The Project Gutenberg EBook of Nature's Miracles, Volume 1, by Elisha Gray
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Title: Nature's Miracles, Volume 1
Familiar Talks on Science--World-Building and Life. Earth,
Air and Water.
Author: Elisha Gray
Release Date: August 11, 2010 [EBook #33405]
Language: English
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Nature's Miracles
_Familiar Talks on Science_
BY
ELISHA GRAY, PH. D., LL. D.
VOL. I
World-Building and Life
EARTH, AIR, AND WATER
NEW YORK
FORDS, HOWARD, & HULBERT
COPYRIGHT, 1899,
BY
FORDS, HOWARD & HULBERT.
THE MERSHON COMPANY PRESS,
RAHWAY, N. J.
CONTENTS.
CHAPTER PAGE
INTRODUCTION, v
EARTH.
I. WORLD-BUILDING AND LIFE, 1
II. LIMESTONE, 12
III. COAL, 22
IV. SLATE AND SHALE, 31
V. SALT, 36
AIR.
VI. THE ATMOSPHERE, 42
VII. AIR TEMPERATURE, 51
VIII. CLOUD FORMATION, 60
IX. CLOUD FORMATION (_Continued_), 69
X. WIND--WHY IT BLOWS, 79
XI. WIND (_Continued_), 88
XII. LOCAL WINDS, 100
XIII. WEATHER PREDICTIONS, 110
XIV. HOW DEW IS FORMED, 115
XV. HAILSTONES AND SNOW, 124
XVI. METEORS, 129
XVII. THE SKY AND ITS COLOR, 134
XVIII. LIQUID AIR, 146
WATER.
XIX. RIVERS AND FLOODS, 152
XX. TIDES, 161
XXI. WHAT IS A SPONGE? 167
XXII. WATER AND ICE, 177
XXIII. STORED ENERGY IN WATER, 182
XXIV. WHY DOES ICE FLOAT? 192
XXV. GLACIERS, 198
XXVI. EVIDENCES AND THEORIES OF AN ICE AGE, 207
XXVII. GLACIAL AND PREGLACIAL LAKES AND RIVERS, 217
XXVIII. SOME EFFECTS OF THE GLACIAL PERIOD, 230
XXIX. DRAINAGE BEFORE THE ICE AGE, 239
INTRODUCTION.
Dear Reader: Please look through this "Introduction" before beginning
with the regular chapters. It is always well to know the object, aim,
and mode of treatment of a book before reading it, so as to be able to
look at it from the author's view-point.
First: A word about the title--"Nature's Miracles." Some may claim that
it is unscientific to speak of the operations of nature as "miracles."
But the point of the title lies in the paradox of finding so many
wonderful things--as wonderful as any miracle that was ever
recorded--subservient to the rule of law.
"But," you say, "a miracle does not come under any rule of law."
Ah! are you sure of that? It is true that we may not understand the law
that the so-called miracle comes under, but the Author of all natural
law does. We do not pretend to dispute but that the Power that made
nature's laws can change them if He sees fit; but we cannot believe that
He will ever see fit. It would destroy all order and harmony, all
advancement in science and knowledge of God's works, not to be able to
rely implicitly upon the laws of nature as consistent and continuous.
In putting out these little volumes, it is not to be understood that the
subjects treated will be more than touched upon, at the most salient
points. To do much more would require volumes of immense size, and life
would be too short for me to write or for you to read them.
Again: these volumes are "familiar talks." The Author wishes to sit down
with you--so to speak--and not hold you at arm's length.
It will be his aim to use the language of common life and to avoid all
technical names so far as possible, or, when they are necessary, to
explain their meaning. The object is to reach the thousands of readers
who have not and cannot have the advantages of a scientific education,
but who can by this means get at least a rudimentary idea of some of the
natural laws with which they are coming in contact every hour, and
through which the inner man has constant communication with the outer
world. It may be, too, that many young students will be helped by these
plain general views of topics which their text-books will give them in
detail.
A knowledge of the real things in the objective world about us and the
laws that govern them in their inter-relations is of practical value to
every man, whatever his calling may be. Not only will it be of value
practically, but it will also be a constant source of interest and
pleasure. Man is so constituted that he must have something to be
interested in, and if he has no resources within himself he looks
elsewhere, and often to his hurt, mentally, morally, or otherwise. If he
could have an interest awakened in him for the study and contemplation
of the natural world he would then have a book to read that is always
open, always fresh, always new. He is dealing with facts and not theory,
except as he uses theory for getting at facts.
A man who is all theory is like "a rudderless ship on a shoreless sea."
All he really knows is that he is afloat, and if he lands at all it is
likely to be in an insane asylum. The mind, in order to keep its
balance, must have the solid foundation of real things. Theories and
speculations may be indulged in with safety only so long as they are
based on facts that we can go back to at all times and know that we are
on solid ground.
It is the desire and aim of all good men to make their nation a truly
great people, with a civilization the highest possible. The character of
all kinds of growth is largely determined by the character of the
material upon which it feeds. The study of natural law can never be
harmful, but is always beneficial, for the student is then working in
harmony with law. It is the violation of law that makes all the trouble
in the world--whether physical, moral, or social. When we speak of
natural law we do not confine ourselves to what is commonly known as
chemistry and physics, and the laws that govern the material world, but
include as well the laws of our own being, as intellectual and spiritual
units. For all law, physical, intellectual, and spiritual, is in a sense
natural.
All departments of science are simply branches of one great science, and
all phases of human activity are touched by it. The preacher is a better
preacher, the doctor a better doctor, the lawyer a better lawyer, the
editor a better editor, the business man a better merchant, and the
mechanic a better workman, if they follow scientific methods. Indeed,
any man will be a better husband, father, and citizen, if he has some
trustworthy knowledge of the laws under which this great universe, down
to his own little part of it, lives, moves, and has its being.
NATURE'S MIRACLES.
EARTH.
CHAPTER I.
WORLD-BUILDING AND LIFE.
"In the beginning God created the heaven and the earth. And the earth
was without form, and void."
Whatever our speculations may be in regard to a "beginning," and when it
was, it is written in the rocks, that, like the animals and plants upon
its surface, the earth itself grew; that for countless ages, measured by
years that no man can number, the earth has been gradually assuming its
present form and composition, and that the processes of growth and decay
are active every hour.
The science that deals with the formations and stratifications that are
found on the earth and under the earth, and all the forces that have
been and are now active in their formation, is called Geology (earth
science). It is a science about which little is known by the average
individual, and yet it is one of transcendent interest, from the study
of which the lover of nature can obtain a vast amount of profit and
pleasure. When the uncultured man sees a stone in the road it tells him
no story other than the fact that he sees a stone and that it would
better be removed; and all the satisfaction he gets out of it is in the
thought that he has saved some unlucky wagon wheel from being wrenched
or broken. The scientist looking at the same stone perhaps will stop,
and with a hammer break it open, when the newly exposed faces of the
rock will have written upon them a history that is as real to him as the
printed page. He is carried back to a far-off time, where he sees the
processes and forces at work that have formed this stone and made it
what it is, not only in its outward form, but in its constitution, down
to its molecules and atoms. (The word "atom" is used in chemistry to
mean the smallest particle of an elementary substance that will combine
with the atoms of another substance to form new compounds of matter. And
molecules are made up of atoms.) The scientist looking at this stone
sees in it not only that mechanical and chemical agencies have
cooperated in the work of its formation, but that animal life itself may
have been the chief agency in bringing the materials together and giving
form to the peculiar architecture employed in its formation. If it is a
piece of limestone this latter statement will be eminently true.
Here is a powerful motive for the study of physical science. It is not
to be expected, nor is it possible, that every individual can be a
scientist in the strict sense of the word, but it is possible for
everyone of ordinary intelligence to become familiar with the salient
facts of science, if only a small portion of the time that is now
devoted to the reading of literature that is rather harmful than helpful
be spent in studying the phenomena and works of nature.
The acquirement of such knowledge would furnish every individual with a
constant source of instructive amusement that would never lose its
interest. He would not be dependent every hour upon people and things
outside of himself; because he would carry about with him inexhaustible
sources of instruction and pleasure that would furnish him continual and
helpful diversion and save him from a thousand morbid tendencies that
are always ready to seize upon an unemployed mind. There are many men
and women in the insane asylum to-day for the simple reason that they
have not made intelligent use of the mental powers that nature has
endowed them with.
Sermons are not always preached from pulpits. They are written in the
rocks and on the flowers of the field and the trees of the forest.
Let us then look a little at the underground foundation of all this
beautiful earth. And before attempting that, the question may arise in
some minds how we know what is so deep down under the surface.
Fortunately this is a question very easily answered. At some period
after the rocks were formed the crust of the earth was broken by
volcanic eruptions at various places and times, and turned up, as in the
formation of mountains, so that the edges of the various stratifications
of the rocks, from those near the surface down to the lowest rocks, are
exposed to view. Another means of knowing what the various formations
are has been by borings of deep wells. These borings, however, are only
confirmatory of what was well known before through the upheavals that
are plentiful in all parts of the world. There is abundant evidence that
all of the rocks and all of the strata of every name and nature (except
perhaps igneous rocks) were originally laid down in water. This is
evidenced not only by the stratifications themselves, but by the
evidences of sea-life everywhere present in the earth's crust. Before
the upheavals in the earth's crust began, the whole surface of the globe
was a great ocean of hot water. The substances of which the rocks were
formed were undoubtedly held in suspension in the air and in the water,
and by a gradual process were deposited in the bottom of the ocean in
layers, forming rocks of various kinds, according to the nature of the
substance deposited. Gradually the crust of the earth was built up until
it acquired a certain thickness; when, either from shrinkage under the
crust a great void was formed until it could not sustain its own weight,
or the pressure caused by confined gases and molten matter produced an
upheaval which broke the crust of the earth outward, causing great
wrinkles that we call mountain ranges. Undoubtedly both forces were
active in producing these results. When the gases and molten matter had
escaped through the rifts in the rocks caused by the upheaval there must
have been great voids formed that were filled up by the shrinkage of the
earth, causing much irregularity in its surface.
In some places there were enormous elevations, and in others
correspondingly deep depressions. The water that before was evenly
distributed over the surface of the globe, after the upheavals ran off
into the lower levels, filling up the great valleys, forming the seas,
and leaving about one-third of the land surface uncovered. It must not
be supposed, however, that the appearance of the land was caused by one
grand movement or upheaval, but that it has been going on in successive
stages through long ages of time. This is clearly evidenced by the rock
formations. The deposition of rock strata is still active in the bottoms
of the oceans, although not to the same degree as in former times. When
the upheaval took place the old stratifications were thrown out of
level, but the new ones that were then formed remained in a level
position until they were in their turn disturbed by some subsequent
upheaval.
The laws of gravitation would tend to precipitate the matter held in
suspension by the water straight down to the bottom, toward the center
of the earth, so that the plane of these stratifications would tend to
be parallel to the surface of the water, that is horizontal, until
disturbed. Then they would be tilted in many directions. Hence it will
be easily seen why the seams in the rocks, especially in and near
mountainous regions, do not lie in a horizontal position after an
upheaval, but are found standing at all angles, up to a perpendicular.
Viewed from this standpoint, the solid portion of the old world has gone
all to pieces. Wherever there is a chain of mountains it marks a
breakage in the earth's crust, and these mountains are not all on the
land, but extend under the seas so deeply that they are unable to lift
their heads above the surface of the water. The earth is no longer
round, except in general outline, but broken up into all sorts of
shapes that give the varied conditions of landscape that we find
whichever way we turn.
There are but few volcanoes that are active in this age, while in former
times they extended for thousands of miles. We still have occasional
earthquakes, but undoubtedly they are very slight as compared with those
that shook the earth millions of years ago.
If, now, we study the constitution of the earth's crust so far as it has
yet been penetrated, we find it divided up into periods called Primary,
Secondary, and Tertiary. The primary period reaches down to the line
where the lowest forms of animal fossils begin to be found. This is
called the "Paleozoic" period, which means the period of "ancient life."
From here let us first go downward. Immediately under this lies a
stratum of "Metamorphic" rocks. To metamorphose is to change; and
metamorphic rocks are those which have been changed by heat or pressure
from their original formation. This class of rocks lie on top of what
are called "Igneous" rocks, which means that they have been formed by or
subjected to heat. All lava-formed rocks are igneous. They are
unstratified,--not in layers or strata, but in a formless mass,--and in
this they differ from water-formed rocks.
If there is a molten center to the earth these igneous rocks are
undoubtedly the offspring of this great internal furnace. The
metamorphic rocks were primarily igneous and are changed somewhat in
their structure by the lapse of time. For instance, marble is a
metamorphic limestone. The difference between common limestone and
marble is in its molecular structure--the way in which its smallest
particles are put together. They are both carbonates of lime. But the
marble is made up of little crystals and will take a polish, while
ordinary uncrystallized limestone will not. The igneous rocks are
chiefly granite; and granite is formed of orthoclase-feldspar, mica, and
quartz. (The word "orthoclase" means straight fracture, and the
orthoclase-feldspar has two lines of cleavage at right angles to each
other.) This is the ordinary composition of granite, but there are a
great many variations, chiefly as to color and proportions of the
ingredients named.
The igneous rocks, then, are the lowest of all; then come the
metamorphic rocks; and as before stated, on top of metamorphic rock
begins the first evidence of life in its lowest form. The Paleozoic
(ancient life) or Primary period is made up of a number of subdivisions.
The first and oldest division is called the "Silurian" age, which is
underlaid by the metamorphic rocks and overlaid by the rocks of the
Devonian period. It is called Silurian, from the name of a kind of fish,
fossils of which are found in the rocks of this age, which are
distinguished for the absence of land-plant fossils and vertebrate
animals.
In the Silurian strata are found limestones, slate, flagstones, shales,
etc. On top of the Silurian begins the "Devonian" age, in which is found
the old red sandstone, as well as limestone and slate; and here begin to
be found the fossils of land-plants. On top of the Devonian lies the
"Carboniferous" series, which complete the series of the primary period.
In the lower part of this stratum is found carboniferous limestone,
which is overlaid by a kind of stone called millstone grit, and on top
of this lie the true carboniferous strata or coal-bearing measures. In
the coal strata are found the first reptile fossils.
On top of the coal measures begins the Secondary period, or "Mesozoic"
(middle life). This period is distinguished for the great development of
reptiles, and is called the "age of reptiles." In this age occur the
first traces of mammals, and birds, and fishes with bony skeletons.
Among plants we find here the first evidence of palms. The formation is
chiefly chalk, sandstones, clays, limestone, etc. We now come to the
last or "Tertiary" period, which brings us to the top earth. This is
chiefly formed of sedimentary rocks--those which have been formed by
the settling of sediment, in water.
While we are forced to these general conclusions in regard to the
building of the world, and to its subsequent distortion by the series of
upheavals that have occurred from time to time, and to the successive
"ages" of the layers of rock foundation of its crust, there are many
mysteries that remain unsolved and many questions will present
themselves to the mind of the reader. One of these questions is, Where
was the water and where was the earthy matter before its precipitation?
Matter, including water, can exist in the gaseous form, and we only need
to assume that there was a core of intense heat, to understand how all
the material that we find on the earth and in the earth could have been
held in suspension in the gaseous state until the cooling process had
reached a stage where the various combinations and recombinations could
take place in the great laboratory of nature. If we study the
constitution of the sun (and with the modern appliances we are able to
do so), we find that it is made up of some and perhaps all of the same
materials that are found here on earth. If there is no water existing,
in the sun, as water, there are the gases present which would produce it
if the conditions were right. And, for all we know, that flaming mass of
burning gases may some time go through the same kind of cooling and
building up in solids that our earth has experienced.
We thus have what may be called an outline sketch of the process of
World-building.
CHAPTER II.
LIMESTONE.
A large part of the structure of the earth's crust is formed of a
substance called limestone. Ordinary limestone is a compound of common
lime and carbon dioxide, a gas that is found mixed with the air to a
very small degree. Carbon dioxide will be better known by the older
people as carbonic acid. It is a gas that is given off whenever wood and
coal are burned, or any substance containing carbon. It is composed of
one atom of carbon to two of oxygen. Every ton of coal that is burned
sends off three and two-thirds tons of this gas. The increase in weight
comes from the fact that every atom of carbon unites with two of oxygen,
which it takes from the air, and the oxygen is heavier than the carbon.
In comparing the relative weights of atoms (the smallest combinable
particle of a solid, liquid, or gas) we use the hydrogen atom as the
unit of comparison and call it "one," because it is the lightest of all
atoms. The carbon atom is twelve times heavier than the hydrogen atom,
and the oxygen atom is sixteen times heavier. Hence it will be seen
readily how a ton of coal will form two and two-thirds times its weight
of carbonic dioxide. Lime, having a strong affinity or attraction for
this gas, has absorbed it from the air and water, forming what is known
as carbonate of lime--which is the ordinary limestone. Chalk and the
various marbles are also carbonates of lime. Limestone strata in the
crust of the earth are found in all the periods of the earth's
formation. All forms of sea shells that were once the homes of animal
life are constructed of this compound; and in the later formations of
limestone, in the Secondary and Tertiary periods, we find this rock to
be made up almost entirely of marine shells, some of them microscopic in
size. The earlier or older formations of limestone that are found deeper
down in the earth's crust are less mingled with these marine shells.
This comes from the fact that the first deposition of limestone strata
occurred before the later forms of sea life had developed. Whatever
signs of life are found in these lower stratifications are of the very
lowest order. It is not to be understood that animal life is a necessary
factor in the formation of limestone, but it has been an incidental
feature which no doubt has been the chief means of gathering up from the
water this compound and precipitating it into the great limestone
strata that are everywhere found.
Carbonate of lime is found in solution in nearly, if not quite, all of
the mineral waters, and is also found in the water of the ocean. In
earlier times it must have been held in solution in much greater
quantities than at present. The myriads of sea animals that existed, and
that still exist, gathered from the water this substance, which formed
their shells, and served as a house in which they lived. New germs were
continually forming new shells, while the older ones ceased to live as
animals, and their houses in which they lived were precipitated to the
bottom of the ocean, where they were bound together as limestone rock.
These sea animals no doubt caused a much more rapid formation of
limestone than would or could have been the case without their
existence.
One can thus readily see what an important factor animal life has been
in the process of world-building. This process is still going on, but
probably not to the same extent as in former ages, because it is not
likely that there is so much carbonate of lime held in solution as there
was before these great limestone beds were formed. Limestone, however,
is easily disintegrated by the action of water. We find the spring water
impregnated with it as well as that of the small streams and rivers.
Pure water is a powerful solvent. When the rains fall upon the earth the
water percolates through it and through the limestone strata, which
gradually wears away the limestone and carries it back to the ocean, so
that the process of tearing down and building up is continually going
on. The great caves that are found everywhere in the limestone regions
were formed by the action of water. The great Mammoth Cave of Kentucky,
which is said to have 200 miles of underground passages, has been
entirely worn out by the action of running water.
Some years ago the writer visited this cave and had an opportunity to
study the wonderful eroding or gnawing-out effect of water on limestone.
At some period earlier in the history of the earth there was evidently
an underground river or large stream of water that found its way through
the crevices of the rocks, and gradually wore out a great bed for
itself, which was fed by lateral streams pouring into the main branch,
each one of which lateral branches cut its own channel. A plan view of
the Mammoth Cave presents a picture not unlike that of a great river
with numerous branches emptying into it, all of them showing the
windings such as we see in a river and its feeders upon the surface of
the earth. There are three sets of these channels, one above the other,
and we do not find the water till we get to the bottom of the third
underground story, so to speak. There is one place in this system of
underground channels where the dripping from the roof of the upper
channels has cut a great well hole many feet in diameter perpendicularly
down through the whole system to a great depth. The sides of this great
well hole are fluted into grooves caused by the constant downflow of the
water. Although the amount of water flowing down through this well hole
is very small, it is continually at work. Like interest on money, it
never rests, each minute that passes has eaten away some of the great
rock.
