influence of _counter-currents from above_, coming
from the west and the south-west, with a high temperature, account
for this anomaly, which, in winter, represents the normal state of
the most northern parts of the European continent." (Walker's Kämtz,
p. 515.--Note.)
Mr. Walker is the only author, so far as I know, who has suspected the
true cause of the phenomenon, viz.: "currents from above coming from the
west and south-west, with a high temperature;" but the caloric theory
"sticks like a burr," and he adheres also to the idea that a snow-clad
surface, in the absence of the sun, can aid, by radiation, in warming the
atmosphere for a distance of several hundred yards above it, increasing
the warmth as the distance from the earth increases!
This contrast between the counter-trade and the adjacent atmosphere, in
winter, in latitudes as low as that of the Brocken, is probably heightened
by the increased warmth of the former, at that season. The S. E. trades
then form under a vertical sun, and the difference of temperature can not
be less than from 6° to 8°. Not unfrequently in winter and spring the rain
will fall with a temperature of 50° to 55°, when the atmosphere near the
earth is 10° or 20° or more, below those points; and it is frozen to every
object upon which it falls. The trade stratum, from which it descends, is
not warmed by "radiation" or by ascending currents from a snow-clad
surface, and during a cloudy day; nor by a "development of heat" at that
particular altitude, but it has brought its heat from the South Atlantic,
and imparts it to the rain which forms within it. There is every reason to
believe that the counter-trade flows north in a regular descending plane,
not materially differing from that of the line of perpetual snow. The
descent of the latter is well ascertained to be from about 16,000 feet at
the equator, to _the surface_ at the poles. The plane of the counter-trade
is probably much the same, varying over different localities, from the
varied action between it and the earth which we are considering; and
probably both correspond with the increase of magnetic intensity.
Lieutenant Maury, in an able and original article upon the circulation of
the atmosphere, conceives the bands of comparative calms at the northern
limits of the trades, which he appropriately terms the "_Calms of
Cancer_," to be nodes in the circulation of the atmosphere, and that the
upper or counter-trade here decends and becomes a surface wind from the S.
W., as the N. E. trade is a surface wind; and that an upper current from
the poles approaches and descends at the same node, to make the N. E.
trade. But it is evident he adopted that conclusion too hastily, as he
obviously did the conclusion that the calms of the horse latitudes were a
type of all. We have seen that the latter are increased by a diversion of
the counter-trade, and that they are avoided by making easting. So it may
be observed that our upper current is a S. W. current, and no northerly
upper current is visible, or exists over the country, however it may be in
western Europe and the North Pacific, on the west of the magnetic poles,
where cold, dry northerly and north-easterly winds are found. The origin
and progress of storms withal demonstrates that no such node can exist.
Two points have been made in relation to the course of the counter-trade
in the tropics, and are relied upon to show its progress there to the N.
E., which deserve consideration.
In the first place, it is well known that "rain dust" falls in
considerable quantities on the western coast of Africa, particularly about
the Cape de Verde Islands, and also upon the Mediterranean and
south-western Europe, where it is termed "sirocco dust."
"This dust," says Lieutenant Maury, "when subjected to microscopic
examination, is found to consist of infusoria and organisms, whose
_habitat_ (place of abode) is not Africa, but South America, and in
the S. E. trade-wind region of South America. Professor Ehrenberg has
examined specimens of sea dust, from the Cape de Verdes and the
regions thereabout, from Malta, Genoa, Lyons, and the Tyrol, and he
has found such a similarity among them as would not have been more
striking had these specimens been all taken from the same pile.
"South American forms he recognizes in all of them; indeed, they are
the prevailing form in every specimen he has examined.
"It may, I think, be now regarded as an established fact, that there
is a perpetual upper current of air from South America to north
Africa, and that the volume of air in these upper currents, which
flows to the northward, is nearly equal to the volume which flows to
the southward with the N. E. trade-winds, there can be no doubt,"
etc.
Now, it is doubtless true that this dust is transported in a
counter-trade, and that such dust is found in South America, and is taken
up there by sand-spouts, like those of the ocean in form and action. Both
Humboldt and Gibbon have graphically described them. Yet I do not think
the point well taken. South-eastward of the Cape de Verdes, where the
surface-trades--which, becoming counter-trades, pass over these islands,
and, recurving, pass over the Mediterranean and south-western
Europe--should originate, there is a vast extent of unexplored continent
in the same latitude as the portion of South America where the dust is
found; and the same dry seasons, and the same spouts, in all probability,
exist in both. Until it be shown that such forms have no "_habitat_" in
central and southern and unexplored Africa, upon the same latitudes as in
South America, it may fairly be presumed that the dust is taken up there.
Indeed, the _curve_ upon which this dust is found to fall, in the greatest
quantities, is very remarkable, and corresponds remarkably with the _law
of curvature_ of the counter-trade we have considered, and with the
progress of a storm upon that coast, and over the Mediterranean,
investigated by Colonel Reid. (See Reid, on Storms and Variable Winds, p.
276.) This _curve clearly indicates the origin of the dust in South
Africa_.
The second point is, that ashes from the volcanos of Mexico and Central
America have fallen to the north-east of the place where they were
ejected. Mr. Redfield has grouped these instances of volcanic eruption
usually cited, and I copy from him:
"We learn from Humboldt, that in the great eruption of Jorullo, a
volcano of southern Mexico, which is 2,100 feet above the sea, in
latitude 18° 45', longitude 161° 30', the roofs of the houses in
Queretaro, more than 150 miles north, 37° east from the volcano, were
covered with the volcanic dust. In January, 1845, an eruption took
place in the volcano of Cosiguina, on the Pacific coast of Central
America, in latitude 13° north, and having an elevation of 3,800
feet, the ashes from which fell on the island of Jamaica, distant 730
miles north, 60° east from the volcano. The elevated currents by
which volcanic ashes are thus transported are seldom or never of a
transient or fortuitous character; and these results, therefore,
afford us one of the best indications of their general course. Thus,
the progress of the higher portion of the trade-wind was marked by
the eruption of Tuxtla, latitude 18° 30', longitude 95°, which
covered the houses in Vera Cruz with ashes, at the distance of 80
miles north, 55° west, and also at Peroté, 160 miles north, 60° west.
The ashes from the volcano, at St. Vincent, which fell at Barbadoes,
and east of that island, in 1812, mark the course of a current from
the westward, which appears there at times, in the region of clouds,
and may, perhaps, be connected with the permanent winds on the
Pacific coast of Mexico."
As to one of the instances cited in the foregoing paragraph, that of
Tuxtla, it may be laid out of the case--the direction conforming
substantially to the assumed course of the counter-trade at that point.
St. Vincent lies W. N. W., or nearly so, of Barbadoes, and a N. W. or
westerly surface-wind, prior to, and during storms, is common in the West
Indies as the N. E. is here--both alike, blowing in opposition to the
progressive course of the storm. There is nothing strange or peculiar,
therefore, respecting that instance, or the existence of variable and
especially S. W. currents, between the trades, with occasional partial
condensation.
The falling of the ashes from Cosiguina, upon Jamaica, has long and often
been cited, as proof that in the West Indies the prevailing upper currents
run from the S. W. But it has been ascertained that, _during the same
eruption, ashes fell 700 miles to the westward, on the deck of the
Conway_, a vessel then upon the Pacific Ocean. That case, therefore, does
not prove the absence of the S. E. counter-trade at the time, but only the
presence of another, and a different current above or below it--and it may
have been either, and transient.
So of the Jorullo instance. Investigation would probably have shown that
ashes fell to the N. W., and that they were carried N. E. by a transient
S. W. wind produced by the existence of a storm to the eastward, or one of
those states of partial condensation of the counter-trade which often
produce currents at greater distances without a storm. Not one of these
cases disproves the existence of a S. E. counter-trade, and the invariable
N. W. progression of the storms of those latitudes demonstrates it.
Occasional anomalous currents, depending upon storm action at considerable
distance, are found in our atmosphere, and doubtless are there also. Thus,
although the N. W. wind is almost invariably a surface wind, I have, in a
few instances, seen a N. W. set at a considerable elevation, converging
toward a peculiarly stormy state of atmosphere far south of us, about the
period of the spring equinox. And so in one or two instances I think I
have seen light cirro-stratus clouds _above_ the counter-trade, when it
ran very low, setting from the N. E., although the usual and almost
invariable location of the N. E. wind is below the counter-trade and the
stratus clouds of the storm. Aeronauts, too, have found these secondary
currents beneath a serene and cloudless sky. Indeed, the S. E.
counter-trade doubtless often induces a thin secondary current of S. W.
wind between itself and the surface-trade, in the same manner that similar
currents are induced with us, and every where.
A question arises here of considerable interest, which, I confess, I can
not answer to my own satisfaction. It is, whether there be, or not, _an
eastern progression of the body of the atmosphere above the machinery of
distribution_. I have thought there was, and that in set fair weather I
had seen a peculiar kind of cirro-cumulus cloud, in patches, the small
cumuli very distinct and rounded, moving due east, which indicated such a
current. But I am not satisfied, from my own observation, that it is so,
nor is it easy to determine the question. The moisture of evaporation
rarely, if ever, ascends to any considerable elevation, and the upper
strata must be very dry. Hence, condensation, if it takes place, is thin,
and perhaps often undiscernable. Investigations upon mountains prove
little, for the winds of the inferior strata rush up their sides and over
them. It is an open question, and future observation may solve it. The
prevailing opinion seems to be that there is. If the theory of Oersted, in
relation to the circular currents of a magnet, be true, there should be
such a progression produced by opposite secondary currents, unless,
indeed, it be also true that those currents are inoperative at so great a
distance, or their influence barely suffices to retain the attenuated
atmosphere in its place. Perhaps the investigations of Ampère conflict
with it. But it is worth while, I think, for philosophers to inquire
whether the transverse position of the needle upon the wire is not the
effect of the central _longitudinal_ currents, conforming to the circular
currents of the wire, and whether it is not owing to the production of the
same currents in a globe by the circular currents of Ampère, that the
globe is magnetized, and the needles made to dip.
CHAPTER VIII.
It is exceedingly desirable, in a practical point of view, to understand
the precise character of the reciprocal action which takes place between
the earth and the counter-trade, and produces the varied phenomena which
mark our climate. We have seen that the same laws, other things being
equal, operate every where, and that analogies may be sought in the
character of those phenomena elsewhere, under the same, or different,
modifying circumstances. Looking, therefore, at the magneto-electric
movable machinery as a whole, and its influence upon the atmospheric
circulation and conditions, we find many facts which point to a primary
action in the counter-trade, and others that point as significantly to a
primary local-inducing-action in the earth. Let us briefly review those to
which we have alluded, and advert to some others, and see what solution of
the question they will justify:
The belt of inter-tropical rains appears to be, in width, and amount of
precipitation, and annual travel north and south, proportionate to the
volume of trades which blow into it, the quantity of moisture they
contain, and the elevation of the surface over which they meet.
South America is the most thoroughly-watered country within the tropics,
except, perhaps, portions of Hindoostan, Burmah, Siam, etc., on
south-eastern Asia. The contrast between both, and Africa, as far as
explored, and as shown by its rivers, is most obvious. The Amazon, alone,
delivers more water to the ocean than all the rivers of Africa.
Of the width of the belt of rains over Africa, in the interior, we know
little. Its northern extension is less, by from 7° to 10°, than the same
belt over South America, the West Indies, and Mexico. Probably its
southern is also. Upon South America, the southern edge is carried down to
Cochabamba, in latitude 18°, and probably to 25°, to the northern edge of
the coast-desert of Peru, while it is rarely, if ever, found over the
Atlantic below 7°, a difference of 12° to 20°. Over South America, too,
the quantity of water which falls is also vastly in excess of that which
falls upon the Atlantic. The main cause of these differences is obvious.
The N. E. counter-trades which blow over Africa, originate on a surface
which is rainless, as eastern Sahara, Egypt, Arabia, etc., or subject to a
dry season by the northern ascent of the southern line of the
extra-tropical belt, as the Barbary States, Syria, Persia, etc., and their
supply of moisture is necessarily scanty. On the south, the S. E. trades
originate, in part, upon the eastern portion of southern Africa, and, in
part, upon the Indian Ocean, and from the latter source, and a portion of
the Mediterranean, doubtless most of the water which falls upon Central
Africa, is derived.
The N. E. and S. E. trades which blow into the inter-tropical belt upon
the eastern portion of the Atlantic, originate upon similar surfaces, and
with like effect. Thus, the S. E. trades, in summer, are from the Southern
portion of Africa, and the N. E., in part, from the Mediterranean; and, in
winter, the N. E. from the deserts, Senegambia, Nigritia, etc., and the S.
E., owing to the narrowing of the African continent, mainly from the South
Atlantic and Indian Oceans. Going west, the belt widens, and its range
increases until the Andes are reached; but under their lee, on the western
side, a totally different state of things is found, and the belt of the
coast becomes broken and irregular, as we have seen in the citation from
Maury.
The width, extension, and excessive precipitation of the belt, over South
America, follow the same law. The South Atlantic widens out by the
trending of the coast to the S. W., and furnishes a large area for the
unobstructed formation and evaporative action of the S. E. trades. So the
trending of the coast to the N. W., from 5° south to the northward, opens
a large area for a like formation and action of the N. E. trades. No
correspondingly favorable circumstances exist any where, except, perhaps,
around Hindoostan, and there the fall of rain is very excessive in some
places, as on the Kassaya hills, to the extent of 400 inches per annum. In
addition to this, the magnetic line of no variation, and of greater
intensity, which runs from our magnetic pole, obliquely, S. S. E., to its
opposite and corresponding pole in the southern hemisphere, enters the
Atlantic on the coast of North Carolina, and traverses it, and the eastern
portion of South America, through the whole trade-wind region. The
table-lands, and slopes, and high mountain peaks, meet the trades
successively, as they go west, and the latter wrench from them, to an
unusual extent, their moisture; depressing the line of perpetual snow, by
an increase of quantity on the eastern sides, several thousand feet, as it
is for a like cause depressed on the southern side of the Himmalayas. On
the eastern slopes and tops of the Andes, as we have seen, and owing to
their elevation, falls the moisture which, according to the working of the
machinery, and the law of curvature, should bless the coast line of Peru
and northern Chili, the eastern Pacific, northern Mexico, California,
Utah, and New Mexico; and, while the Andes stand, the curse of comparative
aridity must rest upon them all.
Southern Chili, and western Patagonia are supplied by the N. E. trades,
which originate in the West Indies, the Gulf of Mexico, and the Caribbean
Sea, and the Pacific, off Central America, in the neighborhood of the Bay
of Panama. But there, again, the same effect of elevation is seen. The
mountain slopes of southern Chili and Patagonia are abundantly supplied,
and their mountain ranges are drenched with rain, while eastern Patagonia
and southern Buenos Ayres, under their lee, are comparatively dry. So the
S. E. trades, which originate off the western coast of South America,
curve in upon, and aided by the oceanic currents, supply, abundantly, the
N. W. coast of this continent, north of California; and there, too, the
coast, and its elevated ranges, receive, as we have seen, a very large
proportionate supply of their moisture. Substantially, the same state of
things, as far as circumstances permit, is reproduced upon Malaysia,
Hindoostan, etc., and the interposition of arid New Holland upon the
evaporating trade-surface may be distinctly traced upon south-western
Asia. Deserts abound there; the Caspian Sea receives the drainage of a
very large surface, without an outlet; their southern line of
extra-tropical rains is carried up very far in summer, and their dry
season is intensely hot. (See an article in the American Journal of
Science, for July, 1846, by Azariah Smith.)
Another fact in this connection is worthy of a moment's consideration. The
magnetic equator, as sought by the dipping needle, is not coincident with
the geographical one. Humboldt found it, on the Andes, at 7° 1' south, and
it has been found still lower in the Atlantic. Over Africa it rises above
the geographical equator, and descends again on the Indian Ocean. About
midway the Pacific, it becomes coincident with the equator of the earth
again. (See diagram, on page 83.) Perhaps it is not known, with certainty,
why this is so. The south pole may be situated nearer the geographical
pole than the north one--but this is not believed to be so, nor could it
make the difference. The greatest southern depression of the magnetic
equator is found where the lines of greatest intensity, and of no
variation, are found; and at the more intense of these lines exists the
greatest depression. From this, I think, it may be inferred that the
needle is affected by the greater magnetic intensity of the northern
hemisphere, to which it may yet appear the obliquity of the earth's axis
is owing. However this may be, or whatever the cause, no marked effect is
produced upon the trades. The S. E. trades, by reason of the greater
extent of ocean-surface on which they originate, are every where the most
extensive, regular, and forcible. The south polar waters, from which they
rise, are every where trenching upon, and overriding, the north polar
ones; and thus, by a most beneficent provision, the greater portion of the
habitable surface is placed in the northern hemisphere, and the principal
portion of the southern is left open to an extensive, active evaporative
action, which supplies the northern habitable surface with a large excess
of the needed moisture.
The condensation, and consequent precipitation, which takes place at the
passing of the trades, as we have already said, over the ocean and
lowlands, takes place mainly in the day-time. Upon the table-lands and
mountain-ranges, it often continues during the evening and night. The
morning, and early part of the day, however, in tropical countries, are
generally fair at all elevations.
Storms also originate in the equatorial belt, and issuing forth in great
volume and with great intensity of action, find their way up even within
the Arctic circle. Those which pass over this continent, or the northern
Atlantic, generally originate in the West Indies, some of them over the
Caribbean Sea, some over the islands, and some over the open ocean to the
east of them; and, nearly all the most violent, during the months of
August, September, and October. It would seem most probable that the
primary action in such cases was in the trades themselves, but it is by no
means certain that such is the case. This is the class of storms of which
Mr. Redfield has industriously investigated some twenty or more; Mr. Espy
some, and Lieutenant Porter two. Their course, when very violent, is often
more directly north than that of storms, however violent, which originate
north of the calms of Cancer, owing, perhaps, to their greater
paramagnetic character. This course I have myself observed, in several
instances, about the period of the autumnal equinox--never, however, more
southerly than from S. W. to N. E., on the parallel of 41°, except in
three, and, perhaps, four, instances, when it has been S. W. by S. to N.
E. by N. I know of no class of storms in relation to which the evidence of
primary action in the counter-trade is stronger than in those of the class
which originate on the ocean east of the Windward Islands. But it is not
satisfactory as to them. Doubtless the conflict of polarities between the
passing trades is sufficient to produce the showers and rains which are
ordinarily found over the ocean and lowlands, in the equatorial belt; but
it is doubtful whether it is sufficient to produce such extensive,
long-continued, and violent action, as that which characterizes the
hurricane autumnal gales.
They occur, too, at the time when the whole machinery of distribution has
reversed its course, and is rapidly pursuing its journey south. It is a
period of great magnetic disturbance, over both land and sea; of more
active gales and local-increased precipitation. At the Magnetic
Observatory of Toronto, Canada West, these disturbances are carefully and
systematically observed, and their maxima, or periods of greatest
disturbance occur in April and September. (See Silliman's Journal, new
series, vol. xvii. p. 145.)
The tendency to volcanic action is not as great at the autumnal, as at the
vernal equinox, for the reason that most of the volcanic action of the
western hemisphere develops itself now upon South rather than North
America. But both exist, and are active, and what are improperly termed
equinoctial storms, and gales, and rains, are proverbial during, or just
subsequent to, both periods with us--as they are when the same change,
called the breaking up of the monsoons, takes place in the line of
magnetic intensity, over southern and eastern Asia. A volume might be
filled with extracts, showing, at least, most remarkable coincidences
between violent volcanic action and great atmospheric disturbance. Perhaps
the increased fall of rain at and after the equinoxes, in the northern
hemisphere, and in certain localities subject to volcanic activity, is as
strikingly illustrated by the register, kept by Mr. Johnson, on the
volcanic Island of Kauai, one of the Hawaiian group, already alluded to,
as in any other case, although it is by no means a singular one. The
greatest fall of rain, in any month except April and October, was eight
inches. In April, the fall was fourteen inches, in October, eighteen
inches. Neither the equatorial, nor extra-tropical belt, were over the
island during those months; but they were the N. E. trades, and the result
was owing solely to the interposition of high volcanic mountains, _in a
state of disturbance_, into, or near, the strata of the counter-trade. Mr.
Dobson, in stating a theory to which we shall hereafter advert, advances
the following proposition:
"7. _Cyclones (hurricanes) begin in the immediate neighborhood of active
volcanoes._ The Mauritius cyclones begin near Java; the West Indian, near
the volcanic series of the Caribbean Islands; those of the Bay of Bengal,
near the volcanic islands on its eastern shores; the typhoons of the China
Sea, near the Philippine Islands, etc."
The peculiar stormy state of the atmosphere, over the Gulf Stream, to
which I have alluded, certainly affords no evidence of primary atmospheric
action. It is a body of south polar water, pursuing its way under the
guidance of magnetism--maintaining its polarity--arched somewhat like the
roof of a house, by the outward pressure of a cold north polar current
which it has met to the east of the Banks of Newfoundland, and forced to
take an in-shore course to the southward, and the bodies of water which
the rivers discharge, and a conflict with the north polar surface-winds
which sweep over it, and fogs, and thunder, and rain, are a matter of
course. Dr. Kane met a portion of this singular current in Baffin's Bay,
north of 75°, which had preserved its characteristics and a considerable
proportionate excess of heat, although it probably had been around
Greenland, or found its way to the west, toward the magnetic pole, through
some of its northern fiords or straits. (Grinnel Expedition, p. 120.)
The investigations of Lieutenant Maury show, that when the Gulf Stream
turns to the eastward, crossing the lines of declination at right angles,
as the counter-trades also seem to do in the same latitude, it is _carried
up, in summer, several degrees to the north_, and descends again in
winter--thus demonstrating its connection with the shifting magnetic
machinery which controls alike the ocean, the atmosphere, and the
temperature of the earth.[7]
There are other irregularities which deserve to be noticed, in this
connection, although the analogical evidence they afford is far from being
decisive.
I have already said that it was within my own observation, that
alternating lines of heat and cold, as well as rain and drought, existed
frequently, without regard to latitude, following, to some extent, the
course of the counter-trade. Such lines have been observed by others.
Thus, Mr. Espy, after describing a snow-storm, which was followed by a
very cold N. W. wind, of several days' continuance, says:
"This cold air covered the whole country, from Michigan to the
eastern coast of the United States, till the beginning of the great
storm of the 26th January; and, what is worthy of particular notice
is, that _the temperature began to increase first in the north and
north-west_. On the morning of the 25th, in the north-western parts
of Pennsylvania, and northern parts of New York, the _thermometer_
had already _risen in some places 30°_, and, in others, _above 40°_.
While in the S. E. corner of Pennsylvania, and in the S. E. corner of
New York it had not _begun to rise_. The _wind_ also began to change
from the _north-west_ to _south_ and _south-east_, _first_ in the
north-west parts of Pennsylvania and New York, some time before it
commenced in the south-east of those States; and, during the whole of
the 25th, the thermometer, in the north of New York, continued to
rise, though the wind was blowing from the southward, where the
thermometer was many degrees lower."
Thus, too, Mr. Redfield (American Journal of Science, November, 1846, p.
329):
"On the contrary, in times of the greatest depression of the
thermometer, in numerous instances, the cold period has been found to
have first taken effect in, or near, the tropical latitudes, and the
Gulf of Mexico, and has thence been propagated toward the eastern
portions of the United States, in a manner corresponding to the
observed progression of storms."
This was because the cold N. W. wind which _followed_ storms began to
follow them as the storms curved and passed to the N. E.
They occur in Europe also. Says Kämtz:
"Such contrasts are not uncommon in Europe, and, in this respect, the
Alps form a remarkable limit; for they separate the climates of the
north of Europe from the Mediterranean climates, where the
distribution of rain is not the same as in the center of Europe.
Hence the differences between the climates of the north and south of
France. _If the winter is mild in the north_, the newspapers are
filled with the lamentations of the _Italians_ and _Provençals_ at
the _severity of the cold_."
These facts seem to indicate a primary action in the counter-trade.
Probably in connection with one class of storms they do, and with another
do not. I shall endeavor to show the distinction when I come to the
classification of storms.
The difference of seasons in this country, and over the entire northern
hemisphere, is often very great. In a remarkable work of a remarkable
man--"A Brief History of Epidemic and Pestilential Diseases," by Noah
Webster, published in 1799, 2 vols.--a history of the weather for about
two centuries--1600 to 1799 inclusive, is given generally, and then in a
tabular form. Those who think that every considerable extreme which occurs
exceeds any thing before known, will do well to consult that work.
Droughts are described, where "there was not a drop of rain for three or
four months, and cattle were fed upon the leaves of the trees." Winters,
so intensely cold that the thermometer fell to 20° below zero, at
Brandywine; or so mild that there was little frost, and people upon
Connecticut River plowed their fields, and the _peach trees blossomed in
Pennsylvania in February_. These extremes generally existed in Europe and
America at the same time, but occasionally they were opposite and
alternate. Says Mr. Webster, in summing up the facts (vol. ii. p. 12): "It
is to be observed that in some cases a severe winter extends to both
hemispheres, sometimes to one only, and in a few cases to a part of a
hemisphere only. Thus in 1607-8, 1683-4, 1762-3, 1766-7, 1779-80, 1783-4,
the severity extended to both hemispheres. In 1640-41, 1739-40, and in
other instances, the severe winter in Europe preceded, by one year, a
similar winter in America. In a few instances, severe frost takes place in
one hemisphere during a series of mild winters in the others; but this is
less common. In general, the severity happens in both hemispheres at once,
or in two winters, in immediate succession; and, as far as this evidence
has yet appeared, this severity is closely attendant on volcanic
discharges, with very few exceptions."
It will be seen that Dr. Webster (LL.D. and not M.D., and therefore the
remarkable character of the work) attributes great influence to
earthquakes and volcanic action. Probably he is correct in this. The
present active volcanic action of the western hemisphere is nearly all
within the trade-wind region, from Mexico to Peru inclusive. The West
India islands are of volcanic origin, and the influence of volcanic action
is not confined to a concussion of the earth, or the eruption of mud and
lava. Its connection with magnetic action, and disturbance, is
unquestionable. But whether they operate to increase or diminish the
trades, and the extent to which they induce violent electric action and
storms within and without the tropics, is a question which further
observation must determine. The ripples of the ocean, compared by
Lieutenant Banvard to that of a "boiling cauldron, or such as is formed by
water being forced from under the gate of a mill-pond," are met with in
the vicinity of volcanic islands, where hurricanes and water-spouts
originate, and have been observed to precede storms, and be connected with
a falling barometer. But whether they are volcanic or magneto-electric,
it is difficult to determine. Dr. Webster remarks, as the result of
observation, during the 17th century, that earthquakes had a N. W. and S.
E. progression in the United States, and especially in New England. In a
recent article, Professor Dana has examined, with great ability, the
general and remarkable trending of coast lines, groups of islands, and
ranges of mountains, from N. E. to S. W. and from N. W. to S. E. (American
Journal of Science, May, 1847.)
The line of magnetic intensity, which connects our magnetic pole with its
opposite, is now upon this continent nearly a N. W. and S. E. line, and
the pole is fast traveling to the west. It may, and probably will yet, be
established, that there is an intimate connection between the cause of
volcanic action within the earth, to which the upheaval of the N. W. and
S. E., and N. E. and S. W. ranges were due, and of magnetic action
without, and between both, and the cause of _the S. E. extension_ of our
summer storms and belts of showers and barometric _waves_, and the
_peculiar N. W. wind_. Our limits do not permit us to pursue the subject.
Much influence upon the weather has been attributed to the spots upon the
sun. These spots are supposed to be breaks or openings in the luminous
atmosphere or photosphere of the sun, through which its dark nucleus body
is seen. Counselor Schwabe, of Dessau, has made them his study since 1826,
and has arrived at some singular results. They seem to be numerous--in
groups--and to appear periodically with minima and maxima of ten years.
As the result of his observations, from 1826 to 1850, he gives us the
following table and remarks:
+-----------------------------------------------+
| Year. | Groups. | Days showing | Days of |
| | | no spots. | Observation. |
|-------|---------|--------------|--------------|
| 1826 | 118 | 22 | 277 |
| 1827 | 161 | 2 | 273 |
| 1828 | 225 | 0 | 282 |
| 1829 | 199 | 0 | 244 |
| 1830 | 190 | 1 | 217 |
| 1831 | 149 | 3 | 239 |
| 1832 | 84 | 49 | 270 |
| 1833 | 33 | 139 | 267 |
| 1834 | 51 | 120 | 273 |
| 1835 | 173 | 18 | 244 |
| 1836 | 272 | 0 | 200 |
| 1837 | 333 | 0 | 168 |
| 1838 | 282 | 0 | 202 |
| 1839 | 162 | 0 | 205 |
| 1840 | 152 | 3 | 263 |
| 1841 | 102 | 15 | 283 |
| 1842 | 68 | 64 | 307 |
| 1843 | 34 | 149 | 312 |
| 1844 | 52 | 111 | 321 |
| 1845 | 114 | 29 | 332 |
| 1846 | 157 | 1 | 314 |
| 1847 | 257 | 0 | 276 |
| 1848 | 330 | 0 | 278 |
| 1849 | 238 | 0 | 285 |
| 1850 | 186 | 2 | 308 |
+-----------------------------------------------+
"I observed large spots, visible to the naked eye, in almost all the
years not characterized by the minimum; the largest appeared in 1828,
1829, 1831, 1836, 1837, 1838, 1839, 1847, 1848. I regard all spots,
whose diameter exceeds 50", as large, and it is only when of such a
size that they begin to be visible to even the keenest unaided sight.
"The spots are, undoubtedly, closely connected with the formation of
faculæ, for I have often observed faculæ, or narben, formed at the
same points from whence the spots had disappeared, while new solar
spots were also developed within the faculæ. Every spot is surrounded
by a more or less bright, luminous cloud. I do not think that the
spots exert any influence on the annual temperature. I register the
height of the barometer and thermometer three times in the course of
each day, but the annual mean numbers deduced from their observations
have not hitherto indicated any appreciable connection between the
temperature and the number of the spots. Nor, indeed, would any
importance be due to the apparent indication of such a connection in
individual cases, unless the results were found to correspond with
others derived from many different parts of the earth. If the solar
spots exert any slight influence on our atmosphere, my tables would,
perhaps, rather tend to show that the years which exhibit _a larger
number of spots_ had a _smaller number of fine days_ than those
exhibiting few spots."
These observations _seem_ to show that the spots exert no influence upon
the weather, and to be satisfactory. But, perhaps, they are not entirely
so. No effect would, of course, be expected from day to day, and perhaps
the annual mean may not be seriously disturbed, and yet the spots may
seriously affect the seasons. Popular tradition has fixed upon certain
periods, of 10, 20, and 40 years, for the return of winters of unusual
severity; and the tables of Mr. Webster, and other facts, show that it is
not wholly without foundation. If we, and those we have cited, are not
mistaken in most of the views expressed, the natural effect of a partial
interception or failure of the sun's rays, by or from the existence of the
spots, would be to decrease the exciting power of the solar rays upon
terrestrial magnetism, and, as a consequence, the volume of the trades and
their amount of moisture. This would increase the _mean_ heat of the
summer in the temperate zone--for the _less_ the volume of trade, the less
precipitation and variable wind, and succeeding polar waves of cooler air,
and the greater mean heat. On the other hand, the same cause, and the
feebler heating power of the sun's rays, would make the winters more
severe, both from an absence of a portion of heat, derived directly from
the sun's rays, and a less mitigating influence, from the action of the
trade, by reason of its decreased volume. So, too, the absence of spots,
and a more powerful influence from the solar rays, may gradually carry
the machinery further north in summer, and further south in winter, and
thus make the _seasons extreme_ without seriously disturbing the mean of
the year. And both these may occur in a more marked degree over our
intense magnetic area than in Europe. I am satisfied that they do so
occur. That the partial failure of the sun's rays limits the transit of
the machinery, and the volume of the trades during the latter half of the
decade, and extends the transit and increases the volume during the first
half, producing an occasional severe summer drought and severe winter, in
the warmest portion of the decade. And that the variations correspond with
the difference in the character and number of the spots in different
decades, and hence the longer and shorter periods.
Turning to the tables of Dr. Webster, we find that a general tendency to
extreme seasons does seem to exist from the 6th to the 10th year of every
decade, and especially of every alternate decade. The periods of 1707-8,
1728, 1737 and 1739, 1749-50, 1758-9, 1779-80, 1798-9, are those in which
the tendency was seen most decided. These tables are very general. The
thermometer was not perfected till about 1700, and did not get into
general use before 1750. There were very few meteorological registers
kept, or accessible to Dr. Webster. Hence he was obliged to resort to such
other sources of information as were open to him, and such statements as
he found are not always entirely reliable. The oldest inhabitant is apt to
express himself very strongly respecting present extremes, and fail
somewhat in his recollection of those which have past. Still his tables
afford general and obvious evidence of the regularity of those periodic
conditions.
+---------------------------------------------------------+
|A. D.| Summer. | Winter. |
|-----|-------------------------|-------------------------|
| 1701| hot and dry | .... |
| 1702| hot and dry | .... |
| 1703| .... | .... |
| 1704| dry Europe | .... |
| 1705| .... | .... |
| 1706| hot, dry Europe | .... |
| 1707| very hot | .... |
| 1708| .... | very severe |
| 1709| .... | .... |
| 1710| .... | .... |
| 1711| .... | cold Europe |
| 1712| wet England | .... |
| 1713| wet England | mild |
| 1714| dry and hot | .... |
| 1715| dry | .... |
| 1716| very dry | severe |
| 1717| .... | severe |
| 1718| hot and wet | .... |
| 1719| .... | cold America |
| 1720| dry Europe | .... |
| 1721| .... | .... |
| 1722| cold, wet | .... |
| 1723| .... | cold |
| 1724| wet England | .... |
| 1725| wet England | .... |
| 1726| .... | .... |
| 1727| dry, hot Amer. | .... |
| 1728| hot Amer. | severe Europe |
| 1729| .... | .... |
| 1730| .... | very cold Eng. |
| 1731| .... | .... |
| 1732| .... | severe Amer. |
| 1733| dry Eng. | .... |
| 1734| .... | .... |
| 1735| wet | .... |
| 1736| wet | .... |
| 1737| .... | very severe Am. |
| 1738| .... | .... |
| 1739| wet England | very severe Eng. |
| 1740| .... | very severe Am. |
| 1741| .... | .... |
| 1742| .... | severe Syria |
| 1743| hot | .... |
| 1744| .... | .... |
| 1745| .... | .... |
| 1746| .... | .... |
| 1747| hot and dry | severe |
| 1748| dry | .... |
| 1749| very dry | .... |
| 1750| very hot | very severe |
| 1751| wet England | severe Amer. |
| 1752| very hot Amer. | .... |
| 1753| .... | severe |
| 1754| .... | mild Amer. |
| 1755| .... | severe Europe |
| 1756| .... | severe Syria |
| 1757| .... | .... |
| 1758| hot | .... |
| 1759| .... | severe |
| 1760| .... | .... |
| 1761| very dry Amer. | .... |
| 1762| very dry Amer. | severe |
| 1763| .... | .... |
| 1764| hot Europe | .... |
| 1765| hot Europe | severe Europe |
| 1766| hot and dry Eur. | very severe |
| 1767| .... | cold |
| 1768| hot | .... |
| 1769| hot | .... |
| 1770| wet England | .... |
| 1771| wet Am. & Eng. | cold Europe |
| 1772| hot America | Am., great snow |
| 1773| .... | .... |
| 1774| .... | severe Europe |
| 1775| .... | .... |
| 1776| hot | severe Europe |
| 1777| .... | .... |
| 1778| hot | mild |
| 1779| hot Eng. | very severe |
| 1780| .... | .... |
| 1781| .... | .... |
| 1782| dry Amer. | .... |
| 1783| hot | very severe |
| 1784| hot | .... |
| 1785| dry Europe | cold |
| 1786| cool | cold |
| 1787| cool | .... |
| 1788| rainy Amer. | cold |
| 1789| cool spring, hot summer | severe Eur., mild Amer. |
| 1790| .... | .... |
| 1791| very hot Am. | cold |
| 1792| .... | .... |
| 1793| hot, dry Am. | mild Amer. |
| 1794| .... | severe Europe |
| 1795| Amer., hot, rainy | .... |
| 1796| Autumn very Dry Am. | cold Amer. |
| 1797| cool Am. | severe Amer. |
| 1798| very hot } | { long & severe |
| 1799| very dry Am. } | { Amer. & Eur. |
+---------------------------------------------------------+
Still more definite evidence is found in the meteorological tables of Dr.
Holyoke and Dr. Hildreth, and an account, by Dr. Hildreth, of the seasons
when the Ohio River was closed or obstructed by ice, found in Silliman's
Journal, new series, vol. xiii. p. 238.
Thus, we have, from the tables of Dr. Holyoke, the following annual means,
from 1786 to 1825, inclusive. I have arranged them in periods of five
years. It will be seen that there are three peculiarities observable.
First, a marked difference between the first and second periods of the
decade, corresponding, generally, with the presence or absence of the
spots. Second, a difference in the mean of the decades which may well be
supposed to correspond with the difference in the number or size of the
spots since a like difference is observable in number and size, and the
time when they reached their maxima and minima, in the table of Schwabe.
And, third, there are occasional single cold years during the warm period,
and these correspond with what the tables of Dr. Webster show for both the
sixteenth and seventeenth centuries. In relation to this, it should be
remembered that volcanic action is a frequent and powerful disturber of
the regular action of terrestrial magnetism, and that the extremes, for
that reason, are frequently meridional or local and alternating; and to
that cause very great extremes, and marked exceptions, may be due,
notwithstanding the spots upon the sun may exert an influence in producing
hot summers and cold winters toward the close of each decade. Thus, to
select an instance to illustrate this and explain an anomaly: The coldest
season during the whole period, embraced in the following tables, is that
of 1812. This occurs during the decrease of spots, and the warm half of
the decade. Turning to the table of volcanic action, and of earthquakes,
found in the Report of the British Association for 1854, we find that year
was remarkable for earthquakes in the United States and South America. In
December, 1811, earthquakes commenced in the valley of the Mississippi,
Ohio, and Arkansas, felt also at places in Tennessee, Kentucky, Missouri,
Indiana, Virginia, North and South Carolina, Georgia, and Florida, though
not so severely east of the Alleghanies, _which continued until 1813_.
About the same time they commenced in Caraccas, and, in March, 1812,
became severe over the greater portion of the northern section of South
America, and in the Atlantic. No such general and continued succession of
earthquakes occurred during the other periods embraced in the tables, and
the mean of the following five years was very low, embracing the memorable
cold summer of 1816.