In other portions of the cave the dripping of the water is so gradual
that the carbonate of lime hardens and forms what are called
stalactites, that hang like icicles from the roof of the cave. Sometimes
the water runs down so slowly upon these stalactites that it evaporates
as fast as it appears, leaving behind its little load of carbonate of
lime. If, however, there is a drip, there are formations built also from
the lime in the dropping water on the floor of the cave, and these are
called stalagmites. In time the stalactites and the stalagmites will
meet, forming a great column reaching from floor to ceiling. Some of
these formations, when they are free from foreign substances, are very
beautiful. They are also very hard, giving off a metallic musical tone
when struck by any hard substance.
We have already stated that limestone is a compound of ordinary lime and
carbon dioxide, forming a carbonate of lime. This statement does not
give a complete analysis of all the elements entering into limestone. In
the first place lime itself is a compound formed of two elementary
substances, calcium and oxygen. The lime molecule is composed of one
atom of calcium and one of oxygen. Neither calcium nor lime is found
pure in nature. Inasmuch as carbon dioxide is composed of one atom of
carbon and two of oxygen, and lime is composed of one atom of calcium
and one of oxygen, when we have the two combined the molecule of
carbonate of lime, or, as it is technically called, calcic carbonate, is
composed of one atom of calcium, one of carbon and three of oxygen,
(lime plus carbon dioxide).
As before stated, lime is not found un-combined with other substances in
nature. And as it is of great economic importance, it will be profitable
to know how it is formed. Lime is produced from ordinary limestone by
burning it in kilns where it is subjected to a heat of a certain
temperature for a number of hours. The heat drives off the carbon
dioxide, which, as we have seen, has taken away from each molecule of
the compound all of the carbon and two atoms of the oxygen, while all
of the calcium is retained with one atom of oxygen, leaving ordinary
lime. Lime, then, is simply oxide of calcium.
As all know, it is used almost exclusively for making mortar for
building purposes. In order to do this we have to put it through the
process of "slacking," by pouring water upon it, and here another
chemical change takes place. The water unites with the lime, when
immediately the heat that was expended in throwing off the carbon
dioxide and was stored in the lime as energy is now given up again in
the form of heat. When a considerable bulk of lime is slacked very
rapidly the heat that is given off is so great that it will produce
combustion. Here is a beautiful illustration of what has been
erroneously called "latent heat." It is "heat stored as potential
energy," that is released by the combination of lime with water.
Slackened lime, then, is called calcic hydrate.
Very little of the limestone that we find is absolutely pure. It is
considered good when it does not contain over five or six per cent. of
foreign substance. When more than this is present the lime is considered
poor, and when it reaches fifteen per cent. or more of impurities it
assumes the property of hardening under water and is called cement.
Carbonate of lime is found in several other forms; for instance, the
various kinds of marble and chalk are carbonates of lime. The
composition of marble and chalk is exactly the same as that of
limestone. The difference is chiefly one of molecular rather than
chemical structure. Marble is what chemists would call an allotropic or
changed form of limestone; and, as before stated, the difference seems
to consist in the fact that the marble assumes a crystalline arrangement
of its atoms and will therefore take a high polish, which is not true of
ordinary limestone. Marble varies greatly in coloring and texture, all
of which differences are explainable under the one head of molecular
arrangement. Nearly pure carbon exists in three distinct forms--the
diamond, graphite, and charcoal. As is the case with marble, these
differences in the different forms of carbon are not chemical, but
molecular differences. The substances are the same, but their
infinitesimal particles are differently arranged.
Carbonate of lime--as it exists in its various forms, as limestone, from
which lime and cement are made, and marble, which is such an important
element in the arts--is a substance of great importance to man. We have
already noted some of the processes that nature uses in gathering up
these substances from the ocean by the employment of various forms of
animal life. Here is another. Whoever has visited the Bermudas has seen
an island wholly formed of what is called coral rock. Coral is a
structure produced by a peculiar form of sea animal that gathers up the
calcareous or lime-like matter floating in the sea water, and builds a
house of it in which to live during the little lifetime that is allotted
to him. When he dies his children do not occupy the old home, but build
a new one, which is a superstructure planted upon the old one as a
foundation. This process of growth sometimes takes the form of a tree or
plant, and coral trees grow upon trees and plants upon plants, until a
structure is erected having its foundation upon the bottom of the ocean,
that finally reaches up until it rises above the surface of the water;
and here--after through years the water has brought sea-weed and drift
to decay and form soil, and the birds have brought seeds and
fertilization, and vegetable life is prospering--another animal called
man builds his home upon it. The material that the coral is formed of is
substantially the same as that we find in the minute shells of the
limestone rocks.
The great chalk cliffs that are found on the coasts of the English
channel are the work of a sea animal microscopic in size. At one time it
was a question among scientists how these chalk cliffs were formed, but
when the microscope was invented this mystery, as well as many others,
was solved. The chemical components of chalk are precisely the same as
those of limestone. The microscope shows that chalk is almost wholly a
product of very small organized shells. The animals who are the
architects of the chalk cliffs are called "foraminifera"--bearing shells
perforated with little holes. The chief difference between chalk and
limestone seems to be in the size of the shells of which they are
respectively made up and in the manner of the bonding of these shells
together. The shells in a lump of chalk are held much more loosely than
those in a lump of limestone. These intrepid workers are still actively
changing the structure of the bottoms of seas and oceans, and forming
new islands, which in turn become the substructure that supports new
life, animal and vegetable. And when we consider the great part
performed by these microscopic architects and builders it is not a
misnomer to speak of the building of a world.
CHAPTER III.
COAL.
Some time, long ago, some man made the discovery that what we now call
coal would burn and produce light and warmth. Who he was or how long ago
he lived we do not know, but as all earthly things have a beginning, we
know that such a man did live and that the discovery that coal would
burn was made. Coal, in the sense that we use the word here, is not
mentioned in the Scriptures. According to some authorities, coal was
used in England as early as the ninth century. It is recorded that in
1259 King Henry III. granted a privilege to certain parties to mine coal
at Newcastle. It is further stated that seven years after this time coal
became an article of export. In 1306 coal was so generally used in
London that a petition was sent to parliament to have the use of it
suppressed on the ground that it was a nuisance. Coal was used in
Belgium, however, about 1200. There is a tradition that a blacksmith
first used it in Liège as fuel. It was first used for manufacturing
purposes about 1713.
Coal is found laid down in great veins, varying in thickness, in various
parts of the world in the upper strata of the Paleozoic period. The age
in which it was formed is called by geologists the Carboniferous
(coal-bearing) age.
Before going on to account for the deposits of coal, let us stop a
moment and consider what it is. Chemists tell us that coal is chiefly
constructed of carbon, compounded with oxygen, hydrogen, and nitrogen.
There are many varieties, but all may be classified under two general
headings--bituminous and anthracite. Bituminous coal contains a large
amount of a tarry substance, a kind of mineral pitch or bitumen, which
burns with a brilliant flame and a black sooty smoke, exceedingly rich
in carbon. Anthracite coal is hard and stone-like in its texture,
burning with scarcely any flame and no smoke. It produces a fire of
intense heat when it is once ignited. There is another form of coal
called cannel coal, which is a corruption of "candle coal," so called
because a piece of this kind of coal when ignited will burn like a match
or pine knot and give light like a candle. This is the richest of all
the coal deposits in gases that are set free by heat, and for this
reason is extensively used in the manufacture of what is commonly
called coal gas. England produces a large amount of cannel coal, as well
as another variety of bituminous coal, which latter, however, does not
burn with such a black smoke as the coal found in the Ohio valley and
the Western States of America. East of the Alleghany Mountains there is
a region of anthracite coal that is very extensively worked and finds
great favor in all parts of the country as fuel for domestic heating,
especially on account of its great cleanliness.
All of the coal beds have a common origin, and the difference in the
quality of coal found in different parts of the country is due to many
circumstances, some of which have never been explained. There is
indisputable proof, however, that all coal beds are of vegetable origin.
Geologists tell us that these coal beds were formed during an age before
the earth had cooled down to the temperature that it has at the present
time--an age when vegetation was forced by the internal heat of the
earth instead of having to receive all its warmth from the sun's rays as
we do now. Some of our readers are familiar with what is commonly termed
a hotbed. A hotbed is made by putting soil on top of substances that
will ferment and create heat underneath the soil. This heat from beneath
will force vegetation and cause a much larger growth than there will be
if left to the sun's rays alone. During the carboniferous age the earth
was a great hotbed.
The fossils of trees and plants, as well as reptiles, that we find in
the great coal measures of the world, show that they were of large
tropical growth, and this is shown not only in the temperate zone, but
in the zone farther north. For ages and ages this rank growth of
vegetation grew up and fell down until a great layer of vegetable matter
was formed, which at a later time was covered over by other
stratifications of earth material, so that these great layers of
vegetable formation were hermetically sealed and pressed down by an
enormous weight that increased as time went on. The formation of coal
may be studied even at this day (for it is now going on) by visiting and
examining the great peat beds that are found in various parts of the
world. It is well known that peat is used as a fuel by many people,
especially the peasantry of the old countries. If peat is pressed to a
sufficient degree of hardness it burns in a manner not unlike some forms
of coal. Peat is a vegetable formation and has been formed by the rank
growth of various kinds of vegetation in swampy places. Of course, it
lacks the purity of the coal that was formed during the carboniferous
age, because of the much slower growth of vegetation now than during
that time, and the opportunity that peat bogs offer for an intermixture
of earthy with the vegetable matter. The fact that we find the imprint
of trees and ferns and other vegetable growth of tropical varieties, as
well as the fossils of reptiles, imbedded in the coal measures, proves
that at one time this stratum was at the land surface of the earth. We
also find that all of the formations of the Secondary and Tertiary
periods are on top of the coal--and this shows that after the age of
rank vegetable growth there was a sinking of the earth in many places
far down into the ocean--so that vast layers of rock formed on top of
these beds of vegetable matter. In England great chalk beds crop out in
cliffs on the southern coast, and, as we have seen, these chalk rocks
are largely made up of the shells of marine animals. London stands on a
chalk bed, from six hundred to eight hundred feet thick. Indeed, England
has been poetically called Albion, White-land, from this appearance of
her coast.
All of the great chalk beds were formed ages after the coal beds, as the
latter are found in the upper strata of the Paleozoic period.
A study of these strata will show that there are many layers of coal
strata varying in thickness and separated by layers of shale and
sandstone. How the shale and sandstone layers are formed will be the
subject of a future chapter.
From the position that the coal measures occupy, being entirely under
the Secondary and Tertiary formations, it will be observed that they are
very old. If we should examine a piece of ordinary bituminous coal we
should find that there are lines of cleavage in it parallel to each
other, and that it is an easy matter to separate the lump on these
lines. If we examine the outcrop of a coal bed we will find that these
lines of cleavage are horizontal. This indicates that the great bulk of
vegetable matter of which the coal formation is made up has been
subjected to tremendous pressure during a long period of time. If we
further examine the structure of a body of coal we find the impressions
of limbs and branches as well as the leaves of trees and various kinds
of plants. We shall further find that these impressions lie in a plant
in the same direction as the line of cleavage. This is a point to be
remembered, as it helps to explain the nature and structure of other
formations than those of coal. Not only are leaves and branches of
vegetable matter found, but fossils of reptiles, such as live on the
land. Sometimes there is found the fossil of a great tree trunk standing
in an erect position, with its roots running down into the rock below
the coal bed, while the trunk extends upward entirely through the coal
and high up into the other strata. All of these facts lead us to the
firm conclusion that when the trees were grown that formed these beds
they were above the surface of the ocean. This, taken in connection with
the fact that the vegetable fossils that are found indicate a tropical
growth of great size, drives us to the conclusion that the climate at
the time these coal measures were formed was much warmer than it is now.
As already remarked, this extra warmth came from the earth itself before
it had cooled down to its present temperature, rather than from the heat
of the sun. There is nothing inconsistent in the thought that the sun
may have been warmer in a former age than now. We may conceive that the
earliest coal formations took place when the land stood above the
surface of the water, and that the conditions were favorable for a rapid
and luxuriant growth of vegetation; after this had gone on for a very
long period of time, by some convulsion of nature the land surface was
submerged under the ocean, when other mineral substances were deposited
on top of this layer of vegetable growth, which hardened into a rock
formation. At a later period the earth was again elevated above the
surface of the water and the same process of growth and decay was
repeated. These oscillations of the earth up and down occurred at
enormously long intervals, until all of the various coal strata with
their intermediate formations were completed. After this we must suppose
that the whole was submerged to a great depth and for a very long period
of time, because of the great number and various kinds of rock
formations laid down by water that lie on top of the coal measures. This
tremendous weight, as it was gradually builded up, subjected these
vegetable strata to an inconceivable pressure. In some places this
pressure was much greater than in others, which undoubtedly is one of
the reasons why we find such differences in the structure and quality of
coal. There were no doubt many other reasons for differences, one of
them being the character of the vegetable growth out of which they were
formed. Again, in some parts of the world these coal strata may have
been subjected to a considerable degree of heat, which would change the
structure of the formation, and in some cases drive off the volatile
gases. One can easily imagine that heat was thus a factor in the
formation of what is known as anthracite coal, so much less gaseous than
the bituminous kinds. The anthracite beds seem to be denser and of a
more homogeneous character. The lines of cleavage are not as prominent,
but there are the same evidences of vegetable origin that we find in the
bituminous formations.
It will be seen from what has gone before that coal was first wood. But
wood is a product of sunshine. Thus the sun was the architect and
builder of the trees and plants that were finally hermetically sealed
under the great earth strata. The sun gathered up the material and set
the forces in play which made the chemical combinations of the various
elements in nature that enter into vegetable growth.
After the lapse of untold ages of time these great beds of stored-up
sun-energy were discovered by man and their contents are dragged out to
the earth's surface, to warm our houses, to drive the machinery of our
factories, to send the locomotives flying across the continents and the
steamships over the oceans. So important has this article become that if
any one nation could control the output it would be able to paralyze all
the navies and the manufacturing of the world.
If the coal of the world should become exhausted we should be confronted
with a great problem. Fortunately for us, this is a problem that will
have to be solved by the people of some future age, as the growth of
wood will scarcely keep pace with the consumption of fuel. By that time
the genius of man will have devised an economical means of storing the
energy of the sunbeams directly for purposes of heat, light, and power.
CHAPTER IV.
SLATE AND SHALE.
Slate is one of the great commercial products of the world. As far back
as the year 1877 the output of slate was not less than 1,000,000 tons
per annum. The chief use to which slate is put is for covering
buildings, and for this purpose it is better than any other known
material. It is also used in the construction of billiard tables and for
writing-slates; these latter uses are very insignificant as compared to
its use in architecture. Slate, like building-stone and limestone, is
quarried from the earth's crust and is found in the strata close above
the Metamorphic rocks, near the beginning of what is called the Primary,
or Paleozoic period. As compared with the coal formations it is very,
very old.
There are different substances called slate that are not slate in the
scientific use of that word. In general all stone formations are called
slates that split up into thin layers. But the true slate is a special
material which is formed by special processes of nature. The difference
between slate and shale, for instance, is not one of ingredients, but of
the process by which the ingredients are put together. All of the
sedimentary rocks are formed by a deposit of sediment from the water on
the bottom of the ocean. At one period the floods have brought down a
certain kind of material in greater profusion than at others, and this
is deposited in thin layers, and as it hardens there will be seams in it
and the stratifications will be differently colored, the color depending
upon the deposit at any particular time.
A bed of shale, like a bed of coal, has lines of cleavage in it, and if
it is examined under a microscope it will be found that the sedimentary
particles, like the twigs and leaves in the coal veins, lie with their
longest dimensions in line with the plane of cleavage. Shale in color
looks like slate, and an analysis of the material of which it is formed
shows that shale and slate are both made from the same. There is,
however, a structural difference between the two which is very peculiar
and very interesting. The slate is ordinarily a denser material and the
lines of cleavage are often at right angles with those that we find in
ordinary shale.
A slab of shale will be of a uniform color on any one line of cleavage.
The color may change at the next line, and generally does, to a slight
extent. It is easy to see, then, if we could change the lines of
cleavage in the shale, so as to run at right angles with their present
lines, the face of a slab would show bands of different colors or
shadings, such as we often see in slate. If you take a piece of clay
that has been thoroughly mixed, and subject it to a very great pressure,
and then examine the piece that has been submitted to pressure under a
microscope and compare it with a piece of the clay after it has been
thoroughly mixed, but has not been submitted to pressure, you will find
that the two are very different in structure. The pressed clay will show
that the particles of which it is made up have all turned, so that their
longest dimensions are in a line at right angles with the direction of
pressure. Here is an interesting fact that we must remember. And it is
in this that we find the reason for the structural difference between
shale and slate. The lines of cleavage in shale are not formed
necessarily by pressure, but because in the disposition of the material
of which it was formed the particles naturally laid themselves down so
that their longest dimensions were on a horizontal line.
Ages after, when other rock and other formations had been laid down on
top of the bed of deposited mud, the upheavals of the earth have so
changed the lines of pressure upon this material and the pressure is so
great that a rearrangement of the particles of which the slate is made
up has taken place, so that their longest dimensions now are in a
direction that crosses the stratifications as originally laid down.
The effect of this is twofold. First, the material is compressed into a
denser, closer form, and then, the lines of cleavage are changed, or to
express it in more common language, the grain has been changed. So that
when it splits up it runs crosswise of the original layers as the water
deposited them, and this produces the different shadings so often seen
in different slate. Shale splits in line with its layers; slate splits
across that line.
Let us go back a moment to our experiment with the lump of clay. If we
examined the mixture before submitted to pressure we should find that
the oblong particles of which it was made up would stand in all
directions, hit or miss, and if we should dry this lump of clay it would
have no special lines of cleavage. But the moment we have submitted it
to a certain amount of pressure we find that lines of cleavage have been
established, and that the particles have been rearranged so that their
longest dimensions are all in one direction, which coincides with the
cleavage lines. If we should now take this same piece of clay and
subject it to a pressure at right angles to that of the first
experiment we should find that the lines of cleavage had also changed
and that the particles had all been rearranged. Apply the principle to
the formation of slate, and we can understand how it happens that what
we call the grain runs crosswise of the deposits that were made at
different times. It is not a chemical, but purely a mechanical
difference. Or, to express it differently--the difference is a
structural one produced by mechanical causes.
The origin of cleavage in slate has been the subject of much speculation
and investigation, but like many other problems it was solved through
the invention and application of the microscope. Thin layers of slate
have been made, the same as with limestone and chalk, so thin that the
light would readily pass through it and that an examination of the
particles could be readily made, showing their arrangement under varied
conditions. Science is indebted to the microscope for the solution of
very many problems that for ages before had puzzled philosophers.
CHAPTER V.
SALT.
It may seem curious to the reader that we should care to discuss a
subject seemingly so simple as common salt. But it is a very usual thing
for us to live and move in the presence of things that are very common
to our everyday experience, and yet know scarcely anything about them,
beyond the fact that they in some way serve our purpose.
Salt is one of the commonest articles used in the preparation of our
food. It has been questioned by some people whether salt was a real
necessity as an animal food, or whether the taste for it is merely an
acquired one. All peoples in all ages seem to have used salt, and
reference to it is made in the earliest histories. Travelers tell us
that savage tribes, wherever they exist, are as much addicted to the use
of salt as civilized people. One of the early African travelers, Mungo
Park, tells us that the children of central Africa will suck a piece of
rock salt with the same avidity and seeming satisfaction as the
ordinary civilized child will a lump of sugar.
All animals seem to require salt, and it is claimed by those who have
tried the experiment that after one has refrained from the use of salt
for a certain length of time the craving for it becomes exceedingly
painful. It is most likely that the taste for salt is a natural craving.
In any event, whether it is a natural or an artificial taste, it has
become an article of the greatest importance in the preparation of food,
as well as on account of its use in the arts. Salt is a compound of
chlorine and sodium. In chemical language it is called sodium chloride.