+---------------------------------------------------------------+
| Cold Period. | Warm Period. | Cold Period. | Warm Period. |
|---------------|---------------|---------------|---------------|
|1786 48°.53 |1791 48°.963|1796 48°.678|1801 50°.432|
|1787 47°.88 |1792 48°.44 |1797 48°.135|1802 50°.794|
|1788 47°.676|1793 50°.96 |1798 49°.471|1803 50°.24 |
|1789 47°.68 |1794 50°.768|1799 48°.291|1804 48°.328|
|1790 46°.53 |1795 50°.173|1800 49°.989|1805 50°.792|
|---------------|---------------|---------------|---------------|
|Mean of | | | |
|period 47°.659|Mean 49°.901|Mean 48°.910|Mean 50°.117|
|---------------|---------------|---------------|---------------|
|---------------|---------------|---------------|---------------|
|1806 47°.982|1811 50°.76 |1816 47°.113|1821 48°.15 |
|1807 48°.132|1812 45°.28 |1817 46°.277|1822 49°.81 |
|1808 49°.485|1813 47°.702|1818 48°.009|1823 47°.58 |
|1809 47°.92 |1814 48°.279|1819 50°.75 |1824 49°.25 |
|1810 49°.001|1815 47°.607|1820 48°.70 |1825 50°.99 |
|---------------|---------------|---------------|---------------|
|Mean 48°.505|Mean 47°.925|Mean 48°.169|Mean 49°.15 |
+---------------------------------------------------------------+
The tables of Dr. Hildreth, from 1826 to 1854, inclusive, furnish,
generally, evidence of a like character. There are, however, an anomaly or
two which will be observed. From 1826 to 1830, the mean is high during
the period when spots were at a maximum. But that maximum embraced a much
less number of spots than the two succeeding ones. A contrast appears in
the tables of Dr. Hildreth, during the early period, for Dr. Holyoke's
register, for 1827, puts it _below the mean_, but Dr. Hildreth's one of
the _highest of the half century_. In 1835 commenced a period when the
spots were much more numerous, and from 1835 to 1838, inclusive, the
seasons were correspondingly below the mean. From that period to 1844 a
gradual and slightly irregular rise took place, excepting the year 1843,
when another cold year intervened. The table of earthquakes, published by
the British Association, closes with 1842, and I have not access to any
others. The occurrence of such cold years, in the warm period, at
intervals during the two centuries previous, and in 1812, and onward, and
evidently owing to increased volcanic action beneath the western portion
of the northern hemisphere, justifies the belief that the low temperature
of 1843 was owing to the same cause. The following are the means from the
tables of Dr. Hildreth:
+----------------------------------------------------------------+
|1826 54°.00|1831 50°.87|1836 50°.03|1841 52°.18|1846 53°.64|
|1827 54°.92|1832 52°.42|1837 51°.57|1842 52°.83|1847 52°.00|
|1828 55°.22|1833 54°.56|1838 50°.62|1843 50°.77|1848 52°.50|
|1829 52°.38|1834 52°.40|1839 52°.54|1844 53°.25|1849 52°.09|
|1830 54°.93|1835 50°.65|1840 52°.35|1845 52°.73|1850 51°.48|
|------------|------------|------------|------------|------------|
|Mean 54°.29|Mean 52°.18|Mean 51°.52|Mean 52°.35|Mean 52°.32|
+----------------------------------------------------------------+
The observations of Dr. Holyoke were made at Salem, Massachusetts; those
of Dr. Hildreth at Marietta, Ohio.
The following, in relation to the freezing of the Ohio River, is evidence
of a different kind, but shows the same general correspondence, and
particularly _the mildness of the winters when there were few spots_, and
their severity from 1836 to 1838, inclusive, when the spots were most
numerous:
1829.--River open all winter--some floating ice.
1830.--River closed 27th January.
1831.--Floating ice--closed 23d January--opened 20th February.
1832.--Closed in December, which was a very cold month--opened January
8, and remained open all winter.
1833.--Open all winter.
1834.--Open all winter.
1835.--Closed January 6--opened the last of the month--cold.
1836.--Closed 28th January--opened 25th February.
1837.--Closed from 8th December to 8th February. Cold year.
1838.--Closed from 13th January to 13th March. Cold year.
1839.--Closed from 6th December to 13th January.
1840.--Closed 29th December--opened 15th January.
1841.--Closed 3d January--opened 8th do.
1842.--Open all winter.
1843.--Closed 28th November--opened 5th December--open all the rest of
the winter.
1844.--Open all winter.
1845.--Open all winter.
1846.--Closed 5th December--opened again a few days--closed again on the
26th. It is not stated how long it remained closed.
1847.--Open all winter.
1848.--Much floating ice, but not closed--heavy rains and floods.
1849.--Floating ice in January, but not closed.
1850.--Floating ice, but not closed.
1851.--Open all winter--a little ice.
(December in the above table, means December previous).
This is more reliable as to the winter season than the tables of annual
means--although the evidence they afford, making due allowance for the
exceptions, is very striking.
I shall return to this part of the subject again.
But there is other evidence of the influence of these spots. Their
connection with the irregular magnetic disturbance of the earth has been
distinctly traced. Colonel Sabine, President of the British Association,
in his opening address, September, 1852, after reviewing the recent
discoveries in magnetism, says:--
"It is not a little remarkable that this periodical magnetic
variation is found to be identical in period, and in epochs of maxima
and minima, with the periodical variation in the frequency and
magnitude of the _solar spots_, which M. Schwabe has established by
twenty-six years of unremitting labor. From a cosmical connection of
this nature, supposing it to be finally established, it would follow
that the decennial period, which we measure by our magnetic
instrument, is, in fact, a solar period, manifested to us, also, by
the alternately increasing and decreasing frequency and magnitude of
observations on the surface of the solar disc. May we not have in
these phenomena the indication of a cycle, or period of _secular
change in the magnetism of the sun_, affecting visibly his gaseous
atmosphere or photosphere, and sensibly modifying the magnetic
influence which he exercises on the surface of our earth?"--American
Journal of Science, new series, vol. xiv. p. 438.
I think it may fairly be inferred, that although these spots do not
occasion the "cold spells" and "hot spells," and other transient
peculiarities, they do materially affect the _mean_ temperature of the
year, and exert an obvious influence when at their maxima; and there is a
tendency to an increase of the heat and dryness of summer, and the
severity of winter, at the periods named, in our excessive climate, and a
well-established connection between the spots and magnetic disturbances
and variations.
Popular opinion has ever attributed to the moon a controlling effect upon
the changes of the weather. If it be dry, a storm is expected _when the
moon changes_; or if it be wet, dry weather. Such popular opinions are
usually entitled to respect, and founded in truth. But every attempt to
verify _this opinion_, by careful observation and registration, has
failed. Weather-tables and lunar phases, compared for nearly one hundred
years, show four hundred and ninety-one new or full moons attended by a
change of the weather, and five hundred and nine without. The celebrated
Olbers, after _fifty years of careful observation_ and comparison, decided
against it. So did the more celebrated Arago, at a more recent
date--summing up the result of his observations by saying--"Whatever the
progress of the sciences, never will observers, who are trustworthy and
careful of their reputation, venture to foretell the state of the
weather." Still, the moon may influence the weather, though she may not
effect changes at her syzygies or quadratures, and this subject should not
be too summarily dismissed. That the moon can not effect changes at the
periods named seems philosophically obvious. She changes, for the _whole
earth_, within the period of twenty-four hours; yet, how varied the state
of things on different portions of its surface. The equatorial belts of
trades, and drought, and rains, cover from fifty to sixty degrees of its
surface, and know nothing of lunar disturbance. The extra-tropical belt of
rains and variable weather moves up in its season, uncovering 10°, or
more, of latitude, and admitting the trades and a six months' drought over
it, as in California, regardless of the moon. Under the zone of
extra-tropical rains, even upon the eastern part of the continent of North
America, "dry spells" and "wet spells" exist side by side; the focus of
precipitation is now in one parallel, and now in another--_storms_ exist
_here_ and _fair weather there_, on the same continent at the same time;
and as the moon's rays in her northing pass round the northern hemisphere
during the twenty-four hours, they, doubtless, pass from ten to thirty or
more storms, of all characters and intensities, moving in opposition to
her orbit--and as many larger intervening areas of fair weather, not one
of which are indebted to her for their existence, or "take thought of her
coming."
The storm, which originates in the tropics, pursues its curving way now N.
W., then N. E., and again north, to the Arctic circle, and, perhaps,
around the magnetic pole, over gulf, and continent, and ocean, _occupying
one third the time of a lunation, and two changes, perhaps, in its
progress_, without any perceptible or conceivable influence from her. Yet
every inhabitant of mother-earth, influenced by _coincidences remembered_,
and uninfluenced by _exceptions forgotten_, looks up within his limited
horizon, and devoutly expects from the agency of some phase of the moon, a
change for the special benefit of his _dot_ upon the earth's surface. Upon
how many of these countless dots is the moon at a particular phase, or
relative distance from the sun, to change fair weather to foul, or foul to
fair? Upon none. The storms keep on their way;--the wet spells, and the
dry spells, the cold and the hot spells alternate in their time, and
though the moon turns toward them in passing, her dark face, her half
face, or her full orb (the gifts of the sun, which confer no power), they
do not heed her. They are originated, and are continued, by a more potent
agent. They are the work of an atmospheric mechanism, as _ceaseless_ in
its operation as _time_, as _regular_ as the _seasons_, _as extensive as
the globe_.
Indeed, it seems as if it was expressly designed by the Creator that the
moon should not interfere materially with this atmospheric machinery. She
is the nearest orb; her influence would be controlling and continuous;
would follow her monthly path from south to north, and with changes too
violent, and intervals too long; and would interfere with the regular
fundamental operation in the trade-wind region, where she is _vertical_.
Aside from the attraction of gravitation, therefore, she seems to have
been so created as to be incapable of exerting any influence. She is
without an atmosphere; the rays which she reflects are polarized, and
without chemical or magnetic power; and, if it be true that Melloni has
recently detected heat in them, by the use of a lens three feet in
diameter, which could not previously be effected, its quantity is
exceedingly small, and incapable of influence. Doubtless, the attraction
of her mass is felt upon the earth, as the tides attest; and upon the
atmosphere as well as the ocean. But the atmosphere is comparatively
_attenuated_, and exceedingly so at its upper surface. Her attraction,
therefore, although felt, is not influential. She seemed, to Dr. Howard,
to produce in her northing and southing, a lateral tide which the
barometer disclosed, but owing to the attenuated character of the
atmosphere, neither the sun nor moon create an easterly and westerly tide,
that is observable, except with the most delicate instruments. Sabine is
believed to have detected such a tide by the barometer, at St. Helena, of
one four thousandth of an inch. But even this _infinitesimal influence_
may prove an error upon further investigation. There is a diurnal
variation of the barometer, but it is not the result of her attraction,
for it is not later each day as are the tides, exists in the deepest mines
as well as upon the surface, and is demonstrably connected with the
_group_ of _diurnal_ changes produced by the action of the sun-light and
heat upon the earth's magnetism.
Can the lateral tide, if there be one, affect the weather? for in the
present state of science it seems entirely certain that the moon can exert
an influence in no other way.
If the received idea of many, perhaps most, meteorologists, on which all
wheel barometers are constructed, that a _high barometer_ necessarily
produces _fair weather_, and a _low one foul_, were true, she certainly
might do so. But that idea can not be sustained, and there is no known
certain influence exerted by the moon upon the weather, in relation to
which we have any reliable practical data.
Humboldt appears to have adopted the impression of Sir W. Herschell, that
the moon aids in the dispersion of the clouds. (Cosmos, vol. iv. p. 502.)
But the tendency to such dispersion is always rapid during the latter part
of the day and evening, when there is no storm approaching, and the full
moon renders their dissolution visible, and attracts attention to them.
The Greenwich observations, also, carefully examined by Professor Loomis,
fail to confirm the impression of Herschell and Humboldt, and those
eminent philosophers are doubtless in this mistaken.
From this general and somewhat desultory view of the general facts, which
bear analogically upon the question, no decisive inference can be drawn in
relation to the seat of the primary influence which produces the
atmospheric changes. The preponderance is in favor of the magnetic, or
magneto-electric, action of the earth. We must come back to our own
country and grapple with the question at home.
CHAPTER IX.
Before proceeding to do this, however, it may be well to look at some
theories which have been advanced, and to a greater or less extent
adopted, and at their bearing upon the question.
The calorific theory is at present the prevailing one in Europe and in
this country. Meteorologists there and here refer all atmospheric
conditions and phenomena to the influence of heat. The principal
applications of that theory have been considered. But within the last few
years the elasticity and tension of the aqueous vapor of the atmosphere
have received much attention, as exerting an auxiliary or modifying
influence. Professor Dove, of Berlin, who ranks perhaps as the most
distinguished meteorologist of that continent, attributes barometric
variations to _lateral overflows_, and, in the upper regions, resulting
from the elevation of the atmosphere by expansion; and in this view
meteorologists of Europe seem generally to acquiesce. In an article sent
to Colonel Sabine, and recently republished in the American Journal of
Science, January, 1855, in thus attempting to account for the annual
variation of barometric pressure, which occurs in Europe and Asia, and,
indeed, over the entire hemisphere. He says:
"From the combined action or the variations of aqueous vapor, and of
the dry air, we derive immediately the periodical variations of the
whole atmospheric pressure. As the dry air and the aqueous vapor
mixed with it, press in common on the barometer, so that the up-borne
column of mercury consists of two parts, one borne by the dry air,
the other by the aqueous vapor, we may well understand that as with
increasing temperature the air expands, and by reason of its
augmented volume rises higher, and _its upper portion overflows
laterally_," etc.
And in another place he says:
"From the magnitude of the variations in the northern hemisphere, and
the extent of the region over which it prevails, we must infer that
_at the time of diminished pressure a lateral overflow probably takes
place_," etc.
Doubtless, the mean pressure of the atmosphere, in summer, in the northern
hemisphere, is less than in winter, in some localities, and greater in
others, and it differs in different countries of equal temperature. And
this is all very intelligible. The mean of the pressure for the month is
made up by _averaging_ all the _elevations_ and _depressions_. During a
month, showing a very low mean, the barometer may, at times, attain its
_highest altitude_, if the depressions below the mean are great or more
frequent. The barometer is depressed during storms, and ranges high during
_set fair_ weather. Ordinarily, therefore, the more stormy the season the
more diminished the mean pressure; and it is a mistake to look to an
overflow to account for the fact. The changes in the location of the
atmospheric machinery, and consequent change in the amount and severity of
falling weather, and the periodic frequency and character of storms, and
consequent _periodic_ depressions and elevations of the barometer,
explain the annual mean variations, as they do the other phenomena. But it
is perfectly consistent with the calorific theory to attempt to account
for these differences by another of those ever-necessary modifications,
viz.: the different tension and elasticity of aqueous vapor in different
countries of equal temperature; and then to _suppose_ an expansion of the
whole body of the atmosphere and a lateral overflow from the place where
the air is expanded, on to some other, where it is not; and thus _suppose_
all necessary currents in the upper regions, setting hither and yon, by
the force of gravity alone. And apparently he who is best at supposition
becomes the most distinguished meteorologist. Perhaps I have already said
all that I ought to be pardoned for saying, in relation to the utter
absurdity of attributing all meteorological phenomena to the agency of
heat; but when I find such views as those which that article contains,
emanating from so distinguished a man, sanctioned by the President of the
British Association, and copied into the leading journal of science in
this country, I can not forbear a further and a somewhat critical
examination of them. There is more error of supposition and less truth in
it, than in any other article regarding the science, of equal length,
which has fallen under my notice.
What is the height of this expansion? The moisture of evaporation ascends,
ordinarily, but a few thousand feet. The atmosphere grows regularly
cooler, from the earth to the trade, and _the increased warmth that is
felt at the surface extends but little way_. Currents of warm air do not
ascend. The strata maintain, substantially, their relative positions; and
this is a most beneficent provision. In northern latitudes of the
temperate zone, all the warmth derived from a few hours' sunshine is
needed at the surface; and, deplorable, indeed, would be our condition, if
the atmosphere, as fast as warmed by the rays of the sun, were to hasten
up, and the frigid strata descend in its place. The earth would not be
habitable. All the warm air on its surface would be rising as soon as it
became warmed, and the cold air above be descending, and enveloping us
with the chilling strata which are ever floating within two or three miles
above us. No. Infinite wisdom has ordered it otherwise. The laws of
magnetism and of static-electric induction and attraction keep the strata
in their places, and preserve to us the warmth which the solar rays afford
or produce. The inhabitant of the valley, in a high northern latitude, in
summer, can plant, and sow, and reap, at the base of the mountain whose
summit penetrates the stratum of continual congelation, and up its sides,
almost to the line of perpetual snow; and, as he looks upon the fruits of
his labor, and up to the snow-clad peak that towers above him, can thank
his Maker for placing a warm equatorial current, a perpetual barrier,
between the fertility and warmth which surround him, and the cold
destructive strata above; and thank Him for not creating such a state of
things, as certain meteorologists insist we shall believe He has created.
Again, where are the _upper regions_, from which the lateral overflow
takes place? The atmosphere is differently estimated, at from thirty to
forty-five miles, or more, in height. Whatever its height may be, it is
exceedingly attenuated in its "upper regions."
Gay-Lussac marked the barometer at 12-95/100 inches at the height of
23,040 feet. Two thirds of the atmospheric density, then, is within five
miles of the earth. Air, too, is _compressible_. Allowing for the latter
and the attenuation, how many miles in vertical depth, of its "_upper
regions_," must move from one portion to another, to depress the barometer
two inches--its range sometimes in twenty-four hours--or even half an
inch? Let the computation be made, and see how startling the proposition,
how utterly impossible that the theory can be true.
The distinguished Professor, in the paper referred to, introduces his
theory of the formation of hurricanes, and we quote--
"If we suppose the upper portions of the air ascending over Asia and
Africa to flow off laterally, and if this takes place suddenly, it
will check the course of the upper or counter-current above the
trade-wind, and force it to break into the lower current.
"An east wind coming into a S. W. current must necessarily occasion a
rotatory movement, turning in the opposite direction to the hands of
a watch. A rotatory storm, moving from S. E. to N. W., in the lower
current or trade, would, in this view, be the result of the encounter
of two masses of air, impelled toward each other at many places in
succession, the further cause of the rotation (originating primarily
in this manner) being that described by me in detail in a memoir 'On
the Law of Storms,' translated in the 'Scientific Memoirs,' vol. iii.
art. 7. Thus, it happens that the West India hurricanes, and the
Chinese typhoons occur near the lateral confines on either side of
the great region of atmospheric expansion, the typhoons being
probably occasioned by the direct pressure of the air from the region
of the trade-winds over the Pacific, into the more expanded air of
the monsoon region, and being distinct from the storms appropriately
called by the Portuguese 'temporales,' which accompany the out-burst
of the monsoon when the direction of the wind is reversed."
The analogy between this, and a theory of Mr. Redfield's, will be noticed
further on. But I remark, in passing, that there is not a fact or
inference in this paragraph which will bear examination.
1. There is no such regular S. W. wind over the surface trade, as he
supposes. Doubtless, there are, occasionally, secondary S. W. currents
between the counter-trade and the surface one, with partial condensation,
for much of both becomes depolarized by their reciprocal action and
precipitation, and these induced S. W. currents are sometimes so strong as
to usurp the place of the surface-trade, and become very violent in the
latter part of hurricanes; but such is not the usual course of the upper
currents of the West Indies, as the progress of storms there, and
observation, prove.
2. There can not be any _periods_ of extensive and _sudden_ expansion over
Africa. If there is any place on the earth which has a more uniformly
progressive temperature, either way, and is more free from _sudden_
extremes, or which is more arid and destitute of aqueous vapor, and sudden
aqueous expansions, than another, it is Africa. No such occasional sudden
expansions are there possible.
3. Winds do not, and can not, "_encounter_." They stratify upon each
other. They are produced by the action of opposite electricity, and are
_connected together_ in their origin and action. The atmosphere is never
free from the regular and irregular currents, however invisible for the
want of condensation. Aeronauts find them in the most serene days. They
exist without encounter or tendency to rotation, every where, and at all
times; even over the head of the distinguished Professor, whether he
sleeps or is awake. We can all see them when there is condensation, and it
is rarely the case that there is not some degree of it in some of them.
4. That "Great region of expansion" is a chimera. It does not exist. It is
a region of _lower temperature_, and of _condensation_, instead of
_expansion_ of _aqueous vapor_. The trade does not rise in it, or the S.
W. wind overflow from it. See the table cited page 165.
5. The hurricanes do not originate _in the surface trades_, as he
supposes. They originate in the belt of rains, the supposed "region of
expansion," and issue out of it; or in the counter-trade, where volcanic
elevations rise far into or above the surface trade.
6. This hypothesis can not be sustained upon his own principles. The
distance between Africa and the West India Islands, where most of the
hurricanes originate, is from 2,500 to 3,000 miles. These gales are small
when they commence, not ordinarily over one or two hundred miles in
diameter, and often less. There are trades all the way over from Africa,
and S. W. winds also, if they exist, as he supposes, in the West Indies.
How can it happen that this lateral overflow should pass _without effect_,
over 2,500 miles of S. W. wind and trade, and concentrating the overflow
of a continent over one small and chosen spot of the West Indies, _pitch
down_ there, and there only, and crowd the S. W. wind into the trade
below? This is too much for sensible men to believe.
What does Professor Dove mean by the term _impulsion_, as applied to the
winds? How are they _impelled_? It is the fundamental idea of his
calorific theory, that they are _drawn_ by the _suction_ caused by a
_vacuum_, and the vacuum created by expansion and overflow above, in
obedience to the law of gravity; that the S. E. trade is drawn to the
great region of expansion, and the S. W. runs from it as an overflow. But
if the S. W. is driven down into the plane and place of the
surface-trades, how does it continue to be impelled, and why is it not
then subject to the suction of the vacuum which draws the trade? Does that
vacuum _select its air_, and so attract the trade, in preference to the
depressed portion of the S. W. current, that the former runs around the
latter to get to the vacuum, and the latter around the former to get away
from it? And does the trade, when it has got around the S. W. current,
instead of going to the vacuum, continue to gyrate, and the S. W. current,
instead of pursuing its regular course, gyrate also about the trade, and
both move off together, regardless of the vacuum of the great region of
expansion, in a new direction to the N. W., in an independent,
self-sustaining, cyclonic movement, increasing in power and extent,
involving extended and increasing condensation, producing the most violent
electrical phenomena, and thus continuing up, even to the Arctic circle?
Yes, says Professor Dove. No, say all fact, all analogy, and his own
principles.
7. His theory relative to the typhoons is unintelligible. If they
originate near the lateral confines of the great region of atmospheric
expansion, they originate in the region of the trade-winds, for the two
are identical. How the direct pressure of the air from the trade-wind over
the Pacific, in the more expanded air of the monsoon region, can occasion
a typhoon upon any principles, passes my comprehension. If, as Lieutenant
Maury supposes, the monsoons are reversed trades, then the trade-wind and
monsoon region are identical. If the monsoons are found in the belt of
rains, then, the trades, upon Professor Dove's principles, pass into the
monsoon region by attraction or suction, without pressure. Either way the
theory is undeserving of consideration.
A new theory has recently been started by Mr. Thomas Dobson, and, although
it is (like all other efforts to get the _upper strata down_ to produce
condensation, or those below _up_, that they may be condensed), without
foundation, his collection of facts is brief and interesting. I copy his
article from the London, Edinburgh, and Dublin Phil. Mag., for December,
1853. It adds to the collection of facts in relation to the connection
between volcanic action and storms for the seventeenth century, made by
Dr. Webster:
The following appear to be the main facts which are available as a
basis for a theory which shall comprehend all the meteors in
question:
1st. The eruption of a submarine volcano has produced water-spouts.
"During these bursts the most vivid flashes of lightning continually
issued from the densest part of the volcano, and the volumes of smoke
rolled off in large masses of fleecy clouds, gradually expanding
themselves before the wind in a direction nearly horizontal, and
drawing up _a quantity of water-spouts_."--(Captain Tilland's
description of the upheaval of Sabrina Island in June, 1811, Phil.
Trans.)
With this significant fact may be compared the following analogous
ones:
"In the Aleutian Archipelago a new island was formed in 1795. It was
first observed _after a storm_, at a point in the sea from which a
column of smoke had been seen to rise."--(Lyell, Principles of
Geology.)
"Among the Aleutian Islands a new volcanic island appeared in the
midst of _a storm_, attended with flames and smoke. After the sea was
calm, a boat was sent from Unalaska with twenty Russian hunters, who
landed on this island on June 1st, 1814."--(Journal of Science, vol.
vii.)
"On July 24th, 1848, a submarine eruption broke out between the
mainland of Orkney and the island of Strousa. Amid thunder and
lightning, a very dense jet black cloud was seen to rise from the
sea, at a distance of five or six miles, which _traveled toward the
north-east_. On passing over Strousa, the wind from a slight air
became _a hurricane_, and a thick, well-defined belt of large
hailstones was left on the island. The barometer fell two
inches."--(Transactions Royal Society, Edinburg, vol. ix.)
2d. Hurricanes, whirlwinds, and hailstones accompany the paroxysms of
volcanos.
"1730. A great volcanic eruption at Lancerote Island, and _a storm_,
which was equally new and terrifying to the inhabitants, as they had
never known one in the country before."--(Lyell, Principles of
Geology, vol. ii.)
"1754. In the Philippine Islands a terrible volcanic eruption
destroyed the town of Taal and several villages. Darkness,
hurricanes, thunder, lightning, and earthquakes, alternated in
frightful succession."--(Edinburgh Philosophical Journal.)
"In 1805, 1811, 1813, and 1830, during eruptions of Etna, caravans in
the deserts of Africa perished by violent whirlwinds. In 1807, while
Vesuvius was in eruption, a whirlwind destroyed a caravan."--(Rev. W.
B. Clarke in Tasw. Journal.)
"1815, Java. A tremendous eruption of Tombow Mountain. Between nine
and ten P.M., ashes began to fall, and soon after _a violent
whirlwind_ took up into the air the largest trees, men, horses,
cattle, etc."--(Raffles' History of Java.)
"1817, Dec. Vesuvius in eruption. In the evening _a hail storm_,
accompanied with red sand."--(Journal of Science, vol. v.)
"1820, Banda. A frightful volcanic eruption, and in the evening an
earthquake and a violent hurricane."--(Annales de Chimie.)
"1822, Oct. Eruption of Vesuvius. Toward its close the volcanic
thunder-storm produced an exceedingly violent and abundant fall of
rain."--(Humboldt, Aspects of Nature.)
"1843, Jan. Etna in eruption. Violent hurricanes at Genoa, in the Bay
of Biscay, and in Great Britain.
"1843, Feb. Destructive earthquakes in the West Indies, a volcanic
eruption at Guadaloupe, followed by hurricanes in the Atlantic."
"1846, June 26. Volcano of White Island, New Zealand, in eruption.
Heavy squalls of wind and hail; it blew as hard as in a
typhoon."--(Commodore Hayes, R.N., in Naut. Mag., 1847.)
"1847, March 20. Volcanic eruption and earthquake in Java; and on the
21st of March, and 3d of April, violent hurricanes."--(Java Courant.)
"1851, Aug. 5. A frightful eruption of the long dormant volcano of
the Pelée Mountain, Martinique. Aug. 17. Hurricane at St. Thomas,
etc.; earthquake at Jamaica, etc.
"1852, April 14. Earthquake at Hawaii, and on the 15th a great
volcanic eruption. On the 18th _a gale of unusual violence_ lasted
thirty-six hours, and did great damage."--(The Polynesian, April 22,
1852.)
3d. In volcanic regions, earthquakes and hurricanes often occur
almost simultaneously, but in no certain order, and without any
volcanic eruption being observed.
In 1712, 1722, 1815, and 1851, earthquakes and hurricanes occurred
together at Jamaica; in 1762 at Carthagena; in 1780 at Barbadoes; in
1811 at Charleston; in 1847 at Tobago; in 1837 and 1848 at Antigua;
in 1819, an awful storm at Montreal, rain of a dark inky color, and a
slight earthquake. People conjectured that a volcano had broken out.
In 1766 the great Martinique hurricane, a _waterspout_ burst on Mount
Pelée and overwhelmed the place. Same night, an earthquake.
1843, Oct. 30. Manilla.--Twenty four hours' rain and two heavy
earthquakes. 10 P.M., a severe hurricane.
"1852, Sept. 16. Manilla--An earthquake destroyed a great part of the
city; many vessels wrecked by a great hurricane in the adjacent seas,
between the 18th and 26th of September."--(Singapore Times.)
"1731, Oct. Calcutta.--Furious hurricane and violent earthquake;
300,000 lives lost."
"1618, May 26. Bombay.--Hurricane and earthquakes; 2,000 lives
lost."--(Madras Lit. Tran., 1837.)
"1800. Ongole, India, and in 1815, at Ceylon, a hurricane and
earthquake shocks."--(Piddington.)
"1348. Cyprus.--An earthquake and a frightful hurricane."--(Hecker.)
"1819. Bagdad.--An earthquake and _a storm_--an event quite
unprecedented.
"1820, Dec. Zante.--Great earthquake and hurricane, with
manifestations of a submarine eruption."--(Edinburg Phil. Journal.)
"1831, Dec. Navigator's Islands.--Hurricane and
earthquakes."--(Williams' Missionary Enterprise.)
"1848, Oct., Nov. New Zealand.--Succession of earthquake shocks, and
several tempests.
"1836, Oct. At Valparaiso, a destructive tempest and severe
earthquakes."--(Nautical Magazine, 1848.)
When an earthquake of excessive intensity occurs, as at Lisbon, in
1755, the volcanic craters, which act as the safety-valves of the
regions in which they are placed, are supposed to be sealed up; and
it is a remarkable and highly-suggestive fact, that _no hurricane
follows such an earthquake_. The number of instances of the
concurrence of ordinary earthquakes and hurricanes might easily be
increased, but the preceding suffice to show the _generality_ of
their coincidence, both as _to time_ and place.
4th. The breaking of water-spouts on mountains sometimes accompanies
hurricanes.
In 1766, during the great Martinique hurricane, before cited.
"1826, Nov. At Teneriffe, enormous and most destructive water-spouts
fell on the culminating tops of the mountains, and a furious cyclone
raged around the island. The same occurred in 1812 and in
1837."--(Espy and Grey's Western Australia.)
"1829. Moray.--Floods and earthquakes, preceded by water-spouts and a
tremendous storm."--(Sir T. D. Lander.)
"1826, June. Hurricanes, accompanied by water-spouts and fall of
avalanches, in the White Mountains."--(Silliman's American Journal,
vol. xv.)
5th. The fall of an avalanche sometimes produces a hurricane.
"1819, Dec. A part (360,000,000 cubic feet) of the glacier fell from
the Weisshorn (9,000 feet). At the instant, when the snow and ice
struck the inferior mass of the glacier, the pastor of the village of
Randa, the sacristan, and some other persons, _observed a light_. A
frightful hurricane immediately succeeded."--(Edinburg Philosophical
Journal, 1820.)
6th. Water-spouts occur frequently near active volcanos.
This is well known with regard to the West Indies and the
Mediterranean. The following notices refer to the Malay Archipelago
and the Sandwich Islands:
"Water-spouts are often seen in the seas and straits adjacent to
Singapore. In Oct., 1841, I saw _six_ in action, attached to one
cloud. In August, 1838, one passed over the harbor and town of
Singapore, dismasting one ship, sinking another, and carrying off the
corner of the roof of a house, in its passage landward."--(Journal of
Indian Archipelago.)
"1809. An immense water-spout broke over the harbor of Honolulu. A
few years before, one broke on the north side of the island (Oahu),
washed away a number of houses, and drowned several
inhabitants."--(Jarves' History of Sandwich Islands.)
7th. Cyclones begin in the immediate neighborhood of active volcanos.
The Mauritius cyclones begin near Java; the West Indian, near the
volcanic series of the Caribbean Islands; those of the Bay of Bengal,
near the volcanic islands, on its eastern shores; the typhoons of the
China Sea, near the Philippine Islands, etc.
8th. Within the tropics, cyclones move toward the west; and, in
middle latitudes, cyclones and water-spouts move toward the N. E., in
the northern hemisphere, and toward the S. E. in the southern
hemisphere.
9th. In the northern hemisphere, cyclones rotate in a horizontal
plane, in the order N. W., S. E.; and in the southern hemisphere, in
the order N. E., S. W.
By applying the principles of electro-dynamics to the electricity of
the atmosphere, I shall endeavor to connect and explain the preceding
well-defined facts. The continuous observations of Quetelet, on the
electricity of the atmosphere, from 1844 to 1849 (Literary Journal,
February, 1850), show that it is always positive, and increases as
the temperature diminishes. It therefore increases rapidly with the
height above the earth's surface. We may, consequently, regard the
upper and colder regions of the atmosphere as an immense reservoir of
electric fluid enveloping the earth, which is insulated by the
intermediate spherical shell formed by the lower and denser
atmosphere. Now, whenever a vertical column of this atmosphere is
suddenly displaced, the surrounding aqueous vapor will be immediately
condensed and aggregated, and the cold rarefied air and moisture will
form a vertical conductor for the descent of the electrical fluid.
This descent will take place down a spiral, gyrating in the order N.
W., S. E., in the northern hemisphere, since the electric current is
under the same influence as that of the south pole of a magnet; and
in the order N. E., S. W., in the southern hemisphere. The air
exterior to the conducting cylinder will partake of the violent
revolving motion, and a tornado or cyclone will be produced.
Upon the foregoing facts I shall comment in another place.
Three theories have been advanced by meteorologists of this country, two
of which profess to explain all the phenomena of the weather. Professor
Espy attributed the production of storms and rain to an ascending column
of air, rarefied by heat, and the rarefaction increased by the latent heat
of vapor given out during condensation, and an inward tendency of the air,
from all directions, toward the ascending vortex, constituting the
prevailing winds. Thus, Professor Espy conceived, and to some extent
proved, that the wind blew inward, from all sides, toward the center of a
storm, either as a circle, or having a long central line, and he conceived
that it ascended in the middle, and spread out above; and that clouds,
rain, hail, and snow, were formed by condensation consequent upon the
expansion and cooling of the atmosphere, as it attained an increased
elevation.
_This ascent_ was not, in fact, _proved_ by Professor Espy, _has not been
found by others_, and _is not discoverable, according to my observations_.
The theory was ingenious, founded on the theory of Dalton, that the vapor
was maintained in the atmosphere by reason of a large quantity of latent
heat, which was given out when condensation took place. This theory is
also unsound. No such elevation of temperature is found in clouds or fogs
when they form near the earth, however dense. Thus the two principal
elements of Professor Espy's theory are found to be untrue, and the theory
untenable. But it was sustained with great ability and research, and the
distinguished theorist deserves much for the discovery and record of
important facts in relation to the weather. Aside from its theoretical
views, his book contains a great mass of valuable information, and will
well repay the cost of purchase and perusal.
Another theory, by Mr. Bassnett, is of recent date, founded on the
influence of the moon, and the supposed creation of vortices in the ether
above, whose influence extends to the earth, producing storms and other
phenomena. No one can peruse his book without conceding to him great
ability and scientific attainment; and if his theory was true, the periods
of fair and foul weather could be calculated with great mathematical
certainty. But it contains inherent and insuperable objections. I will
only add that all herein before contained is in direct opposition to it.
Mr. W. C. Redfield, of New York, as early as 1831, first advanced in this
country the theory of gyration in storms, and investigated their lines of
progress on our coast and continent. His theory is limited in its
character, and does not profess, except indirectly, to explain all, or
indeed any, of the other phenomena of the weather. As far as it goes,
however, it is generally received in this country and Europe, and has
been adopted by Reed, Piddington, and others, who have written on the law
of storms. The position of Mr. Redfield is honorable to himself and his
country. Science and navigation are much indebted to him for his industry
in the collection of facts. Nevertheless, his theory is not in accordance
with my observation, and I deem it unsound. Although expressed disbelief
of the theory has been characterized as an "attack" upon its author, I
propose, with that _respect_ which is due to him, but with that _freedom_
and _independence_ which a search for _truth_ warrants, to examine it with
some particularity. It is a part of the subject, and I can not avoid it.
When the theory was first announced, I adopted it as probably true; and
being then engaged in a different profession, which took me much into the
open air by night and day, I watched with renewed care the clouds and
currents for evidence to confirm it. I discovered none; on the contrary, I
found much, very much, absolutely and utterly inconsistent with its truth.
The substance only of these observations will be adduced.
Mr. Redfield admits that the progression of our storms in the vicinity of
New York, is from some point between S. S. W. and W. S. W., to some point
between N. N. E. and E. N. E. According to my observation, except perhaps
in occasional autumnal gales, they are not often, if ever, from S. of S.
W., and the great majority of them, including, I believe, all N. E.
storms, are between S. W. and W. S. W. Now, the card of Mr. Redfield,
moving over any place from any point between S. W. and W. S. W., calls for
a S. E. wind at its axis, an E. wind at its north front, and a S. wind at
its south front, and does not call _for a N. E. wind on its front at all,
except at the north extreme_, where it could _not continue for any
considerable period_.
[Illustration: Fig. 17.]
In relation to this, I observe, 1st. _About one-half of our N. E. storms,
including some of the most severe ones, not only set in N. E., but
continue in that quarter without veering at all, during the entire period
that the storm cloud is over us_; usually for twenty-four hours; not
unfrequently for forty-eight hours, sometimes for seventy-two or more
hours. This every one can observe for himself, and it can not, of course,
be reconciled with his theory.
2d. N. E. storms, whether they set in from that quarter in the
commencement, or veer to it afterward, when they do "change" round, more
frequently veer by the S. to the S. W. in clearing off, than back through
the N. into the N. W. The former, in accordance with his theory, they can
not do, as the reader can see by passing the left side of the card over
his place of residence on the map from S. W. to N. E.
3d. N. E. storms often pass off without hauling by S. or backing by N.,
and with or without a clearing off shower, the _wind shifting and coming
out suddenly at S. W._ This they could not do in accordance with his
theory, as slipping the card will show.
4th. From June to February it is _exceedingly uncommon_ for a N. E. storm
to back into the N. W. They do so more frequently from February to May,
especially about the time of the vernal equinox and after; and then,
because the focus of precipitation and storm intensity of the extra
tropical zone of rains is S. of 42° east of the Alleghanies. His theory
requires them to back by N. into N. W. _in all cases, when they set in N.