The symbol is NaCl, which means that a molecule of salt is composed of
one atom of sodium and one of chlorine. Chlorine is an exceedingly
poisonous gas.
Formerly the chemist when he wished to obtain sodium extracted it from
common salt and discharged the chlorine gas into the air. It was found
that in establishments where the manufacture of sodium was conducted on
a large scale the destructive properties of the chlorine discharged into
the air was such that all vegetation was killed for some distance around
the manufactory. This came to be such a nuisance that the manufacturers
were either compelled to stop business or in some way take care of the
chlorine. This is done at the present day by uniting the chlorine gas
with common lime, forming a chloride of lime, which is used for
bleaching and purifying purposes.
Salt is found in great quantities as a natural product under the name of
rock salt. It is found in some parts of the world in great veins over
100 feet in thickness. In some cases the rock salt is mined, when it has
to be purified for commercial purposes. The common mode of obtaining
salt, however, is by pumping the solution from these great beds where it
is mingled with water--salt water; the water is then evaporated, and
when it reaches a certain stage of evaporation the salt crystallizes and
falls to the bottom.
Different substances crystallize in different forms. The crystallization
of water when it freezes, as we shall see hereafter, arranges its
molecules in such a form as to make a lump of ice of given dimensions
lighter than the same dimensions of water would be. Salt in
crystallizing does not follow the same law; the salt crystal is in the
shape of a cube and is denser in its crystalline form than in solution,
hence it is heavier and falls to the bottom.
It is said that there is a deposit of rock salt in Galicia, Austria,
covering an area of 10,000 square miles. There are also very large
deposits in England, the mining of which has become a great industry.
There are also great beds of salt in various parts of the United
States, notably near Syracuse, N. Y., where large salt deposits were
exposed in an old river bed formed in preglacial times. The common mode
of preparing salt for domestic purposes is by the process of evaporation
from brine that has been pumped from salt wells. The quality of the salt
is determined largely by the temperature at the time of evaporating the
water from it. Ordinary coarse salt, such as is used for preserving meat
or fish, is made at a temperature of about 110 degrees; what is known as
common salt is made at a temperature of about 175 degrees; while common
fine or table salt is made at a temperature of 220 degrees. Thus it will
be seen that the process of granulation with reference to its fineness
is determined by the rapidity of evaporation. Salt is one of the
principal agents in preserving all kinds of meats against putrefaction.
It will also preserve wood against dry rot. Vessel builders make use of
this fact to preserve the timbers used in the construction of the
vessels.
Salt at the present day is very cheap, but at the beginning of the
present century it was worth from $60 to $70 per ton. The methods of
decomposing salt to obtain its constituents, which are used in various
other compounds, are very simple to-day as compared with the processes
that prevailed in the days before the advent of electricity in large
volume, such as is produced by the power of Niagara Falls. It is curious
to note that a substance so useful and so harmless as common salt should
be made out of two such refractory and dangerous elements as chlorine
and sodium. Both of these elements, standing by themselves, seem to be
out of harmony with nature, but when combined there are few substances
that serve a better purpose.
These great salt beds that are found to exist in England and America and
other parts of the world were undoubtedly deposited from the water of
the ocean at some stage in the formation of the earth's crust. It is
well known that sea water is exceedingly saline; 300 gallons of sea
water will produce a bushel of salt. Undoubtedly beds of salt are also
formed by inland lakes, such as the Great Salt Lake in Utah. Only about
2.7 per cent. of ocean water is salt, while the water of the Great Salt
Lake of Utah contains about 17 per cent. When there is so much salt in
water that it is called a saturated solution, salt crystals will form
and drop to the bottom, which process will in time build up under a
large body of salt water a great bed of rock salt.
The water in all rivers and springs contains salt to a certain degree,
and where it runs into a basin like that of a lake with no outlet,
through the process of evaporation pure water is being constantly
carried off, leaving the salt behind. It is easy to see that if this
process is kept up long enough the water will become in time a saturated
solution, when crystallization sets in and precipitation follows,
accounting for the deposits of rock salt.
AIR.
CHAPTER VI.
THE ATMOSPHERE.
Meteorology is a science that at one time included astronomy, but now it
is restricted to the weather, seasons, and all phenomena that are
manifested in the atmosphere in its relation to heat, electricity, and
moisture, as well as the laws that govern the ever-varying conditions of
the circumambient air of our globe. The air is made up chiefly of oxygen
and nitrogen, in the proportions of about twenty-one parts of oxygen and
seventy-nine parts nitrogen by volume, and by weight about twenty-three
parts oxygen and seventy-seven of nitrogen. These gases exist in the air
as free gases and not chemically combined. The air is simply a mixture
of these two gases.
There is a difference between a mixture and a compound. In a mixture
there is no chemical change in the molecules of the substances mixed. In
a compound there has been a rearrangement of the atoms, new molecules
are formed, and a new substance is the result.
About 99-1/2 per cent. of air is oxygen and nitrogen and one-half per
cent. is chiefly carbon dioxide. Carbon dioxide is a product of
combustion, decay, and animal exhalation. It is poison to the animal,
but food for the vegetable. However, the proportion in the air is so
small that its baneful influence upon animal life is reduced to a
minimum. The nitrogen is an inert, odorless gas, and its use in the air
seems to be to dilute it, so that man and animals can breathe it. If all
the nitrogen were extracted from the air and only the oxygen left to
breathe, all animal life would be stimulated to death in a short time.
The presence of the nitrogen prevents too much oxygen from being taken
into the system at once. I suppose men and animals might have been so
organized that they could breathe pure oxygen without being hurt, but
they were not, for some reason, made that way.
Air contains more or less moisture in the form of vapor; this subject,
however, will be discussed more fully under the head of evaporation. The
air at sea-level weighs fifteen pounds to the square inch, and if the
whole envelope of air were homogeneous--the same in character--it would
reach only about five miles high. But as it becomes gradually rarefied
as we ascend, it probably extends in a very thin state to a height of
eighty or ninety miles; at least, at that height we should find a more
perfect vacuum than can be produced by artificial means. The weight of
all the air on the globe would be 11-2/3 trillion pounds if no deduction
had to be made for space filled by mountains and land above sea-level.
As it is, the whole bulk weighs something less than the above figures.
As we have said, the air envelopes the globe to a height at sea-level of
eighty or ninety miles, gradually thinning out into the ether that fills
all interstellar space. We live and move on the bottom of a great ocean
of air. The birds fly in it just as the fish swim in the ocean of water.
Both are transparent and both have weight. Water in the condensed state
is heavier than the air and will seek the lowest places, but when
vaporized, as in the process of evaporation, it is lighter than air and
floats upward. In the vapor state it is transparent like steam. If you
study a steam jet you will notice that for a short distance after it
issues from the boiler it is transparent, but soon it condenses into
cloud.
If we could see inside of a boiler in which steam had been generated,
all the space not occupied with water would seem to be vacant, since
steam before it is condensed is as transparent as the air. We will,
however, speak of this subject more fully under the head of evaporation
and cloud formation. It is not enough that we have the air in which we
live and move, with all of its properties, as we have described:
something more is needed which is absolutely essential both to animal
and vegetable life--and this essential is motion. If the air remained
perfectly still with no lateral movement or upward and downward currents
of any kind, we should have a perfectly constant condition of things
subjected only to such gradual changes as the advancing and receding
seasons would produce owing to the change in the angle of the sun's
rays. No cloud would ever form, no rain would ever fall, and no wind
would ever blow. It is of the highest importance not only that the wind
shall blow, but that comparatively sudden changes of temperature take
place in the atmosphere, in order that vegetation as well as animal life
may exist upon the surface of the globe. The only place where animal
life could exist would be in the great bodies of water, and it is even
doubtful if water could remain habitable unless there were means
provided for constant circulation--motion.
The mobility of the atmosphere is such that the least influence that
changes its balance will put it in motion. While we can account in a
general way for atmospheric movements, there are many problems relating
to the details that are unsolved. We find that even the "weather man"
makes mistakes in his prognostications; so true is this that it is never
safe to plan a picnic for to-morrow based upon the predictions of
to-day. The chief difficulty in the way of solving the great problems
relating to the sudden changes in the weather and temperature lies in
the fact that two-thirds or more of the earth's surface is covered with
water; thus making it impossible to establish stations for observation
that would be evenly distributed all over the earth's surface. Enough is
known, however, to make the study of meteorology a most wonderfully
interesting subject.
We have already stated that air is composed of a mixture of oxygen and
nitrogen chiefly, with a small amount of carbon dioxide. So far as the
life and health of the animal is concerned we could get along without
this latter substance, but it seems to be a necessity in the growth of
vegetation. There are other things in the air which, while they are
unnecessary for breathing purposes, it will be well for us to
understand, as some of them are things to be avoided rather than
inhaled.
As before mentioned, air contains moisture, which is a very variable
quantity. In a cold day in winter it is not more than one-thousandth
part, while in a warm day in summer it may equal one-fortieth of the
quantity of air in a given space. There is also a small amount of
ammonia, perhaps not over one-sixty-millionth. Oxygen also exists in the
air in very small quantities in another form called ozone. One way to
produce ozone is by passing an electric spark through air. Anyone who
has operated a Holtz machine has noticed a peculiar smell attending the
disruptive discharges, which is the odor of ozone. It is what chemists
call an allotropic form of oxygen, just as the diamond, graphite, and
charcoal are all different forms of carbon, and yet the chemical
differences are scarcely traceable. It is more stimulating to breathe
than oxygen and is probably produced by lightning discharges.
As has been before stated, the oxygen of the air is consumed by all
processes of combustion, and in this we include the breathing of men and
animals and the decay of vegetable matter, as well as the more active
combustion arising from fires. A grown person consumes something over
400 gallons of oxygen per day, and it is estimated that all the fires on
the earth consume in a century as much oxygen as is contained in the air
over an area of seventy miles square. All of these processes are
throwing into the air carbon dioxide (carbonic acid), which, however, is
offset by the power of vegetation to absorb it, where the carbon is
retained and forms a part of the woody fiber and pure oxygen is given
back into the air. By this process the normal conditions of the air are
maintained.
One decimeter (nearly 4 inches) square of green leaves will decompose in
one hour seven cubic centimeters of carbon dioxide, if the sun is
shining on them; in the shade the same area will absorb about three in
the same time.
There is another substance in the form of vegetable germs in the air
called bacteria. At one time these were supposed to be low forms of
animal life, but it is now determined that they are the lowest forms of
vegetable germs. Bacteria is the general or generic name for a large
class of germs, many of them disease germs. By analysis of the air in
different locations and in different parts of the country it has been
determined that on the ocean and on the mountain tops these germs
average only one to each cubic yard of air. In the streets of the
average city there are 3000 of them to the cubic yard, while in other
places where there is sickness, as in a hospital ward, there may be as
many as 80,000 to the cubic yard. These facts go to prove what has long
been well known, that the air of a city furnishes many more fruitful
sources for disease than that of the country. Some forms of bacterial
germs are not considered harmful, and they probably perform even a
useful service in the economy of nature. Within certain limits, other
things being equal, the higher one's dwelling is located above the
common level the purer will be the air. This rule, however, has its
limits, as the oxygen of the air is heavier than the nitrogen, so that
the air at very great altitudes has not the same proportion of oxygen to
nitrogen that it has at a lower level. An analysis that was made some
years ago of the air on the west shore of Lake Michigan, especially that
section where the bluffs are high, shows that it compares favorably with
that of any other portion of the United States.
In view of the foregoing, it is of the highest importance to the
sanitary condition of any city, town, or village that it be not too
compactly built. If more than a certain number of people occupy a given
area, it is absolutely impossible to preserve perfect sanitary
conditions. And there ought to be a State law, especially for all
suburban towns, which are the homes and sleeping places for large
numbers of business men who spend their days in the foul air of the
city, stipulating that the houses shall be not less than a certain
distance apart. Oxygen is the great purifier of the blood, and if one
does not get enough of it he suffers even though he breathes no
impurities. The power to resist the effects of bad air is much greater
when one is awake and active than when asleep, and this is why it is
more important to sleep in pure air than to be in it during our waking
hours. It is best, however, to be in good air all of the time. By pure
air I do not mean pure oxygen, but the right mixture of the two gases
that make air. Too much of a good thing is often worse than not enough.
Pure food to eat, pure water to drink, and pure air to breathe would
soon be the financial ruin of a large class of doctors.
CHAPTER VII.
AIR TEMPERATURE.
The most recent definition of heat is that it is a mode of motion; not
movement of a mass of substance, but movement of its ultimate particles.
It has been determined by experiment that the ability of any substance
to absorb heat depends upon the number of atoms it contains, rather than
its bulk or its weight.
It has also been stated that the atmosphere at sea-level weighs about
fifteen pounds to the square inch, which means that a column of air one
inch square extending from sea-level upward to the extreme limit of the
atmosphere weighs fifteen pounds. The density of the air decreases as we
ascend. Each successive layer, as we ascend, is more and more expanded,
and consequently has a less and less number of air molecules in a given
space. Therefore the capacity of the air for holding heat decreases as
we go higher.
We deduce from these facts that the higher we go the colder it becomes;
and this we find to be the case. Whoever has ascended a high mountain
has had no difficulty in determining two things. One is that the air is
very much colder than at sea-level, and the other that it is very much
lighter in weight. We find it difficult, when we first reach the summit,
to take enough of oxygen into our lungs to carry on the natural
operations of the bodily functions. To overcome this difficulty, if we
remain at this altitude for a considerable time, we shall find that our
lungs have expanded, so as to make up in quantity what is lacking in
quality.
If a man lives for a long time at an altitude of 10,000 feet he will
find that his lungs are so expanded that he experiences some difficulty
when he comes down to sea-level. And the reverse is true with one whose
lungs are adapted to the conditions we find at sea-level, when he
ascends to a higher altitude. There is a constant endeavor on the part
of nature to adapt both animal and vegetable life to the surroundings.
While no exact formula has been established as to the rate of decrement
of temperature as we ascend, we may say that it decreases about one
degree in every 300 or 400 feet of ascent. There is no exact way of
arriving at this, as in ascending a mountain the temperature will be
more or less affected by local conditions. If we go up in a balloon we
have to depend upon the barometer as a means of measuring altitude,
which, owing to the varying atmospheric conditions, is not a reliable
mode of measurement. It is easily understood that a cubic foot of air at
sea-level will contain a great many more atoms than a cubic foot of air
will at the top of a high mountain; or, to state it in another way, a
cubic foot of air at sea-level will occupy much more than a cubic foot
of space 10,000 feet higher up. Suppose, then, that the amount of heat
held in a cubic foot of air at sea-level remained the same, as related
to the number of atoms. In its ascent we shall find that at a high
altitude the same number of atoms that were held at sea-level in a cubic
foot have been distributed over a so much larger space that the sensible
heat is greatly diminished or diluted, so to speak. It was an old notion
that heat would hide itself away in fluids under a name called by
scientists latent heat. This theory has been exploded, however, by
modern investigation.
If we place some substance that will inflame at a low temperature in the
bottom of what is called a fire syringe (which is nothing but a cylinder
bored out smoothly, with a piston head nicely fitted to it, so that it
will be air-tight) and then suddenly condense the air in the syringe by
shoving the plunger to the bottom, we can inflame the substance which
has been placed in the bottom of the cylinder. In this operation the
heat that was distributed through the whole body of air, that was
contained in the cylinder before it was compressed, is now condensed
into a small space. If we withdraw the plunger immediately, before the
heat has been taken up by the walls of the syringe, we shall find the
air of the same temperature as before the plunger was thrust down. This,
however, does not take into account any heat that was generated by
friction.
Let us further illustrate the phenomenon by another experiment. If we
suddenly compress a cubic foot of air at ordinary pressure into a cubic
inch of space, that cubic inch will be very hot because it contains all
the heat that was distributed through the entire cubic foot before the
compression took place. Now let it remain compressed until the heat has
radiated from it, as it soon will, and the air becomes of the same
temperature as the surrounding air. What ought to happen if then we
should suddenly allow this cubic inch of air to expand to its normal
pressure, when it will occupy a cubic foot of space?
Inasmuch as we allowed the heat to escape from it when in the condensed
form, when it expands it will be very cold, because the heat of the
cubic inch, now reduced to the normal temperature of the surrounding
air, is distributed over a cubic foot of space.
This is precisely what takes place when heated air at the surface of
the earth (which is condensed to a certain extent) rises to the higher
regions of the atmosphere. There is a gradual expansion as it ascends,
and consequently a gradual cooling, because a given amount of heat is
being constantly distributed over a greater amount of space. At an
altitude of forty-five miles it will have expanded about 25,000 times,
which will bring the temperature down to between 200 and 300 degrees
below zero.
When we get beyond the limits of the atmosphere we get into the region
of absolute cold, because heat is atomic motion, and there can be no
atomic motion where there are no atoms.
We have now traced the atmosphere up to the point where it shades off
into the ether that is supposed to fill all interplanetary space. As
Dryden says:
There fields of light and liquid ether flow,
Purg'd from the pond'rous dregs of earth below.
By interplanetary space we mean all space between the planets not
occupied by sensible material. It is the same as interatomic space, or
the space between atoms, except in degree, as the same substance that
fills interplanetary space also fills interatomic space, so that all the
atoms of matter float in it and are held together from flying off into
space by the attraction of cohesion. What this ether is, has been the
subject of much speculation among philosophers, without, however,
arriving at any definite conclusion, further than that it is a substance
possessing almost infinite elasticity, and whose ultimate particles, if
particles there be, are so small that no sensible substance can be made
sufficiently dense to resist it or confine it. It is easy to see that a
substance possessing such qualities cannot be weighed or in any way made
appreciable to our senses. But from the fact that radiant energy can be
transmitted through it, with vibrations amounting to billions per
second, we know that it must be a substance with elastic qualities that
approach the infinite. Assuming that the ether is a substance, the
question arises how is it related to other forms of substance? This is a
question more easily asked than answered. The longer one dwells upon the
subject, however, the more one is impressed with the thought that after
all the ether may be the one element out of which all other elements
come.
Chemistry tells us that there are between sixty and seventy ultimate
elements. This is true at least as a basis for chemical science.
Chemical analysis has never been able to make gold anything but gold, or
oxygen anything but oxygen, and so on through the whole catalogue of
elements. It may be, however, that the play of forces under and beyond
those that seem to be active in all chemical processes and relations,
are able to produce certain affections of the ether, the result of which
in the one case is an atom of gold and in the other an atom of oxygen,
etc., to the end of the list. In this case all of the so-called elements
may have their origin in one fundamental element that we call the ether.
I am aware that we are wading in deep water here, but sometimes we love
to get into deep water just to try our swimming powers. The above is a
suggestion of a theory called "the vortex theory," that is taking root
in the minds of many philosophers to-day, and yet there is almost
nothing of known facts to base such a theory upon, and nearly all we can
say about it is that it seems plausible, when viewed through the eye of
imagination.
We do know that substances, such as fluids or gases, assume very
different qualities when put into different rates of motion. A straw has
been known to penetrate the body of a tree endwise by the extreme
velocity imparted to it when carried in the vortex of a tornado.
Instances of the terrific solid power of substances that are mobile when
at rest are often exhibited during the progress of a tornado, especially
when confined in very narrow limits. Sometimes a tornado cloud will form
a hanging cone, running down to a sharp point at the lower end, which
lower end may drag on the ground, or it may float a little distance
above the ground, but more frequently it moves forward with a bounding
motion, now touching the earth and now rising in the air. This cone is
revolving at a terrific speed. The substance revolving is chiefly air,
carrying other light substances that it has gathered up from the ground.
If it comes in contact with a tree or building it cuts its way through
as though it were a buzzsaw revolving at a high rate of speed. This is
not simply the force of wind, but a kind of solidity given to the fluent
air by its whirling motion.
I remember a case in Iowa, where one of these revolving cones passed
through a barnyard, striking the corner of the barn, cutting it off as
smoothly as though done with some sharp-edged tool, but it in no other
way affected the rest of the building. One would suppose that the
centrifugal force developed in this whirling motion would cause the cone
to fly apart, and why it does not no one certainly knows. But we are
obliged to accept the fact.
These cases are cited to show that motion gives rigidity to substances
that in the quiescent state are mobile or easily moved, like the straw
or the air. If we should assume that there are infinitesimal vortices or
whirling rings in the ether, of such rapidity as to give it different
degrees of rigidity, we can get a glimmering idea of how an atom of
matter may be formed from ether.
Referring to the rigidity which motion gives to ordinary matter, it is
well known that when two vessels at sea collide the one having the
higher speed is not so liable to injury as the one with the lower. The
reader will perhaps remember a circumstance said to have occurred a few
years ago on the Lake Shore Railroad, between Buffalo and Cleveland. The
limited express was going west, and while rounding a curve the engineer
suddenly came in sight of a wrecked freight train, a part of which was
lying on the track where the express train had to pass. The engineer saw
that he was too near the wreck to stop his train and that the only way
to save his own train and the lives of his passengers would be to cut
through the wreck. He pulled out the throttle and put on a full head of
steam, and when the train struck the wreck it was going at such a high
rate of speed that it cut through without seriously damaging the train
and without harm to the passengers.
There are other heroes beside those who lead armies in battle.
CHAPTER VIII.
CLOUD-FORMATION--EVAPORATION.
Water exists in different forms without, however, undergoing any
chemical change. It is when condensed into the fluid state that we call
it "water," and then it is heavier than the atmospheric air and
therefore seeks the low places upon the earth's surface, the lowest of
which is the bed of the ocean. Wherever there is water or moisture on
the face of the globe there is a process going on at the surface called
evaporation. This process is much more rapid under the action of heat
than when it is colder. In other words, as the heat increases
evaporation increases within certain limits and bears some sort of a
ratio to it. Evaporation is not confined to water, but as our subject
has to deal with atmospheric phenomena we will speak of it only in its
relation to aqueous moisture.
The heat that is imparted to the earth's surface by the rays of the sun
is able to separate water into minute particles, which, when so
separated, form what is called vapor, which is transparent, as well as
much lighter than the air at the surface of the earth. Being lighter
than the air, it rises when disengaged and floats to the upper regions
of the atmosphere. The atmosphere will contain a certain amount of these
transparent globules of moisture in the spaces between its own
molecules. If the air is warm the molecules will be farther apart and it
will contain more moisture than when it is cold.
The process of evaporation is one of the most important in the catalogue
of nature's dynamics. Without it there would be no verdure on the hills,
no trees on the plains, no fields of waving grain, and no animal life
upon the land surface of the globe. Evaporation is nature's method of
irrigation, and the system is inaugurated on a grand scale, so that
there are but few neglected spots upon the face of the earth which
moisture, carried up from the great reservoirs of water, does not reach.
The rate of evaporation, other things being equal, depends upon the
extent of surface; therefore a smooth surface like that of the lake or
ocean will not send up as much vapor from a given area in square miles
as an equal area of land will do, when it is saturated with moisture,
for the reason that there is a much larger evaporating surface on a
square mile of land, owing to its inequalities, than upon an equal area
of smooth water. Of course, if the earth is dry there can be but little
evaporation. One of the effects of evaporation is to withdraw heat, and
so to produce cold in the substance from which the evaporation takes
place.
If we put water into a vial and drop regularly upon it some fluid that
evaporates readily it will extract the heat from the vial and the water
in it to such an extent that in a short time the water will be frozen.
In hot countries ice is manufactured on a large scale upon the principle
that we have just described. Water is put into shallow basins, excavated
in the earth, over which is placed some substance like straw that
readily radiates heat, and on the straw are placed porous bricks, that
are kept wet, thus furnishing a very large evaporating surface. In this
way the process of evaporation is carried on very rapidly and the heat
is extracted from the water to such an extent that it freezes, often
forming ice in one night over an inch in thickness, and this in the
hottest climates on the globe. Evaporation cannot go on in places where
the air is already saturated with moisture. When the air is dry
evaporation is very rapid, but as it becomes more and more filled with
moisture the evaporation is checked to the same degree. This fact
accounts for the difference of bodily comfort that we experience at
different times in the year when the temperature is the same. Sometimes
we are very uncomfortable although the temperature is not above 75
degrees Fahrenheit, more so even than we are at other times when the
temperature is ten or fifteen degrees higher. If the air is saturated
with moisture, even though the temperature is not above 70 or 75
degrees, the perspiration is not readily evaporated from the surface of
the body. If the air is dry the temperature may be much higher and we be
much more comfortable, because evaporation goes on rapidly, which keeps
the body not only dry, but cool. I remember passing through a desert in
Arizona where there was scarcely a green thing in sight in any
direction, and the temperature was said to be 140 degrees. I did not
suffer as much as I often have done in the East with the thermometer at
80 or 90 degrees, and there was very little show of sensible
perspiration; it was going on rapidly, however, but was being absorbed
by the dry air. This goes to show that temperature is not the only
factor to be considered when we are making an estimate of the good or
bad qualities of a climate.
Evaporation is carried on much more rapidly when the wind blows than at
other times, for the reason that the moisture is carried off laterally
as fast as it is formed, all resistance to its escape into the upper air
being removed. If the air is charged to saturation with moisture at a
certain temperature, it will remain so, and evaporation stops so long
as the temperature remains unchanged. If its temperature rises the
process of evaporation can start up, because the capacity of the air for
holding moisture has been increased. But if a temperature is perceptibly
lowered another phenomenon will manifest itself.
In the uncondensed state vaporized moisture is quite transparent, so
that we are able to see through it as we do through a pane of glass. If,
however, the body of air that is saturated with this invisible moisture
becomes suddenly chilled, the moisture condenses into cloud or mist.
If we watch a passing railroad train we shall notice a mass of fleecy
white mist floating away from the smokestack, assuming the billowy forms
of some of the clouds in summer. This cloud is produced by the sudden
condensation of steam, which was transparent before it came in contact
with the cold, outside air, the effect being much more pronounced in
cold than in warm weather. We may liken these floating globules of mist
to the dust of the earth which floats in the air, and it has not been
inaptly called water-dust. Anyone who has seen an atomizer used or has
stood at the foot of a great waterfall, like Niagara, has seen the fluid
so finely divided that it will float in the air, instead of falling to
the ground. What takes place is that a number of these transparent atoms
of moisture that are released in the process of evaporation coalesce
into one small drop or particle of water, and they will continue to
float in the air as mist or cloud until a sufficient number have
combined into one solid mass to render that mass heavier than the air,
when it falls in the form of rain.
If we live in a region--and there are such on the face of the
earth--where there is very little evaporation and consequently very
little moisture in the air, there is rarely ever a cloud seen nor is
there any rainfall, for the reason that there is no material existing
out of which to form clouds, and the clouds precede the rain. Hence, all
the artificial attempts to produce rain in these arid regions have been
futile. If a body of warm air, when saturated with invisible moisture,
is suddenly chilled by coming in contact with a cold wave, it is
squeezed like a sponge, so to speak, and the invisible particles become
visible because a number of them have coalesced as one particle; the
particles gather in a large mass, and we have the phenomenon of cloud
formation.
Clouds more generally form in the upper regions of the atmosphere
because it is normally colder in the higher regions. In some cases
clouds float very high in the air and in others very low. This is due to
two causes:
If we should send up a balloon containing air rarefied to a certain
extent it would continue to ascend only until it reached a point where
the outside air and that contained in the balloon are of the same
density. If we should send up this same balloon on different days with
the same rarefaction of internal air we should find that on some days it
would float higher than others, because the density of the air is
constantly fluctuating, as is indicated by the rise and fall of the
barometer. Now let us consider the balloon as a globule of moisture of a
definite weight, and this globule only one of an aggregation of globules
sufficient to form a cloud. We can readily see from what has gone before
that a cloud thus formed, having a definite density and weight, would
float higher some days than others.
Assuming again that the density of the air remains the same from day to
day, the clouds will still float high or low in the atmosphere from
another cause. Let us go back to our illustration of the balloon. If we
have a fixed condition of atmosphere, external to the balloon, and vary
the conditions internally, which means varying its weight, the balloon
will float higher or lower as the internal conditions are varied. Now
apply this principle to the moisture globules of which a cloud is formed
and we can understand why a cloud will float high or low from the two
causes that we have described. Clouds are of different color and
density, and this is due to the differences of the make-up of the
moisture globules of which the clouds are formed. If these globules are
in an advanced stage of condensation the cloud is darker and more
opaque. In earlier conditions of condensation the cloud will have a
bright look, which shows that it reflects most of the light, whereas in
the case of the dark cloud the light is largely absorbed.
There is a sort of notion prevailing that clouds come up from the
horizon, and in many cases they do, but they may form directly over our
heads. There always has to be a beginning, and that occurs wherever the
conditions are most favorable for condensation of vapor. If the earth is
wet and the sun is hot the evaporation may be very rapid as well as the
ascent of the invisible moisture, which carries with it the air, which
in turn expands the higher it rises, thus producing cold. This, taken
with the normal cold that exists in the higher regions, may be
sufficient to produce a sudden condensation of this ascending vapor,
which is all that is necessary to form a cloud.
The inquiry may arise, Why is the moisture condensed, almost always, in
the upper regions of the air, where it is rare? Because the more rare
and therefore expanded it is, the more moisture it will hold. This,
taken with the fact that cold currents are encountered high up,
sufficiently answers the question.
It is interesting to know that the processes of nature are
interdependent. It is not enough that we have the evaporation of
moisture that will ascend into the higher regions of the air and there
be condensed into cloud and possibly rain, but we must have the means
for distributing these conditions over a large area, and for this
purpose we have the phenomenon of wind. Why the winds blow can be
accounted for to a certain extent,--we might say to a large extent,--but
there yet remain many unsolved problems relating to wind and weather. Of
the phenomena of wind we will speak more fully in a future chapter.
CHAPTER IX.
CLOUD FORMATION--CONTINUED.
As water in its condensed state is 815 times heavier than air, the
question naturally comes to one why it does not immediately fall to the
earth when it condenses. There are at least two and probably more stages
of condensation. Investigators into the phenomenon of cloud formation
claim to have ascertained that the first effect of condensation is to
form little globes of moisture that are hollow, like a bubble, with very
thin walls. Everyone has recognized the ease with which a soap bubble
will float in the air, and yet it is simply a film of moisture. These
little balloons, so to speak, are called spherules. It is undoubtedly
the case that mingled with these little bubbles of moisture there are
fine particles of solid water hanging on and carried along with them.
Undoubtedly this is true; at least just before the final act of
condensation takes place; and when the little hollow spherules collapse
they are gathered together in drops of water larger or smaller according
to the rapidity of condensation. There is probably another power at
work to prevent the too ready precipitation of moisture when condensed,
and that is the wind. A cloud never stands still, although in some cases
it may appear to do so. If we take a stone in our hand and allow it to
drop without applying any force to it, it will fall directly to the
ground. But if we give it an impetus in a horizontal direction it will
travel some distance before striking the ground. If we could give the
same impetus to a body as light as a globule of water-dust it would
probably travel indefinitely without falling. Dust that would settle
directly to the ground from an elevation in still air would travel
thousands of miles without falling, before a wind having any
considerable velocity.
Suppose the sun to be shining with intense heat upon a certain area of
the earth's surface and the conditions to be right for very rapid
evaporation of moisture. The air which is heated close to the ground,
being expanded, will rise, together with the invisible particles of
moisture, and there will be a column of moisture-laden air continually
ascending until it reaches a point in the upper atmosphere where it is
condensed into a cloud that takes on the billowy form which in summer
time we call a thunder cloud, but which in the science of meteorology is
called cumulus, or heap-cloud. If there were no air currents this
billowy cloud would stand as the capping of an invisible pillar of
ascending vapor, but as it is never the case that air is not moving at
some velocity in the upper regions, it floats away as rapidly as it is
formed. This peculiar kind of cloud is formed in the mid-regions of the
atmosphere, and it is a summer cloud as well as a land cloud. Of course,
it may float off over the ocean and maintain its peculiar shape for a
certain distance, but it is rare that such a cloud would ever be seen in
mid-ocean or in midwinter. As the warm season advances in summer, and
evaporation from the earth is less than the rainfall, there is less and
less moisture in the air, when, of course, the conditions for cloud
formation, especially inland, are not so favorable as in the early
spring or summer. Frequently there comes a time when we have a long
season of dry, settled weather. Probably during most of the days clouds
will form and we think it is going to rain, but before night they have
vanished, and the same thing is repeated the next day and the next,
perhaps for weeks at a time.
The explanation is this: We have already said that so long as the air
remains in a uniform condition as to temperature it will absorb moisture
in a transparent state until it is filled to the measure of its capacity
at a given temperature. If there were no change of temperature, it would
not condense into cloud. Clouds may be absorbed into the atmosphere--or
evaporated--and become invisible; and this process is going on to a
greater or less degree continually. If we watch the steam as it escapes
from a steam boiler, the first effect is condensation into cloud, but as
it floats away it gradually melts and is absorbed into the atmosphere as
invisible vapor. This is especially true on a warm day; the same process
takes place in the air that is going on at the level of a body of water
or at the surface of moist earth.
As before stated, condensation always takes place when a body of
moisture-laden air comes in contact with cold. When the steam escapes
from a boiler, even on the hottest day, it is hotter than the
surrounding air; the first effect is condensation, and then evaporation
takes place the same as it would at the surface of the earth when the
condensed particles of moisture are separated into the invisible atoms
that accompany evaporation.
In settled, dry weather as the sun approaches the zenith, the earth
becomes intensely heated, and there is an ascending column of air partly
laden with moisture; but not to the same extent as earlier in the
season. Condensation takes place and clouds are formed, but as there is
not sufficient moisture to carry them to the point of a further
condensation,--which would result in precipitation,--as the sun lowers
in the west and the heated air becomes more evenly distributed this
condensed vapor is reabsorbed into the air as invisible moisture by a
process allied to that of evaporation. This condition of things would
extend to a much longer period than it does in our latitude if it were
not for the gradual changing of the seasons, which finally destroys the
balance in the dynamics of cloud-land and allows the cold--that has been
held back for the time--in the great northern zone to get the upper
hand. Then we have what is termed in common parlance a change in the
weather, or, more properly in this case, a change in the season.
We have already spoken of the cloud called cumulus (which means heap)
and of its performance during the dry season of summer. There is another
form of cloud that is seen at this season of the year called cirrus (a
curl). It takes the form of a curl at its ends. This cloud usually has a
threaded shape and sometimes takes the form of a feather, and frequently
forms are seen that remind you of frost pictures on a window pane. These
clouds float very high in the atmosphere, away above the tops of the
highest mountains, from six to eight miles above the level of the sea.
They are formed only at a season of the year when the atmospheric
conditions are most uniform. At certain times of the day and night the
moisture will rise to this height before it condenses and when it does
condense it immediately freezes, which makes it take on these peculiar
forms that would no doubt conform very closely to the frost pictures on
the window pane if it were not for the disturbing influences of air
currents at this altitude. The fact that they are ice or frost clouds
instead of water clouds gives them that peculiar whiteness and
brightness of appearance. If ordinary clouds are water-dust these high
clouds may be called ice-dust. Sometimes we see them lying in bands or
threads running across the sky in the direction that the wind blows.
Their form is undoubtedly a resultant of the struggle between the air
currents and the tendency of crystallized water to arrange itself in
certain definite lines or forms. This cloud may be said to be one
extreme, having its home in the highest regions of cloud-land, while the
cumulus, or thunder cloud, is the other extreme and occupies the lower
or mid regions of the air.
There is a still lower cloud of course, as ordinary fog is nothing more
than cloud, which under certain conditions lies on the surface of the
ocean or dry land. Fogs prevail when the barometer is low. As soon as it
rises from the source of evaporation the moisture condenses almost to
the point of precipitation. There is not enough buoyancy in its
globules when the air is light, as it is when we have a low barometer,
to cause the fog to float into the higher regions of the atmosphere.
The high clouds, which are called cirrus, under certain conditions drop
down to where they begin to melt into ordinary moisture globules, and
while this process is going on we have a combined cloud effect which is
called cirro-stratus. This form of cloud may be recognized, when looking
off toward the horizon, by its being formed into long straight bands. It
is sometimes called thread-cloud. As it further descends it takes on a
different form called the cirro-cumulus, or curl-heap. This is just the
opposite in its appearance to the cirro-stratus, as it is broken up into
flocks of little clouds separated from each other and in the act of
changing to the form of the cumulus, or billowy form of cloud; and this
latter takes place when it drops to a still lower stratum of warmer air
and is there called the cumulo-stratus, which is the form of cloud we
most often see in the season of thunderstorms. The lower edge of the
cloud is straight, parallel with the horizon, while the upper part is
made up of great billowy masses, having high lights upon their well
defined projections and blending into darker shades caused by the
shadows in the valleys between the mountains of cloud.
The rain cloud is called the nimbus, and may be said to be the extension
of a cumulo-stratus. When it reaches this condition it is condensed to a
point where the vesicular globules collapse and a number of them run
together, forming a solid drop of water, and here it begins to fall. It
may be very small at first, but in its fall other condensed globules
will adhere to it and if the conditions are right, sometimes the rain
drops will have the diameter of a quarter of an inch by the time they
reach the earth.
Under other conditions, such as we have sometimes during dry weather,
the rain drops will start to fall, but instead of growing larger, they
grow smaller by absorption into the thirsty air, and will not be allowed
to reach the earth. Often there are showers of rain in the air that fall
to a certain distance and are taken up, as in the process of
evaporation, to again be formed into cloud, without ever having touched
the earth.
Thus it will be seen that clouds assume various forms under various
conditions of atmosphere, as it is related to moisture, temperature, and
density. Clouds sometimes appear to be stationary when they are only
continually forming on one side and continually being absorbed into
invisible moisture on the other. I remember seeing some wonderfully
beautiful cloud effects in the regions of the Alps. Almost every day in
summer there appears above the peak of Mount Blanc a beautifully formed
cloud cap standing some distance above it and hollowed out underneath
like an inverted cup. Although this cloud appears to be stationary, it
is undergoing a rapid change; the moisture rises from the snow-capped
peak as invisible vapor to a certain distance, where it is condensed
into a cloud of wonderful brilliancy. As the cloud globules float upward
they are absorbed into the atmosphere again, as invisible moisture at
the upper limit of the cloud. If the wind happens to be blowing, another
phenomenon takes place, giving the appearance somewhat of a volcano. It
is blown off from the peak in the direction of the wind, but within a
short distance it strikes a warmer stratum of air, where it is absorbed
and assumes the transparent condition.
If we ascend a high mountain, we get some idea of the altitude of the
various forms of cloud. A thunderstorm may be in progress far below us,
while the sun may be shining from a clear sky above, with perhaps the
exception of the frost clouds that we have referred to floating high
above the mountain tops.
We have now described in a general way how clouds are formed, how they
are condensed into rain, and how moisture is distributed over large
areas by these rain clouds being borne on the wings of the wind; and now
you ask, Whence the wind? In our next and following chapters we will try
to answer this question.
CHAPTER X.
WIND--WHY IT BLOWS.
We have said that globules of moisture, released by the action of the
sun's rays in the process of evaporation, tend to rise because they are
lighter than the air. Right here let it be said that all material
substances have weight; even hydrogen, the lightest known gas, has
weight, and is attracted by gravitation. If there were no air or other
gaseous substances on the face of the earth except hydrogen, it would be
attracted to and envelop the earth the same as the air now does. Carbon
dioxide is a gas that is heavier than the air. If we take a vessel
filled with this gas and pour it into another vessel it will sink to the
bottom and displace the air contained in it until the air is all driven
out. If we fill a jar with water up to a certain height and then pour a
pint of shot into it the water will be caused to rise in the vessel
because it has been displaced at the bottom by the heavier material. Now
if we remove the shot the water will recede to the level maintained
before the shot was put in. On the contrary, if we should pour an equal
bulk of cork or pith balls into the jar the water would not be
displaced, because the balls are lighter than the water and would lie on
top of it; if, however, the water is removed from the jar, the cork will
immediately go to the bottom of the jar, because the cork is heavier
than the air which has taken the place of the water. We wish to impress
upon the mind of the reader the fact, that all substances of a fluidic
nature, whether in the fluid or gaseous state, have weight, and obey the
laws of gravitation, and the heavier portions will always seek the lower
levels, and in doing this will displace the lighter portions, causing
them to rise. There is no tendency in any substance to rise of itself,
but the lighter substance rises because it is forced to do so by the
heavier, which displaces it. This law lies at the bottom of all of the
phenomena of air currents.