E._
5th. When they do back from the N. E. into the N. W., it rarely indeed
continues to storm after the wind leaves the point of N. E. by N., and
generally, if it does continue stormy, _the wind is light_, and not a
gale, how violent soever the gale from the eastward may have been.
Usually, by the time the wind gets N. W., it has cleared off. This, Mr.
Redfield, as we shall see, evades by embracing the N. W. fair wind as a
part of the same gale. According to my observation, therefore, a _very
large proportion_ of the _N. E. storms_, and they are a majority of the
most violent ones of our climate east of the Alleghanies, do not
_commence, continue_, or _veer_ in accordance with his theory, but the
_reverse_; and so long as this is so, I can not receive his theory as
true.
6th. S. E. storms do not always, or indeed often, conform to the
requirements of his card. When they set in violently at S. E., and
continue so for hours without veering, the axis of the storm should be
over us, and the wind should change _suddenly_ to N. W. This did not occur
in the storm of Sept. 3, 1821, nor does it often, if ever, occur in the
summer or early gales of the autumnal months. In the later storms of
autumn, and as often in those which are very gentle as any, and in the
winter months when S. E. gales are rare, it does sometimes so change after
the storm cloud has passed. But in the winter months, as in the storm
investigated by Professor Loomis, the storms are frequently long from S.
E. to N. W., and the S. E. wind blows nearly in coincidence with its long
axis, for a thousand or fifteen hundred miles, till the barometric minimum
is passed, and the inducing and attracting force of this part of the storm
cloud is spent, and then the N. W. wind follows; sometimes blowing in
under the storm cloud, turning the rain to snow; but oftener following the
storm within a few hours, or the next day. The storm of Professor Loomis,
when over Texas, was not probably more than four or five hundred miles in
length. As it curved more, and passed north and east, it extended
laterally, its center traveling with most rapidity, and when it reached
the eastern coast was about fifteen hundred miles long, and not more than
six hundred broad. Along the eastern part of that storm, except when by
its more rapid progress the front projected much further eastward over New
England than its previously existing line, the S. E. winds blew. When it
bulged out, so to speak, by reason of the increased progress of the
center, the wind veered to the N. E. The center of the storm passed near
St. Louis and south of Quebec, as the _fall of rain_, the _bulging_ of the
_rapidly-moving center_, and the _line of subsequent cold_, attest. It is
utterly impossible for any unbiased mind to look at the description of
that storm, and attribute to it a rotary character. With all the data
before him, Mr. Redfield himself has not attempted it directly.[8]
The September storm of 1821 was more violent in character than any which
have since occurred. My recollection of it is as distinct as if it
occurred yesterday. Peculiar circumstances, not important in this
connection, fixed my attention upon the weather during that day and night.
There were cirro-stratus clouds passing all day, from about S. W. to N.
E., thickening toward night with fresh S. S. W. wind and flocculent scud,
such as I have since seen at the setting-in of S. E. autumnal gales. In
the evening the wind (in the immediate neighborhood of Hartford, Ct.),
veered to S. E., the cloud floated low, it became very dark, and the wind
blew a most violent gale. The trees were falling about the house where I
then resided, the windows were burst in, and I was up and observant. When
the cloud passed off to the east, it was suddenly light, and almost calm.
The western edge of the storm cloud was as perpendicular as a steep
mountain side, and was enormously elevated, and very black. I have
sometimes seen the western side of a summer thunder cloud, which had drawn
a violent gust along beneath it, as elevated and perpendicular, but never
a storm cloud. No cloud of that _depth_, or _intensity_ as exhibited by
its peculiar blackness, ever floated or will float so near the earth,
without inducing a devastating current beneath. After it had passed the
ridges east of the Connecticut valley, its top could be seen for a long
and unusual period over the elevated ranges.
Now that storm was but an _intense portion_ of an extensive stratus-rain
cloud. Such portions frequently exist, and Mr. Redfield admits the fact.
Another like portion, in the same storm, passed over Norfolk, Virginia,
and the adjacent section, where the wind was N. E., and veered round by N.
W. to S. W. Baltimore, and some vessels at sea, were between the two
intense portions of the storm, and were not affected by either. Its
northern limit was bounded by a line, drawn from some point not far north
of Trenton, New Jersey, north-eastward, and north of Worcester,
Massachusetts. I was about forty miles south of its northern limit, and
north of its center. During that day, and the next, there was wind from
S. W. to S. E., inclusive, including the gale, and _from no other
quarter_. It did not at any time veer to the W. or N. W. After the passage
of the storm-cloud, the wind was very light. When this intense portion of
the storm passed over the valley of the Connecticut, its longest axis was
from S. S. E. to N. N. W., and the _wind was S. E. the whole length of
it_. In its passage from the longitude of Trenton to Boston, there was N.
W. wind at one point, and but one, and that was in the iron region, at the
N. W. corner of Connecticut, at the northern limit of the intense cloud,
and owing, doubtless, to some local cause. The direction of the wind in
that storm was in accordance with what is generally true of our storms.
The wind on the front of the storm depends upon its shape. If the storm is
long in proportion to its width (and no other _violent_ autumnal or winter
storm has been investigated, to my knowledge), the wind blows axially, or
obliquely, on its front. Thus, if long from S. E. to N. W., the wind on
its front will blow from the S. E. So, if the storm is long from S. W. to
N. E., and has a south-eastern lateral extension, with an easterly
progression, the wind will blow axially in the center, and obliquely at
the edges. Instances might be multiplied, but I refer to one of recent
date and striking character. All of us remember the drought of 1854. It
ended in drenching rain on the 9th of September. This rain fell from a
belt, half showery and half stormy in character, which had a S. E. lateral
extension.
The evening of the previous day there was some lightning visible at the
north, and the usual S. S. W. afternoon wind _continued fresh after
nightfall_. The next day we had a brisk wind from the same quarter, and,
after noon, the clouds appeared to pile up in the far north, seeming very
elevated. They continued to do so, extending southerly during the
afternoon, _with a high wind from S. S. W._, the cumulus clouds moving E.
N. E. At 5 P.M., gentlemen who left New York at 3 P.M., reported that a
dispatch had been received from Albany, dated 1 P.M., stating that it was
raining very heavily there. About 7 P.M., the belt reached us, and it
rained heavily from that time till morning. Not far from 8 P.M., and
during the heaviest rain, the wind shifted from the S. S. W. to N. E., and
blew fresh and cold from that quarter during the night, and till the belt
had passed south, and then from N. E. by N., cool, with heavy scud, during
the forenoon, veering gradually to the N. N. E., and dying away. After the
rain ceased, the northern edge of the belt was distinctly visible in the
S. and S. E., its stratus-cloud moving E. N. E., and its scud to the
westward.
The front of that storm did not pass over us. It was long and narrow. The
wind blew somewhat obliquely inward, along its southern border, to the
eastward, and, in like manner, to the westward, on its northern border,
but from the N. E. axially along its central portions.
In the last instance, the wind changed from S. W. to N. E. This, too, is
impossible, according to Mr. Redfield's theory. Similar instances, in
summer, and early autumn, are not uncommon. But I shall recur to this in
connection with the different _classes_ of storms.
Again, the manner in which these S. E. winds co-exist with the N. E., and
become the prevailing wind, toward the close of the storm, is instructive,
and inconsistent with the theory of Mr. Redfield. In the West Indies, the
first effect of the storm is to increase the N. E. trade; the wind then
becomes baffling, but settles in the N. W. or N. N. W., _in direct
opposition to the admitted progress of the storm_. At this point, or at S.
W., it blows with most force. Sometimes it veers gradually, and sometimes
falls calm, and comes out from the S. W., blowing violently. It ends by
veering to the S. E., following gently the course of the storm. Thus, Mr.
Edwards, in the third volume of his History of Jamaica, as herein before
cited, "_all hurricanes begin from the north, veer back to W. N. W., W.,
and S. S. W., and when they get round to S. E. the foul weather breaks
up_."
A short, sudden gale, resembling those of our summer thunder-showers, is
sometimes met with from the S. E.; but the violent hurricanes of any
considerable continuance are, in almost every case, as just stated.
Now, there is, in our latitudes, an obvious law on the subject, and it is
this:--If the storm is not disproportionately long, northerly and
southerly, there is a general tendency to induce and attract a surface
current, in opposition to the course of the storm on its front, and
especially its north front. At the same time, there is a tendency to
induce a lateral current on its side, particularly the southerly side, and
sometimes its south front: that the latter current is, in the first part
of the storm, above the former; in the middle and latter part, it becomes
the prevailing current at the surface, and the wind changes accordingly,
with or without a calm--that this lateral change sometimes takes place on
either side, but usually occurs on the side where the water is warmest, or
there is, for other and local reasons, a _greater susceptibility in the
atmosphere to inductive and attractive influence_. Thus, our N. E. storms
very frequently have a southerly current also, drawn from the ocean, south
of us, which forms the middle current, and, in the middle and latter part
of it, becomes the prevailing one. _I have seen more than a hundred such
instances, clearly and distinctly marked._ Since I have been writing this
chapter, January 29th, 1855, such an instance has occurred. On Sunday, the
28th, the cirro-stratus were all day passing from the S. W. to N. E., and
gradually thickening with light air from the E. N. E., in the afternoon.
During the evening the wind set in _violently_ from the N. E., with a
deluging rain. During the night, and after a brief calm, it changed
suddenly to the southward, and blew in like manner. This morning the storm
was gone, and with it, six inches of hard, frozen icy snow; the trade was
clear, with the exception of here and there a broken, melting piece of
stratus, but scud were still running from the southward, and the wind has
been from the south, veering to S. W., all day, with sunshine. As I have
before remarked, this middle current is always present, in this locality,
in stratus storms, when there is a heavy fall of rain or snow, although,
when the latter happens, the middle current is sometimes from the
northward; if it be from the southward, it turns the snow first into very
large flakes, and then to rain in our part of the storm.
Doubtless, the same thing occurs every where. In the West Indies, and
especially over the Leeward Islands, the middle current is most commonly
from the stream of warm water which runs off to the westward into the
Caribbean Sea; as the S. W. moonsoon is from the same current below the
Cape de Verdes. The S. W. winds, which come from those south polar waters,
in the West Indies, appear to be the most violent. But it may be on either
or both sides.
The hurricane cloud of the West Indies moves confessedly N. W. in most
instances, and undoubtedly it does in all. There is an immutable law that
requires it. The seeming exceptions are not such; they are but instances
imperfectly investigated. Now, a circular storm moving N. W. can set in N.
W. only on the left front, and _can not change to S. W. on that side of
the axis_. Nor can the wind blow at the axis from N. W. at all. It should
be N. E. in first half, and S. W. in last half. Strange as it may seem,
the axis of a West India hurricane in conformity with Mr. Redfield's
theory, and a N. W. progression, has never been found, with perhaps a
single exception, in any one of which I have seen a description. On the
west coast of Europe, the gale is commonly from the Atlantic, either
following under the storm from the S. W., or blowing in diagonally from
the W. or N. W.; the N. E. wind of western Europe being a cold, dry wind,
which there is reason to believe has been around the Siberian pole and is
returning, as the cold northerly winds of the North Pacific have around
the North American magnetic pole. "If the N. E. winds always prevailed,"
says Kämtz, speaking of Berlin, "even at a considerable height it would
never rain." This was based on an observation of showers, and not fully
reliable. But the dry and cool character of the N. E. wind of western
Europe is unquestionable. The S. E. wind is also a storm wind, but owing
to the character of the surface from which it is attracted, it is not as
violent as the westerly winds are.
Such, too, is the general course and character of the side wind in the
southern hemisphere. There gales are less frequent, the magnetic intensity
is less, the counter-trades are less; it is not in "the order of
Providence" that as much rain shall fall there. Nevertheless, gales occur,
although rarely, if ever, with equal violence. About New Holland, where
storms are pursuing a S. E. course, they have the wind N. E.,
corresponding to our S. E., veering from thence, _by the north_, to the
westward, clearing off from S. W., with a rising barometer, as ours do
from N. W.
In the Bay of Bengal, the Indian Ocean, and the Arabian Sea, there is more
irregularity.
But the law of progress and lateral winds can be distinctly traced as
_present_ and prevailing, notwithstanding the irregularities. Our limits
do not permit an analysis. In the celebrated case of the Charles Heddle,
there was much evidence to show that she was driven across the front of
the storm by one lateral wind, and back by another. (Diagram of Colonel
Reid, p. 206.)
The waters of the Indian Ocean are hot and confined. Storms there are
often composed of detached masses, move slower--sometimes not more than
three or four miles an hour--and they curve over the ocean, where it is
hotter than in any similar latitude. Yet, notwithstanding all
peculiarities and irregularities, the law we have been considering is
probably the _prevailing_ law there.
No man knows better the existence of these different currents than Mr.
Redfield. Doubtless it has escaped his attention that the upper of two,
after the passage of a considerable proportion of the storm, becomes the
lower, and causes a seeming change of the same wind.
In a series of elaborate articles, substantially reviewing the whole
subject, published in the American Journal of Science, for 1846, he says:
"In nearly all great storms which are accompanied with rain, there
appear two distinct classes of clouds, one of which, comprising the
storm scuds in the active portion of the gale, has already been
noticed. Above this is an extended stratum of stratus cloud, which is
found moving with the general or local current of the lower
atmosphere which overlies the storm. It covers not only the area of
rain, but often extends greatly beyond this limit, over a part of the
dry portion of the storm, partly in a broken or detached state. This
stratus cloud is often concealed from view by the nimbus, and scud
clouds in the rainy portion of the storm, but by careful
observations, may be sufficiently noticed to determine the general
uniformity of its specific course, and, approximately, its general
elevation.
"The more usual course of this extended cloud stratum, in the United
States, is from some point in the horizon between S. S. W. and W. S.
W. Its course and velocity do not appear influenced in any
perceptible degree by the activity or direction of the storm-wind
which prevails beneath it. On the posterior or dry side of the gale,
it often disappears before the arrival of the newly condensed cumuli
and cumulo-stratus which not unfrequently float in the colder winds,
on this side of the gale."
"The general height of the great stratus cloud which covers a storm,
in those parts of the United States which are near the Atlantic, can
not differ greatly from one mile; and perhaps is oftener below than
above this elevation. This estimate, which is founded on much
observation and comparison, appears to comprise, at the least, the
limit or thickness of the proper storm-wind, which constitutes the
revolving gale.
"It is not supposed, however, that this disk-like stratum of
revolving wind is of equal height or thickness throughout its extent,
nor that it always reaches near to the main canopy of stratus cloud.
It is probably higher in the more central portions of the gale than
near its borders, in the low latitudes, than in the higher, and may
thin out entirely at the extremes, except in those directions where
it coincides with an ordinary current. Moreover, in large portions of
its area, there may be, and often is, more than one storm-wind
overlying another, and severally pertaining to contiguous storms. In
the present case, we see, from the observations of Professor Snell
and Mr. Herrick, at Amherst, Massachusetts, and at Hamden, Maine (115
and 135 b.), that the true storm wind, at those places, was
super-imposed on another wind; and various facts and observations may
be adduced to show that brisk winds, of great horizontal extent, are
often limited, vertically to a very thin sheet or stratum."
Much of the foregoing is graphically described, and unquestionably true.
But it may well be asked how he, or others, distinguish which of two or
more currents (for there are frequently three, and sometimes four
visible), are the true currents of the storm, and which interlopers from
another storm? Is the true one always the upper one, and why? If the
upper one, why is the interloper at the surface noted and quoted to prove
what a storm is? How does he know what proportions of the winds he has
recorded to show the revolving motion of gales, were the true storm winds
of the particular storm? or, that every one of them was not an interloping
wind on which the true storm wind was superimposed?
These inquiries are pertinent, for obviously, unless some rule for
distinguishing between the currents is given, and there be evidence of
direct observation to show that the surface wind, whose direction is
noted, is the true wind of the storm, and that the _latter_ is not
_superimposed_, no reliance can be placed upon logs, or newspaper
accounts, or registers. There is another element besides direction, viz.:
superimposition, a determination of which _is_ essential to _truth_. It
will be difficult for Mr. Redfield to say that a determination of that
element has been made, with certainty, in a single storm he has
investigated; and in relation to the convergence of storms, and blending,
and superimposition of their winds, I think he is mistaken.
Mr. Redfield is right in saying (American Journal of Science, vol. ii.,
new series, p. 321) that "too much reliance may be placed upon mere
observations of the surface winds in meteorological inquiries," and yet
_they_ only have thus far been regarded, and he has proved gyration in no
other way. I have frequently, with a vane in sight, asked intelligent men
how the wind was, and been amused and instructed by their inability to
state it correctly. Mr. Redfield, in his inquiries, often found two
reports of the weather at the _same time_, from the _same place_,
materially different; and I have known, from my own observation,
newspapers and meteorological registers to be several points out of the
way; and this, because the vanes are influenced by local elevations, and
change several points, and very often; because few know the exact points
of the compass in their own localities, and because entire accuracy has
not been deemed essential. For these reasons, newspaper and telegraphic
reports are not always reliable; and therefore, and because, also,
storm-winds are easterly and fair winds westerly, and the former veer from
east around to west, on one or both sides in many cases, there are few
storms which can not be represented as whirlwinds, by a proper _selection_
of _reports_, a corresponding _location_ of the _center_, and an
_extension_ of the lines of supposed gyration, so as to include the
_preceding_ winds, the actual winds of the storm, and the _lateral_, and
_succeeding_ fair weather ones.
But, again, Mr. Redfield is right in saying there is, in such cases, "an
extended stratum of stratus cloud," and it is always present. But why does
he say this _covers the storm_? Is it distinct from it, and if so, what is
it doing there? What power placed it there, and for what purpose? Has this
extended stratum of cloud, which forms the canopy of a vast chamber--five
hundred to one thousand miles in diameter, and less than two miles in
vertical depth, while the earth forms the floor--any agency in producing
the whirl that is supposed to be going on within it, and if so, what? Has
the earth any agency, and if so, what? If neither the ceiling nor floor of
the chamber have any agency in producing it, what does? Are we to consider
the _storm-scud_ as possessing the power, and as waltzing around the
aerial chamber, carrying the air with them in a hurricane-dance of
devastation? _What, in short, is the power, and how is it exerted?_
To these questions, Mr. Redfield's essays furnish no comprehensive answer.
There is an intimation that the cause of storms will be, at some future
day, developed. One attempt, and but one, has thus far been made, and that
I quote entire:
"We have seen that the two Cuba storms, as well as the Mexican
northers, have appeared to come from the contiguous border of the
Pacific Ocean.
"Now, are there any peculiarities in the winds and aerial currents of
those regions, which may serve to induce or support a leftwise
rotation in extensive portions of the lower atmosphere, while moving
on, or near the earth's surface? I apprehend there are such
peculiarities, which have an extensive, constant, and powerful
influence. First, we find on the eastern portion of the Pacific, from
upper California to near the Bay of Panama, an almost constant
prevalence of north-westerly winds at the earth's surface. Next, we
have an equally constant wind from the southern and south-western
quarter, which, having swept the western coast of South America,
_extends across the equator to the vicinity of Panama_, thus meeting,
and commonly over-sliding the above-mentioned westerly winds, and
tending to a deflection or rotation of the same, from right to left.
As this influence may thus become extended to the Caribbean or
Honduras Sea, we have, next, the upper or S. E. trade of this sea,
which is here frequently a surface-wind, and must tend to aid and
quicken the gyrative movement, ascribed to the two previous winds;
and lastly we have the N. E. or lower trade, from the tropic, which,
coinciding with the northern front of the gyration, serves still
further to promote the revolving movement which may thus result from
the partial coalescence of these great winds of Central America, and
the contiguous seas.
"Thus, while a great storm is, in part, on the Pacific Ocean, its N.
E. wind may be felt in great force on that side of the continent,
through the great gorges or depressions near the bays of Papagayo or
Tehuantepec, as noticed by Humboldt, Captain Basil Hall, and others,
the elevations which there separate the two seas being but
inconsiderable; and, when the gyration is once perfected, the whole
mass will gradually assume the movement of the predominant current,
which is generally the higher one, and will move off with it,
integrally, as we see in the cases of the vortices, which are
successively found in particular portions of a stream, where subject
to disturbing influences."
The analogy between this and the theory of Professor Dove, cited above,
and prior, in point of time, is obvious. They are substantially alike in
principle, with different locations. They differ also in this, Professor
Dove appears to think something more than over-sliding necessary, and
assigns the duty of crowding the upper current down in to the lower, to
make an _encounter_, to a lateral overflow from Africa. Mr. Redfield seems
to think there may be a tendency to deflection when they "over-slide" each
other. They are both closet hypotheses, the poetry of meteorology, with
something more than poetical license as to facts.
In the first place, _no such concurring winds exist in the same locality
at the same time_. When the inter-tropical belt of rains is over Central
America and Southern Mexico, a S. W. monsoon blows in under it, but it
usurps the place of all other surface winds; and, when the belt is absent,
that portion of the eastern Pacific is most remarkably calm, or is covered
by the N. E. trades. Secondly, the _trade-winds every where pursue their
appointed course without "tendency to deflection" by the meeting, or
"over-sliding," or "breaking in," or "encounter,"_ of other winds. The
great laws of circulation do not admit of any such _confusion_. And,
lastly, _no storm ever came over the eastern United States from that
quarter_. The unchangeable laws of atmospheric circulation forbid it.
Recent observations also have shown that the storms on the west coast of
Central America, and the eastern Pacific, pursue a N. W. course, precisely
as in the West Indies, and every where over the surface-trades of the
northern hemisphere. Indeed _Mr. Redfield himself has recently
investigated several of them, and admits their course to be
north-westerly_. (See American Journal of Science, new series, vol. xviii.
p. 181.)
But, suppose the co-existence of the winds and the course of the storms
admitted as claimed, let us seek for clearer views. What do these
gentlemen mean? Do they intend to have us believe the air has inherent
moving power, and that the "tendency" of which they speak is an attribute
of the winds, and that when they thus meet, and "come into each other,"
"encounter," or "over-slide," and become acquainted, they wheel into a
waltz, and move off northward, "integrally," with unceasing circular
movement, even until they arrive at the Arctic circle? Or is it a mere
mechanical effect of meeting, "coming into each other," or "over-sliding?"
If the latter, why a tendency to rotation from right to left? The
trade-winds, at least, are _continuous, unbroken sheets_, and not
disconnected portions which meet and blow past each other, and there is no
warrant for placing them _side and side_, and attributing to them any
such mechanical effect, and as little respecting the other winds. Outside
of the fanciful hypothesis, there are no facts to show such a tendency one
way rather than the other; and, in accordance with the known facts
regarding stratification of the currents of air, no such "tendency" can
exist.
But what _power_ impels the winds, which thus meet at these points? If
they be impelled, is it consistent with the action of this power that the
_winds_ it has _created_ and _controls_, should thus assume an _opposite
"tendency,"_ and whirl away to the north-eastward, regardless of the power
that originated and controls them? What must this "_tendency_" be, which
thus _occasionally_ not only diverts the winds from the _usually regular
course_ given them by their originating power, but increases their action,
from gentle, ordinary winds, to hurricanes? Nay, which gives them a new,
resistless gyratory and electric energy, increasing as the new,
independent, supposed cyclonic organization moves off, "_integrally_,"
away from "the home of its many fathers," on a devastating journey towards
the north pole?
And, further, if all this were true as to the West Indies and Central
America, what is to be said of the billions of other storms, originating
on a thousand other portions of the earth's surface, and how are they to
be accounted for, inasmuch as such other "meetings," "coming into each
other," and "over-sliding," and "tendency to deflection," is not assumed
to exist?
These questions cannot be satisfactorily answered. The distinguished
theorists are mistaken. The stratus-cloud does not over-lie or cover the
storm. IT IS THE STORM. The winds beneath, whether surface or
superimposed, are but its incidents, due to its static induction and
attraction. Their _direction_ depends on the shape of the storm cloud, and
its course of progression, and the susceptibility of the surface
atmosphere in this direction or that, to its inductive and attractive
influence. Their _force_ to its depth, its contiguity to the earth, and
the intensity of its action; and the scud, are but patches of
condensation, occasioned by the same inductive action which affects and
attracts the surface current in which they form.
Another objection to Mr. Redfield's theory of gyration is based upon the
fact that in order to constitute his _storm_, to get the _gyration_, he
has to include, at least, an equal amount, generally a great deal more, of
_fair weather_. The N. W. wind, the "posterior, or dry side of the gale,"
as he calls it (in the foregoing extract), is a _fair weather wind_. It is
_necessary_, however, to complete the supposed _circle_, and it is
_pressed into the service_. The practical answer given to the question,
"_what are storms?_" is, they are cyclones, part storm, so called, and
_part fair weather_; that is, the stratus-cloud, the scud, the easterly
wind, and rain or snow of day before yesterday, were the _wet side_, or
front part of the storm, and the sunshine, clear sky, and N. W. wind of
yesterday, to-day, and, perhaps, to-morrow, are the posterior or dry side.
When a storm clears off from the N. W. it is not _over_, it is, perhaps,
_just begun_; and, inasmuch as it storms again, very soon after the wind
changes back from the N. W. to the southward, in winter, our weather then
is pretty much all _storms_.
The statement of this claim seems so absurd that it may appear like
injustice to make it. But gyration can not be made out without it, and it
is evident in the extract quoted above; in the claim that the winter
northers of the Mexican Gulf are parts of passing storms; and clearly and
unequivocally advanced as a distinct proposition, as follows:
"1. The body of the gale usually comprises an area of rain or foul
weather, together with another, and, perhaps equal, or greater, area of
fair or bright weather." (Am. Jour. of Science, vol. xlii. p. 114.)
Now, in the first place, we must distinguish between a storm and fair
weather, before we can tell what the former is, and it is difficult to
assent to a theory which explains what a S. E. storm of _twelve hours'_
continuance is, by including _two or three days of succeeding N. W. fair
weather wind_, as a part of it. There is no proportionate relation as to
_time_, nor any relation as to _qualities_, or the attending conditions of
the atmosphere, nor any conceivable _connection_, except the hypothetical
one of _gyration_, between the two winds.
And, in the second place, it is true, and Mr. Redfield is well aware of
the fact, that winds often blow for many days from the N. E., S. W., or N.
W., without any preceding or succeeding winds to which they have any
discoverable relation. If, therefore, truth would justify Mr. Redfield in
including the fair weather wind, a difficulty would remain which his
theory does not cover or explain.
No American, except Mr. Redfield, has been able to discover satisfactory
evidence of the gyration of storms, by actual careful observation, or a
careful unbiased collation of the observation of others. Professor Coffin
is reported to have read to the Scientific Association, at their Buffalo
meeting, a paper, confirmatory, in part, but I have not been able to see
it. The tracks of tornados have been searched as with candles. When they
have been narrow, from forty to eighty rods, their action has been
substantially similar, and, although, as we have herein before stated,
some irregularities have been found which were consistent with
gyration--for irregularities attend the violent action of all forces, and
particularly the motion of electricity through the atmosphere, as every
one who has seen the zig-zag course of a flash of lightning knows--yet the
evidence of two lateral inward currents, or lines of force, has
predominated over all others. In all cases, where the path is narrow,
those lateral currents are the actors; they constitute the tornado; their
_irregularities_ of action produce the exceptions; but the exceptions are
neither numerous nor uniform, and do not prove either the theory of Mr.
Espy or that of Mr. Redfield. The action is not that of moving air,
merely, but of a power exceeding in force that of powder, which nothing
but electricity or magnetism can exert. As the path widens, the wind
becomes more like the straight-line gust which follows beneath the
ordinary severe thunder-showers. His theory finds no substantial
confirmation or support in the path of the tornado.
Several storms were investigated by Professor Espy, some of them the same
which Mr. Redfield had attempted to show were of a rotary character; one
or two by the Franklin Institute of Philadelphia; one by Professor Loomis,
already alluded to; and recently, two by Lieutenant Porter, from logs
returned to the National Observatory. None of these investigations confirm
the theory of Mr. Redfield. Indeed, Mr. Redfield himself has found it
necessary to resort to suppositions of _modifying causes_ to explain the
evident inconsistencies. It is assumed that the axis, or center,
oscillates, and describes a series of circles; and thus, one class of
difficulties is avoided. Again, it is assumed that simultaneous storms
converge and blend upon the same field, and another class of difficulties
are surmounted. And, again, inasmuch as it is notorious that violent gales
are rarely if ever felt with equal violence around the area of a circle,
but from one or two points only, it is assumed, that the storm winds
ascend, superimpose, and descend again, when they return to the place of
their first violent action, etc. The _simple truth_ requires no such
resort to _modifying hypothesis_.
Still, another objection is, that the changes in the barometer, which
occur before, during, and after storms, do not sustain the claims of Mr.
Redfield or the requirements of his theory.
The barometer sometimes rises before storms. It generally commences
falling about the time, or soon after the storm sets in, continues to fall
during its progress, and rises again, sooner or later, afterward. This is
the general rule.
On this subject Mr. Redfield's claim is this:
"EFFECT OF THE GALE'S ROTATION ON THE BAROMETER.--The extraordinary
fall of the mercury in the barometer, which takes place in gales or
tempests, has attracted attention since the earliest use of this
instrument by meteorologists. But I am not aware that the principal
cause of this depression had ever been pointed out, previously to my
first publication in this journal, in April, 1831, when I took the
occasion to notice this result as being obviously due to the
_centrifugal force_ of the revolving motion found in the body of the
storm.
"Since that period, inquiries have been continued by meteorologists
in regard to the periodical and other fluctuations of the barometer,
and the relations of these fluctuations to temperature and aqueous
vapor. But these incidental causes of variation, in the atmospheric
pressure, prove to be of minor influence, and we are left to the
sufficient and only satisfactory solution of this marked phenomenon
which is found in the centrifugal force of rotation."
The average pressure of the atmosphere, at the surface of the ocean, or in
the interior of the country, allowing for elevation, is about equal to the
weight of a column of quicksilver, thirty inches in height; hence the
barometer is said to stand at about thirty inches at the level of the sea.
This is sufficiently accurate for the northern hemisphere, north of the N.
E. trades; but the average is somewhat lower in the trades and in the
southern hemisphere. Thus, the average of sixteen months, during which the
Grinnell expedition was absent, was 30.08/100.
From a large number of logs examined by Lieutenant Maury, the mean
elevation in the N. E. trades of the Atlantic was 29.97/100; the S. E.
trades of the Atlantic, 29.93/100; off Cape Horn, 29.23/100; S. E. trades
of the Pacific, 30.05/100; N. E. trades of the Pacific, 29.96/100. The
height of the barometer off Cape Horn is not a fair index of the general
elevation of the southern hemisphere, inasmuch as it stands lower there
than at the coast of Patagonia and Chili, or at most, if not all, other
stations in that hemisphere.
As the barometer is constantly oscillating up and down (irrespective of
its diurnal oscillation), it has no known fair weather standard. The point
of 30 inches is taken only as it is a mean. I have known it to commence
storming when the barometer was at 30.70, and not to fall before it
cleared off, below 30.30. And I have known it to be below 30 for several
days consecutively, with fair weather. In our climate there is no reliable
fair weather standard for the barometer. It falls below 30 without
storming; it rises far above, and storms without falling below. No
reliance can be placed upon its elevation, except by comparison; but of
that hereafter.
The general rule, nevertheless, is, that it falls more or less during
storms, whatever its height, and rises sooner or later, more or less,
after they clear off.
The difference between its highest and lowest points is called its range.
The greatest range observed, and recorded, is about 3 inches--from about
28 to 31--but this range is rare. The range, in the trade-wind region, is
comparatively small; in this country it is greater than in Europe; and,
generally, the range will be found greatest where the volume of
counter-trade, and magnetic intensity, and the corresponding amount of
precipitation, and extremes of heat and cold are greatest. One of the
greatest ranges during one storm, or two successive portions of a storm,
in this country, which I have seen recorded, occurred at Boston, in
February, 1842. It was as follows--counting the hours as 24, and from
midnight:
Feb. 15..10h..30.36.
" 16..13h..28.47 fall of 1.89 in 27 hours.
" 17..19h..30.39 rise of 1.92 in 30 hours.
" 18.. 2h..30.39 stationary 5 hours.
" 19.. 2h..29.46 fall of 0.93 in 24 hours.
" 20.. 2h..30.43 rise of 0.97 in 24 hours.
Amount of oscillation, 5.71 in 4 days, 11 hours.
These ranges were owing to the alternation of S. E. storms, and N. W.
winds.
Taking the first range as a basis, and allowing the height of the
atmosphere to be 1,100 feet for the first inch, we have nearly 2,000 feet
displaced during one day, if we look for the displacement near the earth,
or some 30 or 35 miles, if we soar aloft in the upper regions to look for
the _lateral overflow_ of Professor Dove, and about the same quantity
restored the next. This brings us to the inquiry, how was it done? It is
perfectly idle to talk about _difference_ of _temperature_ or _tension_ of
_vapor_, the _ascent_ of warm air, or _descent_ of cold in a case like
this; or to say that they were occasioned by a lateral overflow of some
thirty miles of its upper portion, first this way and then that, in such a
brief space of time. The change is equal to nearly 1/15 of the weight of
the whole atmosphere, and the cause, whatever it was, existed within two
or three miles of the earth. Mr. Redfield's explanation I give in his own
words, at length:
"One of the most important deductions which may be drawn from the
facts and explications which are now submitted, is an explanation of
the causes which produce the fall of the barometer on the approach of
a storm. This effect we ascribe to the centrifugal tendency or action
which pertains to all revolving or rotary movements, and which must
operate with great energy and effect upon so extensive a mass of
atmosphere as that which constitutes a storm. Let a cylindrical
vessel, of any considerable magnitude, be partially filled with
water, and let the rotative motion be communicated to the fluid, by
passing a rod repeatedly through its mass, in a circular course. In
conducting this experiment, we shall find that the surface of the
fluid immediately becomes depressed by the centrifugal action, except
on its exterior portions, where, owing merely to the resistance which
is opposed by the sides of the vessel, it will rise above its natural
level, the fluid exhibiting the character of a miniature vortex or
whirlpool. Let this experiment be carefully repeated, by passing the
propelling rod around the exterior of the fluid mass, in continued
contact with the sides of the vessel, thus producing the whole
rotative impulse, by an external force, analagous to that which we
suppose to influence the gyration of storms and hurricanes, and we
shall still find a corresponding result, beautifully modified,
however, by the quiescent properties of the fluid; for, instead of
the deep and rapid vortex before exhibited, we shall have a concave
depression of the surface, of great regularity: and, by the aid of a
few suspended particles, may discover the increased degree of
rotation, which becomes gradually imparted to the more central
portions of the revolving fluid. The last-mentioned result obviates
the objection, which, at the first view, might, perhaps, be
considered as opposed to our main conclusion, grounded on the
supposed equability of rotation, in both the interior and exterior
portions of the revolving body, like that which pertains to a wheel,
or other solid. It is most obvious, however, that all fluid masses
are, in their gyrations, subject to a different law, as is
exemplified in the foregoing experiment; and this difference, or
departure from the law of solids, is doubtless greater in aëriform
fluids than in those of a denser character.
"The whole experiment serves to demonstrate that such an active
gyration as we have ascribed to storms, and have proved, as we deem,
to appertain to some, at least, of the more violent class; must
necessarily expand and spread out, _by its centrifugal action, the
stratum of atmosphere subject to its influence, and which must,
consequently, become flattened or depressed by this lateral movement,
particularly toward the vortex or center of the storm_; lessening
thereby the weight of the incumbent fluid, and producing a consequent
fall of the mercury in the barometrical tube. This effect must
increase, till the gravity of the circumjacent atmosphere, superadded
to that of the storm itself, shall, by its counteracting effect, have
produced an equilibrium in the two forces. Should there be no
overlaying current in the higher regions, moving in a direction
different from that which contains the storm, the rotative effect
may, perhaps, be extended into the region of perpetual congelation,
till the medium becomes too rare to receive its influence. But
whatever may be the limit of this gyration, its effect must be to
_depress_ the _cold stratum_ of the upper atmosphere, particularly
toward the more central portions of the storm; and, by thus bringing
it in contact with the humid stratum of the surface, to produce a
permanent and continuous stratum of clouds, together with a copious
supply of rain, or a deposition of congelated vapor, according to the
state of the temperature prevailing in the lower region."
The italics in the foregoing extract are mine; and, in relation to it, I
observe:
1st. There is no cylindrical vessel around storms, and _air will not thus
resist air_. Confessedly, such resistance is necessary. Let any one watch
his cigar smoke, and see how readily it moves on, with little momentum.
Let any one try the experiment of creating a whirl in the _open air_, or
in a room, or box of paper, or other material, which can be suddenly
removed, with air colored by smoke. I am exceedingly mistaken if he does
not find the presence of a "cylindrical vessel," absolutely essential to
prevent the instantaneous tangential escape of the air.
2d. Turn back to page 3 and look at the fall of the barometer in the polar
regions (recorded in the extract from Dr. Kane), with _scarcely any
wind_, and _as little variation_ in its _direction_, and see how utterly
Mr. Redfield's theory fails to account for the phenomena.
3d. If I understand Mr. Redfield correctly, he has abandoned the claim as
originally made, that the wind moves in circles, expanding, and _spreading
out_ by a "_lateral movement_," and now asserts that it blows spirally
inward, and elevates the air in the center. I quote:
"VORTICAL INCLINATION OF THE STORM WIND.--By this is meant some
degree of involution from a true circular course. In the New England
storm above referred to, this convergence of the surface-winds
appeared equal to an average of about 6° from a circle. In the
present case, such indication seems more or less apparent in the
arrows on the storm figures of the several charts, where the
concentrical circle afford us means for a just comparison of the
general course of wind which is approximately shown by the several
observations.
"Perhaps we may estimate the average of the vorticose convergence, as
observed in the entire storm for three successive days, at from 5° to
10°--out of the 90° which would be requisite for a congeries of
_centripetal_ or center-blowing winds. This rough estimate of the
degree of involution is founded only on a bird's-eye view of the
plotted observations. But, however estimated, this involution seems
to afford a measure of the air and vapor which finds its way to a
_higher elevation_ by means of the vortical movement in the body of
the storm."
If the elevation of the air at the borders of the storm, and depression in
the middle, resulted from the outward tendency and "lateral movement" of
the revolving air, and from the _centrifugal force_, as in the experiment
with the water in a cylindrical vessel, as stated in the first paragraph
quoted, an _involution_ of from 5° to 10° from the action of a
_centripetal force_, must carry the air _inward_, and the _barometer
should stand highest in the middle of the storm_. The change is fatal to
his theory. The two are diametrically opposite in character and effect. In
one, the superior strata would be brought down in the center by the
_lateral pressure outward_; in the other, they would be elevated by the
_involution_, which "affords a measure of the air and vapor which finds
its way to a higher elevation," etc. It is perfectly obvious Mr. Redfield
has refuted his own hypothesis.