If we are at certain points on the seashore in the summer time we may
notice that about 9 o'clock in the morning a breeze will spring up from
the ocean and blow toward the land; this will increase in intensity
until about 2 o'clock in the afternoon, when it has reached its maximum
velocity, and from this time it gradually diminishes, until in the
evening there will be a season of calm, the same as there was in the
early morning. The explanation of this peculiar action of the air is
found in the fact that during the day the land is heated much more
rapidly on its surface than the water is.
The radiant energy from the sun is suddenly arrested at the surface of
the earth, which is heated to only a very shallow depth, while in the
water it is different; being transparent it is penetrated by the radiant
energy to a much greater depth and does not suddenly arrest it, as is
the case on land. As the sun rises and the rays strike in a more and
more vertical direction the earth becomes rapidly and intensely heated
at its surface, and this in turn heats the stratum of air next above it,
which is pressing on it with a force of fifteen pounds to the square
inch at sea-level. When air is heated it expands, and as it expands it
grows lighter. The stratum lying upon the earth as soon as it becomes
heated moves upward and its place is occupied by the heavier, cooler air
that flows in from the sides. We can now see that if there is a strong
ascending current of air on the land near the ocean the cooler air from
the surface of the ocean will flow in to take the place of the warmer
and lighter air that is driven upward, really by the force of gravity
which causes the heavier fluid to keep the lowest level. As the earth
grows hotter this movement is more and more rapid, which causes the
flow of colder air to be quickened, and hence the increasing force of
the wind as the sun mounts higher in the heavens. But when it has passed
the point of maximum heating intensity and the earth begins to cool by
radiation, the movements of air currents begin to slow up, until along
in the evening a point is reached where the surface of the earth and
that of the ocean are of equal temperature, and there is no longer any
cause for change of position in the air.
The earth heats up quickly, and it also cools quickly, especially if
there is green grass and vegetation. While they are poor conductors of
heat, they are excellent radiators, so that when the sun's rays are no
longer active the earth cools down rapidly and soon passes the point
where there is an equilibrium between the land and water. The water
possesses the opposite quality. It is slow to become heated, because of
a much larger mass that is affected, and is equally slow to give up the
heat. And the consequence is that after the sun has set, the land cools
so much faster than the water that we soon have the opposite condition,
and the sea is warmer than the land, which makes the air at that point
lighter, and which in turn causes the denser or colder air from the land
to flow toward the ocean, and displace the lighter air and force it
upward; hence we have a land instead of a sea breeze. So that the
normal condition in summer is that of a breeze from the ocean toward the
land during part of the day and a corresponding breeze from the land to
the ocean during part of the night, with a period of no wind during the
morning and evening of each day.
The forces that work to produce all the varying phenomena of air
currents on different portions of the earth are difficult to explain, as
there are so many local conditions of heat and cold, and these are
modified by the advancing and receding seasons. The unequal distribution
of land and water upon the earth's surface; the readiness with which
some portions absorb and radiate heat as compared with others; the tall
ranges of mountains, many of them snow-capped; the lowlands adjacent to
them that become intensely heated under the sun's rays; the diversity of
coastline and the fact that there is a zone of continually heated earth
and water in the tropical regions--all these conditions, coupled with
the fact that the earth rotates on its axis once in twenty-four hours,
are certainly sufficient to account for all the complicated phenomena of
aërial changes on the various portions of the earth's surface.
The trade winds are so called because they blow in a certain definite
direction during certain seasons of the year, and can be reckoned upon
for the use of commerce. If you trace the line of the equator you will
notice that for more than three-quarters of the distance it passes
through the water. The water, as we have explained in the last chapter,
becomes gradually heated to a considerable depth, and when once
saturated with heat is slow to give it up. It can easily be seen that
there will be a zone extending each way from the equator for a certain
distance that will become more intensely heated than any other parts of
the earth, with the exception of certain circumscribed portions of the
land. The result is that this heated equatorial zone is constantly
sending up warm air caused by the inrush of colder air, which is heavier
than the air at the equator, expanded by the heat. The warm air at the
equator is forced up into the higher regions of the atmosphere, and here
it overflows each way, north and south, causing a current of air in the
upper regions counter to that of the lower. As it travels north and
south it gradually drops as it becomes cooler, and finally at some point
north and south its course is changed and it flows in again toward the
equator. As a matter of fact, the trade winds do not flow apparently
from the north and south directly toward the equator, but in an oblique
direction. On the north side of the equator we have a northeasterly
wind, and a southeasterly wind on the south side. This is caused by the
rotation of the earth from west to east. The direction of the trade
wind, however, is more apparent than real.
The earth in its diurnal revolutions travels at the rate of a little
more than 1000 miles an hour at the equator. But if we should travel
northward to within four miles, say, of the north pole, the surface
point would be moving at the rate of only about a mile an hour. At some
point equidistant between the north pole and the equator the surface of
the earth will be moving at a rate, say, of 500 miles an hour. If we
could fire a projectile from this point that would have a carrying power
to take it to the equator some time after the projectile was fired,
although it would fly in a perfectly direct line, it would appear to
anyone at the equator who observed its approach to be moving from a
northeasterly direction. The reason is that the earth is traveling twice
as fast at the equator as it is at the point whence the projectile is
fired. Therefore it will overshoot, so to speak, at the equator, and not
be dragged around by the increased motion we find there.
To make this still plainer, suppose the earth to be standing still and a
projectile be fired directly across from the north pole in the direction
of the lines of longitude and required one hour to reach the equator,
the projectile would appear to anyone standing at the equator to come
directly from the north. If, however, the earth is revolving at the rate
of 1000 miles an hour at the equator to the eastward, and the
projectile was fired from the pole, where there is practically no
motion, in the same direction along the longitudinal lines as before,
the observer would have to be in a position on the equator 1000 miles
west of this longitudinal line in order to see the projectile when it
arrived; therefore the apparent movement of the projectile would not be
along the line at the instant that it was fired, but along a line that
would cross the equator at a point 1000 miles west. When a southward
impulse is given to the air it follows, to some extent, the same law, so
that to one standing on the equator the northern trade wind will blow
from the northeast and the southern trade wind from the southeast.
Owing to the fact that the air rises in the heated zone there is always
a region of calms at this point where there is no wind and no rain.
There are two other regions of calms in the ocean, one at the north at
the tropic of Cancer and another at the south near the tropic of
Capricorn. As has been stated, there are currents flowing back in the
upper regions at the equator north and south, and these are called the
upper trades--the lower currents being called the lower trades. These
upper trades gradually fall till they reach the tropic of Cancer on the
north, where the lower part of the current stops and bends back toward
the equator, now becoming a part of the lower trade wind. This causes a
calm at that point where it turns. The upper parts of this current
continue on, in a northerly and southerly direction, on the surface
until they meet with the cold air of the north and south polar regions,
where there is a conflict of the elements--as there always is when cold
and warm currents meet.
The only point where the trade wind has free play is in the South Indian
Ocean, and this is called the "heart of the trades."
If the whole globe were covered with water there would be a more
constant condition of temperature; but owing to the great difference
between the land and water, both as to altitude and the ability to
absorb and radiate heat, we have all of these varied and complicated
conditions of wind and weather. The trade winds shift from north to
south and vice versa with the advancing and receding seasons, due to the
fact that the earth has a compound motion. It not only revolves on its
axis once in twenty-four hours, but it rocks back and forth once a year,
which is gradually changing the direction of its axis; and in addition
to these motions it is traveling around the sun as well.
CHAPTER XI.
WIND--CONTINUED.
In our last chapter we discussed the winds that prevail in the regions
of the tropics called trade winds, because they follow a direct course
through the year, with the exceptions noted in regard to their shifting
to the north or south with the changing seasons; we also described the
phenomena of land and sea breezes, which during certain seasons of the
year reverse their direction twice daily. We will now describe another
kind of wind, called monsoons, that prevail in India.
India lies directly north of the great Indian Ocean, and the lower part
of it comes within the tropical belt lying south of the Tropic of
Cancer. During the summer season here the earth stores more heat during
the day than it radiates or loses during the night. This causes the wind
to blow in a northerly direction from the sea both day and night for six
months each year, from April to October. During these months the land is
continually heated day and night to a higher temperature than the water
in the ocean south of it. The winds are probably not so severe during
the night as through the day, as the difference between the temperature
of the land and the water will not be so great during the night; and
difference of temperature between two points usually means a
proportional difference in the velocity of the wind. There is a time in
the fall and spring, while there is a struggle between the temperature
of the land and water for supremacy, when the winds are variable,
attended with local storms somewhat as we have them in the temperate
zone. But after the sun has moved south to a sufficient extent the land
of India loses more heat at night than is stored up in the day; hence
the conditions during the winter months are reversed, the water is
constantly warmer than the land, and there is a constant wind blowing
from the land to the ocean, which continues until April, when after a
season of local storms the conditions are established in the opposite
direction. These winds are called "monsoons."
The word monsoon is probably derived from an Arabic word meaning
"seasons." It is a peculiarity of this monsoon that in summer it blows
in a northeasterly direction from the sea and in the winter in a
southwesterly direction from the land. This divergence from a direct
north and south is caused by the rotation of the earth and the
explanation is the same as that we have given for the trade winds.
In the southern latitudes there is a comparatively constant condition
of wind and weather, because the surface of the globe in these regions
is mostly water; but in the north, where most of the land surface is
located, we have a very different and a very complicated set of
conditions, as compared with the southern zones.
The freaks of wind and weather that we find prevailing upon the North
American continent are not so easily accounted for as the phenomena
heretofore discussed. In the northern part the land reaches far up
toward the north pole, while on the west lies the Pacific Ocean, which
merges into the Arctic Ocean at Bering Strait. The climate of the
western coast is affected by a warm ocean current that sets up as far
north as Alaska, while high ranges of mountains prevent the effects of
this warm current from being felt inland to any great extent; all of
which helps to complicate any theory that may be advanced regarding
changes of weather. Aside from the changes of temperature that are due
to the seasons, which are caused by the oscillating motion of the earth
between the limits of the Tropic of Cancer on the north and the Tropic
of Capricorn on the south, there are other changes constantly taking
place in all seasons of the year. While it is not difficult to account
for the change of seasons and the gradual change of temperature that
would naturally follow--owing to the difference of angle at which the
sun's rays strike the earth--it is more difficult to account for the
violent changes that occur several times during the progress of a
season, as well as the less violent ones that come every few days. In
fact, it rarely happens that the temperature is exactly the same on any
two successive days during the year. The diurnal changes are easily
accounted for by the rotation of the earth on its axis each day. But
there is another class of phenomena with which the "weather man" has to
struggle when he is making up a forecast of the weather from day to day.
In order that we may proceed intelligently, let us say a word about the
barometer. We speak of high and low barometer, and we make the
instrument with graduations marked for all kinds of weather, which
really mean but very little. The reading of a single barometer alone
will give us but a faint idea of what is really going to happen from day
to day. But if we have a series of barometers located at different
stations scattered all over the continent and connected at headquarters
by telegraph, so that we can have the readings from a whole series of
barometers at once, then it becomes a very useful instrument. A
barometer may read low at one station by the scale, but may be high with
reference to some other barometer that reads very low.
What is a barometer? If we should take a glass tube closed at one end,
the area of the cross section of which is one inch square, and fill it
with mercury, and while thus filled plunge the open end into a vessel of
mercury, it will be found that the amount of mercury remaining in the
tube above the level of the mercury in the vessel will weigh about
fifteen pounds, if the experiment has been performed at sea-level. This
will vary, however, according to the temperature of the air. Of course
barometers are tested when the air is at a certain temperature. If the
weight of mercury in the tube is fifteen pounds, since it is sustained
by the air pressing down on the mercury in the open vessel, it shows
that the air-pressure on that open vessel is equal to fifteen pounds to
the square inch. In practice, of course, the tubes are made very much
smaller. If the air changes so that it is lighter than normal the
mercury will fall in the tube, because the pressure on the mercury in
the open vessel is less than fifteen pounds to the square inch. And,
again, conditions may arise that will condense the air and make it for
the time being weigh more than fifteen pounds to the square inch, in
which case the mercury will rise in the tube. Thus it will be seen that
the barometer will register the slightest change in air pressure.
Let us dwell for a moment on the causes of what are commonly called
"changes of weather," when we will again revert to the use of the
barometer.
The use of the telegraph in connection with the establishment of a
weather bureau having stations for observation at convenient points
throughout the country has contributed much to the science of
meteorology. It is found that there are areas of high and low pressure
existing at the same time in different parts of the country. These
usually have their origin in the far northwest, and follow each other,
sweeping down the eastern side of the Rocky Mountains and gradually
bending easterly and from that to northeasterly by the time they reach
the Atlantic coast. The areas of low pressure are called cyclones, while
the areas of high pressure are called anti-cyclones. (By cyclone we do
not mean those cloud funnels commonly called by that name that form at
certain times of the year in certain sections of the country and produce
such destruction of life and property. These storms are usually confined
to a narrow strip and are short-lived. They arise undoubtedly from local
conditions. A description of these tornadoes--for such is their true
name--will be given in some future chapter.)
These centers of high and low pressure may be several hundred miles
apart. In the area of high pressure, if it is in the winter season, the
weather is unusually clear and cold, and generally clear and fairly cool
at any season, and while there may be some wind it is not so strong as
in the cyclone or low-pressure center. At this point it will be warmer
and winds will prevail, with rain or snow, the winds varying in
direction and intensity at a given point as the cyclone moves forward.
In the center of these cyclones and anti-cyclones there will be a region
of comparative calm, and the air is ascending at the center of the area
of low pressure while it is pouring in on all sides from the area of
high pressure where the air is compressed by a downward current from the
upper regions.
The high-pressure or anti-cyclone system usually covers a larger area
than the low-pressure system, where the air is ascending. While the air
moves laterally from high to low, it does not move in a direct line. The
air movement outside of the high-pressure center is usually not at a
very high speed, but in northern latitudes in the direction of the hands
of a clock. As it circles around it widens out spirally until it reaches
the edge of a low-pressure system, when it bends in its course and moves
in the other direction around this center, but constantly moving inward
toward it in a spiral form and in a direction that is reverse to that of
the hands of a clock. When the air current comes within the influence
of a low-pressure or cyclonic system the velocity of its movement is
very much accelerated until it has moved into the zone of quiet air in
the center, where it is ascending.
In the upper regions of the atmosphere there are counter currents
flowing in the opposite direction. The downward flow at the area of high
pressure compresses the air near the surface of the earth and rarefies
it in the higher regions of the atmosphere, while the opposite effect is
going on over the center of low pressure, the air being rarefied nearer
the surface of the earth, but condensed above normal in the higher
regions by the upward current, which causes an overflow back toward the
rarefied upper regions over the area of high pressure.
It will be observed that the ordinary storm has a compound motion. The
whole system moves in an easterly direction, while the winds are blowing
spirally about the storm center. If we should be in the track of a
moving storm so that its center passed over us the winds at the
beginning would blow in one direction and then there would come a
subsidence until it had moved forward through the quiet zone, when we
should feel the wind in the opposite direction until the area of low
pressure had moved forward into the region of high pressure. The
velocity of the wind will be determined by the difference of pressure
between the areas and by the distance that the areas of high and low
pressure are apart. The steeper the grade the more rapidly the fluid
will flow.
Let us now have recourse, for a moment, to Figs. 1, 2, and 3 in order
that the subject may be more fully understood. In looking at these
diagrams we should imagine ourselves looking South, with the left hand
to the East.
[Illustration: FIG. 1.]
Fig. 1 shows the general direction of the air movement between two
areas--one of high and the other of low pressure. The arrows show the
general direction of the wind. You will notice that in the upper regions
it blows in an opposite direction from the air movement on the surface
of the earth.
Fig. 2 shows in a general way how the wind moves spirally around both
centers. Over the area of high pressure the air descends spirally from
the upper regions, circling around a large area--it may be one hundred
miles or more in diameter--in the direction of the movement of the hands
of a clock.
[Illustration: FIG. 2.]
But then the wind at the high-pressure area is lighter than it is at the
low, and circles outwardly until it finally moves off in the direction
of a low-pressure area, gradually bending in the other direction until
finally it moves the reverse of the hands of a clock--although now it is
in a smaller circle, and with a more rapid motion. It moves spirally and
upwardly about the low-pressure area until it reaches a point in the
upper air, where it goes through the same gyrations in an opposite
direction. Now imagine the whole combination moving from west to east at
an average rate of thirty miles per hour, and imagine further that this
system is linked to other systems that are following along, and you have
some idea of the weather changes as they occur in the middle United
States.
By referring to Fig. 3 you will see why the wind changes its direction
when a storm center passes over any point. It has not only a spiral but
also a forward movement.
[Illustration: FIG. 3.]
Now let us go back to the barometer and see what part it plays in
predicting changes in the weather. At the area of low pressure the air
is ascending, as we have seen, and, owing to the peculiar way it
ascends--by circling spirally upward around a region of comparative
calm--it creates a partial vacuum, which is more pronounced in the
center of the area. At the area of high pressure the air will be
condensed by the descending current being arrested by the earth. The
descending current--coming, as it does, from the upper and colder
regions--accounts for the cool weather that most always prevails at a
high-pressure area. In order to know how great the change of weather is
likely to be, we must know what the readings of at least two barometers
are--one at the high- and another at the low-pressure area. If the
difference between the readings of the two barometers is very great, and
the areas are comparatively close together, we may expect the change to
be sudden and violent.
"High" and "low" as applied to a barometer are only relative terms.
There is no fixed point on the index of the instrument that can be said
to be arbitrarily high or low. For this reason a single barometer is not
of much use. If it begins to fall from any point, and falls rapidly, it
indicates that an area of a much lower pressure is approaching. The same
is true of a high-pressure area, if the barometer rises rapidly from any
point.
If we study the air motions in these systems sufficiently to get at
least an inkling of the law of their movements, it becomes a very
interesting subject.
Wind from whatever cause serves a wonderfully useful purpose in the
economy of nature. Without wind, heat and moisture could not be
distributed over the face of the earth and our globe would not be a fit
habitation for man. How wonderful is the machinery of Nature, that can
first forge a world into shape and afterward decorate it with green
grass and flowers that are watered by the "early and latter rain"!
CHAPTER XII.
LOCAL WINDS.
There are so many causes that will produce air motion that it is often
difficult to determine just what one is the chief factor in causing the
direction of the wind at any particular time. There are very many
instances, however, where the cause can be traced without difficulty;
many of these have already been mentioned and there are many more that
might be. Of course, as has been often stated, there is only one remote
cause for all winds, and that is the sun, coupled with the movements of
the earth. But there are certain local conditions that are continually
modifying the phenomena of air movement. The velocity of winds as they
occur from day to day varies very greatly with the height above the
surface of the earth; ordinarily the velocity at 1000 feet above the
earth will be more than three times greater than it is at 50 or 60 feet
above, and even at 60 feet the velocity is much greater than at the
surface of the earth. This is due partly to the retarding effect of
friction caused by contact of the air with the earth's surface, but more
particularly by trees, inequality of surface, and other obstructions on
the earth.
There is a variety of wind called mountain winds that arise from
different causes. As has been stated in a former chapter, under ordinary
conditions the air is more dense at sea-level than at any point above,
and the density is constantly changing from denser to rarer the higher
we ascend. Suppose at a certain point, say halfway up a mountain side,
the air has a certain density, and if it is at rest the lines of equal
density or pressure will seek a level, just as water would under the
same conditions. Suppose we start at a given point on the side of a
mountain and run out on a level till we are 100 feet in a perpendicular
line above the side of the mountain, the air contained within those
lines will be in the shape of a triangle. If now the sun shines upon the
side of the mountain the air is warmed and expands according to a
well-known law, and the amount of expansion will depend upon the depth
of the volume of air; hence the point of greatest expansion in our
figure will be where the air is 100 feet deep, and will gradually
decrease as we go toward the mountain till we come to the point where
our horizontal line makes contact with the mountain side. At that point,
of course, there is no expansion, because there is no depth of air; and
the effect will be that the expanded air will overflow toward the
mountain, and be deflected up its sloping side. If we apply this same
principle to the whole mountain side we can see that there will be,
during the day, a constant current of air flowing up the mountain. As
night comes on this upward movement will cease and there will be a
season of quiet until the earth has become colder than the air, and we
have a phenomenon of exactly the opposite kind, when the air contracts
instead of expands, which produces a downward current from the mountain
top.
These currents are as regular at certain seasons of the year as the land
and sea breeze. Of course, they may be obliterated for the time being,
by the presence of a stronger wind due to some other cause, such as
during the prevalence of a storm. In some of the regions of California
hottest during the day time, the nights are made endurable, and even
delightful, by the cool breezes that sweep down from the tops of the
mountains. It often happens that on the shady side of a high and steep
mountain where the sun's rays strike it so obliquely, if at all, that
the earth will be but little heated, there will be a vast mass of cold
air stored up. After the valley has become intensely heated by the sun
there is an ascending current of air which in turn causes a down rush
of the cold body of air from the mountain side. These local winds are
frequently very severe, only lasting, however, for a short time, until
an equilibrium of temperature and density has been established. A
wonderful exhibition of this sort of wind is said to occur at certain
times of the year on the coast at Tierra del Fuego, where a blast which
they call the "Williwaus," comes down from the mountain side, without
warning, with such tremendous force that no ship could stand the strain
if it should continue for any length of time. Fortunately the shock does
not last more than eight or ten seconds, when it is followed by a
perfect calm. It is as though a great volume of air had been fired from
some enormous cannon from the top of the mountain to the sea. The water
is pulverized into a spray that is driven in every direction.
Sometimes these violent blasts occur in the Alps, but from a very
different cause. Avalanches of great extent often take place on the
sides of the mountains, when a vast amount of material, equal to three
or four hundred million cubic feet of earth, will fall several thousand
feet. Often an avalanche of this kind will produce a wind, which is
confined, of course, to a restricted area, that is said to be so violent
as to tear one's clothes into shreds. This is not caused by any
difference of temperature, but by a violent compression.
There is a peculiar wind that occurs in Switzerland, often, between the
months of November and March. These winds last from two to three days
and are of great violence--especially near the mountains. They are warm
and dry and are caused by an area of low barometer and an ascending
current of air occurring at some point north of the Alps, which causes
the air from Italy to flow over the Alpine range, causing a tremendous
precipitation of snow and rain, which not only takes the moisture from
the air, but sets free in the form of heat the energy that was stored in
the process of evaporation, and this, together with the compression of
the air as it flows down the slope of the mountains, makes it hot and
dry. This wind is called the "Fohn."
There is a similar condition of things existing on the eastern slope of
the Rocky Mountains which has a modifying effect upon the climate of
parts of Colorado, Wyoming, Montana, also extending up into British
America. This wind, which is here called "chinook," arises from causes
similar to those that are active in Switzerland that give rise to the
"fohn" wind.
There is a wind called the "blizzard" that is felt most keenly in
Montana and the Dakotas during the winter, which is exceedingly cold and
lasts sometimes for a period of 100 hours. The temperature falls at
times 30 or 40 degrees below zero and the wind maintains a velocity of
from forty to fifty miles an hour. These winds spread eastward as far as
Illinois, but not with the same severity, and they move southward to the
Gulf of Mexico, spreading over the States of Texas and Louisiana, and
are there called "northers." It is exceedingly dangerous to be caught in
a blizzard in the Dakotas, where the wind reaches its greatest velocity
and the cold its lowest temperature--especially when the wind is
accompanied, as it frequently is, by severe snowing. By the time it
reaches the Gulf States it is very much modified as to temperature, but
it is a very disagreeable wind in that portion of the country, because
of the exceeding dampness of the air. One would be much more comfortable
in dry, still air, even if it were many degrees below zero, than in an
air freighted with moisture, although the temperature has not fallen to
the freezing point.
There are hot winds called by different names according to the
localities in which they occur. In southern California at certain
seasons of the year the inhabitants are afflicted with what they call a
desert wind that blows from the heated regions of Arizona toward the
Pacific Ocean. The temperature sometimes reaches 120 degrees Fahrenheit,
and persons have been known to perish from the effects of these hot
winds in open boats out on the water before they could reach land.
Hot winds prevail on the plains of Kansas during the months of July and
August that are phenomenal in their intensity, so much so that if they
were widespread and of long continuance, like the northern blizzard,
they would be attended with great loss of life and destruction to
vegetation. Fortunately, they come in narrow streaks and in most cases
do not blow more than from ten to thirty minutes at a time. These hot
belts are sometimes not over 100 feet wide, and again they are as much
as 500. They are so hot and dry that green leaves and grass are rendered
as dry as powder in a few minutes. These winds are probably caused by
the fact that at this season of the year, when the prevailing wind is
southwesterly, the air becomes heated to a great height, and are the
resulting effect of certain combinations of air currents in the higher
regions of the atmosphere that force the already heated air toward the
earth. As the air descends it is more and more compressed, which causes
it to become more and more heated. We have already described the heating
effect of compression upon air as shown by the experiment with the fire
syringe. It was shown that air at normal temperature could be suddenly
compressed into so small a space that the condensed heat, which was
before diffused through the whole bulk of air at normal pressure, was
sufficient to cause ignition. A cubic yard of air on the surface of the
earth would occupy a much larger space if carried a mile above it. From
this it is easy to see that if a volume of air at that height had a
temperature of 70 or 80 degrees it would be very hot when condensed into
a very much smaller volume, as it would be if it were forced down to the
surface of the earth. These winds are the result of some superior force
that is active in the upper regions of the atmosphere, because it is
natural for heated air to rise, and this is what happens when the power
that forced it down to the earth is no longer active to hold it there.
Reference has been made in a former chapter to tornado winds; they are
rather exceptional phenomena and not thoroughly understood. The winds
seem to blow in from all directions toward an area of very low pressure
at a single point. The spiral motion that is common to all cyclones, in
a tornado seems to be gathered up into a condensed form, like a funnel.
The direction of movement is the same as that of the cyclone--that is,
in the reverse direction to that of the hands of a watch. The upward
motion of the air inside of the funnel is at a rate of over 170 miles an
hour. The onward movement of the whole system is about thirty miles per
hour.
Tornadoes occur with greater frequency in the United States than in any
other section of the globe. Tornadoes seldom occur in winter, except
perhaps in the Southern States. They are more frequent in the month of
May than at any other time during the year, although they occur
sometimes in April, June, and July.
Between 1870 and 1890 about sixty-five destructive tornadoes occurred in
the United States, involving great loss of life and property. When a
tornado moves off the land on to the ocean it may become what is termed
a waterspout. These probably never originate on the water, but after
they have once formed may be carried over the water to a considerable
distance. A tornado was never known to originate on the shores of Lake
Michigan, but there are a few instances (the most notable one being the
Racine tornado) when they have reached the lake after having traveled
from some distant point inland.
The Racine tornado--so called because it destroyed a large portion of
that city--happened fifteen or more years ago. The tornado originated
about 100 miles southwest of Racine, Wis., in northern Illinois. The
funnel-shaped cloud passed over the lake, but the tornado character of
the storm was broken up before it reached the other shore.
When a tornado passes from land to water it becomes a waterspout only
when the cloud-funnel hangs low enough and the gyratory energy is
sufficiently great. There is a great pressure on the water outside of
the funnel and almost a perfect vacuum inside. This latter fact
contributes largely to the destructive power of the tornado. When a
funnel is central over a building a sudden vacuum is created outside of
it and it bursts outwardly from the internal air pressure.
CHAPTER XIII.
WEATHER PREDICTIONS.
To predict with any great accuracy what the weather will be from day to
day is a somewhat complicated problem, and, as all of us have reason to
know, weather predictions made by those who have the matter in charge
and are supposed to know all about it often fail to come to pass. The
real trouble is that they do not know all about it. There are so many
conditions existing that are outside of the range of barometers,
thermometers, anemometers, and telegraphs that no one can tell just when
some of these unknown factors will step in to spoil our predictions.
In very many cases, perhaps in a large majority of them, the predictions
made by the weather bureau substantially come to pass. It has been
stated in former chapters that the changes of weather accompany the
movements of what are called cyclones and anti-cyclones, the cyclone
being accompanied by low barometric pressure and the anti-cyclone by a
higher one. The winds of the cyclone move spirally around the center of
lowest depression with an upward trend, the motions being in a direction
reversed to that of the hands of a clock. In the centers of high
pressure the current is downward instead of upward and the direction of
the wind around it is opposite to that around the low-pressure area. The
fundamental factor in predicting the weather is the direction of
movement of these areas of low pressure. In almost all cases the
direction of movement is from the west to the east, but not always in a
straight line. These movements, however, are classified so that after
the direction has become established one can predict with considerable
accuracy as to whether it will move in a curved or a straight line. By
movement we do not refer to the direction of the wind at any particular
point, but the onward movement of the whole cyclonic system, which is
usually from twenty-five to thirty miles an hour, but in some cases the
speed is much greater.
Not only does the upward movement of the whole system vary, but the
velocity of the wind around any given cyclonic center varies. There are
about eleven classes of cyclones that appear in the United States, each
class having its own path of movement and origin. A large number of
these appear to originate north of the Dakotas, and move directly east
to the Gulf of St. Lawrence. Three other classes originate on about the
same line, a little west,--say, north of Montana,--moving first in a
southeasterly direction, passing over the center of Lake Michigan and
bending northerly through Lake Ontario and finally landing in the Gulf
of St. Lawrence. Two other classes start at the same point, one of them
going as far south as Cincinnati, and the other as far south as
Montgomery, Ala., and both turning at these points northeasterly to the
Gulf of St. Lawrence. Two other classes originate in Colorado, one
moving in a northeasterly direction slightly curved, and the other
directly east. Still others have their origin farther south in the Gulf
of Mexico, and move in a northeasterly direction. Very rarely they
originate in the Atlantic east of Savannah, moving first in a
northwesterly direction, but finally bending to the northeast.
Every day there is a weather map made up showing the locations of the
high and low barometers, direction of wind, lines of equal pressure, as
well as those of temperature. By study from year to year all of these
phenomena have become systematized, so that by tracing an area of low
barometer from its origin in its progress easterly it is soon seen to
fall under one of these classes and we are able to predict about what
its course will be. Knowing the speed of its movement as well as the
velocity of wind and all the conditions attending it, taken in
connection with the weather conditions in the region for which the
prediction is made, an expert can ordinarily forecast with some degree
of accuracy. After all that can be said, however, weather predictions
based upon maps are and have been far from satisfactory. One who has
been a close student of local conditions for a number of years will
often predict with as great accuracy as the weather bureau. Areas of low
pressure are followed sooner or later by a fall of temperature; this is
especially true in the winter months. Sometimes this fall is very
marked, and then it is called a cold wave. These sudden changes of
temperature are not thoroughly understood, but are supposed to be due
partly at least to rapid radiation of heat into the upper regions, as
the clear atmosphere which usually attends areas of high pressure is
favorable to such a condition. Undoubtedly, too, there are dynamic
causes, forcing the colder air from the upper regions to the earth, when
it immediately flows off toward an area of low barometer.
Long-time predictions are purely guesses. They sometimes guess on the
right side, and this gives them courage to make another. It is an old
saying that "all signs fail in dry weather." In time of a drought it is
true that the indications which at ordinary times would be surely
followed by a rain are of no value. When a season is once established,
either as a rainy season or a dry season, it is likely to persist in
this character until a change comes that is produced by the movement of
the sun in its course northerly and southerly, and the change produced
from this cause requires several weeks of time.
If accurate weather predictions could be made for a long time in
advance, or for even a week, they would be of incalculable value. But it
is doubtful if ever this will be brought about, as there are too many
necessarily hidden factors which enter into the calculations. If
stations could be established all over the oceans with sufficient
frequency, and an equal number at a sufficient altitude in the air, I
have no doubt that much that is now mysterious might be made plain.
CHAPTER XIV.
HOW DEW IS FORMED.
Reader, did you ever live in the country? Were you ever awakened early
on a summer's morning to "go for the cows"? Did you ever wade through a
wheat field in June--or the long grass of a meadow--when the pearly
dewdrops hung in clusters on the bearded grain, shining like brilliants
in the morning sun? Have you not seen the blades of grass studded with
diamonds more beautiful than any that ever flashed in the dazzling light
of a ballroom? If not, you have missed a picture that otherwise would
have been hung on the walls of your memory, that no one could rob you
of.
Everyone has noticed that at certain times in the year the grass becomes
wet in the evening and grows more so till the sun rises the next day and
dispels the moisture, and this when no cloud is seen. Dew is as old as
the fields in which grass grows. It was as familiar to the ancients as
it is to us, and yet it is only about three-quarters of a century since
the cause of it has been understood. We even yet speak of the dew
"falling" like rain. In former times some scientists supposed that it
was a fine rain that fell from the higher regions of the atmosphere.
Others supposed it to be an emanation from the earth, while still others
supposed it was an exudation from the stars.
"By his knowledge the depths are broken up and the clouds
drop down dew" (Prov. iii. 20).
The first experiments carried on in a scientific way were by Dr. Wells,
a physician of London, between the years 1811 and 1814.
Everyone has noticed in warm weather the familiar phenomenon of water
condensed into drops on the outside of a pitcher or tumbler containing
cold water. This condensation is dew. It always forms when the
conditions are right, summer and winter. In cold weather we call it
frost. It has been stated in a former chapter on evaporation that the
capacity of the air for holding moisture in a transparent form depends
upon its temperature. If the temperature is at the freezing point it
will contain the 160th part of the atmosphere's own weight as aqueous
vapor. If it is 60 degrees Fahrenheit the air will retain six grains of
transparent moisture to the square foot of air, while at 80 degrees it
will contain nearly eleven grains. When the air is charged with this
vapor to the point of saturation (which point varies with the
temperature) a slight depression of the temperature is sufficient to
condense this vapor into cloud or drops of water. Between 1812 and 1814
Dr. Wells made a series of experiments with flocks of cotton wool. He
weighed out pieces of equal weight and attached a number of them to the
upper side of a board and as many more to the lower side, and exposed it
to the night air under varying conditions. One experiment was made with
a board four feet from the earth, so that half of the bunches of cotton
faced the ground and the other half the sky. He found upon weighing
these after a night's exposure under a clear sky that the cotton wool on
top of the board had gained fourteen grains in weight from the moisture,
or dew, that had formed upon it, while the same amount of cotton on the
under side of the board had only increased four grains. He tried further
experiments by making little paper houses, or boxes, to cover a certain
portion of grass or vegetation. He found that while there would be a
heavy dew on the grass outside there was little or none within the
inclosure. These experiments were conducted in various ways and closely
watched to see that none of the phenomena were in any way connected with
falling rain. It has been determined that substances like grass and
green leaves of all kinds, hay and straw, while they are poor
conductors of heat, are excellent radiators. In another chapter we have
referred to this quality of straw, that is taken advantage of by the
inhabitants of hot countries in the manufacture of ice and in our own
land for storing it.
Perhaps everyone who has lived in the country has noticed that on a
summer's morning when the grass is laden with dewdrops a gravel walk or
a dusty road will be perfectly dry. This is due to the fact that the
gravel will retain heat and not radiate it, for a much longer time than
grass or green leaves. Dew begins to form upon the grass very soon after
the sun is set because the moment the sun's rays are withdrawn the heat
is rapidly radiated by the blades of grass, which cools the earth under
it and the air above and surrounding it, so that if the air is anywhere
near the moisture saturation point on cooling at the surface of the
ground it will readily give up a part of its moisture, which condenses
in drops upon the blades of grass.
If the night is still and clear and there is much moisture in the air,
the dew will be heavy, but if the night is cloudy there will be little
or no dew formed. The clouds form a screen between the earth and the
upper regions of the atmosphere, which prevents the heat from radiating
to a sufficient extent to form dew. For the same reason no dew will
form under a light covering spread over the ground even at some distance
above it. The covering acts as a screen, which prevents the heat from
radiating to the dew point. From what has gone before it will be seen
that if the atmosphere is not charged with moisture up to the point of
saturation it will require a greater amount of depression of temperature
to cause condensation, and this is why we usually have heavier dews in
June when the air is more highly charged with moisture than we do in
August when it is dry. This also accounts for the ice clouds, called
cirrus, being formed so high up in the atmosphere during dry weather.
There is so little moisture in the air that it requires a very great
difference of temperature to cause condensation to take place, and the
necessary depression is not reached in these cases except at an altitude
of several miles.
Dr. Wells has shown that if we take the reading of two thermometers on a
clear summer night, one of them lying on the grass and the other
suspended two feet above it, we shall find that the one lying on the
grass will read 8 or 10 degrees lower than the one suspended in the air.
If the night is still there will be a cold stratum of air next to the
earth, which will not tend to diffuse itself to a very great degree and
dew will form. If, however, it is cloudy or the wind is blowing there is
rarely any formation of dew. The reason in the former case, as we have
explained, is that the radiated heat is held down to the earth in a
measure, and in the latter case there is a constant change of air; so
that in either case no part of it is allowed to cool down sufficiently
to precipitate moisture.
It is a curious fact that often there will be a heavier dew under the
blaze of a full moon on a clear night than at any other time. The moon
has no screens about it of any kind to obstruct the free radiation of
heat. It is supposed to be a dead cinder floating in space and not
surrounded by an atmosphere, so that the sun's rays have full effect
upon it during the time it is exposed to them, and at that time it
becomes heated to a temperature of something like 750 degrees
Fahrenheit. For half the month, say, the sun is shining continuously
upon all or a part of it. In other words, the days and nights of the
moon are about two weeks long. The moon does not revolve upon its own
axis like the earth, therefore the same side or a portion of it is
exposed to the sun for 14 days. During the time that the moon is in the
earth's shadow it is supposed to fall to 187 degrees below zero, which
is 219 degrees below the freezing point. When the moon is full and is
heated up to over 700 degrees there is sufficient heat radiating from it
to be felt sensibly upon the face of the earth, and it would be felt if
it were not for the great envelope of atmosphere and its attendant cloud
formations that surround the earth. There are but few days in summer
when there is not a haze in the atmosphere, although we call the sky
clear, which intensifies the light and gives everything a warmer tone.
The heat coming from a full moon on a clear night is absorbed in causing
the aqueous vapors that are partly condensed in the higher regions of
the atmosphere, to be reabsorbed into transparent vapor. This clears
away the heat screen in the atmosphere and allows radiation to go on
more rapidly at the earth's surface, and thus cools it to a greater
extent when the moon is shining brightly than when it is dark and in the
shadow of the earth.
As we have already mentioned, the cold that is produced by radiation
through the blades of grass and other radiating substances may be
indicated by placing one thermometer on the ground and fixing another at
some point in the air. Sometimes the difference is very marked,
amounting to as much as 20 or 30 degrees. If under these conditions a
cloud floats overhead, forming a heat screen, its presence will be
readily noticed by a rise in the thermometer. Radiation into the upper
regions of the atmosphere is checked, which causes a sudden rise in the
temperature near the surface of the earth. By taking advantage of this
principle of heat radiation from the earth's surface it is a very easy
matter to protect tender vegetation from even quite a severe frost, if
it occurs in the early fall, by a slight covering, such as thin paper.