In doing this, he is met by the other difficulty alluded to, which he does
not attempt to explain. This gathering of the air inward, spirally, by a
centripetal force, if it took place, not only would not depress, but _must
elevate the barometer in the center, above that of the adjoining
atmosphere_.
When he first attributed the depression of the barometer to a lateral
movement and centrifugal force, he supposed the superior strata descended
into the depression, and their frigidity occasioned the condensation, and
cloud, and rain. How he now proposes to account for the formation of cloud
and rain during storms, while the warm air of the inferior stratum finds
its way to a higher elevation in the center of the storm, he does not
inform us, and we must wait his time.
"I have," he says, "long held the proper inquiry to be, _what are
storms_? and not, _how are storms produced_? as has been well
expressed by another. It is only when the former of these inquiries
has been solved that we can enter advantageously upon the latter."
The former does not seem to be yet solved, or the solution of the latter
commenced. Mr. Redfield tells us (page 259, and onward), that there is an
extended stratum of stratus-cloud, which overlies the storm, and that it
does not differ greatly from one mile in height. We are not told how the
air, which finds its way to a higher elevation during several days
continuance of such a storm, _gets through the stratum_. If he is right it
_must_ do so, and it would not answer to _suppose_ a very small opening or
gentle current through it, to carry off all the air which works inward in
a hurricane, during several days continuance. But he does not seem to
recognize either the necessity or existence of any _vent_ at all; nor is
there any; and this fact is open to the observation of every school-boy in
the country; and it is equally open to his observation that _when and
where the barometer is most depressed, the stratus storm-cloud is nearest
the earth_. Colonel Reid has much to say about the "_storm's eye_," or
"treacherous center" of a storm. A careful analysis of the instances where
the "storm's eye" is noticed will show that the term is applied, in the
northern hemisphere, to that lighting up in the W. or N. W., which is the
commencement of the clearing-off process, and attended with a shift of
wind to the fair-weather quarter: _i. e._, to W. or N. W. Just such an
"eye" as is seen when the last of the storm cloud has passed so far to the
east as to admit the rays of the sun under the western or north-western
edge of it. The same kind of "storm's eye" is described in the southern
hemisphere, except that the wind shifts to S. W. instead of N. W., that
being the clearing-off wind there. No instance of a "_storm's eye_" in
the center of the extended stratum of stratus-cloud, which overlies the
storm, can be found recorded, to my knowledge; and it is obvious that
Colonel Reid adopts the view of Mr. Redfield, that the westerly and N. W.
_fair weather_ winds are a part of the storm. So long as these gentlemen
hold to that opinion they will never solve the question, "_what are
storms?_" or reach the other, "_how are storms produced?_"
Notwithstanding, Mr. Redfield asserts, or adopts the assertion, that the
inquiry should be, "What are storms?" not "How are storms produced?" that
inquiry should be a _rational_ one, and should not violate all analogy, or
call for an explanation which science can not _rationally_ furnish. Mr.
Redfield does not seem to have formed any just conception of the
_immeasurable power_ of a hurricane, _five hundred miles in diameter_; or
of the nature of that _rod_ which the _Almighty must insert in it, to
whirl it with such violent and long-continued force_; nor any just
conception of the tendency of the whirling mass, in the absence of his
"cylindrical vessel," to fly off, tangentially, into the surrounding air;
or of the nature or power of the centripetal force necessary to hold the
gyratory mass in its current, and gather it in involute spirals toward a
center. Nor has any other man who has witnessed, or read of
mountain-tossed waves; of the largest ships blown down and engulfed; of
towns submerged, and vessels carried far inland, and left in cultivated
fields, by the subsidence of the sea; of sturdy forests and strongly-built
edifices prostrated; or listened to the howling of the tempest, and felt
his own house rock beneath him, been able to conceive of any known form of
calorific or mechanical, or other power, acting from a comparatively small
center, which could hold such an immense irresistable mass of whirling air
in a circle, and _gather it_ in toward the center in gradually contracting
spirals. I confess that, to my mind, it seems little less than a mockery
of our intelligence for Mr. Redfield, or Professor Dove, or any other man,
how distinguished soever he may be, to tell us that all this is the result
of a "tendency to left-wise rotation" of ordinary winds, "coming into each
other," or "over-sliding," or "meeting," or "encountering," on this
"front," or that, down in Central America, or in the West Indies, or the
monsoon region; or to talk of "lateral overflows" from mere gravity; of
the ascent of warm air, or the descent of cold strata; of the _resistance
of adjacent passive air_, or other mere _atmospheric resistances_ in
connection with such _awful manifestations of power_. Their explanations
of these phenomena are not rational, nor can they be believed by any
rational man, who will bestow upon them half an hour of _comprehensive,
unbiased reflection_.
Waiving many minor points of great force, for this notice of Mr.
Redfield's theory is already too much extended for my limits, I am
constrained to take issue with him on the fact, and to assert,
unhesitatingly, that in a _majority of instances no such barometric curve
exists_.
Doubtless the depression beneath the storm is found, and exterior lateral
elevations may also be had by _extending the line into the usual fair
weather elevation on each side_, as Mr. Redfield is obliged to do, to get
his supposed circle of winds at all. Doubtless, too, the seamen sailing
out of a storm, on either _side_, and approaching fair weather, will have
a rising barometer. But from _front to rear, on the line of progression_,
in tropical storms, the curve does not exist on shore, in this latitude,
oftener than in two, or possibly three, cases in ten; and then only upon a
single state of facts--that is, when there is an interposition of N. W.
wind; and this, at some seasons, rarely occurs. An elevation usually
occurs before the storm, on its front, if it present an extensive easterly
front, as one of these classes does, and a _depression is left_ after it
has passed off, unless a considerable body of N. W. wind interposes, as
heretofore stated. But when there is not such interposition of N. W. wind
(for W., W. N. W., or even N. W. by W. will not suffice), there is not an
immediate rise of the barometer corresponding in rapidity and extent with
the fall, and frequently none during the first twenty-four hours of
bright, fair weather. Let the reader, if he has access to a barometer,
note this fact, for it is obvious and conclusive.
Finally, there are other atmospheric conditions to which the barometric
changes are obviously due:
1st. The counter-trade is of a different _volume_, at different times,
over the same locality, and hence a difference in the normal elevations of
the barometer.
2d. It is at a different _elevation_, at different times, over the same
locality. It was so found by the investigations of the Kew Observatory
Committee referred to; has been so found by other aeronauts, and may
readily be seen by a careful, practiced observer.
It is highest, with a high barometer, in serene weather, when a storm is
not at hand; and can sometimes be plainly seen to ascend when a
considerable volume of N. W. wind is blowing in beneath, and elevating,
simultaneously, the trade and the barometer.
Opportunities occur every year, when the northern edge of the dissolving
stratus-cloud is attenuated, and the storm is clearing off in the N. W.,
with wind from that quarter, and a rising barometer, when its gradual
elevation may be observed to correspond with the _volume_ of that wind.
3d. During storms, with a low barometer, the _trade_ and the _clouds run
low_. This, too, is clearly observable, especially when the stratus-cloud
passes off abruptly, very soon after the rain ceases. In such cases the
barometer will remain depressed for a considerable time, unless another
storm supervenes speedily, or the wind sets in from the N. W.
4th. The _trade, in a stormy state, moves faster_ than when in a normal
condition. This is observable during the partial breaks which frequently
occur in storms, and at other times. It is also inferable from the more
rapid progress of the more intense center, and other intense portions of
storms, and the consequent greater depression of the barometer, under such
centers or intense portions. (See the storm of Professor Loomis.) It is
obvious, also, from the greater rapidity of progress attending the more
intense and violent storms which all investigations discloses.
These simple facts explain all the phenomena:
1st. The trade stratum is a continuous unbroken sheet, and its descent
must displace a portion of the surface atmosphere. A portion of it is
impelled forward, aiding in the precedent elevation of the barometer, and
a portion is attracted backward, into the space from which a like portion
had been previously attracted by the passing storm cloud, forming the
easterly wind.
2d. The increased progress of the stormy portion of the counter-trade
occasions an accumulation in front of the storm, and an elevation of the
barometer, and tends also to increase the _depression_ under the spot from
which it moves. The latter is, to some extent, counteracted by the thin
sheets of surface wind which are drawn in under the stratus from the
sides. That which is drawn from the front in successive portions, fills
the space from which like portions had been drawn to the westward, and
left behind in a passive state by the passing storm. Thus, the surface
atmosphere of New England may pass under the entire width of a storm, as a
gale; moving now in puffs with great violence, as it passes beneath
irregular and intense portions of the cloud, and now moderately; and be
left, in a passive state, in Kentucky, occupying the space from which the
atmosphere had been previously drawn by the same storm, _in like manner_,
on to northern Texas.
3d. The nearer the stratus-cloud to the earth, the greater the
displacement of surface atmosphere, the lower the barometer, and,
ordinarily, the more violent the wind. First, because the same intensity,
which, by attraction, brings the trade near the earth, acts with greater
force upon the surface atmosphere; and, secondly, the storm winds, which
are often most rapid beneath the clouds and above the earth, are likely to
be felt with more violence at its surface, where the stratus cloud runs
low, especially at sea.
I desire to commend all these facts, in relation to the theory of Mr.
Redfield, to the careful attention and observation of those who, although
believers in the theory, are not wedded to it; and who have a sincere
desire to understand the phenomena which are continually, and thus far,
_mysteriously_, occurring within two or three miles of us, while our
knowledge of the distant worlds around us--the science of astronomy--seems
almost perfect.
I will return to a further and a careful consideration of the nature of
the reciprocal action between the earth and the counter-trade, and the
facts bearing upon the question, in another chapter. It is obvious that
received theories can not aid us materially in the inquiry.
CHAPTER X.
We are yet ignorant of the true nature of magnetism. We trace its lines,
as in the diagrams, upon and around the magnet; but we can only do this
with soft iron, or other substance, in which magnetic action may be
induced. We know that these lines are currents, or lines of force, for
that force produces sensible effects, and we measure it by the movements
of the needle. We know that these lines may be _deflected_ by other
magnetic bodies, and concentrated upon them. We know that the earth, and
the smallest magnets, exhibit properties in common. The poles of the
magnet are some distance from its extreme ends--so are those of the earth.
The intensity increases, from the center, or near it, to the poles of the
magnet, as shown by its attraction; and the same increase of magnetic
intensity, from the magnetic equator to the magnetic poles, or near them,
is traced upon the earth.
We know that there are two lines, or rather _areas_, of greater intensity
upon the globe. One extending from the American magnetic pole,
south-eastwardly, to a corresponding pole in the southern hemisphere; and
another, the Asiatic, extending from the Siberian pole to a corresponding
southern one, in like manner. We know that, from those lines or areas,
the intensity, east and west, on the same parallel of latitude, decreases
each way, to about midway between them. Thus, calling the intensity where
Humboldt found the magnetic equator over South America, in 7° 1' south
latitude, 1, or unity--the least intensity known is, .706, found at the
magnetic equator, over the South Atlantic, and at its most southern
depression; and it increases to 1.4 in the West Indies, and to 2.0099 upon
one or more points of the North American continent, south of the magnetic
pole, and about the meridian of 92°. That it is 1.805, at Warren, Ohio, in
latitude 41° 16', and longitude 72° 57', and decreases to 1.774 at New
Haven, Connecticut, in latitude 41° 18'. That it is but 1.348 at Paris,
nearly one third less than on the same latitude in some portions of this
continent. That the line of equal intensity, or "_iso-dynamic_" line, of
1-8/10, is a closed curve of an oval shape, extending somewhat below 40°,
in the longitude of Cincinnati, and reaches off nearly to Bhering's
Straits, on the west; rising in a similar manner, though not so abruptly,
on the east; including the great northern lakes and a considerable part of
Hudson's Bay. While the iso-dynamic lines of 1-85/100, and 1-875/1000, are
smaller ovals, included within the former. Such, at least, is the present
belief from such investigations as have been made. (See an article by
Professor Loomis, American Journal of Science, new series, vol. iv. p.
192.)
Our subject demands a still closer examination of the elements of
magnetism and its associated electricities, and their influence upon
climate and the atmosphere with a view to the solution of the questions in
hand, and we will pursue the inquiry in the present chapter.
Waiving, for the present, any further notice of the fact that the
counter-trades are concentrated over, and contiguous to, this area of
intensity, for the purpose of examining the magnetic phenomena
independently, and intending to return to a consideration of their
connection with it, we observe:--That it is now well settled that the
iso-geothermal lines, or lines of equal terrestrial heat, are coincident,
or nearly so, with the lines of equal magnetic intensity. The points where
the magnetic intensity is at a minimum, on the magnetic meridian, are the
warmest points of that meridian, and those where it is most intense, the
coldest.
The magnetic elements of a place may be computed from its thermal ones.
The laws producing or governing the distribution of one, have an intimate
physical relation with those producing or governing the other. Professor
Norton ably sums up a discussion of the subject (in the American Journal
of Science for September, 1847), omitting the theoretic propositions, as
follows:
"1. All the magnetic elements of any place on the earth may be
deduced from the thermal elements of the same; and all the great
features of the distribution of the earth's magnetism may be
theoretically derived from certain prominent features in the
distribution of its heat.
"2. Of the magnetic elements, the horizontal intensity is nearly
proportional to the mean temperature, as measured by Fahrenheit's
thermometer; the vertical intensity is nearly proportional to the
difference between the mean temperatures, at two points situated at
equal distances north and south of the place, in a direction
perpendicular to the iso-geothermal line; and, in general, the
direction of the needle is nearly at right angles to the
iso-geothermal line, while the precise course of the inflected line
to which it is perpendicular may be deduced from Brewster's formula
for the temperature, by differentiating and putting the differential
equal to zero.
"3. As a consequence, the laws of the terrestrial distribution of the
physical principles of magnetism and heat must be the same, or nearly
the same; and these principles themselves must have, toward one
another, the most intimate physical relations."
The magnetic elements, of which Professor Norton speaks, are the
declination, dip, and horizontal and vertical forces or intensities.
I have said, that toward the areas of greatest magnetic intensity, the
needle every where declines. So as intensity increases, from the magnetic
equator toward the poles, the needle, when so suspended as to permit of
the motion, _dips_, inclines downward, and the dip is greatest, on the
same parallel, where intensity is greatest. To my mind, the magnetic
elements are very intelligible. They are all attributable to attraction,
and attraction is greatest where intensity is greatest. There is nothing
in the earth or atmosphere to make the needle point northerly rather than
in any other direction, except magnetic intensity. Thus, the greater
intensity of magnetism near the northern and southern points of the globe,
attracts the corresponding ends of the needle in those directions. And, as
magnetism increases in quantity or intensity, and the poles are
approached, the attraction increases, and the needle dips more and more,
till the focus of intensity and attraction is reached, and then it becomes
perpendicular. So magnetism is unequally diffused, meridionally, in or
over the earth, and there are two equidistant areas where its quantity or
intensity is greatest. These exert a lateral attraction upon the needle;
it yields to this attraction, and hence its declination. If it is carried
on to one area of intensity, and to the center of it, it will point to the
northern focus of intensity or magnetic pole; and, if carried a trifle
further west, it will yield to an eastern attraction, and point directly
north. If carried still further west, its declination _east_ will
increase. Thus its normal direction is to the pole, on the central focus
of intensity, and when it points directly north it is west of the central
line of intensity. And thus, it seems to me, all the magnetic elements may
be resolved into the one element of attraction by excess of intensity or
activity.
This impression is strengthened by the fact that the needle moves to the
east in the morning, when the solar rays increase magnetic activity in
that direction, and west again, as their influence increases there.
Now, these elements--the declination and horizontal and vertical
forces--all these periodical, regular, and irregular variations of
magnetic activity, are intimately connected with the variations of
atmospheric condition:
First, They show an increase of activity during certain hours of the day,
corresponding to, and obviously connected with, the diurnal atmospheric
changes.
Second, They show an increase of activity during the northern transit of
the atmospheric machinery--an _annual_ variation.
Third, They show an increase in that activity during the latter portion of
each decennial period, conforming to the occurrence of solar spots.
And, fourth, _Irregular variations_ of activity, corresponding with the
_irregular changes_ of atmospheric condition.
We will examine these results, and in doing so, take those of the element
of declination--one answering for all.
The magnetic needle moves to the west in summer, from about 8 A.M. till
about 2 P.M., and the extent of its progress, during that period,
constitutes the magnitude of its daily variation. It is found that this
variation differs in different months, and that it is normally greatest in
the summer months, and least in the winter, in the ratio of about two to
one. It is further found, that in different years the maximum activity
occurs in different months, and that the years differ also, and there is a
distinctly marked decennial period, corresponding most remarkably with the
decennial maxima of recurring solar spots, as observed by Schwabe. Dr.
Lamont, of Munich, gives us the following table of magnitude of
declination there, for the ten years preceding 1851, which clearly
exhibits this fact, and also the greater intensity during the northern
transit of the atmospheric machinery. He says:
"The magnitude of the variations of declination have a period of ten
years. For five years there is a uniform increase, and during the
following five years a uniform decrease in the variations. With us
the magnetic declination is a minimum at about eight o'clock in the
morning, and is greatest at two o'clock in the afternoon. Subtracting
the declination at eight o'clock from that at two o'clock, we obtain
_the magnitude of the diurnal motion_. From the hourly observations,
conducted in this observatory since the month of August, 1840, we
ascertain the following to be the magnitude of the diurnal motion for
each month separately."
+-------------------------------------------------------------------+
| | Jan. | Feb. | March.| April.| May. | June. | July. | Aug. |
+-------------------------------------------------------------------|
| 1841 | 3.72 | 5.13 | 8.43 | 11.49 | 11.47 | 11.49 | 10.07 | 9.86|
| 1842 | 3.65 | 4.74 | 8.34 | 10.33 | 9.31 | 9.78 | 8.38 | 9.03|
| 1843 | 3.82 | 4.08 | 6.87 | 9.71 | 9.24 | 10.14 | 9.57 | 10.08|
| 1844 | 2.81 | 3.43 | 6.95 | 9.53 | 8.42 | 8.88 | 8.38 | 9.28|
| 1845 | 2.20 | 4.69 | 8.26 | 11.93 | 10.88 | 10.73 | 9.44 | 10.42|
| 1846 | 3.30 | 6.94 | 9.53 | 12.27 | 12.58 | 11.21 | 11.37 | 11.49|
| 1847 | 3.30 | 6.35 | 9.85 | 12.43 | 11.81 | 11.76 | 10.94 | 12.87|
| 1848 | 6.52 | 9.01 | 11.96 | 14.56 | 14.22 | 13.80 | 14.67 | 15.40|
| 1849 | 7.27 | 8.42 | 14.08 | 16.86 | 13.67 | 13.86 | 12.57 | 11.54|
| 1850 | 5.98 | 8.84 | 12.15 | 14.32 | 14.05 | 13.39 | 12.53 | 12.68|
+-------------------------------------------------------------------+
+----------------------------------------------------+
| Sept. | Oct. | Nov. | Dec. | Autmn | Spring| Year.|
| | | | |& Wint.| & Sum.| |
|----------------------------------------------------|
| 8.78 | 6.82 | 3.71 | 2.89 | 5.12 | 10.53 | 7.82|
| 7.72 | 7.05 | 3.86 | 2.81 | 5.07 | 9.09 | 7.03|
| 8.81 | 6.82 | 3.82 | 2.79 | 4.70 | 9.59 | 7.15|
| 8.23 | 6.54 | 3.94 | 2.98 | 4.44 | 8.79 | 6.61|
| 8.82 | 7.34 | 4.49 | 8.34 | 5.89 | 10.87 | 8.13|
| 10.39 | 7.82 | 5.66 | 3.22 | 6.08 | 11.25 | 8.81|
| 12.06 | 11.53 | 7.06 | 4.70 | 7.63 | 11.98 | 9.55|
| 14.00 | 10.30 | 5.78 | 3.53 | 7.85 | 14.44 | 11.05|
| 10.79 | 9.12 | 5.41 | 4.09 | 8.06 | 13.21 | 10.64|
| 12.64 | 9.04 | 6.20 | 3.45 | 7.61 | 13.27 | 10.44|
+----------------------------------------------------+
The Philadelphia and Toronto observations disclose the same state of
facts.
Dr. Lamont, also, in his article, gives us the following table of the
magnitude of the variations derived from observations at Gottingen:
+--------------------+
| Year.|Mean of Year.|
|--------------------|
| 1835 | 9.57 |
| 1836 | 12.34 |
| 1837 | 12.27 |
| 1838 | 12.79 |
| 1839 | 11.03 |
| 1840 | 9.91 |
| 1841 | 8.70 |
+--------------------+
A comparison of these tables, and particularly the latter, with Schwabe's
table of spots, is interesting. There is obviously a greater mean
variation when the spots are most numerous. Comparing the two with the
tables of Hildreth, in relation to the temperature, from 1830 to 1840,
there is, to say the least, a most remarkable coincidence. And there are
others equally remarkable.
There are also irregularities of action disclosed by all, in different
months of the different years, and of the same year, which are obviously
connected with the difference of the seasons; and there are constantly
occurring irregularities and disturbances which correspond with the, as
constantly occurring, irregular atmospheric phenomena. A wide field is
here opened for investigation and research. I have not time or opportunity
to pursue it. Enough appears, so far as I have examined, to confirm the
belief that magnetism is actively concerned in the production of the
varied changes, as well as the normal conditions of the weather.
In what manner does it act? An answer to this requires an extension of the
inquiry. The lines of magnetic force are every instant passing upward from
the earth, _around_ and _through_ us. Their connection with heat is
unquestionable. They are intimately associated, also, with another equally
obvious and intensely active agent--electricity. We speak of this as an
independent, imponderable, elementary body, but how little we yet know of
it. It is every where, in every thing, easily excited into action, and
then traceable to a certain, but limited extent. It is set in motion, and
becomes obvious to us, by the chemical action of the acids and metals of
a galvanic apparatus. We separate it from the atmosphere by friction and
excitation, upon non-conductors, as in the electric machine; by the
cleavage of crystals and other exciting operations. We obtain it from
magnets, by the magneto-electric machine, and from the lines of magnetic
force which are ever passing into the atmosphere from the earth, by
intersecting them with a movable iron wire, properly insulated. _From the
current of magnetism which has passed through us from the earth,
electricity may thus be separated and collected over our heads._ We set it
in motion, and obtain it _by heating_ different metals in connection, or
the same metal unequally; and from certain animals--like the torpedo and
the gymnotus--whose organization is such as to enable them to evolve it.
In all these cases, and they constitute an epitome of the principal
methods by which we obtain it in a distinct form, it is made to flow in
currents. When thus obtained, and imprisoned in non-conductors, it may be
discharged, and with somewhat different effect, as it is discharged in a
mass, disruptively, as it is called, as from the clouds in lightning, or
permitted to flow convectively, in currents, along the wires of a galvanic
apparatus, or in heated air, as from the earth to a cloud in the tornado.
It is, moreover, capable of division into positive and negative, and when
concentrated or disturbed in one body, it tends to create a similar
disturbance or division in a contiguous mass. To this action of
electricity, the term static induction is applied. Thus, a positively
electrified body _induces_ a division of the electricity in a contiguous
body, if both are insulated or surrounded by a non-conducting medium; the
negative electricity of the contiguous body being attracted by, and
tending to pass to, the positive of the adjoining body, and the positive
being repelled to the opposite side. That, in its turn, if sufficiently
powerful, tends to disturb the electricity of its neighbor, and attract
away its negative electricity; or, if the body which contains it is free
to move, to attract that. Thus, by the conflicting action of a positive
atmosphere, and a negative earth, and perhaps counter-trade, influenced by
magnetism and the solar rays, the currents and winds of the atmosphere are
produced, the atmosphere moving with exceeding ease and rapidity.
Electricity, excited into currents, or obtained and discharged in either
of the methods enumerated, is identical in character, and produces certain
well-known effects:
1st. Physiological.--Shocking and convulsing the animal system; producing
a peculiar sensation on the tongue, and a flash before the eyes, and in
sufficient quantity destroying life.
2d. Magnetic.--_Deflecting the needle_, and, by a suitable arrangement of
wire into helices, _conferring magnetic power_, or constituting magnets.
3d. Luminous.--Producing light--by a spark, as it does in natural
phenomena--by the glow, the brush discharge, the ball of flame, the flash,
or the chain of lightning, and probably the aurora.
4th. Evolving heat.--Melting metallic substances by concentration, with a
great intensity of heat--as the wire of the galvanic apparatus, and as is
sometimes seen in the effects of lightning in fusing metals on persons
stricken; and setting combustibles on fire.
5th. Attraction and repulsion.--Attraction, when the currents flow
parallel with each other, or are of opposite natures, and repelling when
of like character.
6th. Induction.--Inducing attendant circular or other secondary currents,
such as may be seen in the atmosphere during its most violent displays of
active energy.
7th. Capable of being dissipated by heated air, or carried off by
moisture, although isolated by dry air, of ordinary temperature, which is
a bad conductor.
Now, although magnetism can not be collected, imprisoned, or discharged,
like electricity, or collected at all, but by its adherence to some
substance capable of magnetization, it is obvious there is an intimate
association, at least, between it and electricity. _They are never found
alone._ All _electricity_ will _magnetize_. All _magnetism_ will evolve
electricity. All _currents_ of _electricity_ have _encircling currents_ of
_magnetism_, and all deflect the magnetic needle. All magnetic currents
give out to intersecting wires, _currents of electricity_, and all magnets
_induce_ them.
Electricity, therefore, whether identical in substance with magnetism, but
differing in form, or whether merely associated with it, as is variously
believed, should be present with magnetism in greater quantity or
intensity where magnetism is most intense, and active, and whenever
present, should be active and influential. And so we find, from
observation, the fact to be. No inconsiderable effort has been made by the
advocates of the caloric and mechanical theories, to ignore the agency of
electricity and of magnetism, in the production of the varied
meteorological phenomena. But it will not do. The phenomena, grouped and
analyzed, disclose a potential-controlling, magneto-electric agency, and
meteorology will advance rapidly to perfection, as a simple, intelligible,
and practical science, _as soon as that agency is admitted_.
Electricity is always perceptibly present in storms and showers within the
tropics. Most of the rain, from the tropical belt, falls from "thunder
showers." So hurricanes and typhoons, and all tropical storms, are
confessedly, and in proportion to their intensity, "_highly electric_."
This excess of quantity or activity of electricity, exists in connection
with the movable atmospheric machinery. When it moves up north in summer,
and arrives at its highest point of northern transit, _storms_ are very
_uncommon_, and the tropical forms of cloud and showers, with thunder and
lightning, prevail. This is most obvious, if not most influential, where
the magnetic intensity is greatest. Violent showers, and gusts, and
tornadoes, are more frequent in this country than in Europe; and over the
area of greatest intensity, as in Ohio, than at a distance on the extreme
eastern or western coast. And the same is true over the intense magnetic
area of Asia.
Electricity, too, like magnetism, has its diurnal, and doubtless its
annual and decennial variations, and also its irregular ones, and they are
most obviously and intimately connected. Magnetism and electricity
together, constitute the aurora. Its culmination is in the magnetic
meridian--it affects the telegraph wires--is connected with the irregular
disturbances which affect the magnetic needle, and does not exist in the
limits of the trades, although occasionally seen from thence, when it
passes south, and near them.
The aurora sometimes extends south in waves, as do the magneto-electric,
atmospheric, periodical changes of cold and heat, and storm, and sunshine.
_The aurora is connected with the formation of cloud_, and with a smoky
atmosphere, similar to that with which we are familiar in summer and
autumn. Thus Humboldt (Cosmos, vol. i. pp. 191, 192).
"This connection of the polar light with the most delicate cirrus clouds,
deserves special attention, because it shows that the electro-magnetic
evolution of light is a part of a meteorological process. Terrestrial
magnetism here manifests its influence on the atmosphere, and on the
condensation of aqueous vapor. The fleecy clouds seen in Iceland, by
Thienemann, and which he considered to be the northern light, have been
seen in recent times by Franklin and Richardson, near the American north
pole, and by Admiral Wrangel on the Siberian coast of the Polar Sea. All
remarked 'that the aurora flashed forth in the most vivid beams when
masses of cirrus-strata were hovering in the upper regions of the air, and
when these were so thin that their presence could only be recognized by
the formation of a halo round the moon.' These clouds sometimes range
themselves, even by day, in a similar manner to the beams of the aurora,
and then disturb the course of the magnetic needle in the same manner as
the latter. On the morning after every distinct nocturnal aurora, the same
superimposed strata of clouds have still been observed that had previously
been luminous. The apparently converging polar zones (streaks of clouds in
the direction of the magnetic meridian), which constantly occupied my
attention during my journeys on the elevated plateaux of Mexico, and in
northern Asia, belong, probably, to the same group of diurnal phenomena."
Mr. William Stevenson gives us (in the London, Edinburgh, and Dublin
Philosophical Magazine for July, 1853) an interesting article on the
connection between aurora and clouds. His observations on this most
important branch of the subject trace a connection between the aurora and
the formation of cloud, and open up, as he says, "a most interesting field
for observation which promises to lead to very important results." Such
observations point with great significance, to the primary influence of
the magneto-electricity of the earth.
To the difference in the magnetic intensity of the eastern portion of this
continent, compared with Europe and our western coast, very much of the
difference of climate, so far as temperature is involved, may be
attributed. We have seen in what manner the iso-thermal lines surround
these areas of intensity. So the most excessive climate--that is, the
climate where the greatest extremes alternate, other things being equal,
is upon or near the line or area of greatest magnetic intensity. I say
other things being equal, because large bodies of water modify climates by
equalizing the seasons--making the summers cooler and the winters warmer
than the mean of the parallel.
Thus, our great interior lakes modify the climate in relation to
temperature in their vicinity. Their summers are cooler and their winters
warmer; but westward of them the same line of equal summer temperature, or
iso-thermal line, rises with considerable abruptness, and the winter, or
iso-cheimal line of equal temperature, falls in a similar manner. Thus,
the range of the thermometer, from the highest elevation to the lowest
depression, for the year, is very great, while in the tropics the range is
comparatively small. From observations made at the military posts of the
United States, Dr. Forrey deduced summer and winter lines of equal
temperature, starting from the vicinity of Boston and running west, which
showed most remarkably the rise of the summer lines as intensity
increased, and the fall of the winter lines in like manner.
The influence of the lakes was also most obvious. The elevation of the
earth increases, going west, to about 700 feet at the surface of the
lakes, and to nearly 4,000 feet at the eastern base of the Rocky
Mountains; and, although temperature does not decrease to as great a
degree when the elevation above the level of the sea is _gradual_, yet
some allowance should doubtless be made for that elevation on this line.
When that allowance is made, the ascent of the summer line, to the north,
over the area of greatest intensity, is strikingly apparent.
Dr. Forrey also instituted a comparison between Fort Snelling, where the
climate is as excessive, and the range of the thermometer as great, as in
any portion of the continent in the same latitude, with Key West, and I
copy his diagram. It is very instructive, showing the gradual mean rise of
the temperature, from January to December, inclusive, while the cross
lines show the _extremes of each month_.
Perhaps the most interesting part of it, is the illustration of the
monthly extremes, and the contrast between them, in the excessive climate
of Fort Snelling, and the tropical one of Key West. Each is a type of the
climate in which it is situated. The annual range and monthly extremes are
small in tropical countries, and large in extra-tropical ones. The extreme
range, or greatest elevation of heat, contrary to what is generally
supposed, is greater at Fort Snelling than at Key West. But the climate of
the latter is modified by the adjoining ocean.
I copy, also, a table (p. 304), showing the range of the thermometer for
the year, and the maxima and minima, during each month, at several other
places in this country, and at London and Rome, for the purpose of showing
the extent of the ranges compared with those places; and also, that these
great changes in each month occur very uniformly all over the country,
and may always be expected, and with considerable regularity. They are
incident to our climate. I wish I could engrave the foregoing diagram, and
the following table, upon the mind of every man, woman, and child in the
country; and under it, in ever-visible letters, these words of precaution:
CONFORM TO THE PECULIARITIES OF YOUR CLIMATE, AND CLOTHE YOURSELVES, AT
ALL TIMES, IN ACCORDANCE WITH THE ALTERNATIONS OF THE WEATHER. If heeded,
they would save thousands, every year, from premature death.
[Illustration: Fig. 18.]
The effect of this difference of magnetic intensity upon the climate of
Europe is marked. There, the excessive summer heat, which our greater
magnetic intensity and larger volume of counter trade give us, is unknown.
Hence, while we can grow Indian corn (which requires the excessive summer
heat) over all the Eastern States, up to 45°, and in some localities east
of the lakes to 47° 30', and to 50° west of them, to the base of the Rocky
Mountains, and notwithstanding the increase of elevation, they can not
grow it except over a limited area, and with limited success. Nor can
they, or the inhabitants of any other country except China, grow
profitably the kind of cotton which is so successfully grown in the
Southern States of the Union. Nor can China do so to a considerable
extent, because of the mountainous character of the surface. To a level
and remarkably watered country, greater magnetic and electric intensity,
and a greater volume of counter-trade, we are, and ever shall remain,
indebted, for an almost exclusive monopoly in the growth of two of the
most important staple productions of the earth. On the other hand,
although the same magnetic intensity, and its winter excess of positive
electricity and cold, make our winters extreme, there are but few of the
productions of temperate latitudes which we can not grow successfully, and
they are comparatively unimportant.
A Fort Vancouver, Oregon Territory
B Fort Brady, outlet of Lake Sup.
C Hancock Barracks, Houlton, Me.
D Fort Armstrong, Rock Island, Ill.
E West Point, New York
F Washington, D. C.
G Jefferson Barracks, near St. Louis
H Fort King, interior of East Florid.
I Environs of London
K Rome, Italy
A B C D E F H I J K
Lat. 45° 46° 46° 41° 41° 38° 38° 29° 51° 41°
37' 39' 10' 28' 22' 53' 28' 12' 31' 54'
Annual
Range. 78 110 118 106 91 84 89 78 67 62
Jan. Min. 17 -21 -24 -10 -1 14 10 33 16 29
Max. 58 40 41 48 53 57 60 83 49 58
Feb. Min. 32 -22 -11 -6 2 16 11 43 19 33
Max. 55 44 42 56 56 62 70 84 54 60
Mar. Min. 32 -7 -1 13 16 28 31 39 24 37
Max. 60 51 54 70 72 70 76 87 60 65
Apr. Min. 32 18 24 33 40 36 38 54 26 44
Max. 70 62 74 78 62 73 83 93 69 74
May. Min. 32 32 81 44 47 50 45 64 33 52
Max. 75 79 83 84 72 85 88 97 78 80
June. Min. 45 41 38 57 57 59 59 73 39 60
Max. 95 86 90 89 79 92 95 105 80 88
July. Min. 40 39 45 62 64 64 50 73 41 64
Max. 95 84 90 95 86 94 96 102 83 91
Aug. Min. 44 49 46 60 62 63 66 72 42 62
Max. 95 84 85 91 87 93 96 104 79 91
Sept. Min. 43 40 33 51 56 51 51 70 34 55
Max. 88 75 78 87 83 88 88 99 75 85
Oct. Min. 50 27 24 82 42 33 38 41 30 46
Max. 66 70 72 73 69 77 80 91 68 77
Nov. Min. 32 15 4 26 36 28 27 30 22 39
Max. 58 58 60 64 63 66 69 82 56 67
Dec. Min. 32 -7 -4 15 20 17 14 36 20 31
Max. 55 42 53 62 56 61 64 79 53 60
This excess of magnetic intensity and electricity not only gives a
peculiar character to our vegetation, but also to our race, our animals,
and every thing. He who supposes that the restless activity and energy of
the people of the United States is the result of habit, or education, or
any fortuitous circumstances alone, is mistaken. Let him watch the
contrast in his own feelings during those occasional languid, damp, and
sultry, although not thermometrically, hot days--which so much resemble
the summer weather of England--with those days of bright, bracing, N. W.
and S. W. air, so much more frequent here, and he will appreciate the
difference. That term "bracing," so much in use, will express the effect
of this peculiar weather. It "girds up the loins," both of body and mind.
Men and animals can work with more ease, even in our peculiar extremes of
heat, than they can in England, and fatten with less.
A similar difference in degree is found between our climate and that of
the Pacific portion of our country. Something is due to the difference in
the volume and moisture of the counter-trades, and something to the
contiguity of the Pacific Ocean; but to the difference in
magneto-electric intensity, the contrast is mainly due. Corn and cotton
will be grown, to some extent, in the valleys west of the meridian of
105°, but never as successfully as east of it.
The aurora is periodical, like all the other atmospheric phenomena, but
its periodicity is not accurately ascertained. It is believed to have
occurred much oftener during the second quarter of this century, than
during the first. It is known, however, to occur most frequently in the
spring and fall; and during those periods when the active and rapid
transit of the atmospheric machinery produces the greatest degree of
magnetic disturbance. This identifies it with terrestrial magnetism.
Dalton gives us the following table of observations, arranged according to
the months when they were seen.
Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.
(1) 18 18 26 32 21 5 2 21 23 36 38 9
(2) 21 18 23 13 3 2 1 3 35 22 22 21
(3) 21 27 22 12 1 5 7 9 34 50 26 15
(4) 5 6 4 8 10 7 6 14 14 17 5 6
(1) contains those observed by him at Kendall; (2) are taken from another
list; (3) is MARIAN'S list of those observed before 1732; and (4), those
seen in the State of New York in 1828 and 1830.
Mr. Stevenson's table of those observed by him at Dunse, from 1838 to
1847, inclusive, is as follows:
Jan. Feb. Mar. Apr. May. June. July. Aug. Sept. Oct. Nov. Dec.
32 20 18 18 3 0 2 14 43 34 30 23
Observations in this country correspond substantially with the foregoing.
They are, however, seen here in the summer months more frequently than in
Europe. See an article by Mr. Herrick (American Journal of Science, vol.
33. p. 297). In this, also, they conform to our greater magnetic intensity
and more excessive climate.
The auroras appear to follow the polar belts of condensation and
precipitation. Dalton considers them indications of fair weather. They are
often most brilliant just after a storm has passed, but their continuance
is no indication that another will not follow within the usual period.
The condensation with which the aurora is connected, is not, in my
judgment, often in the counter-trade, or below it, but above, where feeble
condensation has been seen by aeronauts when invisible at the surface of
the earth. Neither the height of this condensation, not that of the
aurora, have been satisfactorily ascertained. The aurora of April 7th,
1847, was a favorable one for observation. It was carefully and
attentively watched by Professor Olmsted, Mr. Herrick, Dr. Ellsworth, and
others, and they are intelligent and skillful observers.[9] But the nature
of the aurora forbids reliance on parallax, or measurements founded on the
time when, any portion of the bow or arch rises in range of a particular
star. The bow or arch moves southwardly, but the same rays or currents do
not. The wave of magnetic _activity_ moves south, and each successive
current, as it is reached by the _impulse_, becomes luminous. Hence the
observers, when distant, do not see, at the same time, or at different
times, the same rays. The phenomenon is unquestionably magneto-electric.
Electricity becomes luminous in a vacuum, and De la Rive, by combining the
electric currents with those of magnetism, produced all the peculiarities
of the aurora. The magnetic currents, passing from the earth, have
associated electric ones in connection, and these, in the upper attenuated
atmosphere, become luminous. Whether, as De La Rive supposes, by combining
with the positive electricity existing there, or because the associated
electric currents are _then_ in excess, not being intercepted by
atmospheric vapor and returned to the earth in rain, we can not know, nor
is it very important we should.
Having thus taken a general view of the nature of magnetism and its
associated electricities, and their connection with the general and
obvious peculiarities of climate, let us approach more nearly the varied
atmospheric phenomena, resulting from variations of pressure, temperature,
condensation, and wind, and give them a closer consideration. They all
have regularity and periodicity--they all occur in degree, and in
connection with magnetism and electricity, during the twenty-four hours of
every serene and normal summer's day. Grouped together, in comparison with
the changes in the activity and force of the magnetic elements, their
connection is clearly discernible.
The day may be said, with truth, to commence, in some portion of the
summer, at 4 A.M. The atmospheric does at all seasons. At that hour the
barometer is at its morning minimum. It has, as we have said, a
perceptible diurnal variation of two maxima and two minima. Its periods of
depression are at 4 A.M., and 4 P.M., and of elevation at 10 A.M., and 10
P.M. The difference between the elevation and depression is considerable
within the tropics, where Humboldt tells us the hour of the day can be
known by the height of the barometer, and it decreases toward the poles.
At 4 A.M. it is then at one of its minima, and rises till 10 o'clock.
At, or about the same period, and sometimes when the barometer is falling,
and previous thereto, there is a tendency to fog in localities subject to
that condensation. This tendency is sometimes observed at the other
barometric minimum, late in the afternoon or early in the evening, but
less frequently. The tendency to fog condensation is greatest in this
country about the morning minimum. It seems to be owing to the influence
of the earth; it is confined to the surface atmosphere, and is apparently
produced by the inductive agency of the negative electricity of the earth.
It disappears, whether it be high or low fog, about the time when the
barometer attains its morning maximum, or about 10 A.M.
At about that period, when there has been fog, or earlier, when there has
not, and sometimes as early as 8 A.M., there is a tendency to trade
condensation--cirrus in mid-winter, and a cumulus in mid-summer, and,
during the intermediate time, a tendency to cirro-stratus, partaking more
or less of the character of one or the other, according to the season.
Temperature, in summer, commences its diurnal elevation about 4 A.M.,
also, and rises till about 2 P.M. From that time it falls with very little
variation till 4 o'clock the next morning. It has but one maximum and one
minimum in the twenty-four hours.
As the morning barometric maximum approaches, and the heat increases the
magnetic activity, condensation in the trade appears, or induced
condensation in the upper portion of the surface atmosphere, that portion
near the earth is affected and attracted--and the "wind rises," according
to the locality, the season, and the activity of the condensation. The
tendency to blow increases with the tendency to trade and cumulus
condensation, and continues till toward night, when it gradually dies
away, unless there be a storm approaching. As the heat increases, and
stimulates magnetism into activity, the magnetic needle commences moving
to the west, its regular diurnal variation, and continues to do so until
about 2 P.M., when it commences returning to the east, and so continues to
return until 10 P.M., when it moves west again until 2 A.M., and from
thence to the east, till 8 A.M.
Similar variations also take place in the horizontal force, as evinced by
the action of the magnetometer needle, and in the vertical force, as shown
by the oscillations. So that it is evident that there are two maxima, and
two minima of magnetic activity every day, shown by all the methods by
which we measure magnetic action and force--more than double at the acme
of northern summer transit over that of winter, and proceeding _pari
passu_, with the other daily phenomena--evincing the same irregular action
which the other phenomena evince. Still another phenomenon, which has a
daily change, is electric tension, or the increase or decrease in the
tension of the positive or true atmospheric electricity.
[Illustration: Fig. 19.]
The following table shows the mean two hourly tensions for three years, at
Kew, viz.:
Hours 12 P.M. 2 A.M. 4 A.M. 6 A.M. 8 A.M. 10 A.M.
Number of observations 655 784 804 566 1,047 1,013
Tension 22.6 20.1 20.5 34.2 68.2 88.1
Hours 12 A.M. 2 P.M. 4 P.M. 6 P.M. 8 P.M. 10 P.M.
Number of observations 848 858 878 874 878 1,007
Tension 75.4 71.5 69.1 84.8 102.4 104
From this it will be seen that the tension of electricity is at a minimum
at 4 A.M., also, that it rises till 10, falls till 4 P.M., but not as
rapidly, rises till 10, falls again till 4 A.M., or the close of the
meteorological day--having two maxima and minima, as have most of the
phenomena thus far considered.
In order to see what the connections between these ever-present, daily
phenomena are, and their connection with other phenomena, and that we may
understand their normal conditions, I will trace them approximately in a
diagram (figure 17.)
The foregoing diagram of the daily phenomena of a summer's day, when no
disturbing causes are in operation, no storm existing within influential
distance, and no unusual intensity or irregular action of any of the
forces present, affords a basis for considering the various phenomena of
the weather in all its changes and conditions.
It is obvious that the other phenomena do not all depend upon temperature
merely, if indeed any of them do.
Temperature has but one maximum and minimum, and that is exceedingly
regular, and does not correspond with any other.
The barometer has two; electric tension, two; magnetic activity, two;
condensation, two--one the formation of cloud, and the other the formation
of fog and dew; wind, one--resembling temperature in that respect, but
embracing a much less period.
Fog forms at one barometric minimum, and cloud at another.
Fog forms at one period of the magnetic variation, cloud at another.
The formation of cloud corresponds with the greatest intensity of magnetic
action, and its associate electricities. But the oscillations of the
barometer do not correspond with either. And thus, then, we connect them:
CAUSE. | EFFECT. | EFFECT.
| |
Increase of magnetic|Decrease of pressure. |Increase of primary
or magneto-electric | |condensation.
activity, as shown |Of positive electric |
by declination and |tension. |Of wind.
increase of | |
horizontal and |Of surface condensation,|Of electrical disturbance
vertical force. |_i. e._, fog and dew. |and phenomena in the
| |trade and its vicinity.
This connection is equally obvious if the order is reversed--thus;
CAUSE. | EFFECT. | EFFECT.
| |
Decrease of magnetic|Increase of pressure. |Disappearance of primary
or magneto-electric | |condensation.
activity. |Of tension of |
|atmospheric electricity.|Of wind, and
| |
|Of surface condensation,|Of electric disturbance
|_i. e._, fog and dew. |in the trade and its
| |vicinity.
If we examine still more particularly the different phenomena, we shall
find the same relative action of the forces carried into all the
atmospheric conditions, however violent.
1. The barometer falls when horizontal magnetic force, and a tendency to
cloud and wind, increase; and rises when they decrease. This corresponds
with the character of the irregular barometric oscillation. Barometric
depressions accompany clouds and winds, and are in proportion to them, and
are all greatest where magnetic force is greatest. The barometer also
rises as the magnetic energy decreases. Do the magnetic currents, passing
upward with increased force, lift, elevate the atmosphere? How, then, are
we to explain the increased range of the oscillations, as the center of
atmospheric machinery is reached, where magnetism has least intensity, and
the perpendicular currents are less, and attraction is less? Attraction is
greatest where intensity is greatest, and there the barometer stands
highest, and the diurnal range is least. Is it then the attraction of
magnetism which produces the barometric oscillations? If so, how then can
we explain the diurnal fall while magnetism is most active?
Perhaps we have not yet arrived at such a knowledge of the nature of
magnetism as is necessary to a correct answer of those questions. Faraday
has taught us that the lines of magnetic force are close curves, passing
into the atmosphere, and over to the opposite hemisphere, and returning
through the earth, out on the opposite side in like manner, and back
again, passing twice through the earth and twice through the atmosphere.
All we know of this is what the iron filings indicate, and we do not know
how much reliance to place upon the indications they give. But if Faraday
is right, the sun will, twice each day, intersect and stimulate into
increased activity the same closed magnetic curve--once when it is coming
out of the earth, during our day, when its influence will be the most
active, and once when it is returning on the opposite side of the earth;
and a second, but feebler magnetic and electric maximum, may be occasioned
by its action on the opposite and returning closed curve of the same
current. However this may be, it is exceedingly difficult to conceive, of
any adequate influence exerted by the tension of vapor.
So the mid-day barometric minimum may be caused by the attraction of the
earth, in a state of increased magnetic activity and intensity, upon the
counter-trade, and its consequent approach or settling toward the earth.
Observation, as I have already said, pointedly indicates such a state of
things. So the increased magnetic activity, with or by its associate
electricity, acts upon the electricity of the counter-trade, condensation
takes place, the electricity is disturbed in the surface-atmosphere, by
induction, and its tension is changed. Opposite electrical conditions are
induced in the surface strata, and attraction takes place. The air moves
easily, and thus the attractions originate the winds. Secondary currents
are induced, as in all other cases of electric activity, and winds, in
_different strata_ and directions, occur, with or without cumulus, or scud
condensation, according to their activity, and the proportion of moisture
of evaporation they may contain.
I am well aware that the various received theories of meteorology
attribute condensation to the action of cold, mingling of colder strata,
etc. But I think that view will have to be abandoned.
It assumes that moisture is evaporated and held in the atmosphere by
latent heat, which is given out during condensation, and actually warms
the surrounding atmosphere. Thus, the Kew Committee undertook to explain
the development of greater heat, at the elevation where they, in fact,
found the counter-trade. But how unphilosophical to suppose a portion of
the air or vapor contained in it, can give out to another adjoining
portion _more heat than is necessary to produce an equilibrium_. This can,
indeed, be done by experiment--_but the experiment is made with currents
of electricity_. How unphilosophical, too, to talk of latent heat in
connection with evaporation, _at the lowest temperature known_.
Meteorologists must revise their opinions on the subject of condensation.
This latent heat has never been actually met with; on the contrary, the
most sudden and complete condensations of the vapor of the atmosphere are
attended by as sudden and extraordinary productions of cold, and
consequent hail, and the connection between condensation and electricity
is shown by too many facts to permit the old theory to stand.
_Fog never forms with the thermometer below 32°._ It is mainly a _summer
condensation_, especially high fog. It has been attributed to the cooling
effect of an atmosphere colder than the earth, but it often occurs when
the earth is the coldest, and when the vapor, as it rises, is colder than
the air, and could not give out heat to a warmer medium. (See American
Journal of Science, vol. xliv. p. 40.) Again, it is not mere condensation,
but a formation of globules or vesicles, hollow, and the air expanded in
them, by means of which they float like a soap bubble which contains the
warm air of the breath. Is not every vesicle a model shower, positively
electrified on the outside, negatively in the center, or the reverse,
according to the strata, with the air expanded in the middle by the excess
of heat which negative electricity detains? Look at them, as they attach
themselves to the slender nap of the cloth you wear, when passing through
them, and see how many of them it would require to form a large drop of
rain. The clouds are of a similar vesicular character, and rain does not
fall till the vesicles unite to form drops. Sudden and extreme cold is
indeed produced in the hail-storm, when, above, below, and around it, the
temperature is unaffected. Testu, Wise, and other aeronauts, have so found
it, and the hail tells us it is so. But it is idle to say it results from
radiation. All the phenomena of the sudden, violent hail-storms are
electric in an extraordinary degree. The electricity is disturbed and
separated--the associated heat continues with the negative, and leaves the
positive portion of the cloud, and a corresponding reduction of
temperature results. So Masson found in his eudiometrical analytical
experiments the _negative_ wire would heat to fusion, while the positive
was cold. (See London, Edinburgh, and Dublin Journal of Science for
December, 1853.) This disturbed electricity is diffused over the vesicles.
Listen to the thousand _crackling_ sounds which initiate the clap of
thunder, and may be heard when the lightning strikes near you; produced by
the gathering of the lightning from as many points of the cloud where it
was diffused, to unite in one current and produce the "clap" or
"peal"--and to the "pouring" of the rain, which follows the union of the
vesicles, after the excess of repelling electricity is discharged.
No _change_ of temperature is observed when fogs form, except the ordinary
change between night and day; and it seems perfectly obvious, in looking
at all the phenomena, that fogs form at a temperature of 70° or 75°, in
consequence of the electric influence of the earth upon the adjoining
surface-atmosphere; and, when formed, they withstand the most intense
action of a summer sun, till the time of day arrives for the barometric
and electric tension to fall, condensation to take place in the
counter-trade above, and wind to be induced. Who that has noticed the
almost blistering force of the solar rays, as they break through a section
of high fog, about 10 A.M., can forget them.
Fogs form near the earth, during the night, when the atmosphere above is
loaded with moisture many degrees colder, and yet remains free from
condensation. On the other hand, during the heat of the day, and of the
hottest days, the heavy rains condense above--nay, they frequently fall at
a temperature of 75° to 80°, in the tropics, and of 50° to 55° in
mid-winter here.
Thus far, an adherence to the opinion that condensation was simply a
cooling process; the driving out of its latent heat, not merely to another
body to make an equilibrium, but "_getting rid of it_" by positive active
radiation, or in some other way, so as to cool off and condense, has
involved the formation and classification of clouds in obscurity. Hopkins
(Atmospheric Changes, p. 331) laments this, but fettered by a false and
imperfect theory, in relation to the tension of vapor, he falls into a
similar error.
Now, there are, as we have seen, peculiar, distinctly-marked varieties of
cloud, connected with peculiar and distinctly-marked conditions of the
atmosphere, _irrespective of temperature_. None of the theories advanced,
account, or profess to account for the differences in either. No
modification of the calorific theory will account for them. They differ in
shape, in color, in tendency to precipitation, in line of progress, and in
electrical character. The explanation of this is found in the fact, that
they form in distinct and different strata, partake of the positive
electric character of the one, or the negative of the other; or are
secondary, induced by the action of a primary condensation in a different
stratum. There is not any mingling of the different strata, as has been
supposed; and many other facts than those to which we have alluded, show
that the formation of cloud is a magneto-electric process.
The observations of Reid show that every violent shower cloud has the
electricities disturbed, and portions of it are positive, and others
negative. Howard gives us the following _résumé_ of Reid's observations:
"From an attentive examination of Reid's observations I have been
able to deduce the following general results:
"1. _The positive electricity, common to fair weather, often yields
to a negative state before rain._
"2. _In general, the rain that first falls, after a depression of the
barometer, is_ NEGATIVE.
"3. _Above forty cases of rain, in one hundred, give negative_
electricity; although the state of the atmosphere is positive, before
and afterward.
"4. _Positive rain, in a positive atmosphere, occurs more rarely_:
perhaps fifteen times in one hundred.
"5. _Snow and hail, unmixed with rain, are positive, almost without
exception._
"6. _Nearly forty cases of rain, in one hundred, affected the
apparatus with both kinds_ of electricity; sometimes with an
interval, in which no rain fell; and so, that a positive shower was
succeeded by a negative; and, _vice versâ_; at others, the two kinds
alternately took place during the same shower; and, it should seem,
_with a space of non-electric rain between them_."
Howard attributes, with great apparent probability, the successive
differences in the electrical character of the rain, to the passage of
different portions of the cloud, having different polarity, over the place
of observation. So _positive hail_, and _negative rain_ fall in _parallel
bands_ from the same cloud. Many such instances are on record. It should
be remembered that he is describing the phenomena in the showery climate
of England.
But the most decisive, perhaps, as well as practically important evidence
of the influence of magnetism, or magneto-electricity, in meteorological
phenomena, is derived from the action of storms. My observation has been
limited, for my life has been, and must be, a practical one. But, subject
to future, and I hope speedy corroboration, or correction, by extensive
systematic observation, I think I may venture to divide all storms into
four kinds:
1. Those which come to us from the tropics, and constitute the class
investigated by Mr. Redfield. That these are of a magneto-electric
character is evident. They originate near the line of magnetic intensity,
over, or in the vicinity of, the volcanic islands of the tropics; are
largely accompanied by electrical phenomena; extend laterally as they
progress north; induce and create a change of temperature in advance of
them, and do not abate until they pass off over the Atlantic to the E. or
N. E., and perhaps not until they reach the Arctic circle. Their extensive
and continued action is not owing to any mere _mechanical agency_ of the
adjoining passive air, or other supposed currents, originated, no man can
tell how, but they concentrate upon themselves the local magnetic currents
as they pass over and intersect them, and, by their inductive action upon
the surface-atmosphere, in different directions, attract it under them,
and within their more active influence. Here the action of the magnetic
currents is probably the primary cause, but the power of the storm to
concentrate upon itself the new magnetic currents which it intersects as
it enters each new, successive field, enables them to maintain and extend
their action.
The following diagram illustrates the course and gradual enlargement of a
mid-autumn tropical storm, which induces a S. E. wind in front, and
occasions a thaw.
[Illustration: Fig. 20.]
2. Another class originate at the N. W., and extend gradually south
easterly on the magnetic meridian. These are most frequent in summer,
forming belts of showers, but occur, I believe, at all seasons of the
year. They seem to be produced by magnetic waves passing south, and are
followed in autumn and winter, and sometimes in summer, by the peculiar N.
W. wind and scud, and a term of cooler weather.
Thus, it is believed that many, perhaps all of the alternating terms of
heat and cold, are dependent on magnetic waves passing over the country in
a similar manner, with a greater or less belt of condensation between
them, and depending on peculiar magnetic action traveling in the same
way. The S. E. extension of showers and storms, and the cooler changes of
temperature which immediately follow them; with light N. W. wind in
mid-summer, and with it fresher at earlier and later periods, in the form
of northers blowing violently, according to the season, are intimately
connected, and indicate such waves. The indication is strengthened also by
the frequent progress of auroras in like manner, occurring usually after
the belt of condensation has passed, and frequently following it. The
clouds and currents of the atmosphere, so far as I have been able to
discover, show no permanent current from the pole to the atmospheric
equator, compensating for the counter-trade; and that compensation is
furnished by the periodical but frequent atmospheric waves, connected with
the periodical changes of storm, and cloud, and sunshine, which gradually
extend from north to south, in or near the magnetic meridian. Perhaps such
compensating currents are found west of the magnetic poles, as we have
suggested, and make the N. E. and northerly dry winds of Western Europe
and the Pacific; but, in the present state of our knowledge, it is
impossible to say that they are. If it be so, the compensation they
furnish must be small; for the volume of counter-trade which is not
depolarized before it reaches the Arctic circle, and which passes round
the magnetic pole, must be very small. A majority of our periodical
changes, during the northern transit, and I believe at all seasons, are of
this character; and, I have reason to believe, from observation, in one
or two cases, that where belts of rains and showers begin, over _any
locality_ in the United States, they may assume this character. I have
been in Saratoga when an easterly storm commenced _south of that place_;
the condensation and mackerel sky being visible at the south, and no cloud
formation or rain occurring there at the time, and have traced it
afterward as a belt which had a lateral extension south-eastward. Leaving
that place immediately after a belt had passed south, I have overtaken it
by railroad, and run into it again before arriving at New York; and
witnessed its subsequent extension south-eastwardly, out over the
Atlantic. I have witnessed the approach of such a belt in the spring, at
Sandusky, upon Lake Erie, and its passage over to the S. E., followed by
the N. W. wind, as Mr. Bassnett describes them at Ottawa, and run under
the attenuated edge of the same belt, on the same day, on the way to
Pittsburg, leaving the N. W. wind behind, but finding it present again
with clear sky on the following morning. I have seen hundreds of them
approach from the north, and pass to S. E., out over the Atlantic;
followed by the N. W. wind in spring and autumn. This class of storms pass
off toward, and doubtless over the track, of our European steamers and
packets. I know this, for I witness it nearly every month in the year. It
is not a matter of speculation, but of actual, long-continued observation.
Probably, as one approaches the Gulf Stream, and when over it, its induced
winds may be more violent. It is time our navigators understood this; and
that all the gales of the North Atlantic, certainly, are not rotary; and
do not approach from the S. W. in the same manner as the class
investigated by Mr. Redfield do. Where a fresh southerly or south-westerly
wind is followed by any considerable cirro-stratus or stratus-condensation,
it is usually of this character.
The following diagram exhibits the peculiarities of this class of storms.
It is intended to represent the same storm or belt of showers, on _two
successive_ days, and, of course, its usual rate of southerly extension:
[Illustration: Fig. 21.]
This class of storms, or belts of showers, present the following
succession of phenomena in summer:
1. Still warm weather, one or more days.
2. Fresh southerly wind, one or more days; if more than one, dying away at
the S. W., at night-fall, but continuing into the evening of the day
before the belt of condensation arrives.
3. Belt of condensation, with or without rain or showers, with the
easterly wind blowing axially, if the condensation is heavy and the belt
wide; westerly if the condensation is feeble or the belt narrow--the
clouds moving about E. N. E.
4. Cooler air, light N. W. in summer, heavy N. W. in autumn, winter, and
spring.
And, the next period--
5. Still warm weather or light airs.
6. Southerly wind, fresh.
7. Belt of condensation.
8. Cool northerly wind.
And so on, successively, unless broken in upon by some other class.
Sometimes these periods are exceedingly regular, at other times the other
classes prevail. I have much reason to believe that this is the _normal,
periodic_ provision for condensation of our portion of the northern
hemisphere, and probably of every other where rain falls regularly in the
summer season, and that the other classes are exceptions, as the
hurricanes are exceptions to the normal condition of the weather every
where. Perhaps in some seasons, during the northern transit, the
exceptions may equal the rule, but I do not now remember such a season. In
other years nearly all the storms are of this character. Thus, Dr.
Hildreth (in Silliman's Journal for 1827), speaking of the year 1826, in a
note to his register of that year, says: "There have been, this year, an
unusual number of winds from N. or N. W. Nearly every rain the past summer
has been followed with winds from the northward, when, in many previous
summers, the wind continued to the southward after rain." The immediate
occurrence of northerly wind after the passage of the belt of
condensation, is a peculiar feature of this class of storms.
As this also will be new, and is of great practical interest, I shall be
pardoned for referring to other evidence. Bermuda is in latitude 32°
north. In the summer season they are within the range of the Calms of
Cancer, as Lieutenant Maury terms them, and not subject to storms. From
November to May, inclusive, they have successions of revolving wind.
Colonel Reid gave them much attention, and studied them barometrically:
that is, he studied the changes of the wind during the successive periodic
depressions. He found them revolving like ours, and hence inferred the
truth of the gyratory theory in relation to all winds. But it is perfectly
evident the same polar belts which pass over us reach them during the
southern transit. The precedent southerly wind, the _central
condensation_, the appearance of lightning, and the rotation of the wind
by both the east and west, but most frequently by west, are the same. In
his chapter on observations at the Bermudas, he gives us many examples.
Probably the existence of the Gulf Stream to the west and north has a
modifying influence upon them, and their action becomes less intense in
that latitude, but they are very similar. I copy a record of the weather,
for a month, which may be found on pages 252, 253, and 254, and a portion
of his remarks:
"The month of December, 1839, presents a continual succession of
revolving winds passing over the Bermudas, with scarcely an
irregularity, as regards the fall and rise of the barometer
accompanying the veering of the wind. One, however, occurred on the
10th and 11th. The S. W. wind abated, and changed to W. N. W., with
the barometer still falling. But in the column of remarks it is noted
that there was lightning seen in the N. and N. W., from 7 P.M.,
during the night. This irregularity may, therefore, have been
occasioned by a gale passing over the banks of Newfoundland,
influencing the direction of the wind at Bermuda.
"REVOLVING WINDS.
+-----------------------------------------------------------------+
| Date. | Hour. |Direction of| Wind's | Weather. | Bar.|Ther.|
| | | Wind. | Force. | | | |
|--------|---------|------------|--------|-----------|------|-----|
| 1839. | | | | | | |
|Nov. 30 |Midnight.| S. S. E. | 1 |b. c. | 30·06| 65 |
|Dec. 1 | Noon. | S. S. W. | 3 |b. c. | 30·07| 71 |
| 2 | " | S. W. | 5 |g. m. q. | 29·86| 70 |
| 3 | " | S. S. W. | 3 |g. c. | 29·76| " |
| 4 | " | S. W. | 6 |g. m. r. | 29·62| 68 |
| 5 | " | W. N. W. | 5 |p. q. | 29·56| " |
| 6 | " | N. W. | 6 |p. q. |*29·55| " |
| 7 | " | N. N. W. | 5 |b. c. | 29·78| 70 |
| " |Midnight.| N. N. W. | 3 |b. c. | 29·89| 68 |
| 8 | Noon. | W. N. W. | 2 |b. c. | 29·82| 71 |
| 9 | " | S. S. W. | 5 |p. q. | 29·84| 70 |
| 10 | " | S. W. | 2 |b. c. | 29·96| " |
| 11 | " | W. N. W. | 6 |b. c. m. |*29·88| 68 |
| 12 | " | S. S. W. | " |b. v. | 29·99| 69 |
| 13 | " | N. N. by W.| " |b. v. | 30·01| 66 |
| 14 | " | N. N. W. | 5 |b. c. v. | 30·06| 64 |
| " |Midnight.| N. W. | 2 |b. c. p. | 30·05| 63 |
| 15 | Noon. | S. W. by S.| 6 |g. m. r. | 29·72| 65 |
| " | P.M. 2 | S. S. W. | 7 |m. q. r. | 29·92| 64 |
| " | " 4 | S. S. W. | " |g. m. q. r.| 29·55| " |
| " | " 6 | W. S. W. | " |q. w. |*29·53| " |
| " | " 8 | N. W. | 6 |b. c. q. | 29·54| " |
| " | " 10 | N. N. W. | " |b. c. | 29·55| " |
| 16 | Noon. | N. W. | 7 |b. c. m. | 29·53| 62 |
| 17 | " | N. W. by N.| " |p. q. | 29·67| 60 |
| 18 | " | N. W. | 6 |c. q. | 29·86| " |
| 19 | " | N. W. by N.| 7 |m. q. r. |*29·73| 59 |
| 20 | " | N. N. W. | " |p. q. c. | 29·89| 58 |
| 21 | " | N. W. by N.| 6 |c. q. | 29·96| 56 |
| " |Midnight.| S. W. | 1 |b. c. | 29·95| 55 |
| 22 | Dawn. | ---- | 0 | | | |
| " | Noon. | S. S. W. | 5 |g. m. | 29·83| 56 |
| " | P.M. 4 | S. | 7 |g. m. | 29·79| " |
| " | " 6 | S. S. E. | " |g. m. r. | 29·61| " |
| " | " 8 | S. S. E. | " |w. r. | 29·52| " |
| " | " 10 | S. E. | " |m. w. r. | 29·48| " |
| 23 | Noon. | S. W. | 6 |b. c. m. |*29·44| 57 |
| 24 | " | W. N. W. | " |b. m. | 29·71| 59 |
| 25 | " | W. N. W. | 5 |b. c. | 29·88| 56 |
| 26 | " | N. | 3 |c. | 30·09| 62 |
| 27 | " | S. E. | 5 |c. q. r. | 30·07| 61 |
| 28 | " | S. W. | 6 |c. q. | 29·88| 66 |
| " |Midnight.| S. S. W. | " |b. c. | 29·76| 65 |
| 29 | Noon. | S. W. | 7 |c. b. |*29·48| 64 |
| 30 | " | W. N. W. | 6 |b. c. q. | 29·83| 55 |
| 31 | " | N. W. | 5 |b. c. | 30·12| 58 |
+-----------------------------------------------------------------+
"_Remark printed in the Register._
"The changes of the wind during the December gales have been nearly
the same in all: _i. e._, commencing with a southerly wind at first,
the wind has veered by the west, toward the north-west, sometimes
ending as far round as N. N. W."
These extracts show the passage of several successive belts, each with the
phenomena in regular order.
The first commences with blue sky and detached clouds, barometer up,
thermometer down to 65°, and nearly calm, on the 30th of November.
Dec. 1 (at noon). Wind freshens from S. S. W.; thermometer rises;
barometer still up.
Dec. 2. Barometer has fallen; thermometer up; wind increasing from S. W.,
with gloomy, squally appearance.
Dec. 3. Wind S. S. W.; barometer slowly falling; thermometer slightly.
Dec. 4. Wind fresh; S. W.; condensation and rain has reached them, and it
carries barometer and thermometer down.
Dec. 5. Wind shifting by the west, and squally.
Dec. 6. Winds gets N. W.; blows fresh; barometer at its minimum, probably
at the time of the change of wind, although the register does not show the
precise time.
Dec. 7. Wind N. N. W.; blue sky and detached clouds (N. W. scud), cleared
off; barometer elevated by the N. W. wind, from 29.55 to 29.78. Midnight:
blue sky; detached clouds (N. W. scud probably); barometer up to 29.89;
thermometer fallen, from the cooler character of the northerly wind.
Dec. 8. Wind having lulled as a northerly wind has got round to S. W.
again; thermometer up; barometer falling, and another belt approaching,
and so on.
The first and last part of December show each two regular occurrences of
substantially the same phenomena. The middle is somewhat more irregular.
There were five distinctly-marked periods, and one squally, long-continued
period, with a slight tendency to condensation, and a slight fall of
barometer and rain on the 19th (N. W. squall probably), but not sufficient
to reverse the wind to the south. In Colonel Reid's opinion there were
five revolving gales which passed over Bermuda during the month. In my
opinion, there were five perfect polar waves of condensation, and one
imperfect one, with as many successive southerly winds preceding the
condensation, with or without rain in the center, followed by as many cold
N. W. or N. N. W. winds, with squalls, in the rear, about five days apart.
(See the * in the barometric column.)
_We are at issue._ Let the question be determined by _actual observation_,
and not by _speculation_. It is of fundamental and exceeding importance to
the science.
Now, let us take a month in summer, from the observations of Mr. Bassnett,
at Ottawa. Here the climate differs somewhat from that east of the
Alleghanies; the magnetic intensity is greater, and the action more
violent and irregular. That part of the country, it should be remembered,
has a greater fall of rain in summer, for reasons we have stated, and
those periodic revolutions are more frequent.
"A brief abstract from a journal of the weather for one sidereal
period of the moon, in 1853.
"_June_ 21st. Fine clear morning (S. fresh): noon very warm 88°; 4
P.M., plumous _cirri in south_; ends clear.
"22d. Hazy morning (S. very fresh) arch of cirrus in west; 2 P.M.,
black in W. N. W.; 3 P.M., overcast and rainy; 4 P.M., a heavy gust
from south; 4.30 P.M., blowing furiously (S. by W.); 5 P.M.,
tremendous squall, uprooting trees and scattering chimneys; 6 P.M.,
more moderate (W.).
"23d. Clearing up (N. W.); 8 A.M., quite clear; 11 A.M., bands of
mottled cirri pointing N. E. and S. W., ends cold (W. N. W.); the
cirri seem to rotate from left to right, or with the sun.
"24th. Fine clear, cool day, begins and ends (N. W.).
"25th. Clear morning (N. W. light); 2 P.M. (E.), calm; tufts of
tangled cirri in north, intermixed with radiating streaks, all
passing eastward; ends clear.
"26th. Hazy morning (S. E.), cloudy; noon, a heavy, windy-looking
bank in north (S. fresh), with dense cirrus fringe above, on its
upper edge; clear in S.
"27th. Clear, warm (W.); bank in north; noon bank covered all the
northern sky, and fresh breeze; 10 P.M., a few flashes to the
northward.
"28th. Uniform dense cirro-stratus (S. fresh); noon showers all
round; 2 P.M., a heavy squall of wind, with thunder and rain (S. W.
to N. W.); 8 P.M., a line of heavy cumuli in south; 8.30 P.M., a very
bright and high cumulus in S. W., protruding through a layer of dark
stratus; 8.50 P.M., the cloud bearing E. by S., with three rays of
electric light.
"29th. A stationary stratus over all (S. W. light); clear at night,
but distant lightning in S.
"30th. Stratus clouds (N. E. almost calm); 8 A.M., raining gently; 3
P.M., stratus passing off to S.; 8 P.M., clear, pleasant.
"_July_ 1st. Fine and clear; 8 A.M., cirrus in sheets, curls, wisps,
and gauzy wreaths, with patches beneath of darker shade, all nearly
motionless; close and warm (N. E.); a long, low bank of haze in S.,
with one large cumulus in S. W., but very distant.
"2d. At 5 A.M., overcast generally, with hazy clouds and fog of
prismatic shades, chiefly greenish-yellow; 7 A.M. (S. S. E.
freshening), thick in W.; 8 A.M. (S. fresh), much cirrus, thick and
gloomy; 9 A.M., a clap of thunder, and clouds hurrying to N.; a
reddish haze all around; at noon the margin of a line of
yellowish-red cumuli just visible above a gloomy-looking bank of haze
in N. N. W. (S. very fresh); warm, 86°; more cumuli in N. W.; the
whole line of cumuli N. are separated from the clouds south by a
clearer space. These clouds are borne rapidly past the zenith, but
never get into the clear space--they seem to melt or to be turned off
N. E. The cumuli in N. and N. W., slowly spreading E. and S.; 3 P.M.,
the bank hidden by small cumuli; 4 P.M., very thick in north,
magnificent cumuli visible sometimes through the breaks, and beyond
them a dark, watery back-ground (S. strong); 4.30 P.M., wind round to
N. W. in a severe squall; 5 P.M., heavy rain, with thunder, etc.--all
this time there is a bright sky in the south visible through the rain
15° high; 7 P.M., clearing (S. W. mod.).
"3d. Very fine and clear (N. W.); noon, a line of large cumuli in N.,
and dark lines of stratus below, the cumuli moving eastward; 6 P.M.,
their altitude 2° 40'. Velocity, 1° per minute; 9 P.M., much
lightning in the bank north.
"4th. 6 A.M., a line of small cumulo-stratus, extending east and
west, with a clear horizon north and south 10° high. This band seems
to have been thrown off by the central yesterday, as it moves slowly
south, preserving its parallelism, although the clouds composing it
move eastward. Fine and cool all day (N. W. mod.)--lightning in N.
"5th. Cloudy (N. almost calm), thick in E., clear in W.; same all
day.
"6th. Fine and clear (E. light); small cumuli at noon; clear night.
"7th. Warm (S. E. light); cirrus bank N. W.; noon (S.) thickening in
N.; 6 P.M., hazy but fine; 8 P.M., lightning in N.; 10 P.M., the
lightning shows a heavy line of cumuli along the northern horizon;
calm and very dark, and incessant lightning in N.
"8th. Last night after midnight commencing raining, slowly and
steadily, but leaving a line of lighter sky south; much lightning all
night, but little thunder.
"8th. 6 A.M., very low scud (500 feet high) driving south, still calm
below (N. light); 10 A.M., clearing a little; a bank north, with
cirrus spreading south; same all day; 9 P.M., wind freshening (N.
stormy); heavy cumuli visible in S.; 10.30 P.M., quite clear, but a
dense watery haze obscuring the stars; 12 P.M., again overcast; much
lightning in S. and N. W.
"9th. Last night (2 A.M. of 9th) squall from N. W. very black; 4
A.M., still raining and blowing hard, the sky a perfect blaze, but
very few flashes reach the ground; 7 A.M., raining hard; 8 A.M. (N.
W. strong); a constant roll of thunder; noon (N. E.); 2 P.M. (N.); 4
P.M., clearing; 8 P.M., a line of heavy cumuli in S., but clear in N.
W., N., and N. E.
"10th. 3 A.M., Overcast, and much lightning in south (N. mod.); 7
A.M., clear except in south; 6 P.M. (E.); 10 P.M., lightning south;
11 P.M., auroral rays long, but faint, converging to a point between
Epsilon Virginis and Denebola, in west; low down in west, thick with
haze; on the north the rays converged to a point still lower;
lightning still visible in south. This is an aurora in the west.
"11th. Fine, clear morning (N. E.); same all day; no lightning
visible to-night, but a bank of clouds low down in south, 2° high,
and streaks of dark stratus below the upper margin.
"12th. Fine and clear (N. E.); noon, a well-defined arch in S. W.,
rising slowly; the bank yellowish, with prismatic shades of
greenish-yellow on its borders. This is the O. A. At 6 P.M., the bank
spreading to the northward. At 9 P.M., thick bank of haze in north,
with bright auroral margin; one heavy pyramid of light passed through
Cassiopeia, traveling _westward_ 1-1/2° per minute. This moves to the
other side of the pole, but not more inclined toward it than is due
to prospective, if the shaft is very long; 11.10 P.M., saw a mass of
light more diffuse due east, reaching to _Markab_, then on the prime
vertical. It appears evident this is seen in profile, as it inclines
downward at an angle of 10° or 12° from the perpendicular. It does
not seem very distant. 12 P.M., the aurora still bright, but the
brightest part is now west of the pole, before it was east.
"13th. 6 A.M., clear, east and north; bank of cirrus in N. W., _i.
e._, from N. N. E. to W. by S.; irregular branches of cirrus clouds,
reaching almost to south-eastern horizon; wind changed (S. E. fresh);
8 A.M., the sky a perfect picture; heavy regular shafts of dense
cirrus radiating all around, and diverging from a thick nucleus in
north-west, the spaces between being of clear, blue sky. The shafts
are rotating from north to south, the nucleus advancing eastward.
"At noon (same day), getting thicker (S. E. very fresh); 6 P.M., moon
on meridian, a prismatic gloom in south, and very thick stratus of
all shades; 9 P.M., very gloomy; wind stronger (S. E.); 10 P.M., very
black in south, and overcast generally.
"14th. Last night, above 12 P.M., commenced raining; 3 A.M., rained
steadily; 7 A.M., same weather; 8.20 A.M., a line of low storm-cloud,
or scud, showing very sharp and white on the dark back-ground all
along the southern sky. This line continues until noon, about 10° at
the highest, showing the northern boundary of the storm to the
southward; 8 P.M., same bank visible, although in rapid motion
eastward; same time clear overhead, with cirrus fringe pointing north
from the bank; much lightning in south (W. fresh); so ends.