The paper will act as a heat screen and in a measure prevent the heat
from radiating from the earth immediately under it. Frost--which of
course is but frozen dew--at this season of the year will form on a
still autumn night, although the atmosphere at some distance above the
ground is some degrees above the freezing point. The reason for this
will be obvious when we consider the facts that have been set forth
concerning the power of radiation to produce cold.
It has been estimated by meteorologists that the amount of water
condensed upon the surface of the earth in the form of dew amounts to as
much as five inches, or about one-seventh of the whole amount of
moisture that is evaporated into the air. It will thus be seen that dew
performs an important part in supporting vegetation.
The same operation in nature's great workshop that forms the dews of
summer creates the frosts of winter. The moisture in cold weather is
condensed the same as in warm. When it is condensed at the surface of
the earth we have the phenomenon of frost, but when condensed in the
upper regions of the atmosphere we have that of snow.
Heat radiation from the earth goes on in winter, which is evidenced by
the fact that a thick covering of snow is a great benefit to vegetation
as a protection against the injurious effects of frost. The writer has
seen flowers blooming abundantly at an altitude of 12,000 feet above the
sea-level, protected only by the friendly shelter of a snowbank. In some
cases the blooming flowers were in actual contact with the snow. By
experiment it has been determined that the earth under a thick coating
of snow is usually warmer by nine or ten degrees than the air
immediately above the snow covering.
CHAPTER XV.
HAILSTONES AND SNOW.
A hailstone is a curious formation of snow and ice, and most of the
large hailstones are conglomerate in their composition. They are usually
composed of a center of frozen snow, packed tightly and incased in a rim
of ice, and upon this rim are irregular crystalline formations jutting
out in points at irregular distances. Frequently, however, we find them
very symmetrically formed as to outline, and the snow centers are almost
without exception round. Hailstones and hailstorms differ in different
climates, but they are more pronounced in the torrid than in the
temperate zone. Historians give accounts of hailstones of enormous size;
the very large hailstones being undoubtedly aggregations of single
stones that have been thrown together and congealed in the clouds during
their fall to the earth.
It is recorded that on July 4, 1819, hailstones fell at Baconniere
measuring fifteen inches in circumference, and very symmetrically
formed, with beautiful outline. Hailstones in India are said to be very
large--from five to twenty times larger than those in England or
America--seldom less than walnuts and often as large as oranges and
pumpkins. It is recorded that in 1826, during a hailstorm at Candeish,
the stones perforated the roofs of houses like cannon shot, and that a
single mass fell that required several days to melt, weighing over 100
pounds. It is further recorded that on May 8, 1832, a conglomerate mass
of hailstones fell in Hungary a yard in length and nearly two feet in
thickness. Still another instance is recorded of a hailstone having
fallen in 1849 of nearly twenty feet in circumference. This hailstone is
said to have fallen upon the estate of Mr. Moffat of Ord. We will only
ask our readers to listen to one more hailstone story, in which it is
related that during the reign of Tippoo, sultan, a hailstone fell as
large as an elephant. Undoubtedly one of two things was true regarding
this latter story; it was either a very large hailstone or a very small
elephant. The historian fails to give the size of the elephant. There is
no doubt, however, but that hailstones may adhere and form large masses
owing to the violent agitation of the elements that always attends a
hailstorm.
Hailstorms are almost universally attended by constant and heavy thunder
and lightning, together with violent winds. They usually occur on a
very hot day, and when the air is filled to saturation with moisture.
When this is the case a column of air is very highly heated at some
point, when it ascends with great force into the upper regions of the
atmosphere to a greater altitude than is common in the case of ordinary
thunderstorms. Here it meets with an intensely cold body of air, when it
is suddenly condensed and readily frozen as soon as condensed, which not
only forms hailstones, but sets free the energy that has been carried up
in the moisture globules. This results in frequent electrical
discharges, causing great waves of condensed and rarefied air, which, in
the rarefied portions, produces still more intense cold; so that we have
the conditions for a mighty struggle between the elements, which is
intensified by a constant and terrific electric cannonade. Undoubtedly
there are also whirlwinds in the cloud, similar to those that sometimes
visit the earth, which would tend to gather up the hailstones and
aggregate them into large masses. It is a mighty battle between the
moisture-laden, superheated air, ascending from the surface of the
earth, and the powers residing in the upper regions of cold. Nature is
constantly struggling to find an equilibrium of her forces, and a
hailstorm is only one of the little domestic flurries that take place
when she is setting her house to rights. Hailstorms are usually
confined to very narrow limits, and they can prevail on a grand scale
only in hot climates, where we have the conditions for wide differences
of temperature between the upper and lower regions of the atmosphere;
and, also, where the conditions are favorable, for an enormous amount of
absorption of moisture into the atmosphere.
When snow is formed in the atmosphere, the conditions are quite
different from those of a hailstorm; it is usually in a lower plane of
the atmosphere, and there is no violent commotion, as is the case with
the latter. A volume of air laden with moisture comes in contact with a
colder volume of air, when condensation takes place, as in the case of
rain, except that the moisture is immediately frozen. In this case both
volumes of air may be below the freezing point, but one is very much
colder than the other. If the snow reaches the earth it will be because
the air is below the freezing point all the way down. Snow is formed at
all seasons of the year. We may have a snowstorm on a high mountain when
we have extreme heat at sea-level.
In summer time of course the snow melts as soon as it falls into a
stratum of air with a temperature above the freezing point, and
continues its journey from that point as raindrops instead of
snowflakes. In the formation of a snowflake Nature does some of her
most beautiful work. A snowflake first forms with six ice spangles,
radiating from a common center. Shorter ones form on these six spokes,
standing at an angle of about sixty degrees, on each side of each spoke,
of such length and arrangement as to form a symmetrical figure or
flower. They do not always take the same form, but follow the same laws
that govern the formation of ice crystals. The structure of a snowflake
may be often found upon a window pane of a frosty morning. Here,
however, the free arrangement of the parts of a snow crystal are
interfered with by its contact with the window pane, but while floating
gently in the air there is the utmost freedom for the play of nature's
forces as they apply to the work of crystallization.
The difference in structure of snowflakes is chiefly due to the
conditions under which they are formed. If the moisture is frozen too
rapidly the molecular forces that are active in crystallization do not
have time to carry out the work, in its completeness of detail, as it
will where the freezing process, as well as the condensing process, goes
on more slowly.
CHAPTER XVI.
METEORS.
Meteors are the tramps of interplanetary space. They sometimes try to
steal a ride on the surface of the earth, but meet with certain
destruction the moment they come within the aërial picket line of our
world's defense against these wandering vagrants of the air. They have
made many attempts to take this earth by storm, as it were, and many
more will be made. They fire their missiles at us by the millions every
year with a speed that is incredible, but thanks to the protecting
influence of the great ocean of air that envelops our globe they become
the victims of their own velocity.
Meteors or shooting stars are as old as the earth itself, and they are
the material of which comets are made. Before it was determined what
these meteors or shooting stars were, many theories were promulgated as
to their origin. One was that they were masses of matter, large and
small, projected by volcanic action from the face of the moon with such
violence as to be brought within the attraction of the earth. Others
supposed them to be the effect of certain phosphoric fluids that
emanated from the earth and took fire in the upper regions of the
atmosphere. This, however, was mere speculation and without any
scientific basis of fact. Anyone who has been an observer of shooting
stars will have learned that there are certain periods of the year when
they are more numerous than at other times; notably in August and
November. Then again there are longer periods of many years apart. By
persistent observation it has been established that there are great
numbers of schools or collections of cosmic matter that fly through
interplanetary space, having definite orbits like the planets. Any one
of these collections may be scattered through millions of miles in
length. A comet is simply one of these wandering collections of meteoric
stones having a nucleus or center where the particles are so condensed
as to give it a reflecting surface something like the planets or the
moon. This enables us to see the outline of the comet to the point where
the fragments of matter become so scattered that they are no longer able
to reflect sufficient light to reach our eyes. The fringe of a comet,
however, may extend thousands or even millions of miles beyond the
borders of luminosity.
There is scarcely a day or night in the year when more or less of these
meteoric stones do not come within the region of our atmosphere, and
when this happens the great velocity at which they travel is the means
of their own destruction. They become intensely heated by friction
against the atmosphere just as a bullet will when fired from a gun--only
to a greater extent owing to the greater velocity. They disintegrate
into dust which floats in the air for a time, when more or less of it is
precipitated upon the surface of the earth. Disintegrated meteors, or
star dust, as they are sometimes called, are often brought down by the
rain or snow. Most of the shooting stars that we observe are very small,
resembling fire-flies in the sky, but once in a while a very large one
is seen moving across the face of the heavens, giving off brilliant
scintillations that trail behind the meteor, making a luminous path that
is visible for some seconds. These brilliant manifestations are due to
one of two causes. Either there is a very large mass of incandescent
matter or else they are so much nearer to us than in ordinary cases that
they appear larger. It is more likely, however, that it is due to the
former cause rather than the latter, from the fact of its apparently
slow movement as compared with the smaller shooting stars. It has been
determined by observation that the average meteor becomes visible at a
point less than 100 miles above the earth's surface. It was found as far
back as 1823 that out of 100 shooting stars twenty-two of them had an
elevation of over twenty-four and less than forty miles; thirty-five,
between forty and fifty miles; and thirteen between seventy and eighty
miles. It was determined by Professor Herschel that out of sixty
observations of shooting stars the average height of their first
appearance was seventy-eight miles and their disappearance was at a
point fifty-three miles above the earth.
It is a matter of history, however, that sometimes these meteoric stones
descend to the surface of the earth before they are entirely
disintegrated. A fine specimen of this kind is to be seen in the
Smithsonian Institution. There are over forty specimens of these
aërolites (air-stones) in the British Museum, labeled with the times and
places of their fall. Instances of falling to the earth are so rare that
there is little to fear from these wandering missiles of the air. We do
not remember a case where life or property has suffered from the fall of
a meteor.
This brings us to the consideration of the part which the great air
envelope surrounding the earth plays as a protection against many
outside influences. For instance, if it were not for the air, millions
of these meteoric stones would be showered upon our earth every year and
at certain times every day, which would render the earth untenable for
human existence. We should be at the mercy of those wandering comets
whose fringes strike our atmosphere more or less deeply at frequent
intervals. It is not impossible that the earth may at some time pass
directly through one, and yet there is little danger that in such a case
there would be more than an unusual display of celestial fireworks.
From the facts that have been above stated it will be apparent to anyone
that the number of these meteoric stones in the air is being constantly
reduced by their constant collision with the atmosphere and consequent
reduction to ashes or dust. Another conclusion is that the earth must be
gradually, but imperceptibly perhaps, increasing in size on account of
the constant settling upon its surface of meteoric dust.
CHAPTER XVII.
THE SKY AND ITS COLOR.
In the chapters on light in Vol. II. it will be stated that we see all
objects by a reflected light, except those that are self-luminous, such
as the sun or any other source of light. We see the moon and many of the
planets entirely by reflection. There are myriads of smaller objects,
too small to be seen as such, even under a microscope, that still have a
power to reflect light that is sensible to our vision. The air
surrounding the globe is literally filled with these microscopic light
reflectors. They serve to give us a diffused light which enables us to
see clearly all visible objects. We have all noticed the effect of a
single electric arc light, situated at a distance from any other source
of light, and how it casts extremely dark shadows and very high lights;
so much so that it is difficult to see an object perfectly in this
light, because the part of an object that is under the direct rays of
the lamp is so highly illuminated that the shadow, by comparison, has
the effect of simply a dark blot without form or shape. Many of you
have noticed in a country village, where the streets are lighted with
electric arc lamps, what a difference there is in the illuminating
effect between a clear and a foggy night. When there is a fog, or when
the clouds hang low down, we get a reflection from these which tends to
diffuse and soften the powerful light rays that are sent out by these
lamps. This effect is especially noticeable when the night is only
moderately foggy. Each globule of moisture floating in the air becomes a
reflector of light, and by myriads of reflections and counter
reflections the light (which on a clear night is concentrated) is
diffused over a large area, producing an illumination which for
practical purposes is far superior to that produced on a clear night.
When the latter condition prevails the rays of light are so intense on
objects immediately surrounding the lamps that one is blinded; so that
the places which are in shadow seem darker than they would be if there
were no light at all. The only way to prevent this effect is to have the
lights so close together that there will be cross lights, which tend to
break up the intensity of the shadows. This principle of light diffusion
is taken advantage of to produce an even illumination in stores that are
lighted only on one or two sides. This is effected by a series of prisms
or reflecting surfaces that are cast upon the panes of glass.
If now there were no atmosphere--or, to state it differently--if there
were no floating substances in the atmosphere, the sun would produce an
effect upon the earth similar to that of a single electric light. The
lights would be extremely high, and the shadows extremely dense. To one
looking off into space, the sky, instead of having the blue appearance
that we see, would have the effect of looking into a deep, dark abyss
without illumination.
Tyndall has shown us by a beautiful experiment that if there be in a
glass tube a mixture of gases related to each other in a certain way
chemically, they will combine into small globules or particles similar
to moisture in the air. If now a beam of light is thrown upon this tube
and a dark screen put behind it, we shall, in the beginning of the
experiment, simply see the dark screen. As soon, however, as the
molecules of the gases have combined in sufficient numbers to produce
particles of sensible size we begin to have a reflection of light from
them, the color of which is constantly changing as the combining
particles grow in size. At a certain stage in its progress the color
which the mixture of gases assumes is a beautiful azure blue, rivaling
in purity the finest skies of Greece or southern Italy.
The sun is the great lamp that illuminates the world, while the
atmosphere, which is filled with particles of various substances,
becomes the shade of the lamp which diffuses and softens the light and
gives it its color tones, whether of warmth or coldness. We could not
well do without the reflected light of the sky. The poetry of life would
be sadly marred. The beautiful effects of color and purity of tone would
be wanting. We need to bathe in light as much as in water, and the
character of the light is almost as important as the character of the
water. Imagine a world with an atmosphere devoid of all substances that
would in any way reflect light or give to it softness or color tone.
Imagine a sun or a moon without visible rays--for without a reflecting
atmosphere there would be none. Imagine a sky that was no sky at all,
but only a dark void, with no protecting vault. Think of the shadows, so
dark that you could see nothing in them. These would be some of the
effects that would come from an atmosphere that had no sky substance in
it. Imagine the world lighted by one great arc light. The reflex action
upon the race living in such a light would be anything but desirable.
The world would develop into an arc-light civilization--if one can
imagine what that would be like; certainly one of intensely violent
contrasts. Look on this picture and let us be thankful for the blue sky
and golden sunsets.
"But," you ask, "why is the sky blue?"
In one of the chapters on the subject of light in Vol. II. the
properties of soap bubbles are discussed. It is shown that when a film
is stretched across the mouth of a tumbler held in a position so that
the film is perpendicular, by the action of gravity (the moisture
constantly falling to the lower part of the film) it will continually
grow thinner, and horizontal bands of color will appear upon it,--first
red, then followed by the other colors of the solar spectrum, ending
with violet.
It is also stated that every color of light has a definite wave length.
Where a band of blue color appears upon the film we know that its
thickness is right for the wave length of that particular color which is
reflected from the back of the film to the eye. If we could conceive the
blue vault of the heavens to be half a sphere of a soap bubble, the
color that the sky would appear to us (if the light could be thrown upon
it from beneath) would be determined by the thickness of this film. If
the film was 1-156,000 of an inch the sky would be red instead of blue.
To reflect the other colors the film would have to grow thinner for each
color, in the progression from red to violet. The color of the sky is
determined by a light-reflection from minute globules of moisture
floating in the air. If the sky is blue, then the globules must be of
the right diameter to reflect that color. The various tints and
colorings of the sky are determined by what is found in the atmosphere,
and this is the reason why skies differ in coloring and tone in
different sections of the globe. The finest skies are probably found in
semi-tropical regions like southern Italy, Greece, and California.
In 1892 I visited Greece in the early part of June. In crossing the
Adriatic, from Brindisi to Patras in Greece, the route was through the
Ionian Islands that are grouped along the southwestern shore of Albania.
The sky was without a cloud, and its beautiful blue color was reflected
in the waters of the Adriatic, and I never shall forget the impression
made upon my senses when we first came in sight of the mountains on the
west coast of Albania. At this point they rise abruptly from the water
and are colored with that peculiar azure haze, mixed with a shading of
warmth, which is an effect that distance gives in the classic atmosphere
of old Greece. The effect upon the beholder is to intoxicate the senses
and to fill him with that deliciously poetic feeling that always comes
when standing in the presence of the sublime in nature. It was not the
mountains themselves that produced the effect, for I had seen grander
than these; but it was the sky on the mountains. When we look at a
distant mountain it seems to be partly hidden by a peculiar haze that is
the color of the sky at that time; we are really looking at the mountain
through a portion of the sky. While in Athens I took a trip to the top
of Mount Pentelicus, which separates the plains of Athens on the south
from those of Marathon on the north. From the summit of this mountain we
have a most wonderful view of the archipelago of the Ægean Sea--a
beautiful map of blue water and brown islands that melt together in the
distance. At our feet lay the historic plains of Marathon, and in the
distance rose the snow-capped peaks of Mount Olympus. It is doubtful if
the world furnishes a more beautiful combination of ocean, island,
continent, and sky than can be seen from Mount Pentelicus. Myriads of
brown islands set in the bluest of water--graceful in outline and
multiform in shape--jutting headlands and land-locked harbors--strong in
color and outline in the immediate foreground, but gradually melting
together in the distance, the brown becoming bluer and the blue a softer
blue till the whole is lost on the horizon in a sky that shades back to
the zenith in an ever-changing azure that for purity of tone baffles all
description.
What wonder that a people born under such skies and whose eyes have
feasted on such beauties in nature should conceive and execute such a
masterful work of art as the Parthenon! While the variation of
landscape, the stretch of water filled with islands, and the mountains
capped with eternal snow were a prominent part of the picture, it was
the sky with its beautiful color-tones that after all gave it its
wonderful charm.
The skies in a northern latitude are colder and grayer, due to the fact
that nearly always there is a certain degree of condensation of moisture
existing, which, while it does not take the form of a cloud, still gives
a toning to the sky.
There is no doubt but that the color-tones of the sky have an influence
upon the character and temperament of the people who live under them.
Under semi-tropical skies the poetic nature is more strongly appealed
to, and a man is more likely to be controlled by his dreamy imaginings
than his cold calculations. We find this latter characteristic
prevailing to a greater or less extent among the people who live under
colder and sterner skies. If all these qualities or influences could be
combined in the right way, the race would be stronger intellectually and
in other ways. It is always dangerous to a race of people to be
developed along certain lines only. The development should be
symmetrical. The strongest men are not those who are simply coldly
intellectual, neither those who are simply emotional and sentimental,
but those in whom heart, mind, and soul are so related that each one of
these elements re-enforces and strengthens the others.
At certain seasons of the year and in certain localities it is not
uncommon to have wonderfully beautiful displays of coloring upon the
skies and clouds at sunset. The question is often asked why we do not
see these displays at other times in the day than at sunrise and at
sunset--for the same effects are seen in the morning, but they are not
noticed so often, because to do so would interfere with the habits of
the average man and woman.
The reason for this change of coloring is the angle at which the sun's
rays strike the clouds of an evening sky, which are reflected to our
eyes. When the sun is high in the heavens it shines against the back of
the clouds, from the point of view of a person standing on the surface
of the earth. It also shines a shorter distance through the air at
midday than at sunset. At sunset the rays are able to shine on the under
side of a cloud, especially if it is high in the air. The moisture
globules of which the cloud is made up are much larger than the
transparent ones that are uncondensed and just as they were when
released in the process of evaporation.