"15th. Last night a black squall from N. W. passed south without
rain; at 3 A.M., clear above but, very black in south (calm below all
the time); 9 A.M., the bank in south again throwing off rays of cirri
in a well-defined arch, whose vortex is south; these pass east, but
continue to form and preserve their linear direction to the north; no
lightning in south to-night.
"16th. Clear all day, without a stain, and calm.
"17th. Fine and clear (N. E. light); 6 P.M., calm.
"18th. Fair and cloudy (N. E. light); 6 P.M., calm.
"19th. Fine and clear (N. fresh); I. V. visible in S. W.
"20th. 8 A.M., bank in N. W., with beautiful cirrus radiations; 10
A.M., getting thick, with dense plates of cream-colored cirrus
visible through the breaks; gloomy looking all day (N. E. light)."
The letters in a parenthesis signify the direction of the wind.
During this month there were three distinctly marked periods of belts of
showers, preceded by "fresh" or "strong" south wind, and followed by the
N. W. There was a period when a belt of less intense stratus, without much
wind, occurred (28th, 29th, and 30th of June). This was followed by a
distinct belt of showers and _fresh_ S. wind, on the 2d of July, and by
the N. W. wind and clear weather, on the 3d.
During the rest of July it was more irregular, with the exception of the
7th, 8th, and 9th, when another belt and revolution occurred.
Now, these periods, when distinctly marked, exhibit the same succession of
phenomena--viz., elevation of temperature, fresh southerly wind, belt of
condensation, cumulus or stratus with cirrus running east, but extending
south, followed by N. W. wind, and clear, cold air. Can any one believe
they were successive rotary gales?
I wish, in this connection, to make a suggestion to Lieutenant Maury and
others. The descriptions of M. Bassnett, although not perfect, are very
intelligible. He describes things as they were, and as they should be
described. He distinguishes the clouds, and the scud, and other
appearances.
But Colonel Reid's descriptions are unmeaning and unintelligible. G.
M.--Gloomy, misty! Gloomy from what? fog, or stratus, or a stratum of
scud, or what? We can not know. Again, C. The table tells us this stands
for detached clouds. But of what kind? Cumulus, broken stratus, patches of
cirro-cumulus or cirro-stratus, or scud? All these, and indeed every kind
of cloud or fog formation, except low fog, may exist in detached portions.
These abbreviations will not answer; they do not describe the weather. The
clouds must be studied and described. There is no difficulty in doing it.
Sailors will learn them very soon after their teachers have; and those who
teach them should see to it that the logs contain terms of description
which convey the meaning which may, and ought to be, conveyed. The use of
these indefinite terms can not be continued without culpability.
Again, the observations of seamen off our coast are in accordance with the
progress of this class of storms on land, and prove that they continue S.
E. over the Atlantic, abating in action as they approach the tropics.
There is abundant evidence of this in the work of Colonel Reid, and the
charts of Lieutenant Maury, but I can not devote further space to them.
The third class form in the counter-trade, over some portion of the
country, from excessive volume or action of the counter-trade, or local
magnetic activity, without coming from the tropics or being connected with
a regular polar wave of magnetic disturbance.
The following diagram exhibits their form, progress, and accompanying
induced winds.
[Illustration: Fig. 22.]
The gentle rains of spring, particularly April, and the moderate and
frequent snow-storms of winter, are often of this character; and so are
the heavy rains, which commence at the morning barometric minimum, rain
heavily through the forenoon, and light up near mid-day in the south,
followed by gentle, warm, S. W. winds. This class are more frequent in
some years than others--probably the early years of the decade, while
polar storms are, during the later ones. It is this class which have
_violent_ easterly winds _in front_, and on the _south side_, with two or
more currents, and which Mr. Redfield has also supposed to be cyclones.
The fourth class are isolated showers, occurring over particular
localities, or belts of drought and showers alternating; sometimes a
general disposition to cloudy and showery weather for a longer or shorter
interval over the whole country; at others, limited to particular
localities in the course of the trade. Such a period occurred during the
wheat harvest of 1855. This class I attribute to a general increased
magnetic action, but it may be induced by an increased volume, or greater
south polar magnetic intensity of the counter-trade, exciting and
concentrating the regular currents of the field, and increasing their
activity and energy. These also often work off south gradually, and are
followed by a cold N. W. air for a day or two; showing a tendency, in the
excited magnetism, to pass as a wave toward the tropics.
The following diagram will give some idea of this class:
[Illustration: Fig. 23.]
There are sometimes very obvious local tendencies to precipitation over
portions adjoining an area affected with drought, as there are other
magnetic irregularities over particular areas.
All these classes of storms are variant in intensity. Sometimes the
general or local cloud-formation is weak, and does not produce
precipitation at all; so of that which extends southerly. Probably the
tropical storm are always sufficiently dense and active to precipitate.
Their action is often violent over particular localities, and hence the
more frequent occurrence of the tornado over the more intense area of
Ohio, and other portions of the west. All violent local storms are
doubtless owing to local magneto-electric activity.
CHAPTER XI.
The reader who has attentively perused and considered the facts stated,
and the principles deduced, in the preceding pages, and is ready to make a
practical application of them by careful observation, will have little
difficulty in understanding the varied atmospheric conditions; and will
soon be able to form a correct judgment of the immediate future of the
weather, so far as his limited horizon will permit.
But there are other facts and considerations, not specifically alluded to,
which will materially aid him in his observations; and there is a degree
of philosophical truth in the proverbs and signs, which ancient popular
observation accumulated, and poetry and tradition have preserved, that
meteorologists have been slow to discover or admit, but which will be
obvious upon examination, and commend them to his attention.
The classical reader is doubtless familiar with that part of the first
Georgic of Virgil, which contains a description of the signs indicative of
atmospheric changes. Much of it is beautifully poetic, and, if read in the
light of a correct philosophy, is equally truthful.
I copy from a creditable translation, found in the first volume of
Howard's "Climate of London":
"All that the genial year successive brings,
Showers, and the reign of heat, and freezing gales,
Appointed signs foreshow; the Sire of all
Decreed what signs the southern blast should bring,
Decreed the omens of the varying moon:
That hinds, observant of the approaching storm,
Might tend their herds more near the sheltering stall."
PROGNOSTICS.--_1st. Of Wind._
"When storms are brooding--in the leeward gulf
Dash the swell'd waves; the mighty mountains pour
A harsh, dull murmur; far along the beach
Rolls the deep rushing roar; the whispering grove
Betrays the gathering elemental strife.
Scarce will the billows spare the curved keel;
For swift from open sea the cormorants sweep,
With clamorous croak; the ocean-dwelling coot
Sports on the sand; the hern her marshy haunts
Deserting, soars the lofty clouds above;
And oft, when gales impend, the gliding star
Nightly descends athwart the spangled gloom,
And leaves its fire-wake glowing white behind.
Light chaff and leaflets flitting fill the air,
And sportive feathers circle on the lake."
_2d. Of Rain._
"But when grim Boreas thunders; when the East
And black-winged West, roll out the sonorous peal,
The teeming dikes o'erflow the wide champaign,
And seamen furl their dripping sails. The shower,
Forsooth, ne'er took the traveler unawares!
The soaring cranes descried it in the vale,
And shunn'd its coming; heifers gazed aloft,
With nostrils wide, drinking the fragrant gale;
Skimm'd the sagacious swallow round the lake,
And croaking frogs renew'd their old complaint.
Oft, too, the ant, from secret chambers, bears
Her eggs--a cherished treasure--o'er the sand,
Along the narrow track her steps have worn.
High vaults the thirsty bow; in wide array
The clamorous rooks from every pasture rise
With serried wings. The varied sea-fowl tribes,
And those that in Cäyster's meadows seek,
Amid the marshy pools, their skulking prey,
Fling the cool plenteous shower upon their wings,
Crouch to the coming wave, sail on its crest,
And idly wash their purity of plume.
The audacious crow, with loud voice, hails the rain
A lonesome wanderer on the thirsty sand.
Maidens that nightly toil the tangled fleece,
Divine the coming tempest; in the lamp
Crackles the oil; the gathering wick grows dim."
_3d. Of Fair Weather._
"Nor less, by sure prognostics, mayest thou learn
(When rain prevails), in prospect to behold
Warm suns, and cloudless heavens, around thee smile.
Brightly the stars shine forth; Cynthia no more
Glimmers obnoxious to her brother's rays;
Nor fleecy clouds float lightly through the sky.
The chosen birds of Thetis, halcyons, now
Spread not their pinions on the sun-bright shore;
Nor swine the bands unloose, and toss the straw.
The clouds, descending, settle on the plain;
While owls forget to chant their evening song,
But watch the sunset from the topmost ridge.
The merlin swims the liquid sky, sublime,
While for the purple lock the lark atones:
Where she, with light wing, cleaves the yielding air,
Her shrieking fell pursuer follows fierce--
The dreaded merlin; where the merlin soars,
_Her_ fugitive swift pinion cleaves the air.
And now, from throat compressed, the rook emits,
Treble or fourfold, his clear, piercing cry;
While oft amid their high and leafy roosts,
Bursts the responsive note from all the clan,
Thrill'd with unwonted rapture--oh! 'tis sweet,
When bright'ning hours allow, to seek again
Their tiny offspring, and their dulcet homes.
Yet deem I not, that heaven on them bestows
Foresight, or mind above their lowly fate;
But rather when the changeful climate veers,
Obsequious to the humor of the sky;
When the damp South condenses what was rare,
The dense relaxing--or the stringent North
Rolls back the genial showers, and rules in turn,
The varying impulse fluctuates in their breast:
Hence the full concert in the sprightly mead--
The bounding flock--the rook's exulting cry."
_4th. The Moon's Aspects, etc._
"Mark with attentive eye, the rapid sun--
The varying moon that rolls its monthly round;
So shalt thou count, not vainly, on the morn;
So the bland aspect of the tranquil night
Will ne'er beguile thee with insidious calm.
When Luna first her scatter'd fires recalls,
If with blunt horns she holds the dusky air,
Seamen and swains predict th' abundant shower.
If rosy blushes tinge her maiden cheek,
Wind will arise: the golden Phoebe still
Glows with the wind. If (mark the ominous hour!)
The clear fourth night her lucid disk define,
That day, and all that thence successive spring,
E'en to the finished month, are calm and dry;
And grateful mariners redeem their vows
To Glaucus, Inöus, or the Nereid nymph."
_5th. The Sun's Aspects, etc._
"The sun, too, rising, and at that still hour,
When sinks his tranquil beauty in the main,
Will give thee tokens; certain tokens all,
Both those that morning brings, and balmy eve.
When cloudy storms deform the rising orb,
Or streaks of vapor in the midst bisect,
Beware of showers, for then the blasting South
(Foe to the groves, to harvests, and the flock),
Urges, with turbid pressure, from above.
But when, beneath the dawn, red-fingered rays
Through the dense band of clouds diverging, break,
When springs Aurora, pale, from saffron couch,
Ill does the leaf defend the mellowing grape;
Leaps on the noisy roof the plenteous hail,
Fearfully crackling. Nor forget to note,
When Sol departs, his mighty day-task done,
How varied hues oft wander on his brow;
Azure betokens rain: the fiery tint
Is Eurus's herald; if the ruddy blaze
Be dimm'd with spots, then all will wildly rage
With squalls and driving showers: on that fell night,
None shall persuade me on the deep to urge
My perilous course, or quit the sheltering pier.
But if, when day returns, or when retires,
Bright is the orb, then fear no coming rain:
Clear northern airs will fan the quiv'ring grove.
Lastly, the sun will teach th' observant eye
What vesper's hour shall bring; what clearing wind
Shall waft the clouds slow floating--what the South
Broods in his humid breast. Who dare belie
The constant sun?"
I copy also the following from Howard:
"Dr. Jenner's signs of rain--an excuse for not accepting the
invitation of a friend to make a _country_ excursion.
"The hollow winds begin to blow,
The clouds look black, the glass is low,
The soot falls down, the spaniels sleep,
And spiders from their cobwebs creep.
Last night the sun went pale to bed,
The moon in halos hid her head,
The boding shepherd heaves a sigh,
For see! a rainbow spans the sky.
The walls are damp, the ditches smell;
Closed is the pink-eyed pimpernel.
Hark! how the chairs and tables crack;
Old Betty's joints are on the rack.
Loud quack the ducks, the peacocks cry;
The distant hills are looking nigh.
How restless are the snorting swine!--
The busy flies disturb the kine.
Low o'er the grass the swallow wings;
The cricket, too, how loud it sings!
Puss, on the hearth, with velvet paws,
Sits smoothing o'er her whisker'd jaws.
Through the clear stream the fishes rise
And nimbly catch the incautious flies;
The sheep were seen, at early light,
Cropping the meads with eager bite.
Though _June_, the air is cold and chill;
The mellow blackbird's voice is still;
The glow-worms, numerous and bright,
Illumed the dewy dell last night;
At dusk the squalid toad was seen,
Hopping, crawling, o'er the green.
The frog has lost his yellow vest,
And in a dingy suit is dress'd.
The leech, disturbed, is newly risen
Quite to the summit of his prison.
The whirling wind the dust obey
And in the rapid eddy plays.
My dog, so altered in his taste,
Quits mutton-bones, on grass to feast;
And see yon rooks, how odd their flight!
They imitate the gliding kite:
Or seem precipitate to fall,
As if they felt the piercing ball.
'Twill surely rain; I see, with sorrow,
Our jaunt must be put off to-morrow."
Howard attributes the foregoing to Jenner; but Hone, in his "Every-Day
Book," attributes it to Darwin, and gives it, with several couplets, not
found in that attributed to Jenner. These I add from Hone, as follows:
"Her corns with shooting pains torment her--
And to her bed untimely send her."
That couplet is included by Hone with what is said of Aunt Betty.
"The smoke from chimneys right ascends,
Then spreading back to earth it bends.
The wind unsteady veers around;
Or, settling in the south is found."
Those are as philosophically accurate and valuable as any.
"The tender colts on back do lie;
Nor heed the traveler passing by.
In fiery red the sun doth rise,
Then wades through clouds to mount the skies."
The first of those couplets is untrue. It is doubtless alluded to as one
of the acts of the animal creation, indicating sleepiness and inaction,
which precede storms; but colts do not lie on the back. The other couplet
is both true and important. This collection entire, whether written by
Darwin or Jenner, contains most of the signs which have been preserved,
and which are of much practical importance in our climate.
It is unquestionably true that "appointed signs foreshow the weather," to
a great extent, every where, but with more certainty in the climate in
which Virgil wrote than in our variable and excessive one. "Showers" and
"freezing gales" we can, perhaps, as well understand; but the "_reign of
heat_," by which he probably meant the dry period, when the southern edge
of the extra-tropical belt of rains is carried up to the north of them, we
do not experience. Something like it we did indeed have, during the
excessive northern transit, in the summer of 1854; but it was an
exception, not the rule.
Some of the most important of those signs from Virgil and Jenner I propose
to allude to in detail; but it is necessary to look; in the first place,
to the character of the season and the month.
We have seen that the years differ during different periods of the same
decade. That they incline to be hot and irregular during the early part of
it, and cool, regular, and productive during the latter portion--subject,
however, to occasional exceptions. The latter half of the third decade of
this century (1826 to 1830, inclusive) was comparatively warm; and, in the
latitude of 41°, was very unhealthy, and so continued during the early
part of the next, over the hemisphere, embracing the _cholera seasons_.
The spots upon the sun were much less numerous than usual, during the
latter half of the third decade. Thus the spots from
1826 to 1830, inclusive, were 873
1836 to 1840 " " 1201
1846 to 1850 " " 1168
and the size of those from 1836 to 1840 exceeded those of the other
years.
The attentive observer will very soon be satisfied that the seasons have a
character; and those of every year differ in a greater or less degree from
those of other years in the same decade, and those of one decade not
unfrequently from those of some other. _Periodicity_ is stamped upon all
of them, and upon all resulting consequences. Like seasons come round,
and, like productiveness or unproductiveness, healthy or epidemic
diatheses, attend them. We have seen that, in relation to mean
temperature, there are such periodical diversities, but they are more
strongly marked in the character of storms, and other successions of
phenomena. "_All signs fail in a drouth_," for then all attempts at
condensation are partial, imperfect, and ineffectual. "_It rains very
easy_," it is said, at other times, and so it seems to do, and with
comparatively little condensation. In the one case, no great reliance can
be placed upon indications which are entirely reliable in the other. So
"_all our storms clear off cold_," or, "_all our storms clear off warm_,"
are equally common expressions--as the _prevailing classes_ of storms give
a _character_ to the _seasons_. It "_rains every Sunday now_," is
sometimes said, and is often peculiarly true--the storm waves having just
then a weekly or semi-weekly period, and one falls upon Sunday for several
successive weeks; and when it is so, _that_ coincidence is sure to be
noticed and commented upon, and the other perhaps disregarded.
If the seasons depended upon the northward and southward journey of the
sun alone, entire regularity might be expected--for we have no reason to
believe that magnetism and electricity contain, within themselves,
inherently, any tendency to irregularity, or periodicity; and, the sun
being constant in his _periods_, would be constant in his _influence_. But
he is inconstant and variable in his influence, and it is apparently
traceable to the existence of spots; but I am not quite sure that it is
occasioned by the _observable_ spots alone. Grant that the intensity and
power of his rays differ on the same day, in different years, and that
difference may be attributable in part to causes which our telescopes can
not discover.
But the differences in the seasons do not depend on the variability of the
sun's influence alone. This appears from the frequent meridional and
latitudinal diversities and contrasts, to which allusion has been made.
The sun can not be supposed to exert a _less_ influence on a middle, than
a more northern latitude; nor on one series of meridians, than another.
There must, therefore, be another local and powerful disturbing cause,
varying the magnetic and electric activity and influence upon the trades,
as well in their incipiency as in their circuits, and thus controlling the
atmospheric conditions locally and in _the opposite hemispheres_. That
other disturbing cause is _volcanic action_. We can conceive of none
other, and we can detect and trace the influence of that to a considerable
extent. Unfortunately we know, and can practically know, comparatively
little of it. It has been busy with the earth since the creation, and will
continue to be so till, possibly, by a collision, it shall burst into
asteroids--its molten interior flowing out in seeming combustion--each
fragment retaining its magnetic polarities entire, and continuing on in an
independent orbit in the heavens, an asteroid, or meteorite.
While, therefore, the agency of magnetism in itself may be regular, and
the transit of the sun is regular, and "seed-time and harvest shall not
cease," yet the sun is not regular in his influence, and the magnetic
agency is disturbed by another and irregular power. And, although we can
trace the influence of both upon the seasons, we can not measure that
influence, and from it reliably foretell the weather. The discoveries of
Swabe, and future ones, relative to solar irregularities, will assist us,
but, till we understand better, and to some extent anticipate, the
changes of volcanic action, we shall not be able to understand or foresee
all the differences in the seasons. That time may come; for progress is
yet to be read in the front of meteorology, and simultaneous practical
observations made and interchanged at every important point on the globe.
Nevertheless, the seasons have a character--often a regular one--one class
of storms prevailing over all others--one series of phenomena occurring to
the exclusion of others--and we must regard it if we would arrive at
intelligent estimates of their future condition.
The most difficult part to understand are the meridional contrasts. Last
year we had one of the worst drouths which has occurred since the
settlement of the country. But while all the eastern portion of the United
States was dry, New Mexico was unusually wet; and the North-western
States, on the same curving line of the counter-trade, were not affected
by the drouth.
Extract from a letter written by Governor Merriweather, to Mr. Bennett, in
answer to a circular, published in the "New York Herald," and dated
"SANTA FE, NEW MEXICO, Oct. 25th, 1854.
"More rain has fallen during the last six months, within this
territory, than ever was known to have fallen in the same length of
time, in this usually dry climate. Generally, little or no crops have
been produced without irrigation; but this season some good crops
have been produced without any artificial watering."
We have seen that there was an apparent connection between the remarkable
volcanic action, exerted beneath the western continents during the second
decade of this century, and the remarkable coldness of that decade. And
it is easy to see that the comparative absence of volcanic action from
immediately beneath the Old World, and its presence in great excess
beneath the New, may disturb the regular action of terrestrial magnetism
above it in the earth's-crust here, and affect seasons, diatheses, and
health unfavorably; while from its absence they may be favorably affected
there. I have some general views in relation to this, but they are
necessarily speculative, for the data are few, and I reserve them.
I am, however, induced to believe that the transit of the atmospheric
machinery is greater over some portions of the northern hemisphere, in
some seasons, than others. The most natural explanation of the unusual
contrast between the drouth of the Eastern States, and the wet of the
Territories, during the last summer, is, that the concentrated
counter-trade was carried west, by some irregular magnetic action in the
South Atlantic or West Indies. But there was much evidence that the
northern extension of the atmospheric machinery was greater than usual.
The transit began _early_--it was evidently _rapid_; the rains of May fell
in April, and the spring was wet; _summer set in earlier_--all the
appearances then were unusually tropical--the polar belts of condensation
descended upon us, but they were feeble, as they doubtless become, when
they reach the tropics, and did not precipitate; the summer continued full
twenty days later--no rain falling till about the 10th of September. The
season throughout was excessive, but otherwise regular. Spring came
earlier; summer commenced earlier and continued longer; autumn held off
later, and cold weather, when it came, was uniform and severe. This season
the transit has seemed to be less than for several years.[10] The spring
was backward; the summer cool, but exceedingly regular; the autumn thus
far without extremes, and the whole year healthy and productive. It is the
normal period of the decade, between the irregular heat of the first part,
and the irregular cold of the last; and it has been normal in character,
and conformed beautifully to its location. If the transit of 1854 was
further north than the mean, as it seemed to be over this country, that of
itself would convey the showers which follow up in the western portion of
the concentrated trade, on the east of the mountains of Mexico, and cause
them to precipitate further north, over New Mexico, and thus, rather than
from a diverted trade, they may have derived their unusual supply of
moisture during the summer of 1854. On this subject I can but conjecture,
and leave to future observation a discovery of the truth.
Enough appears, however, to show the importance of taking the location of
the year in the decade, and even the character of the decade itself, into
the account.
But whatever the remote cause of the difference in the seasons, the
character of the seasons is directly influenced by the character of
storms, or periodic changes. Sometimes the tropical storms are most
numerous; at others the polar waves; and at others the irregular local
storms, or general tendency to showers. The seasons when the polar waves
are most prevalent, are the most regular, healthy, and productive. Those
where the tropical tendency is greatest, are irregular; and so are those
where the other classes predominate. These differences in the character of
the storms, are but the varying forms in which magnetic action develops
itself. I have said that there was a decided tendency to cirrus without
cumulus, in mid-winter, and cumulus without cirro-stratus or stratus, in
midsummer, and during the intermediate time an intermediate tendency. But
there is a difference between spring and autumn. Dry westerly (not N. W.)
gales prevail in March, and N. E. storms in April and May, but violent S.
E. gales are not as common. On the other hand, the dry westerly gales of
March are comparatively unknown in autumn, and the violent, tropical,
south-easters are then common.
Snow-storms occur during the northern transit, not unfrequently in April
and May; but they do not occur so near the acme of the northern transit on
its return; nor until it approaches very near its southern limit. The
quiet, warm, and genial air of April, is reproduced in the Indian summer
of autumn, but they present widely different appearances. Those, and many
other peculiarities of the seasons, deserve the attentive consideration of
every one who would become familiar with the weather and its prognostics.
These irregularities in the character of the seasons have doubtless always
existed, and always been the objects of popular observation. There are
some very old proverbs which show this. I copy a few of the many, which
may be found in Foster's collection. Mr. Graham Hutchison does not seem to
think any of those ancient proverbs worthy of notice. But he misjudges.
They are the result of popular observation, and many of them accord with
the true philosophy of the weather.
_Irregular_ seasons are unhealthy, and unreliable for productiveness. When
the southern transit was late, or limited, and the autumn ran into winter,
our ancestors feared the consequences in both particulars, and expressed
their fears, and hopes also, in proverbs. Thus,
"A green winter
Makes a fat churchyard."
There is very great truth in this proverb. Again,
"If the grass grows green in Janiveer,
It will grow the worse for it all the year."
This is emphatically true, for the season which commences irregularly will
be likely to continue to be irregular in other respects.
Another of the same tenor:
"If Janiveer Calends be summerly gay,
It will be winterly weather till Calends of May."
Janiveer is an alteration of the French name for January, and the proverb
is very old.
So March should be normally dry and windy.
This, too, they understood, and hence the strong proverb:
"A bushel of March _dust_
Is worth a king's ransom."
And another:
"March hack ham,
Come in like a lion, go out like a lamb."
So April and May should be cool and moist. It is their normal condition in
regular, healthy, and productive seasons. The grass and grain require such
conditions; and the spring rains are needed to supply the excessive summer
evaporation. This, too, they well understood. And hence the proverbs:
"A cold April the barn will fill."
"A cool May, and a windy,
Makes a full barn and a findy."
And--
"April and May are the keys of the year."
This was not very favorable, to be sure, for corn; but their consolation
was found, as we find it, in the truth of another proverb:
"Look at your corn in May, and you'll come sorrowing away;
Look again in June, and you'll come singing in another tune."
This difference in the character of the seasons occasioned the adoption of
a great variety of "Almanac days;" and they are still very much regarded.
Candlemas-day (2d of February) was one of them.
Says Hone, in his "Every-Day Book":
"Bishop Hall, in a sermon, on Candlemas-day, remarks, that 'it has
been (I say not how true) an old note, that hath been wont to be set
on this day, that if it be clear and sunshiny, it portends hard
weather to come; if cloudy and lowering, a mild and gentle season
ensuing.'"
To the same effect is one of Ray's proverbs:
"The hind had as lief see
His wife on her bier,
As that Candlemas-day
Should be pleasant and clear."
St. Paul's day, or the 25th of January, was another great "Almanac day,"
and so the verse:
"If Saint Paul's day be fair and clear,
It does betide a happy year;
But if it chance to snow or rain,
Then will be dear all kinds of grain.
If clouds or mists do dark the sky,
Great store of birds and beasts shall die;
And if the winds do fly aloft,
Then war shall vex the kingdom oft."
St. Swithin's day was another of these "Almanac days." Gay said truly,
"Let no such vulgar tales debase thy mind;
Nor Paul, nor Swithin, rule the clouds or wind."
Yet "_Almanac days_" are still in vogue to a considerable extent--such as
the _three first days_ of the year, old style--the first three of the
season--the last of the season--different days of the month--of the
lunation, etc., etc. And some still look to the breastbone of a goose, in
the fall, to judge, by its whiteness, whether there is to be much snow
during the Winter, etc.
These _Almanac days should all be abandoned_; they have no foundation in
philosophy or truth. There is one proverb, however, in relation to
Candlemas-day, which the "oldest inhabitant" will remember, and which it
may be well to retain. It has a practical application for the farmer, and
in relation to the length of the winter:
"Just half of your wood and half of your hay
Should be remaining on Candlemas-day."
The months, too, have a character which must be remembered and regarded.
_January_ is the coldest month of the year, in most localities. The
atmospheric machinery reaches its extreme southern transit, for the
season, during the month--usually about the middle. It remains stationary
a while--usually till after the 10th of February. One or more thaws,
resulting from tropical storms, occur during the month, in normal winters,
but they are of brief duration. Boreas follows close upon the retreating
storm with his icy breath. There is a remarkable uniformity in the
progress of the depression of temperature, to the extreme attained in this
month, over the entire hemisphere. It differs in degree according to
latitude and magnetic intensity; but it progresses to that degree,
whatever it may be, with as great uniformity in a southern as northern
latitude. The table, copied from Dr. Forrey, discloses the fact, and so
does the following one, taken from Mr. Blodget's valuable paper, published
in the Patent Office Report for 1853:
TABLE SHOWING THE MEAN TEMPERATURE FOR EACH MONTH AT SEVERAL PLACES, VIZ.:
+---------------------------------------------------------------------+
| | Lat. | Jan. | Feb. |March.|April.| May. |June. |
|-------------------|-------|------|------|------|------|------|------|
|Quebec, Canada E. |46° 49'| 9.9 | 12.8 | 24.4 | 38.7 | 52.9 | 63.7 |
|New York, N. Y. |40° 42'| 30.2 | 30.8 | 38.5 | 49.1 | 59.6 | 69.1 |
|Albany, N. Y. |42° 39'| 24.5 | 24.3 | 34.8 | 47.7 | 59.8 | 68.0 |
|Rochester, N. Y. |42° 45'| 26.1 | 25.8 | 33.0 | 45.8 | 56.2 | 64.5 |
|Baltimore, Md. |39° 17'| 33.1 | 34.3 | 42.4 | 53.0 | 63.2 | 71.6 |
|Savannah, Ga. |32° 05'| 52.6 | 54.7 | 60.0 | 68.4 | 74.8 | 79.4 |
|Key West, Fla. |24° 33'| 70.0 | 70.7 | 73.8 | 76.3 | 80.2 | 82.1 |
|Mobile, Ala. |30° 40'| 51.3 | 53.7 | 59.4 | 67.1 | 74.1 | 77.8 |
|New Orleans, La. |30° 00'| 54.8 | 54.5 | 61.5 | 67.6 | 74.0 | 78.6 |
|Marietta, Ohio |39° 25'| 32.2 | 34.1 | 42.6 | 53.0 | 61.8 | 69.2 |
|San Antonio, Tex. |29° 25'| 52.7 | 57.9 | 65.5 | 69.7 | 76.4 | 80.5 |
|San Francisco, Cal.|37° 48'| 50.1 | 51.0 | 53.8 | 57.7 | 55.9 | 58.8 |
+---------------------------------------------------------------------+
+-----------------------------------------+
|July. | Aug. | Sept.| Oct. | Nov. | Dec. |
|------|------|------|------|------|------|
| 66.8 | 65.5 | 56.2 | 44.1 | 31.5 | 17.3 |
| 74.9 | 73.3 | 65.9 | 54.3 | 43.5 | 33.9 |
| 72.2 | 70.3 | 61.4 | 49.2 | 39.4 | 28.3 |
| 69.7 | 67.8 | 60.1 | 47.7 | 38.2 | 28.8 |
| 76.6 | 74.5 | 67.7 | 55.8 | 45.0 | 37.8 |
| 81.3 | 80.6 | 76.9 | 67.2 | 58.3 | 52.2 |
| 83.3 | 83.5 | 82.5 | 79.1 | 75.6 | 72.8 |
| 79.8 | 79.4 | 76.1 | 65.7 | 57.0 | 52.8 |
| 80.4 | 79.6 | 77.1 | 69.1 | 57.5 | 56.2 |
| 72.7 | 70.9 | 63.5 | 51.8 | 42.6 | 34.7 |
| 82.3 | 83.3 | 79.9 | 72.2 | 62.2 | 52.1 |
| 57.9 | 62.2 | 61.6 | 61.9 | 56.2 | 50.0 |
+-----------------------------------------+
Snows during this month are much heavier, and more frequent, in some
localities than others. The reasons why this is so have been stated. The
mountainous portions of the country receive the heaviest falls. They
affect condensation somewhat, and according to their elevation. They
intercept the flakes before they melt, and retain them longer without
change. The thaws, or tropical storms, also sometimes have a current of
cold air, with snow setting under them on their northern and north-western
border. Such was the case with that investigated by Professor Loomis.
January is without other marked peculiarities. It shows, of course, those
extremes of temperature found, to a greater or less degree, in all the
months, and differs, as the others differ, in different seasons. Normally,
in temperate latitudes, it is a healthy month. The digestive organs have
recovered from that tendency to bilious diseases which characterizes the
summer extreme northern transit, and the tendency to diseases of the
respiratory organs, which characterizes the southern extreme and the
commencement of its return, is not often developed till February.
February, in its normal condition until after the 10th, and about the
middle, is much like January. Often the first ten days of February are the
coldest of the season. The average of the month is a trifle higher, in
most localities, as the tables show. This results from the increasing
warmth of the latter part of the month. There are localities, however,
where the entire month is as cold as January. Such (as will appear from
Blodget's table) are Albany and Rochester, in the State of New York, and
New Orleans, in Louisiana. At most places the difference is slight, either
way. South of the latitude of 40° heavy snows are more likely to occur in
the last half of January and first half of February than earlier. About
the middle of the month we may expect thaws of more permanence in normal
seasons. They are followed, as in January, by N. W. wind and cold weather,
but it is not usually as severe. Many years since, an observing old man
said to me, "_Winter's back breaks about the middle of February_." And I
have observed that there is usually a yielding of the extreme weather
about that period. Here, again, it is interesting and instructive to look
at the tables, and see how regularly and uniformly the temperature rises
in all latitudes, at the same time; as early and as rapidly at Quebec as
at New Orleans or San Antonio; and subsequently rises with greatest
rapidity where the descent was greatest. The elevation of temperature does
not progress northwardly, a wave of heat accompanying the sun, but is a
magneto-electric change, commencing about the same time over the whole
country, and indeed over the hemisphere.
March is a peculiar month--the month of what is termed, and aptly termed,
"unsettled weather." It, may "come in like a lion," or be variable at the
outset. The northern transit is fairly started, and is progressing
rapidly, and there is great magnetic irritability. A reference to the
table of Dr. Lamont will show that the declination has increased with
great rapidity. Normally, the early part is like the latter part of
February, and the latter part approaches the milder but still changeable
weather of April. Its distinguishing feature is violent westerly wind. Not
the regular N. W. only--although that is prevalent--but a peculiar
westerly wind, ranging from W. by N. to N. W. by W., often blowing with
hurricane violence. This wind was alluded to on page 130. With the change
and active transit to the north, in February and in March, comes the
tendency to diseases of the respiratory organs--pneumonias and lung
fevers--and this is the most dangerous period of the year for aged people.
April is a milder and more agreeable month. During some period of it, in
normal seasons, and at other times in March, there is a warm, quiet,
genial, "lamb-"like _spell_, exceedingly favorable for oat seeding. When
it comes, advantage should be taken of it, for long heavy N. E. storms are
liable to occur, and frequently with snow. On the latitude of 41° heavy
snow-storms are not uncommon in April. Within the last fifteen years two
such have occurred after the 10th of the month. April, as we have seen,
should be cool and moist. If dry, the early crops are endangered by a
spring drouth; if very wet, there is danger of an extreme northern
transit, and an early summer drouth. It is emphatically true that
"April and May are the keys of the year."
Its distinguishing peculiar feature is the gentle, _warm_, _trade_
rains--"_April showers_"--which, in the absence of great magnetic
irritability, that current drops upon us. There is great _mean_ magnetic
activity, but it is not so _irregularly excessive_ as in March.
May, in our climate, should be, and normally is, a wet month, and a cool
one, considering the altitude of the sun. The atmospheric machinery which
the sun moves is, however, ordinarily about six weeks behind it--the
latter reaching the tropic the 20th of June, and the former its farthest
northern extension about six weeks later. Hence it is not a cause for
alarm if May be wet and cool. The great staples, wheat, grass, and oats,
are benefited; and corn, according to the proverb, will not be seriously
retarded. The movable belt of excessive magneto-electric action, with its
tropical electric rains, so exciting to vegetation, and its periods or
terms of excessive heat, is on its way north, and sure to arrive in
season, and remain long enough to mature the corn. There have been but two
seasons in this century when corn did not mature in the latitude of 41°.
One during the cold decade, and the cold part of it, between 1815 and
1820; and the other, during the cold half of the fourth decade, between
1835 and 1840.
The distinguishing feature, if there be one, of May, is its long, and, for
the season, cool storms. These have, in different localities, different
names. In pastoral sections we hear of the "_sheep storms_"--those which
effect the sheep severely when newly shorn--killing them or reducing them
in flesh by their coldness and severity.
In relation to this too early shearing, there is an old English proverb,
in "Forster's Collection," viz.:
"Shear your sheep in May,
And you will shear them all away."
So there are others called "_Quaker storms_," which occur about the time
when that estimable sect hold their yearly meeting. And there are other
names given in different localities to these long spring storms. But they
are all _mere coincidences_--equinoctial and all.
Notwithstanding the storms, however, the temperature rises at a mean. The
declination is often as great as in mid-summer. The earth is growing
warmer by the increase of magneto-electric action, whatever the state of
the atmosphere. The yellow, sickly blade of corn is extending its roots
and preparing to "_jump_" when the atmosphere becomes hot, as it is sure
to do, when the machinery attains a sufficient altitude, how backward
soever it may seem to be. The farmer need not mourn over its backwardness,
unless the season is a very extraordinary one, like those of 1816 and
1836. The storms ensure his hay, wheat, and oat crops; the warming earth
is at work with the roots of his corn, and is filling with water, and
preparing for the hot and rapidly-evaporating suns of mid-summer. The
earth would grow warmer if every day was cloudy.
By the middle of June the atmospheric machinery approaches its northern
acme, the summer sets in, and not unfrequently, as extremely hot days
occur during the latter part of the month, as at any period of the
summer. But the heat is not so continuous, or great, at a mean.
From the middle of June to the latter part of August is summer in our
climate, and during that period from one to three or four terms of extreme
heat occur, continuing from one to five or six days, and possibly more,
terminating finally in a belt of showers overlaid with more or less
cirro-stratus condensation in the trade, and controlled by the S. E. polar
wave of magnetism, and followed by a cool but gentle northerly wind.
During these "heated terms," a general showery disposition sometimes,
though rarely, appears, with isolated showers, which bring no mitigation
of the heat. Not until a southern extension of them appears, followed by a
N. W. air, does the term change, so far as I have observed.
By the 20th of August, in the latitude of 42°, an evident change of
transit is observable, by one who watches closely, although the range of
the thermometer in the day-time may not disclose it. A greater tendency to
cirrus-formation is visible. The nights grow cooler in proportion to the
days. The swallows are departing, or have departed; the blackbirds, too,
and the boblinks, with their winter jackets on, _their plumage all changed
to the same colors_, are flocking for the same purpose, and hurrying away.
The pigeons begin to appear in flocks from the north, and the first of the
blue-winged teal and black duck are seen straggling down the rivers. At
this season, and nearly coincident with the change, the peculiar annual
catarrhs return. These are colds (so called) which at some period of the
person's life were taken about or soon after the period of change, and
have returned every year, at, or near the same period. They soon become
_habitual_, and no care or precaution will prevent them. I know one
gentleman who has had this annual cold in August for twenty-seven years,
with entire regularity; and another who has had it nineteen years; and
many others for shorter periods. I never knew one which had recurred for
two or three years that could be afterward prevented, or broken up. _Very
instructive are these annual catarrhs_ to those who think health worth
preserving, and in relation to the change of transit.
_The change is felt over the entire hemisphere._ Between the 20th of
August and the 10th of September hurricanes originate in the tropics and
pursue their curving and recurving way up over us; or long "north-easters"
commence in the interior and pass off to E. N. E. on to the Atlantic,
followed now in a more marked degree by the peculiar N. W. wind, so common
over the entire Continent in autumn and winter.
By the 10th of September the pigeons may be seen in flocks in the morning,
and just prior to the setting in of a brisk N. W. wind, hurrying away
southward with a sagacity that we scarcely appreciate, to avoid the
anticipated rigors of winter, and to be followed soon by all the migratory
feathered tribes that remain.
The nights grow cooler, although the sun shines hot in the day-time, and
woe to the person, unless with an iron constitution, who disregards the
change, and exposes himself or herself without additional protection, to
its influence. Nature has taken care of those who depend upon her, or upon
instinct, for protection. The feathers of birds and water-fowl are full;
the hair and the fur are grown. Beasts and birds have been preparing for
the change, and are ready when it begins. They know that the earth is
changing. The shifting machinery is fast carrying south that excess of
negative electricity which has so much to do with giving it its summer
heat. They feel its absence, even during the day, and the contrast between
that and the positively electrified northern atmosphere, which now follows
every retreating wave of condensation.
The musk-rat builds, of long grass and weeds, his floating nest in the
pond, that he may have a place to retire to, when the rain fills it up and
drives him from his burrow in its banks.
But man, with all his intellect, is too heedless of the change. Additional
clothing is now as necessary to him as to animals, but it is burdensome to
him in the day time, and therefore he will not wear it, how much soever it
would add to his comfort and safety during the night. He stands with his
thin summer soles upon the changed ground, or sits in a current, or in the
night air, less protected than the animals, and dysentery or fever sends
him to his long home. He has _intelligence_, but he lacks _instinct_. He
has time for the changes of dress which fashion may require, but none for
those which atmospherical changes demand. _Fashion_ has attention in
_advance_; _death_ none till _at the door_.
Now the southern line of the extra-tropical belt of rains descends upon
those who, living between the areas of magnetic intensity, have a dry
season; and the focus of precipitation in that belt descends every where.
"_Winter no come till swamps full_," the Indians told our fathers, and
there is truth in the remark; although like other general truths
respecting the weather, it is not always so in our climate. Rains fall
during the autumnal months, as during the spring months, and while the
transit of the machinery is active and the evaporation is less. And the
magnetic comparative rest, and the seed time and equable "spell" of April
is reproduced in the Indian summer of autumn.
The machinery gradually and irresistibly descends, and with an excess of
polar positive electricity, comes snow; Boreas controls, and winter sets
in, reaching its maximum of cold in January again.
Remembering, then, the differences in the normal conditions of the seasons
and months, and the different characters that the winds, and storms, and
clouds, and other phenomena bear in them respectively, let us now look at
the signs of foul or fair weather not herein before fully stated, upon
which practical reliance may be placed.
In the first place, we must look to the forming condensation. There are
many days when the atmosphere is without visible clouds, but few when it
is entirely without condensation. Such days are seen during the dry season
in the trade-wind region; and with us, in mid-summer drouths, which
partake of this tropical character; and when, at any season, but
particularly in winter, the N. W. wind in large volume has elevated the
trade very high. Condensation is not necessarily in form of visible cloud.
It may be of that smoky character which sometimes attends mid-summer
drouths, giving the sun a blood-red appearance; or it may be like that
change from deep azure to a "lighter hue," obscuring the vision, which
Humboldt describes as preceding the arrival of the inter-tropical belt of
rains. Gay-Lussac, and other aeronauts, have seen a thin cloud stratum at
the height of 20,000 to 30,000 feet, not visible at the earth, although
some degree of mistiness and obscurity were observed. At that elevation
the clouds are thin, and always white and positive. Some degree of
turbidness is frequent; it may occur, as we have stated, with N. W. wind,
but, if it does, the wind soon changes round to the southward.
This turbidness or mistiness, where it exists, and indicates rain, does
not disappear toward night, as it should do if but the daily cloudiness
which results from ordinary diurnal magnetic activity, but becomes more
obvious at nightfall; and, when hardly visible at mid-day, or during the
afternoon, may then be observed, obscuring in a degree, the sun's rays;
and, later in the evening, forming a circle round the moon. Thus Jenner--
"Last night the sun went _pale to_ bed,
The moon in _halos_ hid her head."
And so, too, Virgil--
"The sun, too, rising, and at that still hour,
When sinks his tranquil beauty in the main,
Will give thee tokens; certain tokens all,
Both those that morning brings, and balmy eve.
* * * * *
When Sol departs, his mighty day-task done,
How varied hues oft wander on his brow.
* * * * *
If the ruddy blaze
Be _dimm'd_ with _spots_, then all will wildly rage
With squalls and driving showers: on that fell night
None shall persuade me on the deep to urge
My perilous course, or quit the sheltering pier.
But if, when day returns, or when retires,
_Bright_ is the orb, then fear no coming rain:
Clear northern airs will fan the quiv'ring grove.
Lastly, the sun will teach th' observant eye
What vesper's hour shall bring; what clearing wind
Shall waft the clouds slow floating--what the South
Broods in his humid breast. Who dare belie
The constant sun?"
More frequently this kind of condensation is sufficiently dense at
night-fall to take shape, and show a bank when the sun shines horizontally
through a mass of it. I am now speaking of _storm_ condensation, or that
which indicates the approach of a storm. Thunder clouds at nightfall,
dark, dense, and isolated, are, of course, to be distinguished. Those,
every one understands to indicate a shower, and immediate succeeding fair
weather.
The halos do not, in cases of incipient storm condensation, always appear.
The moon may not be present: though, in her absence, I have seen them in
the light of the primary planets; or she may be in the eastern portion of
the heavens. When this is so, and the condensation forms slowly, there may
be less appearance of it, after the sun disappears, than before, although
a storm is approaching, and sure to be on by the middle of next day, and
perhaps with great violence. When the failure of the light no longer
reveals the denser condensation in the west, the stars may shine, as did
the sun, dimly but visibly, through the partial and invisible
condensation; and one who did not notice the bank in the west, at
nightfall and before dark, may be deceived by the seeming clearness of the
evening. Thus Virgil--
"Mark, with attentive eye, the rapid sun--
The varying moon that rolls its monthly round;
So shalt thou count, not vainly, on the morn;
_So the bland aspect of the tranquil night
Will ne'er beguile thee with insidious calm_."
All early condensation and indications derived from it, must be looked for
in the west. From that quarter all storms come. These indications at
nightfall are of a varied character. They may consist of primary
condensation in the trade, or of secondary condensation, scud running
north toward a storm, the condensation of which has not yet visibly
reached us, but which will extend south and pass over us. It may be a
heavy bank, or consist of narrow cirrus bands. Cirro-stratus cloud banks,
in the S. W., in the fall and winter, of a foggy and uniform character,
are indicative of snow. The body of the storm will pass south of us, and a
portion over us, the wind be north of east, and the snow will not be
likely to turn to rain before it reaches the earth, by reason of a
southern middle current.
Banks in the N. W. indicate rain at all seasons. The storm is north of us,
working southerly, and such storms rain on the southern border--in winter
even--because they have the wind on that border from south of east. It
may, indeed, snow, but if so, probably in large flakes, soon turning to
rain. There are other appearances at nightfall which deserve
consideration. A red sun, with smoky air, is indicative of continued dry
weather, a frequent appearance in dry terms, lasting three or four days,
at least, from the commencement. So is a red appearance of the sky, when
there are no clouds, indicative of a fair day following. On this subject
we have an allusion to the weather, by our Saviour while on earth, which,
like all such allusions found in the Bible, is of remarkable philosophical
accuracy. It is found in Matthew, chapter xvi., verses 2 and 3: "He
answered and said unto them, When it is evening ye say, It will be fair
weather, for the sky is red. And in the morning, It will be foul weather
to-day, for the sky is red and lowering. O, ye hypocrites, ye _can
discern_ the face of the sky," etc.
Another allusion to the weather, though not applicable to this point, I
will refer to in passing. It is found in Luke, chapter xii., verses 54 and
55: "And he said also to the people, When ye see a cloud rise out of the
west straightway ye say, There cometh a shower; and so it is. And when ye
see the south wind blow, ye say, There will be heat; and it cometh to
pass."
This is all very true, and might have been cited to show the universality
of the phenomena. But to return.
We have an old English proverb alluding to the same phenomena, of great
value and truth, viz.:
"An evening red and a morning gray
Are sure signs of a fair day;
Be the evening gray and the morning red,
Put on your hat or you'll wet your head."
The sky is red if there be no condensation at the west to obscure the rays
of the sun; if there be, it is gray, or there is a bank or cloud, and it
is obscured. So if there be no condensation over, or to the east of us, in
the morning, to reflect the rays of the sun, the sky is gray; if there be
such condensation, the sun is reflected from it, and the sky is red. Such
morning condensation is indicative of foul weather. It is, as we have
said, the eastern edge of an approaching storm, on, or under which, the
sun shines and illumines it. Thus, at night, it shines through a portion
at the west, which is situate between the sun and us, making the sky gray:
but shines on, or under, a portion in the morning, east of us, but not far
enough east to obscure the horizon, and the rays of the rising sun are
reflected from it. In either case the red or gray appearance results from
the relative situation of the sun and the eastern edge of an approaching
storm.
The following couplet of Darwin is an apt description of the morning
appearance:
"In fiery red the sun doth rise,
Then wades through clouds to mount the skies."
The sun is often reflected in vivid colors, from the under surface of
clouds, at sunset. This is an indication of fair weather. It is evident
the sun shines through a _clear atmosphere beyond the cloud_, or his rays
would not reach and illume the lower surface of the cirro-stratus with
such distinctness. He "_sets clear_," as is said; the clouds are passing
off, and there are none beyond. It is this appearance, in different forms,
when there happen to be patches of broken, melting cirro-stratus above the
horizon, which makes the beautiful sunsets that attract attention. So the
sun is reflected, in beautiful colors sometimes, from the cumulus clouds
which have passed over to the east. The most beautiful and variegated I
have ever seen, were reflected from that imperfect cumulus condensation
which takes place occasionally during long drouths--doubtless resembling
that which is seen over Peru, hereinbefore alluded to, as described by
Stewart.
It is not, then, the presence of cloud condensation at the west, at
nightfall, which alone indicates foul weather; but such condensation,
whatever its form, as evinces that it is not the _dissolving_ cloud of the
day, but the eastern, approaching portion of a _still denser portion
beyond, through, or under which, the sun can not shine clearly, but which
wholly or partially obscures it_. _Remembering this philosophy of the
matter_, the observer will soon be able to detect the various forms of
condensation which originate or exhibit themselves at nightfall, and
whether they indicate an approaching storm or not, without a more explicit
specification of them. It is an important hour for observation; "Let not
the sun go down" without attention.
When the condensation is obvious, but thin, at nightfall, it may not, as I
have said, be discernible in the evening. But there are methods by which
the incipient storm condensation may be detected. The number of the stars
visible, and the _distinctness_ with which they may be seen, indicate the
absence or presence of condensation and its density. Virgil, alluding to
the indications of fair weather, says:
"_Brightly_ the stars shine forth; Cynthia no more
_Glimmers_ obnoxious to her brother's rays;
Nor fleecy clouds float lightly through the sky."
The brightness of the stars and the clear appearance of the moon show the
absence of condensation and the _dissolution_ of the fleecy clouds at the
close of the day is, as we have seen, always a fair-weather indication.
There is much true philosophy in the allusions of Virgil to the moon.
Thus--
"When Luna first her scatter'd fires recalls,
If with _blunt horns_ she holds the _dusky_ air,
Seamen and swains predict th' abundant shower."
The horns, or angles of the moon will, of course, appear distinct and
sharp or indistinct and blunt, in proportion to the amount of
condensation in the atmosphere which impedes the passage of the light. For
the same reason, when the moon is new, her entire disk is visible when the
atmosphere is very clear, by reason, as is supposed, of light reflected
from the earth to the moon and back to us. This double reflection can only
take place when the atmosphere is very clear. Hence, Virgil alludes to it,
and correctly, as an indication of continued fair weather:
"If (mark the ominous hour!)
The clear fourth night her lucid disk define,
That day, and all that thence successive spring,
E'en to the finished month, are calm and dry."
Probably Virgil alluded to a month of the summer trade-wind drouth which
reaches up on Southern Italy. But that appearance of the moon is
occasionally seen here, and the indication is, in degree, philosophically
true.
It is somewhat more difficult to determine what will be the result of the
condensation seen at the west in the morning, and which is not so far
east, or of such a character, as to reflect the rays of the sun; for,
although always suspicious, it is sometimes of a foggy character, and
disappears between eight and nine o'clock. If it increases in density
after ten o'clock, or is of a dense cirro-stratus character, rain may
generally be expected. If of a decided _cirro-cumulus_ character, it is
certain to disappear. Cirro-cumulus is seen in small patches, with small,
distinct, and rounded masses, in summer, in the morning, and sometime,
during the day, after high fog has disappeared, and at other times, and is
always, when of that _distinct_ character, a fair weather indication. I
have seen it thus when the wind was blowing from the N. E., and the scud
running toward a storm passing near, but to the south of us, when those
who relied upon the existence of the wind and scud as evidences that we
were to have the desired rain, were deceived. Thus, the couplet from an
old almanac:
"If _woolly fleeces_ strew the heavenly way,
Be sure no rain disturb the summer day."
When this morning condensation is not high fog, and is dense and passing
east with a wavy appearance, it is very certain to rain. Jenner says:
"The boding shepherd heaves a sigh,
_For see, a rainbow spans the sky_."
An old almanac had the following verse:
"A rainbow in the morning
Is the shepherd's warning;
A rainbow at night
Is the shepherd's delight."
So the proverb was originally made; but as our ancestors were not
shepherds, and had a horror of ocean storms, it was commonly quoted, in
this country, in the following form:
"A rainbow in the morning,
The sailors take warning," etc.
Rainbows are not reflected from _clouds_, but falling rain, and a morning
rainbow at the west is, of course, evidence that it is _actually raining
there_, and will, in all probability, pass over us. "Thunder in the
morning, rain before night," is a common saying, and a true one. There is
a belt of showers, or showery period approaching, of unusual
intensity--for thunder showers in the morning are rare. The afternoon is
their most common period, and they are very apt to appear then, when the
morning is showery.
Of the different forms of cirrus and cirro-stratus, which appear during
the day, and indicate approaching storms, or of cumulus indicative of
showers, it is difficult to give an intelligible description without very
many illustrations. I have many daguerreotype views, taken at different
seasons of the year, and at a time when different forms of cirrus and
cirro-stratus condensation, indicative of storms, exhibited themselves.
They differ, as I have said, and it must be remembered, very much at
_different seasons_ of the year, and in _different years_, and their
delicate shades are taken with difficulty by the artist, and reproduced
with difficulty, and only at considerable expense, by the engraver; and I
have omitted them. The time will come when a knowledge of their language
will be sought for and read--when the "countenance of the sky" will be an
object of intelligent interest to all whose business may be affected by
the weather, or who love to learn of nature. But it is not yet. This is
the age of theory and speculation. The time of actual, practical,
connected observation and prognostication, which may justify expensive
illustration, is yet to arrive.
The reader will find in the general plates representations of several
kinds of cirri. They are delicate, always white, more or less fibrous, and
form in the upper part of the trade or the adjoining atmosphere above it.
Their character and elevation should be studied, and the observer should
be careful to distinguish which is the most elevated. Not unfrequently it
may seem, to a hasty observer, that the cirrus is below the cirro-stratus
or forming stratus. But the genuine cirrus never is. It forms near, and
above, the point of congelation, and is often composed of crystals of ice
or snow. If they fall, they melt and evaporate, when there is no storm,
before reaching the earth. Aeronauts have met with them and their crystals
when there was no fall of moisture at the surface of the earth; and the
angles of reflection exhibited by halos and other optical phenomena which
form in them, enable us to detect their crystallization and the form of
it.
They are produced by electric changes which condense the vapor, and the
coldness of the air at that elevation freezes it at the _instant of its
condensation_.
Congelation is crystallization, and all crystallization is electric, or
magneto-electric. The snow-flakes differ in form and size according to the
suddenness of the condensation, the amount of moisture condensed, the
polarity of the strata through which they pass, and their consequent
attraction and adhesion to each other.
The connection of electricity with these formations of cirri has
frequently been admitted, and it is perfectly obvious that the long
fibrous bands, shooting from horizon to horizon, could not be formed by
commingling of currents any more than the perfectly isolated, distinct,
enlarging-outward cumulus hail-storm, could be so formed. Cirri form at
the line of meeting, between the trade and the upper atmosphere, and in
one or the other, or both, very much according to the season, and the
suddenness with which storms are produced. These often _induce_ a layer of
cirro-stratus or stratus at the lower line of the counter-trade, and in
the surface-atmosphere, which precipitates; and this operation is clearly
discernible, and very frequently, before gentle rains. Condensation in the
whole body of the trade is usually in the form of turbidness or mistiness,
a bank or incipient stratus, without cirri.
It seems matter of astonishment that water should float so far condensed,
in strata where the air is so much lighter, without being precipitated.
But electric attraction and repulsion between the different strata and the
vesicles, explain it.
In mid-winter, the cirrus forms are prevalent and most distinct. After
severe cold weather, when a storm approaches, the cirri form in long,
narrow threads, parallel to each other, extending from about W. S. W. to
E. N. E., gradually thickening and forming, or inducing, cirro-stratus and
stratus, and dropping snow. This form is called the _linear_-cirrus. The
tufted, and other fibrous forms, are seen in patches also, in great
distinctness, during these mid-winter days, when the wind gets around to
the southward, and the weather is pleasant. Such days are called
"_weather-breeders_," and their _offspring_ the patches of cirrus, which
are to extend and compose, or induce the storm, and indeed are an advance
part of it, are then never absent. A clear, moderate day, in a normal
winter, with wind from any southern point, however light, between the 1st
of January and the middle of February, without these patches of cirrus, is
very uncommon. Watch and see whether they tend to cirro-stratus, or
whether the wind gets around to the N. W. at nightfall, and they
disappear. If the former, a storm may be expected; if the latter, fair
weather.
Thus there are three peculiarities attending the forming cirrus of
mid-winter (1st of January to 10th of February): long, fibrous, parallel
bands in the morning (linear cirrus), gradually coalescing as the day
advances, after severe cold; the comoid, curled, or tufted cirrus, in
curling bunches, called "_mares'-tails_," and the _transverse_, when the
fibers are in bands or threads, which are not parallel, but cross each
other at angles, more or less acute. The two former varieties are
represented on Figure 5, page 26, indicated by one bird, but the last form
is a very prevalent one in our atmosphere.
Various names have been given to different forms of _cirro-stratus_. Those
represented in Figure 5, page 26, are the "_cymoid_" on the right, the
"_mottled_" on the left, below the cirro-cumulus; and the "_linear_"
below that. The form known as the "_mackerel sky_" is not represented
there. It consists of regular forms, resembling the _waves_ on the surface
of the water when the wind blows a gentle breeze. But the _wavy_ form, and
of all sizes, is very frequently assumed by cirro-stratus, which is
rapidly condensing, and turning to stratus. In the "mackerel sky,"
strictly so called, the waves are small, parallel, nearly distinct and
equi-distant, and resembling the appearance of a school of mackerel,
swimming in the same direction, one above another. All _wavy_ forms of
cirro-stratus indicate a disposition to increased condensation and rain.
When the waves are very large and dense, and cross obliquely, or unite at
one end, rain is very certain to fall soon, if the line of progress of the
condensation is over the observer, and the clouds are seen in the western
or N. W. quarter of the sky.
But there are few forms which are not occasionally seen when no rain or
snow falls. The intensity of the electric action which produces them may
not be sufficient to effect precipitation, or they may be the attendant,
attenuated _lateral_ condensation, which frequently "thins out" a
considerable distance from the dense, precipitating portions of the storm.
If that denser portion is north of us, the probabilities of rain are
greater, for there is always a probability that the storm may be of the
character which is extended south, by a polar wave. The observer must
watch the formation of cirri, and the different forms of cirro-stratus and
stratus, and become familiar with their appearance. It is not a difficult
task. With the aid of a few general directions he will soon be familiar
with them:
1. Get a correct idea of the different characters of the primary clouds.
The true fibrous _cirrus_--the different forms of _cirro-stratus_--the
smooth, uniform _stratus_--the _cirro-cumulus_, which is nothing but a
cirro-stratus, separated into _distinct masses_ by the repulsion of static
electricity--and the _cumulus_, too distinct ever to be mistaken. There is
no difficulty, except with the varied forms of cirro-stratus. It is
useless to attempt to give, or the observer to rely on, names for these
numerous forms, without as numerous illustrations. Those in use are rarely
applied correctly. I have never met with ten persons who applied even the
term "mackerel sky" to the same precise form of cirro-stratus. In relation
to all of them it is to be observed that polar belts of condensation, and
local appearances of considerable extent, are often too feeble in action
to precipitate, even when the mackerel form is present; and all may be the
lateral attendants of passing storms. Therefore,
2. Satisfy yourself whether the cirrus or cirro-stratus increases in
density and tends to the formation, or induction, of stratus; and whether
it is isolated, or an extension of the condensation of a storm, and if the
latter, _where that storm is_. The time will come when an intelligent use
of the telegraph will do this for you.
3. Look also to the character of the wind, if there be any. On this
subject I have perhaps said all that is necessary in the preceding pages.
Next to condensation, the direction and character of the wind is the most
valuable prognostic. Indeed it often tells us that a storm is approaching,
and the quarter from which it will come, and its character, before the
condensation is visible.
4. See if there is any _secondary_ condensation or scud. These are
sometimes seen running toward a storm, when there are not distinct clouds
visible in the western horizon, at nightfall, or in the evening, as in the
instance stated in the introduction, and sometimes from the north-east, as
in cases heretofore so often stated. But the easterly scud do not often
form in winter, until after the cirrus has passed into the form of
cirro-stratus, or has induced the latter forms in the inferior portion of
the trade, or the surface atmosphere.
The inductive effect of the primary condensation, therefore, is not
always, and especially in winter, sufficient to create the easterly
current and scud, and it is often the case that the easterly wind is not
felt, or the scud seen, in snow-storms, until the snow has begun to fall,
and the first snow will fall with a S. W. air, as I have heretofore
stated. But when the condensation has so far advanced toward stratus that
the easterly wind and scud are obvious, there is little or no doubt that
rain or snow will fall speedily. The occasional occurrence of easterly
wind and scud, without rain, however--dry north-easters, as I have termed
them--in connection with storms passing south of us, or condensation too
feeble to precipitate, should be remembered. The long, dry,
north-easterly winds of spring have been attributed to the icebergs, but
they are overlaid by feeble stratus or cirro-stratus condensation, or are
the result of attraction, by a more southern precipitation. The observer
must be careful to distinguish between the various forms of N. W. scud and
cirro-stratus, which they sometimes resemble. This he may do _from the
direction in which they move_. Cirro-stratus always moves from some point
between S. S. W. and W. S. W. to some point between N. N. E. and E. N. E.
The various forms of N. W. scud move to the S. E. The March, foggy scud,
from between W. and N. W., rarely have any cirro-stratus above them, but
rather a peculiar turbid condensation.
The character of the primary condensation, the direction and force of the
wind, and the direction of the secondary condensation or scud, must be the
main reliance of the observer. But I must reiterate that they all differ
in different kinds of storms, in different seasons of the same year, and
the same seasons of different years; and the observer must be careful to
make due allowance for those differences.
There are, however, divers other secondary signs, which, although not
alone to be relied upon, will aid the observer, if carefully studied, when
the character of the clouds, and the pressure of easterly or southerly
wind and scud, are not decisive. Of these, a large class are electrical.
The smoke descends the adjoining chimney-flues, or outside of the chimney,
toward the ground.
Thus, Darwin, as quoted by Hone:
"The smoke from chimneys right ascends,
Then, _spreading_, back to earth it bends."
Smoke is electrified _positively_, by the act of combustion; the earth and
the adjacent atmosphere, when storms are gathering or approaching, is
_negative_. Hence the smoke spreads, and is attracted downward by an
opposite electricity. On the other hand, it is interesting to see, at
other times, and when the difference in temperature is not material, but
the whole atmosphere is positive, with what rapidity and compactness the
smoke will ascend in a _straight and elevated column_ from the chimney,
repelled by a similar electricity. I am aware it is generally supposed the
smoke descends because the _air is lighter_. But it is a mistake. I have
seen it descend when the barometer was at 30°.60, or .60 above the mean.
There is, too, a draught downward in chimneys, in such cases when there is
no smoke or fire in any of its flues. Thus Jenner says: "The soot falls
down;" whether he meant by this that there was an actual fall of soot
other than what is occasioned by the rain falling in through the chimney
top, and disturbing the soot, as sometimes happens, I do not know. It
occurs rarely, and is of very little practical importance. But every
housewife knows that chimneys, which have been used in winter, and are
full of soot, _smell_ before storms. The odor results from a downward
draught and the dampness of the air. So the smoke from one flue will
descend another, into some unused room, on such occasions. Another class
of these electrical signs are felt by those who are suffering from chronic
diseases, which have affected the nerves and made them sensitive. Thus
Jenner:
"Old Betty's joints are on the rack."
And Hone adds:
"Her corns with shooting pains torment her,
And to her bed untimely send her."
But Old Betty's rheumatism or corns are not alone in this. Those whose
bones have been broken feel it. All invalids feel it. And, indeed, all
observing healthy persons may, and do, although all are not distinctly
conscious of it. It is common for such to say, I feel sleepy, or I feel
dull, or, It _feels_ like snow, or _feels_ like rain, and thus from their
own feelings to be able to predict, not only falling weather, but its
_character_, whether snow or rain, at a time when either may occur
consistently with appearances.
This change is a change from the positive electricity which is so
congenial to the active--"bracing" is the usual term--to negative and
damp--for this change is accompanied by condensation, as I believe all
changes from positive to negative are. Certain it is, if the atmosphere is
highly charged with negative electricity, condensation takes place; if
with positive, evaporation. Perhaps it is a change of the associated
electricity which accompanies magnetism, and not of the free atmospheric
electricity alone. Hence another phenomenon alluded to by Jenner:
"The walls are damp, the ditches smell."
There are localities where this dampness is very obvious. The celebrated
William Cobbett, many years since, when a farmer on Long Island, observed
and published the fact that the stones grew damp before a storm. I know of
flagging stones that usually grow damp two or three hours before rain,
especially in spring and fall, and every step taken upon them is made
visible by a corresponding increase of condensation.
The reverse of this takes place just before the close of storms. Flagging
stones, and walls under cover, will frequently become dry before the rain
ceases. The negative electricity becomes less as the positive prevails,
although the clouds above are still dropping rain.
In the comparatively moist, showery climate of England, these changes from
positive to negative alternate rapidly between successive showers; but
observations of electric phenomena, or of clouds, in that climate, are
not, without qualification, safe guides for us.
So "the ditches smell," particularly in the evening before a rain, when
the immediate surface-atmosphere is charged with negative electricity, and
the _condensing moisture_ prevents the diffusion of the odors. For the
same reason the candle will not relight, and there is crackling in the
ashes or lamp. Thus, again, Virgil:
"Maidens that nightly toil the tangled fleece
Divine the coming tempest; in the lamp
_Crackles_ the oil, the gathering wick grows dim."
Virgil did not live in our cold climate, and knew nothing of the crackling
in the fire, or in the ashes or coals which remain after the wood is
consumed. The lamp exhibits it on a smaller scale, and perhaps he had
noticed it when in company with the maidens. But it is sometimes
noticeable even in the lamp or candle with us. A small particle of
moisture will produce it, in a marked degree, at any time.
In winter, when the air is highly positive and cold, the candle can be
blown out, and by another puff of the breath relighted, with ease. But
when the electricity before a storm becomes negative, and partial
condensation takes place, this can not be done. This partial condensation
before storms and showers shows itself upon vessels containing cold-water,
in summer. It seems to be the received opinion, that the condensation is
evidence of a greater _quantity_ of moisture in the atmosphere. But this,
too, is a mistake, and hence the little reliance to be placed on
hygrometers.
This partial condensation is sometimes visible. When the sun shines
clearly, at the east or west, through a _small opening_ in the clouds, the
condensing vapor is shown by the streaks of sunlight, just as the fine
particles of dust are seen in a dark room, when a few rays of sunlight are
admitted through a small aperture. This phenomenon is often observed, and
it is said of it--"It's a going to rain; _the sun is drawing water_."
Virgil alludes to this as seen in the east in the morning, thus:
"But when beneath the dawn _red-fingered rays_
Through the dense band of clouds _diverging_ break,
* * * * *
Ill does the leaf defend the mellowing grape;
Leaps on the noisy roof the plenteous hail,
Fearfully crackling."
It is well ascertained that storm-clouds of great intensity have polarity
in the different portions, and that in the less intense magneto-electrical
climate of England isolated showers are often of this character--the
polarity existing in rings. Showers are doubtless thus found with us. Mr.
Wise got into one of them; see his description (Theory and Practice of
Aeronautics page 240).
I have, in another place, alluded to the upward attraction of the dust
beneath the advance condensation of a shower. Jenner alludes to it in the
following lines:
"The whirling winds the _dust_ obeys,
And in the rapid eddy plays."
So Virgil:
"Light chaff and leaflets, _flitting, fill the air_,
And sportive feathers circle on the lake."
All these are electrical.
In England, where the action of such isolated clouds is less intense, the
different electricities in different portions of the cloud, whose opposite
and changing action produce all the phenomena, the condensation, the cold
and congelation, the currents, etc., have been accurately ascertained. We
can not get into the situation occupied by Mr. Wise. But every man may
observe these _intestine motions_ occasionally, in the advance
condensation of an isolated thunder-shower, in front of, but near the
smooth line of falling rain. They are more lateral than upward or
downward, and are often exceedingly rapid in movement.
I have said that hail has often been found to fall from particular and
well-defined portions of a cloud, and rain from the other portions, the
hail being positive, and rain negative. An instance of very striking
character may be found in Espy's Philosophy of Storms (Introduction, page
xx.) Doubtless in all cases thunder-showers, which are isolated and
distinct, have opposite electricity in different portions, to whose active
agency all the phenomena are owing. And the return of electricity to the
earth in the rain explains the greater fertilizing effect of the latter
compared With all artificial watering. He was a true philosopher who
attempted to stimulate vegetation by electricity.
Sounds may sometimes aid the observer in doubtful cases in foretelling the
weather. The roar of the surf, or breaking of the waves on the shore, when
great bodies of water are disturbed by a precedent storm-wind, often heard
before the wind is perceived on the land, I have already alluded to. And
thus Virgil:
"When storms are brooding--in the _leeward gulf_
Dash the swelled waves; the mighty mountains pour
A harsh, dull murmur; far along the beach
Rolls the deep rushing roar."
The moaning or whistling of the wind all have noticed. It is not uncommon
to hear the expression, "The wind sounds like rain." Jenner says:
"The _hollow_ winds begin to blow."
And Virgil:
"The _whispering_ grove
Betrays the gathering elemental strife."
This whispering is the motion of the leaves; and they are often stirred by
a peculiar motion which is not that of wind. Sometimes every leaf upon a
tree may be seen _vibrating_ with an _upward and downward_ motion, when
there is not wind enough to stir a twig. This interesting phenomenon is
electrical. Trees, and all vegetables, confessedly discharge electricity,
and such discharges move the leaves, when very active.
With us, sounds can be heard more distinctly from the east or south,
before storms, according to the character of the coming wind. Howard
mentions an instance when he heard carriages five miles off. Steamboat
paddles, rail-road cars, and other sounds, are often heard a great
distance. The distance at which the now common steam-whistle is heard, and
the direction, is not an unimportant auxiliary indication of the weather.
Howard attributes these peculiar phenomena to the "_sounding board_," made
by the _stratum of cloud_; but sounds may be heard from the north-west,
when there is no condensation, and the wind is from that quarter, and also
from the east when it is not cloudy; and in a level country the village
bells often tell the direction of the current of air just over our heads
when we do not feel it at the surface. The wind is undoubtedly moving in a
rapid, and perhaps invisible current, not far above us. If from the east
or south, it betokens rain; if from the western quarter, fair weather.
The conduct of the different animals furnish a considerable portion of the
signs alluded to by Virgil and Jenner, and are never unimportant auxiliary
evidence of the approaching changes, whether from dry to wet, or wet to
dry.
The observer will find, in the conduct of our birds and animals,
especially those which are not domestic, ample evidence of the truth of
the descriptions of Virgil. He denies the animals and birds foresight, but
he does not seem to have observed that the swallow leaves for the south as
soon as the _autumnal_ change begins to be felt, and in August; nor the
evident sagacity of other _migratory_ birds. They do not act from the
"_varying impulse_" produced by an actual state of things, but a knowledge
or apprehension of those which are to come. This is nothing more or less
than foresight. So foresight tends to prudence and skill, and they
exercise both, and with reference to the future. The goldfinch does not
build her nest in the hole of the tree, or in the crotch of the limb; but
_hangs it_ with _exquisite skill_ on the slender _waving, outward branch_,
where no animal, or larger bird, or any depredator, can be sustained. She
is not more timid than others; why does she invariably thus build? What
makes her "_impulses_" differ from those of other birds, and always in the
_same manner_?
Jenner, too, has grouped, in admirably descriptive language, many of the
peculiarities exhibited by animals and birds before approaching storms,
some of which exhibit foresight, and others not.
Perhaps the rooster, who keeps ceaseless watch over his harem, is the most
reliable weather-watcher we have. In my earlier days, when it was the
practice to keep valuable birds of the kind much longer than it now is,
and they had opportunity to become _experienced_, it was interesting to
observe how closely they watched the weather. I well remember a venerable
chanticleer, who, perched on the tree among his hens, would always
foretell the coming storm of the morrow, by sounding forth _in the
evening_, and _often_, his defiant note. Such note in the evening was
invariable evidence of foul weather. And during the night, their earlier
and more frequent crowing is often indicative of it. It is, however, in
the earlier part of the day, in doubtful cases, that no inconsiderable
reliance may be placed on their sagacity. Often, when a storm is gathering
in the forenoon, they will announce it by an almost incessant crowing. The
habits of an _experienced_, old-fashioned bird, of this kind, will well
repay attention; but I can not answer for the Shanghai and other _fancy
breeds_.
Jenner says:
"The leech disturbed, is newly risen
Quite to the summit of his prison."
Few have had, or will have, opportunities to observe this, but it is
strikingly true. It is difficult to conceive how mere condensation, from
an increase of vapor in the atmosphere, should be foreseen by the leech in
his watery prison. It is obvious, I think, there is an electric change
which reaches him, as it does the whole animal creation, the once broken
bones, and the joints of Aunt Betty. Thus much of the philosophy of signs.
_The barometer_ is a useful instrument, in connection with observations of
the other phenomena. It is especially useful to the sailor, as its
indications relative to the winds are much the most certain. But it is
not, _alone_, to be relied upon. This is well settled, although the
reasons for it have not been understood. Why it should rise sometimes
before storms, in opposition to the general rule--or fall at others
without rain--or rise occasionally during the heaviest gales, has been a
mystery, and impaired the confidence in its accuracy and usefulness even
of the class of philosophers of whom Sir George Harvey spoke, in the
sentence quoted in the introduction. But, as I have already intimated, it
is all very intelligible.
I have said that the barometer has no fair weather standard--the mean of
30 inches at the level of the sea being an _average_ of the _fair weather_
elevations and the _foul weather_ depressions. Its fair weather position,
it would seem, must be above the mean, therefore, and as much above as its
foul weather depressions are below. But this is not precisely true. Its
extreme fair weather range is 31 inches, and it rarely reaches that; while
its lowest storm range is down to 28, and is the most often reached of
the two. My barometer stands about 40 feet above ordinary high-water mark.
It is not a "wheel," but an open, "scale" barometer, and a perfectly good
one. Its most reliable fair weather standard is about 30-30/100 inches. It
is its _most common summer, set fair position_, but that position is often
at other and different elevations, at other periods of the year, during
fair weather. The reader must observe for his own locality, and satisfy
himself what the most common set fair position for the barometer is, at
the different periods of the year, where he resides. When he has
ascertained this, he may apply the following principles to illustrate its
exceptional action, and in judging of the future of the weather:
1st. _As to its rise before storms._--Supposing it to have been
stationary, at or about a set fair position, _for the period_, and for one
or two or more days, a very _gradual_ and _moderate_ rise is an indication
of continued fair weather; and a _sudden_ and _considerable rise_ is
indicative of a storm. If the sudden and considerable rise occurs in the
latter part of spring, summer, or early autumn, it indicates a storm of
the _first_ or _third classes_ described in Chapter X., if in winter, a
storm of the _first class_ only. If the elevation is _very_ sudden and
considerable, the storm will probably be _severe_. The philosophy of this,
according to my present apprehension of it, is, that these storms present
an _extended easterly front_--_settle very near the earth_--and _have a
rapid progress_--thus accumulating the atmosphere somewhat, in advance of
them.
2d. _As to its fall before storms without previous rise._--This is always
very regular before the second class of storms, or polar belts of showers
and storms. It is very fairly exemplified in the table from Reid, on page
329. The barometer, so far as I have opportunity to observe, does not rise
from a stationary position on the approach of this class of storms. At the
commencement of heated, summer, dry terms, my barometer has most
frequently ranged at about 30.30, and gradually, but slowly, fallen below
30 inches before the belt of showers arrived, and the term closed. The
fourth rule of Dalton (Meteorology, page 183) indicates a similar law in
England. It is as follows:
"In summer, after a long continuance of fair weather, with the
barometer high, it generally falls gradually, and for one, two, or
more days, before there is much appearance of rain. If the fall be
sudden and great for the season, it will probably be followed by
thunder."
3d. _It falls frequently and considerably without rain._--This is owing to
the fact that _all_ regular, periodic efforts at condensation do not
result in rain. The second, third, and fourth classes of storms described,
may not (as we have said) _be sufficiently active to precipitate_,
although the _series of phenomena_ (including the fall of the barometer)
may be, in other respects, perfect. Such an instance may be found in
Reid's table, on page 329, and on the 11th of the month. But the fall in
such cases is not as great, unless the wind be violent.
4th. _It rises during considerable gales._--But these are of the kind so
often alluded to--viz., the N. W., in the northern hemisphere, and the S.
W., in the southern; and the _philosophy_ of it has been explained, and is
observable.
With these explanations, the reader will be able to understand, and
practically apply, the barometric changes, in connection with the other
phenomena, in forming an opinion of the weather.
_The thermometer_ is also an auxiliary. It _rises_, during the winter half
of the year, in the _advance portion of the storm_, and falls when it
passes off again; and the reverse is true, as we have seen, when its range
is very high in summer. It is, therefore, to some extent, a useful
auxiliary, although of minor importance.
_The hygrometer_ is of less importance still. It is not in general use as
a practical guide to the changes of the weather, and does not deserve to
be.
A question, which has been much mooted, deserves a passing notice in this
connection--viz., whether our climate has gradually become ameliorated and
milder on the eastern part of our continent, since its settlement. I have
not space left for its discussion. Humboldt (Aspects of Nature, page 103)
is of opinion that there has been no material change. He says:
"The statements so frequently advanced, although unsupported by
measurements, that since the first European settlements in New
England, Pennsylvania, and Virginia, the destruction of many forests
on both sides of the Alleghanys, has rendered the climate more
equable--making the winters milder and the summers cooler--are now
generally discredited. No series of thermometric observations worthy
of confidence extend further back, in the United States, than
seventy-eight years. We find, from the Philadelphia observations,
that from 1771 to 1824, the mean annual heat has hardly risen 2°.7
Fahrenheit--an increase that may fairly be ascribed to the extension
of the town, its greater population, and to the numerous
steam-engines. This annual increase of temperature may also be owing
to accident, for in the same period I find that there was an increase
of the mean winter temperature of 2° Fahrenheit; but, with this
exception, the seasons had all become somewhat warmer. Thirty-three
years' observation, at Salem, in Massachusetts, show scarcely any
difference, the mean of each one oscillating within 1° of Fahrenheit,
about the mean of the whole number; and the winters of Salem, instead
of having been rendered more mild, as conjectured, from the
eradication of the forests, have become colder, by 4° Fahrenheit,
during the last thirty-three years."
The facts hereinbefore stated show that there is nothing like a _regular_
amelioration; that the seasons differ during the same decade, and
different decades. The cold decade, from 1811 to 1820, has not been
reproduced. But it may be, and we know not how soon. Since that period
there has certainly been a change--for even the cold period from 1835 to
1840 did not equal that from 1815 to 1820, nor indeed those of 1775 to
1780 or 1795 to 1800. But as these variations, so far as we are enabled to
judge, depend upon the varying influence of the sun's rays, and of
volcanic action, it is impossible to say that equally cold periods will
not return, during the latter half of this century.
If the influence of the sun was constant, and volcanic action regular, two
causes would tend to modify the seasons:
1st. The exposure of the surface to a more effective action of the solar
rays, by a removal of the forests, and by drainage. That such action would
be more effective upon a surface thus uncovered and drained, can not be
doubted.
2d. _The movement of the area of magnetic intensity, and the magnetic
pole, to the west._--There is such a movement, and its progress can be
measured by the increase of declination on the east of it, and its
decrease on the west. And the effect of it on climate is unquestionable.
In all probability it has had an influence upon ours; and a removal of
that area and pole still further west--60° or 80°--would change the
location of the concentrated trade, and the Gulf Stream, and restore to
Greenland the fertility she once had, and which the Faroe Islands now
enjoy. And, on the other hand, its removal as far east of its present
position would again depopulate Greenland, and render it again
inaccessible. But I can not pursue this subject.
Finally, assistance may be derived from the occasional, although
imperfect, accounts of the state of the weather elsewhere, which the
newspapers afford. I have been much indebted to the Associated Press of
New York for intelligence contained in their telegraphic reports.
Occasionally they have been very full and instructive.
On this point, however, there is less of reality in the present than of
hope in the future. The time must come when the collection and
dissemination of meteorological truth, will be deemed an object of
national importance, and national duty. Population is increasing, by
immigration and propagation, in a rapidly progressive ratio. There has
been great danger that it would outrun agricultural production. A short
crop this year would have been disastrous to our prosperity--and the
danger was imminent. Every description of business, and every financial
circle, felt that fever of anxiety it was so well calculated to induce.
The importance of extended agricultural production, and the dependence of
all classes upon its success, are now in a greater measure appreciated;
and none can fail to see the value of a correct understanding of the
weather to the agriculturist, how short-sighted soever they may be, in
relation to its direct influence upon their own prosperity and happiness.
Our country is, physically, a most favored one. The facts disclosed or
alluded to in this volume show that it is without a parallel on the face
of the globe; and our facilities for meteorological observation, and the
ascertainment and practical application of meteorological truth, are
equally pre-eminent. The great extent and unbroken surface of the eastern
portion of the continent; its excessive supply of magnetism and
atmospheric currents, and the consequent marked character of the
phenomena; the existence and prospective increase of telegraph lines over
most of its surface; the homogeneous and energetic character of a
population united, upon so large a surface, under one government; the
freedom of that government from debt, and the excess of its revenue; the
possession of a National Observatory, with a competent philosopher at its
head; and a national institution, liberally endowed, and adapted to the
collection and diffusion of practical and scientific intelligence, give
us an opportunity and a capacity for connected observation and
investigation, and an ability to profit by it, that no other nation can
boast.
We have, too, a just national pride. Our exploring ships have penetrated
and made discoveries in both hemispheres, and our travelers have visited
successfully every clime; and thus our national interests, and
obligations, and pride, demand an organization, practical and permanent,
in relation to this subject, and the time will come when we shall have it.
When that time comes--when the present _limited horizon_ of each of us is
_practically extended over the entire country_--and when the actual state
of the weather over every part of it is known, at the same time, to the
inhabitants of every other, and every where _read in the light of a
correct philosophy_, prognostication will be comparatively simple and
certain; and A PROGRESS will have been made, productive of an amount of
pecuniary, intellectual, and social benefit to the people, which can not
be overestimated. May it come before the shadows of the night of death
have gathered around us, that we may have a more perfect view of that
atmospheric machinery which distinguishes our planet from others, and is,
with such infinite wisdom, adapted to make it a fit habitation for man!
THE END.
APPENDIX.
Since this work was completed I have received a very valuable publication,
entitled, the "Army Meteorological Register." It is a compilation of the
observations made by the officers of the medical department of the army,
at the military Posts of the United States, from 1843 to 1854 inclusive,
prepared under the supervision of the Surgeon-general, and published by
direction of the Secretary of War. To this, there is appended a report or
general review of the prominent features of American climatology, so far
as the basis afforded by the published observation of the army medical
Bureau would warrant positive deduction, by Mr. Lorin Blodget, a
distinguished meteorologist, accompanied by temperature and rain charts,
for each of the four seasons;--exhibiting the various local differences
and peculiarities relative to temperature and precipitation in each.
These local differences and peculiarities and contrasts are deduced and
delineated by Mr. Blodget with much ability. He was fettered, however, by
the prevailing calorific theories, and the unfortunate practice of
grouping the phenomena into means for the seasons, Spring, Summer, Autumn,
and Winter, which grouping is arbitrary, and comparatively uninstructive.
Hence, he failed to discover what the tables and summaries most clearly
disclose--the principles and system unfolded in the foregoing work.
But the summaries of this register contain observations made at posts in
Western and Southwestern Texas, in Kansas and Nebraska, and in New Mexico
and California, where there has been a dearth of such observations
hitherto, and enable me to demonstrate, more conclusively, and I think so
that none can fail to understand it, the truth of the philosophy I have
endeavored to exhibit.
To do this, I will take a _year_,--divide it into two seasons, the periods
of northern and southern transit, the only natural and correct
division--and note the phenomena in each, as each progresses.
And I will take the year 1854, because that is the last year for which the
record of observation is complete; because it had marked peculiarities
which are remembered; and because I have alluded to those peculiarities,
and those allusions should be confirmed or disproved by the record. Unless
I mistake exceedingly, the confirmation will be found signal and
convincing.
I have assumed, pp. 187, 351, that the transits were greater in some
seasons than others; that the drought of 1854 was owing to an extreme
northern transit, or to an extension west of the concentrated
counter-trade, or both, leaving us less supplied with moisture than
usual.
In point of fact, it appears from these observations that it resulted from
_both_ causes, operating _connectedly_; and the annals of Science rarely
furnish a more striking instance of analogical inference proved true by
subsequent investigation.
Commencing then with the commencement of the northern transit about the
1st of February, we are enabled to trace the then location of our
concentrated trade, and its subsequent progress to the north till August,
and its influence upon temperature and precipitation. And we can also
trace the situation during the same period, of the intervening drought,
and the inter-tropical belt of rains, and the extension of the latter
north over Florida and the cotton-planting States.
On the 1st of February, 1854, our counter-trade was somewhat more
concentrated on its extreme winter curve, over the Southern States, than
usual. Its line of excess reached up from Fort Brooke, on the peninsula of
Florida, to the northwest, a little east of Pensacola on the gulf, cutting
Mount Vernon Arsenal north of Pensacola, and extending thence
north-westwardly on to Eastern Louisiana, and curving thence and passing
N. E. or E. N. E., to the Atlantic, about the waters of the Chesapeake
Bay. It thinned out to the west over New Orleans and Baton Rouge,
supplying them moderately, but did not extend to the forts of Texas on the
west, nor the posts in the Indian Territory at the N. W. It was east of
Fort Towson, which is the south-eastern one. It did not reach St. Louis on
the north, nor extend north of the Ohio River, as will appear from the
tables hereinafter given. The following cut shows substantially its
situation on the 1st of February.
[Illustration]
Now, during the month of January, we find the following state of things.
_Under_ this concentrated trade, the temperature was above the mean, even
if Forts Monroe and McHenry on the Atlantic are included; but Mr. Blodget
discredits their returns, and some others which do not conform to general
results. On the west and north of its curving line, both precipitation and
temperature were below the mean.
Under the counter trade, we have the following stations, with their actual
and mean temperature. I have inserted the temperature for several
subsequent months, to show a depression in April.
TABLE I.
-------------------------------------------------------------------------
| LAT. | LON. | JAN. | FEB. | MAR. | APRIL.| MAY. |
------------------------------------------------------------------------|
Fort Moultrie | 32.45 | 79.51 | 50.83 | 53.09 | 62.72 | 62.76 | 73.35 |
Mean of 28 yrs.| | | 50.36 | 52.41 | 58.68 | 65.44 | 73.42 |
Fort Pierce | 27.30 | 80.20 | 67.91 | 67.33 | 73.01 | 71.10 | 78.41 |
Mean of 5 yrs. | | | 62.75 | 64.42 | 69.77 | 73.63 | 76.92 |
Fort Meade | 28.01 | 82.00 | 63.75 | 63.33 | 70.64 | 68.10 | 76.31 |
Mean of 3 yrs. | | | 58.40 | 63.23 | 69.02 | 69.89 | 76.69 |
Fort Brooke | 28.00 | 82.28 | 62.94 | 62.36 | 70.06 | 70.07 | 77.49 |
Mean of 25 yrs.| | | 61.53 | 63.54 | 67.72 | 71.82 | 76.64 |
Fort Myers | 26.38 | 82.00 | 67.56 | 67.39 | 73.74 | 71.07 | 79.13 |
Mean of 4 yrs. | | | 63.39 | 67.98 | 72.19 | 73.86 | 80.13 |
Key West | 24.32 | 81.48 | 71.75 | 71.95 | 76.56 | 73.89 | 80.84 |
Mean of 14 yrs.| | | 66.68 | 68.88 | 72.88 | 75.38 | 79.10 |
Fort Barrancas | 30.18 | 87.27 | 54.71 | 54.56 | 64.98 | 62.93 | 75.40 |
Mean of 17 yrs.| | | 53.61 | 55.58 | 61.80 | 68.51 | 75.45 |
Mt. Vernon Ars'l| 31.12 | 88.02 | 51.52 | 53.18 | 65.24 | 62.30 | 74.64 |
Mean of 14 yrs.| | | 50.44 | 53.69 | 60.26 | 66.87 | 73.92 |
Baton Rouge | 30.26 | 91.18 | 53.43 | 56.48 | 66.24 | 64.63 | 75.10 |
Mean of 24 yrs.| | | 53.47 | 55.02 | 61.93 | 69.30 | 75.60 |
-------------------------------------------------------------------------
-------------
JUNE. | JULY.
-------------
78.55 | 82.06
79.01 | 81.72
82.09 | 84.16
79.02 | 82.50
79.10 | 80.17
78.24 | 79.76
80.51 | 81.08
79.46 | 80.72
82.35 | 81.91
81.25 | 82.87
83.34 | 83.30
81.63 | 83.00
81.00 | 84.55
80.80 | 82.26
79.17 | 78.90
78.03 | 78.62
80.61 | 80.09
80.56 | 81.81
-------------
It will be seen that the temperature was above the mean in January at
every post except Baton Rouge, and there it was at the mean. We shall see
hereafter that Baton Rouge was near its western line.
Under this trade during this month, and at the same posts, the fall of
rain was as follows, compared with the mean:--
TABLE II.
--------------------------------------------------------------
| JANUARY. | FEBR'Y. | MARCH. |
--------------------------------------------------------------
| 1854. | Mean.| 1854. | Mean.| 1854.| Mean.|
--------------------------------------------------------------
Key West. | 1.77 | 2.86 | 2.55 | 1.38 | 0.51 | 4.21 |
Fort Myers. | 1.15 | 3.90 | 4.70 | 2.16 | 0.20 | 4.60 |
" Brooke. | 3.88 | 2.20 | 6.89 | 3.01 | 2.44 | 3.37 |
" Mead. | 1.30 | 1.07 | 2.21 | 1.01 | 1.85 | 1.64 |
" Pierce. | 3.55 | 4.45 | 3.40 | 2.72 | 1.05 | 3.01 |
" Barrancas. | 3.45 | 3.87 | 5.55 | 4.95 | 7.21 | 5.87 |
Mt. Vernon Ars'l | 11.01 | 6.80 | 12.83 | 6.04 | 6.22 | 4.59 |
Baton Rouge. | 2.85 | 5.26 | 5.50 | 4.91 | 6.15 | 4.68 |
Fort Moultrie. | 3.80 | 2.39 | 2.84 | 2.33 | 0.25 | 4.06 |
--------------------------------------------------------------
-------------------------------------------
| APRIL. | MAY. | JUNE.| JULY.
| 1854.| Mean.| 1854. | Mean.| |
-------------------------------------------
| 2.99 | 1.55 | 3.14 | 2.58 | 4.54 | 3.45
| 2.75 | 3.14 | 5.65 | 3.33 | 6.75 | 9.70
| 8.82 | 1.95 | 6.21 | 3.24 | 9.44 | 15.53
| 3.19 | 1.78 | 10.51 | 5.34 | 7.24 | 8.55
| 7.00 | 3.85 | 5.70 | 4.27 | 6.63 | 4.97
| 0.50 | 2.94 | 3.47 | 4.05 | 3.39 | 5.43
| 1.96 | 4.21 | 4.45 | 4.62 | 6.72 | 6.13
| 3.58 | 5.22 | 8.05 | 5.18 | 4.00 | 6.55
| 2.20 | 1.75 | 3.70 | 4.08 | 4.20 | 5.69
-------------------------------------------
It will be observed that in February the counter-trade and extra-tropical
belt had moved up from Key West, and a drought, which sometimes intervenes
between the concentrated counter-trade and the inter-tropical belt,
appeared there in February and March. In April, the inter-tropical belt
appeared at that point, and went on increasing till September. As the
counter-trade commenced moving north in February, an increased
precipitation above the mean commenced at all the more southern stations
under the concentrated-trade--an earnest of that irregularity which
followed, and marked the season as the most excessive of the century.
In March, the intervening drought appeared at the other posts on the
peninsula, and also at Fort Moultrie, followed _much more closely than
usual_, by the inter-tropical belt of rains. In April, the drought
appeared at Fort Barrancas and Mount Vernon Arsenal (the wave of
precipitation having moved to the west), and slightly in comparison at
Baton Rouge.
If now we look at the condition of things, _west_ and _north_ of the
curving line of concentrated trade, from Fort Brown, at the mouth of the
Rio Grande, in South-western Texas, through that State, the Indian
Territory, Arkansas, Missouri, Kentucky, and Northern Pennsylvania, to the
Atlantic, we find the thermometer every where in January below the mean.
The following table will show this, and the precipitation for that month
and February:--
TABLE III.
------------------------------------------------------------------------
| JANUARY. | FEBRUARY. | MARCH. |
|-----------------------------------------------|
| 1854. | Mean. | 1854. | Mean. | 1854. | Mean. |
-----------------------------------------------------------------------|
_Western Texas._ | | | | | | |
Fort Brown | 59.34 | 60.41 | 62.45 | 63.63 | 71.87 | 68.95 |
" Ewell | 50.47 | 52.92 | 58.12 | 57.61 | 70.34 | 67.00 |
" Inge | 47.24 | 49.46 | 56.04 | 55.39 | 67.54 | 62.63 |
| | | | | | |
_Indian Territory._ | | | | | | |
Fort Towson. | 36.32 | 43.14 | 49.29 | 45.97 | 59.55 | 53.40 |
Forts Gibson, Washita, | | | | | | |
and Arbuckle, in much| | | | | | |
the same proportions.| | | | | | |
| | | | | | |
_Arkansas._ | | | | | | |
Fort Smith. | 33.92 | 40.18 | 47.01 | 43.89 | 57.01 | 51.58 |
| | | | | | |
_Missouri._ | | | | | | |
St. Louis Arsenal. | 25.47 | 31.44 | 36.66 | 33.43 | 46.10 | 42.30 |
| | | | | | |
_Kentucky._ | | | | | | |
Newport Barracks. | 31.75 | 34.04 | 39.60 | 36.94 | 46.74 | 45.46 |
| | | | | | |
_Pennsylvania._ | | | | | | |
Allegheny Arsenal. | 29.08 | 29.25 | 33.49 | 31.16 | 40.36 | 39.02 |
| | | | | | |
_Delaware._ | | | | | | |
Fort Delaware | 32.38 | 33.67 | 34.56 | 35.84 | 43.18 | 42.90 |
| | | | | | |
_New York Harbor._ | | | | | | |
Fort Columbus. | 28.71 | 30.18 | 28.17 | 30.44 | 36.17 | 38.28 |
------------------------------------------------------------------------
--------------------------------------
| Rain in January. | Rain in February.
--------------------------------------
| 0.45 | 1.50
| 0.22 | 2.86
| 0.20 | 2.15
| |
| 1.01 | 2.00
| |
| 1.37 | 2.05
| |
| 0.65 | 2.40
| |
| 3.20 | 5.30
| |
| 2.23 | 2.33
| |
| 2.30 | 5.45
| |
| 2.60 | 4.00
--------------------------------------
We find, also, from this and table first, that every where, except at Fort
Brown, and upon the Atlantic coast, the temperature had risen above the
mean in February.
The situation of the belt which supplied the western coast in winter, and
its excess of precipitation, are also represented upon the cut. The
intervening area was not without counter-trade and precipitation--the
latter, of course, greatest over the area of intensity--but they were
_comparatively_ less, as the tables will show.
The following cut and table show the situation of the concentrated
counter-trade in March.
[Illustration]
TABLE IV.
------------------------------------------------------------------------
| JAN.|FEBR.| MAR.| APR.| MAY.|JUNE.|JULY.
------------------------------------------------------------------------
Fort Barrancas, Pensacola Bay| 3.45| 5.55| 7.21| 0.50| 3.47| 3.39| 5.43
Mean. | 3.87| 4.95| 5.87| 2.94| 4.05| 4.66| 6.80
Baton Rouge, Louisiana | 2.85| 5.50| 6.15| 3.58| 8.05| 4.00| 6.55
Mean. | 5.26| 4.91| 4.68| 5.22| 5.18| 5.52| 7.42
Fort Towson, Indian Territory| 1.01| 2.00| 5.10| 2.22|Recr'd stops here.
Mean. | 3.13| 2.97| 4.38| 5.33| | |
Fort Gibson, Indian Territory| 0.30| 1.43| 7.83| 3.16| 7.67| 2.80| 0.21
Mean. | 1.33| 2.26| 2.54| 4.19| 4.65| 4.30| 2.75
Fort Smith, Arkansas | 1.37| 2.05| 7.05| 6.55| 6.25| 2.26| 1.02
Mean. | 1.96| 2.17| 2.92| 5.10| 4.46| 4.74| 3.82
St. Louis Arsenal | 0.65| 2.40| 7.10| 4.30| 4.65| 2.20| 1.70
Mean. | 1.93| 3.37| 3.82| 4.16| 4.88| 6.94| 0.04
Newport Barracks, Kentucky | 3.20| 5.30| 8.10| 2.10| | |
(No Mean given.) | | | | | | |
------------------------------------------------------------------------
We see from this table that its focus had extended west in Florida over
Fort Barrancas, and over Baton Rouge in Louisiana; N. W. to Forts Towson
and Gibson in the Indian Territory, and Smith in Arkansas; north to St.
Louis Arsenal at St. Louis, and to Newport barracks in Kentucky; but it
was spread over a larger surface east of the mountains. Its greatest
progress for the month, was a west and north-west progress.
In April, we find it had progressed rapidly west and north-west, and its
position is shown by the following cut and table.
[Illustration]
TABLE V.
------------------------------------------------------------------------
| JAN.|FEBR.| MAR.| APR.| MAY.|JUNE.|JULY.
------------------------------------------------------------------------
Fort Riley, Kansas. | 0.00| 0.94| 1.86| 4.55| 4.35| 1.10| 0.00
Fort Leavenworth, Kansas. | 0.04| 1.78| 1.33| 3.35| 5.55| 4.50| 0.18
Mean | 0.72| 1.01| 1.61| 2.74| 3.62| 5.80| 3.15
Alleghany Arsenal, Pittsburgh | 2.23| 2.33| 2.82| 4.21| 2.24| 2.06| 1.45
Mean | 2.18| 2.17| 2.70| 3.10| 3.58| 3.56| 2.97
Fort Columbus, New York Harbor| 2.60| 4.00| 0.70| 8.80| 7.70| 2.20| 1.90
Mean | 2.78| 2.92| 3.44| 3.33| 4.78| 3.46| 3.17
Fort Independence, Boston | 2.50| 3.36| 2.55| 5.40| 4.28| 2.00|
West Point. | 3.52| 5.04| 2.81|10.53| 2.00| 1.62|
Mean | 3.50| 3.44| 3.71| 4.55| 6.18| 4.79|
----------------------------------------------------------------------
We see, too, that both east and west of the mountains, its focus of
precipitation was one month in advance of the mean. At all the stations
where the greatest fall was in March, it should have been in April, and
the fall at those points was greatly in excess of the usual quantity. And
the same was true of stations reached in April. The concentrated trade,
instead of spreading out, and precipitating over the whole south-eastern
portion of the continent (its normal condition), was gathered into a wave
of greater volume, resulting in greater precipitation, and was rapidly
hastening its curve to the west over Texas, and to the north-west over the
Indian Territory, and northward on its usual curve to the north and east
of them.
The observations for April disclose another singular and instructive
condition. The temperature, that had every where been above the mean in
March, fell below it in April under the concentrated trade. And snow fell
on three days in some localities, and four in others.
Along the Ohio River, it fell to the depth of 8 to 10 inches on the 17th,
and east of the mountains to a greater depth on the 18th, one day later.
It fell to the depth of 4 inches at Marietta on the 29th also. Dr.
Hilldreth, American Journal of Science for March, 1855, says:--
"It is a singular fact that the deepest snow, 8 inches, fell on the 17th
of April, and at the head waters about Pittsburg over a foot. Also, on the
29th of the month, at Marietta, 4 inches, a very rare occurrence." This
depression of the temperature was quite general, but the fall of snow was
local. The latter was north of a line drawn from Fort Laramie, at the base
of the Rocky Mountains, in an E. S. E. direction--north of Forts Kearney
and Leavenworth, and of St. Louis, but south of Newport barracks in
Kentucky, and from thence to the Atlantic. Snow fell at every station
north of this line, at no station south of it. The depression of
temperature, however, was experienced over the continent, east of the
Rocky Mountains, under, and south of, the belt of precipitation. Now what
occasioned this general depression of temperature, and local fall of snow?
It will not do to say, as perhaps some calorific theorist may be inclined
to say, because the concentrated trade had been carried up where it was
cold, a month too soon; or that the sun had heated the land in advance of
it, and drawn it up.
For, 1st, it might be asked how, if it was warm enough to draw it up,
could it be cold enough to make it snow; or, 2d, how happened it to start,
when, as we have seen, it was warmer than the mean under it, and colder
than the mean to the north and west of it, when it commenced its journey?
But again, it snowed at posts north of the line, while the thermometer
remained above the mean; and the thermometer fell below the mean down to
Fort Brown in south-western Texas, and at Key West in the southern part of
Florida; and what is more remarkable still, at Key West, Fort Barrancas,
and every other south-eastern station, except Forts Brooke and Moultrie,
it not only fell below the _mean_ of the month, but _below the actual
temperature of March_. (See Table I.) At Forts Brooke and Moultrie it did
not rise above that temperature. West of the Rocky Mountains the
depression was not felt; nor at stations north, or north-west of the belt
of precipitation.
It is obvious, the calorific theory can furnish no rational explanation of
this matter; for the reason that, whatever the cause, it operated not
only under, but south, and far south of the belt of precipitation. It
could not have been spots upon the sun, or other general cause, for then
it would have operated in New Mexico and California, and at the
north-western stations. It operated most intensely in Florida and the
South-Eastern States, which approach most nearly the volcanic areas of
South America and the West Indies. I believe it to have been occasioned by
volcanic action affecting the local magnetism of our intense area; but it
is a most important development, and should be thoroughly investigated. We
may find in it the key to the mysterious, but unquestionable, influence of
volcanic upon magnetic action; and I hope the distinguished
surgeon-general will cause the records of that month to be published "in
extenso."
In May and June, the trade became more concentrated, a perfectly developed
belt from the Rio Grande to the Lakes and British possessions, and
doubtless to the Atlantic, with every where a central focus of excessive
precipitation, gathering to itself in one vast wave the current that
should have been spread out over the whole country; and leaving every
where on its eastern and southern borders, down to the northern edge of
the inter-tropical belt of rains--(which extended up to lines drawn from
Baton Rouge to Charleston)--a _perfectly well developed_ and _defined
drought_. That drought will long be remembered. The following cuts show,
approximately, the location of the belt of precipitation and drought for
those months, and the table which follows will show their correctness.
The tables also show that this wave was occasionally a double, or divided
one--evinced by an intervening _partial_ precipitation. Tables IV., V.,
and VI., also show the commencement of the drought at the several
stations, as the wave moved to the west and north.
[Illustration: MAY.]
[Illustration]
TABLE VI.
JAN. FEBR. MAR. APR. MAY. JUNE. JULY. AUG. SEPT.
Fort Brown 0.45 1.50 1.15 0.05 4.10 7.65 4.25 5.00 11.31
Mean 1.61 2.25 1.20 0.56 2.21 4.55 1.95 2.76 6.73
Ringgold Barracks 0.70 1.69 0.22 0.00 2.83 10.98 4.06 1.58 3.02
Mean 1.24 1.18 0.72 1.08 2.09 3.47 3.18 1.50 3.22
Fort Merrill 0.11 1.99 0.05 1.16 7.66 4.70 5.44 3.13 5.01
Mean 0.23 2.09 0.09 1.62 3.43 4.10 6.13 3.40 4.60
Fort Duncan 0.05 0.69 1.50 0.00 2.53 6.83 0.83 0.90 4.81
Mean 0.26 1.27 1.34 0.71 1.50 5.63 3.35 0.93 3.28
Fort Inge 0.20 2.15 3.00 0.75 3.88 2.09 0.97 1.67 4.80
Mean 0.64 2.21 1.79 1.26 3.01 5.38 3.66 2.02 2.21
Fort McKavet 0.01 0.77 2.10 0.28 3.72 0.15 2.91 0.04 3.86
" Belknap 0.11 1.10 1.42 1.75 4.97 8.33 0.00 0.75 1.53
" Massachusetts,
Northern New
Mexico 3.93 0.24 2.14 2.61 1.53
Fort Kearney 0.23 1.33 1.87 2.56 4.15 5.40 3.51 1.18 4.60
Mean 0.50 0.48 1.55 2.68 6.57 4.36 5.07 2.62 1.83
Fort Laramie 0.18 0.40 0.80 3.98 4.46 3.67 3.26 1.27 1.60
Mean 0.27 0.71 1.37 1.93 5.39 2.95 1.83 0.92 1.33
Fort Ridgley 1.20 0.01 1.18 2.83 6.84 2.70 2.49 2.28 2.58
" Snelling 0.72 0.03 1.03 2.51 4.30 3.31 3.92 1.75 6.55
Mean 0.73 0.52 1.30 2.14 3.17 3.63 4.11 3.18 3.32
Fort Ripley 0.67 0.03 0.79 0.97 4.34 3.68 0.62 1.69 4.40
Mean 0.86 0.37 1.80 1.42 3.09 5.15 5.20 2.27 4.92
Fort Mackinac 2.59 1.23 1.56 1.04 2.65 6.35 5.67 4.26 3.22
Mean 1.25 0.82 1.14 1.21 2.32 2.81 3.20 2.87 2.97
Fort Brady 2.49 1.18 1.34 2.14 3.61 1.23 3.21 3.86 3.18
Mean 1.84 1.13 1.37 1.83 2.24 2.83 3.73 3.39 4.33
Fort Niagara 1.63 2.52 1.87 2.25 3.90 1.71 4.08 1.52 2.61
Mean 2.25 1.89 2.12 2.20 2.55 3.28 3.49 3.04 3.95
But the belt of trade continued its progress to the west and north, and
during the months of July and August the drought extended in both
directions, reaching, in August, from Mississippi, Alabama, Georgia, and
South Carolina, to the Lakes, and from the Rocky Mountains to the
Atlantic. Its position is shown by the following cut, and the position of
the belt of precipitation by the following table.
[Illustration]
TABLE VII.
_Situation of the focus of Precipitation in July and August._
-----------------------------------------------------------
| JUNE.| JULY.| AUG. | SEPT.| OCT.
-----------------------------------------------------------
_New Mexico._ | | | | |
| | | | |
Fort Thorne | 0.08 | 2.23 | 6.01 | 3.50 | 0.00
Albuquerque | 0.28 | 2.50 | 1.19 | 2.67 | 1.37
Santa Fe | 0.32 | 4.11 | 3.86 | 4.06 | 2.50
Fort Defiance | 1.24 | 3.94 | 5.24 | 3.47 | 0.62
" Yuma | 0.00 | 0.01 | 2.37 | 0.17 | 0.30
San Diego | 0.02 | 0.07 | 1.35 | 0.13 | 0.01
Fort Snelling, Minnesota | 3.31 | 3.92 | 1.75 | 6.35 | 1.23
" Brady | 1.23 | 3.21 | 3.86 | 3.18 | 3.40
" Mackinac | 6.35 | 5.67 | 4.26 | 3.22 | 2.28
-----------------------------------------------------------
I have not space for all the comment which this exposition is calculated
to induce. The reader will not only find in it an explanation of the
extraordinary character of the summer of 1854, but will see from the
_means_, that it was but an _excessive development_ of an ANNUAL
PHENOMENON,--THE PROGRESS OF A CONCENTRATED COUNTER-TRADE.
It is not necessary to follow with particularity the return transit. It
required no great degree of sagacity to predict, at the time, that the
drought would continue in the vicinity of New York till about the 10th of
September. The return of the belt to that latitude, was not to be expected
before that time, and the drought continued, in fact, until the 9th of
September.
Its return progress was slow, and it was every where behind time. The
autumn was warm, and so, indeed, were December and January, west of the
area of magnetic intensity, although upon, and east of it, there was a
depression in December. The retreating but lingering edge of
counter-trade, with its excess of snow for the season, caught the Iron
Horse, with its train and passengers, upon the prairies of the west, and
laid its embargoing hands upon them. Few, if any, can have forgotten the
thrilling accounts which reached us from that section, of the sufferings
endured by those who were thus embargoed for days and nights, far from the
comfortable habitations of their fellow men.
But the return transit, though slow, was extreme, and February and March
were exceedingly cold for the season. The transit to the north, again, did
not commence as early as usual, and the spring was backward, and the
summer cool. Both were without irregularity, and the season was
productive. The following table exhibits the temperature on a line of
posts, running north and south at the west, during the winter months of
1855, and will illustrate what has been said.
TABLE VIII.
---------------------------------------------------
1855. |JANUARY |FEBRUARY.| MARCH.| APRIL.
---------------------------------------------------
Key West | 67.18 | 65.94 | 70.28 | 75.09
Mean | 66.58 | 68.88 | 72.88 | 75.38
Fort Snelling | 17.09 | 12.62 | 25.30 | 49.86
Mean | 13.76 | 17.57 | 31.41 | 46.34
Fort Kearney | 23.55 | 25.69 | 32.86 | 54.39
Mean | 21.14 | 26.11 | 34.50 | 47.13
Fort Laramie | 35.85 | 29.01 | 36.41 | 52.94
Mean | 31.03 | 32.60 | 36.81 | 47.60
Fort Arbuckle | 41.94 | 39.86 | 49.09 | 67.43
Mean | 39.10 | 43.69 | 53.22 | 61.85
Fort Belknap | 45.92 | 44.49 | 53.09 | 70.00
Mean | 42.80 | 47.47 | 56.90 | 65.79
Fort Chadbourne | 48.89 | 45.87 | 56.68 | 68.51
Mean | 44.29 | 46.75 | 58.01 | 65.52
Fort McKavitt | 46.74 | 44.51 | 53.66 | 67.05
Mean | 44.75 | 46.87 | 57.39 | 66.25
Fort Merrill | 54.51 | 54.65 | 61.82 | 74.50
Mean | 54.82 | 57.20 | 68.66 | 73.27
Fort Brown | 60.23 | 61.60 | 66.24 | 74.98
Mean | 60.41 | 63.63 | 68.95 | 75.05
Fort Inge | 52.21 | 50.63 | 61.22 | 74.48
Mean | 49.46 | 55.39 | 62.63 | 68.02
---------------------------------------------------
The return transit to the south for this winter, 1855-6, has been an
extreme one. It is too early yet (Feb. 18th) to write its history, but the
extreme southern transit is as obvious as the unusual severity of the
cold. The rains which usually fall upon the Southern States are
precipitated further south upon the West Indies, and threaten a
deterioration of their sugar crop. The snow, and cold winds, and ice, of
the middle latitudes, are felt even in Florida. Our sheet of
counter-trade has been exceedingly thin, and the barometer has ranged, in
fair weather, much below the mean. Occasional, and for a part of the time,
_weekly_ periods of an increase of its volume, with a corresponding
elevation of the barometer, and a consequent moderation of the intense
cold, and a storm, have occurred. But those periods have been few and
brief. No regular thaw has yet occurred. From the 26th of December to this
date, at Norwalk, there have been but two periods when the wind has blown
from the south-west with sufficient force to stir the limbs of the trees.
There has been no wind from south of that point, or east of north-east;
and even our storm-winds, with one exception, have been north of
north-east--owing to the situation of the focus of precipitation far to
the south of us--and there is reason to fear that a cold summer like those
of 1816 and 1836 may follow. If this extreme transit is owing to defect in
the influence of the sun, from spots, or other causes, such will probably
be the result. If from volcanic action at the south, the influence of that
action may cease, and a rapid return transit, and an ordinary season, may
follow. Believing in the laws of periodicity in relation to the weather
and disease, I planted an early kind of corn (the Dutton), in 1836, and
had a crop when few around me succeeded. We must watch this return
transit, with hope, indeed, but not without fear, and be wise in time.
There is a mass of other evidence in these summaries which shows the truth
of what I have written. There is not a deduction of Mr. Blodget which it
will not explain. The ascent of the summer lines of temperature to the
west is explained by the diminution of magnetic intensity. Their descent
in winter by the location and attractions of the concentrated trade. The
excess of precipitation in Alabama and Mississippi by the succession of
summer and winter belts. That of the interior of the Atlantic slope in
summer, by the showers which fall upon the elevations; and of the coast,
by the easterly storms and their attraction of the surface atmosphere of
the ocean, at other seasons. But I cannot further particularize. Even the
influence of the spots is clearly demonstrated by the observations at
_interior stations_, which were unaffected by contiguous oceans or
elevations. At Forts Washita, Gibson, Scott, Smith, and others, the years
1847 and 1848 were below the mean. All that evidence, and those
deductions, however, I must pass by for want of space, and take leave of
the subject.
Footnotes:
[1] See the diagram for summer at page 55.
[2] Law of Storms, p. 42.
[3] Kearakakua Bay (called Cavrico above), is on the S. W. side of the
island, and the trade was reversed during the day by the cloud
condensation inland.
[4] Lieutenant Wilkes spent twenty days upon the top of this or an
adjoining mountain, and his observations there will be alluded to in
another connection.
[5] All attempts to produce this result by the sudden exhaustion of air
about the chickens in receivers, or shooting them from cannons, have
failed, and no patent for a chicken-picker has been applied for.
[6] A meter is 1 yard, and .0936 of a yard.
[7] See his map, accompanying the Geography of the Sea.
[8] See Am. Jour. of Science, New Series, Vol. 18. p. 187.
[9] Their estimate was 100 to 120 miles.
[10] Since the text was in type, and, as might have been anticipated, we
have intelligence confirmatory of this, from the Cape De Verde Islands.
The inter-tropical belt of rains has not moved as far north as the
northern islands--they have had no rain--and the people are in a starving
condition.
Transcriber's Notes:
Passages in italics are indicated by _italics_.
Punctuation has been corrected without note.
The following misprints have been corrected:
"appearnces" corrected to "appearances" (page 44)
"Faroday's" corrected to "Faraday's" (page 84)
"gentleman" corrected to "gentlemen" (page 96)
"two" corrected to "too" (page 105)
"surise" corrected to "sunrise" (page 111)
"acion" corrected to "action" (page 164)
"Stanta corrected to "Santa" (page 167)
"Augugst" corrected to "August" (page 167)
"baloon's" corrected to "balloon's" (page 192)
"mannner" corrected to "manner" (page 214)
"1198" corrected to "1798" (page 221)
"sevententh" corrected to "seventeenth" (page 240)
"maner" corrected to "manner" (page 254)
"particulary" corrected to "particularly" (page 256)
"are are" corrected to "are" (page 288)
"iso-theral" corrected to "iso-thermal" (page 299)
"the the" corrected to "the" (page 360)
"phenonema" corrected to "phenomena" (page 403)
"calorifice" corrected to "calorific" (page 409)
Other than the corrections listed above, inconsistencies in spelling and
hyphenation have been retained from the original.
Tables throughout this text version have been adjusted for readability.
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Thomas Belden Butler
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