As we have already seen, the reflections from these minute globules
give us the blue coloring of the sky and are very much smaller in
diameter than a globule that is able to reflect the red ray. When these
small globules are condensed into cloud a great number are combined into
one globule, and they are of all sizes, from the globule of evaporation
to that of the raindrop when precipitation takes place. We have, then,
in the various stages of cloud formation all conditions present for
reflecting the various colors and combinations of colors that are found
in the solar spectrum. Hence it is that, under certain conditions of
atmosphere and cloud formation, we see at sunset painted upon the sky
those wonderful combinations of colors, more beautiful and delicate in
shading, more various in combination and purer of tone, than any artist,
however cunning his fingers or brilliant his pigments, has ever been
able to truthfully reproduce. Even when the sky is cloudless it often
assumes a brilliant hue, which is partly a reflection from invisible
moisture globules and partly due to floating particles of dust that may
have been driven up from the surface of the earth, or may be the ashes
of meteorites disintegrated by contact with the air.
Some years ago, commencing in August, 1883, there was a wonderful
exhibition of red skies at sunset that lasted for several hours after
twilight ordinarily disappears. This phenomenon ran through a period of
several weeks, gradually fading away. It was afterward determined that
these displays were occasioned by small particles of ashes or dust
floating high in the air, that were thrown off from the volcanic
eruption of Krakatoa in the Island of Java. By the general circulation
of the air the ashes were carried to all parts of the world, making a
circuit of the earth in from twelve to thirteen days--which showed a
velocity of over eighty miles an hour. This is an instance of the high
velocity of the air currents in the upper regions of the atmosphere. The
reason why the illumination extended so late in the night was because of
the great height that these particles of dust attained. The higher the
reflecting surfaces are in the air the longer they may be seen after
sunset. Ordinary twilight is caused by a reflection of sunlight from the
upper air; and from its duration as ordinarily observed it is estimated
that the reflection does not proceed from a point more than thirty-six
miles high. In the higher latitudes the twilight is long, from the fact
that the sun does not go directly down, and if we go far enough north
the whole night is twilight. In the tropical regions the twilight is
shorter than at any other point on the globe for reasons that are
obvious. The sun there goes directly down and is soon hidden behind the
earth.
There are other optical effects to be seen sometimes on the horizon
somewhat resembling twilight. The "aurora borealis" (northern lights),
which we describe in Vol. III., is seen in the northern skies at certain
times, and has very much the appearance of twilight in some of its
phases. It is constantly changing, however, and is easily distinguished
by anyone who has observed both. These appearances are undoubtedly
electrical. There is another phenomenon seen in the arctic regions that
causes a band of white light to appear on the horizon called "ice
blink," and it is caused by the reflections from the great icebergs that
abound in that region.
Curious optical effects are sometimes observed a little after sunset in
the form of streamers or bands of light that shoot up into the sky,
sometimes to a great height. These are undoubtedly due to cloud
obstructions that partially shut off the sun's rays from a part of the
sky, but allow it to shine with greater brilliancy in the path of these
bands of light.
It will be seen from the foregoing that the sky in all of its phases is
a product of sunlight and the substances that float in the air,
including moisture, not only in the invisible state, but in all the
stages of condensation, as well as particles of floating dust.
CHAPTER XVIII.
LIQUID AIR.
Air, like water, assumes the liquid form at a certain temperature. Water
boils and vaporizes at 212 degrees Fahrenheit above zero, while liquid
air boils and vaporizes at 312 degrees below zero.
Heat and cold are practically relative terms, although scientists talk
about an "absolute zero" (the point of no heat), and Professor Dewar
fixes this point at 461 degrees Fahrenheit below zero. Others have
estimated that the force of the moon during its long night of half a
month, is reduced in temperature to six or seven hundred degrees below,
which is far lower than Professor Dewar's absolute zero. However this
may be, to an animal that is designed to live in a temperature of 70 or
80 degrees Fahrenheit, any temperature below zero would seem very cold.
If, however, we were adapted to a climate where the normal temperature
was 312 degrees Fahrenheit below zero, we should be severely burned if
we should sit down upon a cake of ice. Such a climate would be
impossible for animal existence, for the reason that there would be no
air to breathe, since it would all liquefy.
Liquid air is not a natural product. There is no place on our earth cold
enough to produce it. If the moon had an atmosphere (which it probably
has not) it would liquefy during the long lunar night, for heat radiates
very rapidly from a planet when the sun's rays are withdrawn from it.
As you have already surmised, liquid air is a product of intense cold.
Any method that will reduce the temperature of the air to 312 degrees
Fahrenheit below zero will liquefy it. Great pressure will not do this,
for we may compress air in a strong vessel until the pressure on every
square inch of the vessel is 12,000 pounds, or six tons, and still it
will not liquefy unless the temperature is brought down to the required
degree of coldness. If this is done it will change from a gas to a
liquid, but will occupy as much space as before, if it is condensed to a
pressure of six tons to the square inch.
Until twenty years ago it was supposed that oxygen and atmospheric air
(the latter a mixture of oxygen and nitrogen) were fixed gases and could
not be liquefied. In 1877, it is said that Raoul Pictet obtained the
first liquid oxygen, but only a few drops. About fifteen years later
Professor Dewar of the Royal Institution, London, succeeded in
liquefying not only oxygen but atmospheric air. And besides liquefying
the air he made ice of it.
In 1892 I visited London, where I met Professor Dewar, who invited me to
witness an exhibition of the manufacture of liquid oxygen--and
incidentally liquid air--at the Royal Institution. To me it was a most
wonderfully interesting event. I saw air, taken from the room, gradually
liquefy in a small glass test tube open at the top. When the tube was
withdrawn from the refrigerating chamber it boiled by the heat of the
room, and rapidly evaporated. We lighted a splinter of wood and blew it
out, leaving a live spark on the end of it, and held it over the mouth
of the tube, knowing that if anything like pure oxygen were evaporating
the splinter would relight and blaze (an old experiment with oxygen
gas). At first the splinter would not relight, because the evaporating
gases were a mixture of oxygen and nitrogen in the proportions to form
air. But owing to the fact that nitrogen evaporates sooner than oxygen,
a second trial was successful, for the splinter immediately began to
blaze, showing that the gas evaporating then was pure, or nearly pure,
oxygen.
When the liquid oxygen was poured into a saucer and brought into
proximity with the poles of a powerful magnet the liquid immediately
rushed out of the saucer and clung to the magnet poles; showing that
oxygen is magnetic.
Since that time other experimenters have succeeded in making liquid air
on a comparatively large scale, and the process is simple when we
consider some of the old methods.
Mr. Tripler of New York, who has made liquid air in great quantities,
does it substantially as follows: First, he compresses air to about 2500
pounds to the square inch. Of course the air is very hot when it is
first compressed because all the air in the tank has been reduced in
bulk about 166 times, and all the heat that was in the whole bulk of air
is concentrated into one-166th of the space it occupied before it was
compressed. It is 166 times hotter. There are two sets of pipes running
from the compressor to a long upright tank called the liquefier. These
pipes pass through running water, so that the compressed air is quickly
cooled down to the temperature of the water (about 50 degrees
Fahrenheit). The pipes--at least one set of them--run the whole length
of the liquefier, and most likely are coiled. This set of pipes contains
the air to be liquefied. A second set of pipes runs to the bottom of the
liquefier, where there is a valve. By opening this valve a jet of
compressed air is allowed to play on the other set of pipes, when
intense cold is produced by the sudden expansion of the air. This cold
air rushes up around the pipe containing the air to be liquefied and
escapes at the top, thus absorbing the heat until the temperature is
reduced to 312 degrees below zero. Then the air liquefies and runs into
a receptacle, where it may be drawn off at pleasure.
It will be seen that a large part of the compressed air is wasted in
cooling the remainder sufficiently to liquefy.
The use to which liquid air may be put, advantageously, is an unsolved
problem; but no doubt it will have a place in time. All great
discoveries do. Electricity had to wait a long time for recognition; but
what a part it plays now in the everyday life of the whole civilized
world!
Curious effects are produced by this intense cold. Meat may be frozen so
hard that it will give off a musical tone when struck. Here is a pointer
for the seeker of novelties in the line of musical instruments.
Liquid air furnishes a beautiful illustration of the fact that a burning
gas jet is continually forming water as well as giving out heat and
light. If we put liquid air into a tea kettle and hold it over a gas
jet, ice will form on the bottom from the water created by the flame,
and it will freeze so hard that the flame will make no impression upon
it, other than to make the ice cake grow larger.
Although liquid air is not found in nature, and is therefore called an
artificial product, it is produced by taking advantage of natural law.
Without the intellect of man it never would have been seen upon this
earth; and the same may be said concerning many things in our world,
both animate and inanimate. The genius of man is God-like. He lifts the
veil that shrouds the mysteries of nature, and here he comes in very
touch with the mind of the Infinite. Man interprets this thought through
the medium of natural law, and lo, a new product!
How much life would have been robbed of its charm and interest if all
these things had been worked out for us from the beginning! For there is
no interest so absorbing and no pleasure so keen as that of pursuit when
the pursuer is reaching out after the hidden things that are locked up
in Nature's great storehouse. From time to time she yields up her
secrets, little by little, to encourage those who love her and are
willing to work, not only for the pleasure of the getting, but for the
highest and best good of their fellows.
WATER.
CHAPTER XIX.
RIVERS AND FLOODS.
Water covers such a large proportion of the earth's surface and is such
an important factor in the economy of nature that it becomes a matter of
interest to study the process of its distribution. Water is to our globe
what blood is to our bodies. A constant circulation must be kept up or
all animal and vegetable life would suffer. Here, as in every other
operation of nature, the sun is the great heart and motive power that is
active in the distribution of moisture over the face of the globe.
The total annual rainfall on the whole surface of the earth amounts to
about 28,000 cubic miles of water. Only about one-fourth of this amount
ever reaches the ocean, but it is either absorbed for a time by animal
and vegetable life or lifted through the process of evaporation into the
air as invisible moisture, when it is carried over the region of
rainfall and there condensed into water and falls back upon the
earth--only to go through the same operation again. The whole surface of
the earth is divided into drainage areas that lead either directly
through rivulets and rivers to the ocean, or into some land-locked
basin, where it either finds an outlet under ground or is kept within
bounds through the process of evaporation, the same as is the case with
our great oceans. In North America the amount of drainage area that has
no outlet to the ocean amounts to about 3 per cent. of the whole
surface. In other countries the percentage of inland drainage is much
larger. The great Salt Lake in Utah is an instance where there is no
outlet for the water except through the medium of evaporation. Inasmuch
as all rivers and streams contain a certain proportion of
salt,--especially in such strongly alkaline land regions as the Great
Basin of the North American continent,--these inland lakes in time
become saturated with this and other mineral substances.
Salt is constantly being carried into the lake by the water of the
stream that feeds it, and the water is continually being evaporated,
leaving the salt behind. This process has been going on in the valley of
Utah for so long a period that 17 per cent. of the contents of the lake
is salt. The Humboldt River in Nevada, which empties into a small lake
of the same name, and lies at the foot of the Humboldt Mountains, is
said to have an underground outlet. This must be the case, because the
area of the lake is very small as compared with Salt Lake, while the
river that feeds the latter is very small compared with the one that
flows into the former. That is to say, in the one case a very small
stream empties into a large lake, while in the other case a much larger
stream feeds a very small lake. Besides, Humboldt Lake, unlike the Great
Salt Lake, is said to be a fresh-water lake; if it had no outlet it
would become in time saturated with salt. The largest body of water in
the world having no outlet to the ocean is the Caspian Sea, on the
border between Asia and Russia in Europe, it being 180,000 square miles
in extent.
Where rivers empty into large bodies of water, such as the great chain
of lakes on the northern border of the United States (and these lakes
have an outlet connecting one with the other, and finally by a river to
the ocean) a constant circulation is being kept up, and the water
remains fresh. Owing to the fact, however, of the great evaporating
surface that these lakes afford, there is a greater disproportion
between the rainfall upon the drainage area tributary to these lakes,
and the amount of discharge through the St. Lawrence River, than would
be the case with a river that was not connected with a system of lakes.
The amount of rainfall upon the area drained by the Mississippi River
during one year amounts to about 614 cubic miles of water, while the
discharge at the mouth of the Mississippi River is only about 154 cubic
miles. The difference between the two figures has been carried up by the
process of evaporation or stored in vegetation. These figures vary
considerably, however, with different years.
The proportion of rainfall to discharge will vary greatly in different
rivers from other causes than having a large evaporating surface. This
variation is due to the difference in the ability of the soil to retain
water after a rainfall. In some drainage areas the ground is more or
less impermeable to water, and in this case the water runs readily off,
causing a sudden rise in the river; and as suddenly it reaches the
low-water mark. In other drainage areas the ground is very permeable to
water, so that the rain penetrates to a greater depth into the earth,
where it is held, and by a slow process drains into the rivers, while
much more of it is carried off by evaporation and into vegetation than
is the case in the drainage district before mentioned.
The courses of rivers are determined by the topography of the country
through which they flow. The sinuous windings, that are found to be a
characteristic of nearly all rivers, are caused by the water, through
the force of gravity, seeking the lowest level, and avoiding
obstructions, which they can flow around more easily than remove.
Great rivers often change their courses, especially where they flow
through a region of made earth, such as is the case with the lower
Mississippi River, and in other great rivers of the world. The loose
earth is continually shifted by the current, and where the current is
not very strong it will often hold the water back to such an extent of
accumulated weight that the flood will break over at some weak point on
its banks and make a new course for itself.
One of the great rivers of China--the Hwangho--often causes dire
destruction to life and property owing to change in its bed from time to
time. It is estimated that between the years of 1851-66 this river
caused the loss of from 30,000,000 to 40,000,000 lives through drowning
and famine by the destruction of crops.
Floods in rivers are occasioned from various causes. Of course the
primary cause is the same in all cases, that is, from precipitation of
moisture in the form of rain or snow. Some rivers are so related to the
area of rainfall and to the permeability of the soil that there is but
little variation in the amount of discharge throughout the year. The
great river of South America, the Amazon, is an instance of a river of
this class. A certain number of the smaller rivers that feed it lie in
the area of rainfall during the whole of the year; for instance, the
streams of the upper Amazon are being fed by rains at one season of the
year, when those feeding the river lower down are at the lowest stage.
When the rainy season prevails in the upper section of the river the dry
season prevails farther down, while at another season of the year these
conditions are reversed. Therefore, though the Amazon has a larger
drainage basin than any other river in the world, and in some parts the
yearly rainfall is 280 inches, there is no very great fluctuation in the
stages of water. The Orinoco River, which flows through Venezuela, and
whose drainage area is largely covered with mountains, has a greater
fluctuation than any other river, the difference between high and low
water amounting to seventy feet.
The River Nile has an annual rise of from fourteen to twenty-six feet.
This river is the sole dependence of the inhabitants of lower Egypt, and
their sustenance depends upon the height to which the river rises; if it
does not rise high enough the agricultural lands are not sufficiently
irrigated, and if it rises too high their crops are destroyed by the
floods. In this section they depend entirely upon the overflow of the
Nile for irrigation, and not upon the rainfall. There is scarcely ever
a rainfall in lower Egypt except about once a year on the coast of the
Mediterranean. After ascending the river for a short distance we come
into an area of no rain for a distance of 1500 miles along the river.
Egypt has a superficial area of about 115,200 square miles, and only
about one-twelfth of this area is in a position to be cultivated.
As there is no rainfall in this region, the sole dependence for
agricultural purposes is from the River Nile when it rises to a
sufficient height to admit of irrigation. The river brings down
quantities of rich earth which during the overflow is deposited, and
thus the agricultural regions are refertilized annually.
The River Nile is what is called a tropical river and is fed by the
rains in upper Egypt caused by the monsoon winds that prevail in that
section of Africa during the summer season, as they do in India. As has
been explained in a former chapter, the monsoon winds blow steadily for
about six months from off the southern ocean. These winds are highly
charged with moisture, which is not precipitated till it strikes the
mountainous regions of the interior. Here the high mountains, which are
often snow-capped, cause a profuse precipitation, which runs off into
the various feeders of the Nile, causing a gradual rise in the river
that reaches the highest point about September of each year. If the
Nile should dry up, or if the annual floods should materially change in
height, it would make a desert region of all that portion of Egypt now
so productive.
The great rivers of China, the Yang-tse-Kiang and the Hwangho, are also
tropical rivers and have an annual flood. Sometimes the rise is as much
as fifty-six feet. These annual floods are also caused by the monsoon
winds that carry moisture from the ocean, which is condensed and
precipitated in the mountains of central Asia. The conditions are
substantially the same as those which prevail at the sources of the Nile
in Africa.
Rivers are produced from all sorts of causes, some of them flowing only
during the rainy season, while others are fed by melting snow from the
higher mountains, and as the snow is rarely melted away entirely during
the summer, in the high mountains, there is a continual flow from this
source. The snow forms a system of storage, so that the water is held
back and is gradually given up as it melts. If this were not true
mountainous regions would be subjected to disastrous floods. If the
precipitation were always in the form of rain it would immediately run
off instead of being distributed over a whole season. The Platte is an
instance of a river largely fed by the melting snows--of the Rocky
Mountains.
In the region of glaciers in the mountains of Alaska and Switzerland
rivers are fed by the melting ice. These rivers are usually of a milky
color occasioned by the pulverization of rock caused by the grinding of
the great glaciers as they flow down the gulches in the mountain side.
In some regions these glacial rivers have a diurnal variation. This is
caused by the fact that the glacier is so situated that it freezes at
night, which checks the flow, and thaws in the daytime, which increases
it.
Rivers are to the globe what the veins are to the animal organization.
They pick up the surplus moisture not needed in the growth of vegetation
and for the sustenance of animal life, and carry it on, together with
the débris that it gathers in its course, to the great reservoirs, the
seas and oceans, where it is redistilled and purified by the action of
the sun's rays. From here it is carried back in the form of invisible
moisture and again precipitated in the purified state, to help carry on
the great operations of growth--animal and vegetable. The vaporized
moisture that is carried back by the winds and redistributed corresponds
to the blood, after it has been purified and is carried back through the
arteries to the extremities and capillary vessels which feed and nourish
the bodily organs.
CHAPTER XX.
TIDES.
Anyone who has spent a summer at the seashore has observed that the
water level of the ocean changes twice in about twenty-four hours, or
perhaps it would be a better statement to say that it is continually
changing and that twice in twenty-four hours there is a point when it
reaches its highest level and another when it reaches its lowest. It
swings back and forth like a pendulum, making a complete oscillation
once in twelve hours. When we come to study this phenomenon closely we
find that it varies each day, and that for a certain period of time the
water will reach a higher level each succeeding day until it culminates
in a maximum height, when it begins to gradually diminish from day to
day until it has reached a minimum. Here it turns and goes over the same
round again. It will be further observed that the time occupied between
one high tide and the next one is a trifle over twelve hours. That is to
say, the two ebbs and flows that occur each day require a little more
than twenty-four hours, so that the tidal day is a little longer than
the solar day. It corresponds to what we call the lunar day.
As all know, the moon goes through all its phases once in twenty-eight
days. The tide considered in its simplest aspect is a struggle on the
part of the water to follow the moon. There is a mutual attraction of
gravitation between the earth and the moon. Because the water of the
earth is mobile it tends to pile up at a point nearest the moon. But the
earth as a whole also moves toward the moon, and more than the water
does, keeping its round shape, while its movable water (practically
enveloping it) is piled up before it toward the moon and left
accumulated behind it away from the moon. So that in a rough way it is a
solid sound earth, surrounded by an oval body of water: the long axis of
the oval representing the high tides, which, as they follow the moon,
slide completely around the earth once in every twenty-four hours. Thus,
there are really two high tides and two low tides moving around the
earth at the same time; and this accounts for the two daily tides.
We have accounted for the time when they occur in the fact that the
water attempts to follow the moon, but this does not account for the
gradual changes in the amount of fluctuation from day to day. The
problem is complicated by the fact that the sun also has an attraction
for the earth as well as the moon. But from the fact that the sun is
something like 400 times further from the earth than the moon is, and
also the fact that the attraction of one body for another varies
inversely as the square of the distance, the moon has an immense
advantage over the sun, although so much smaller. If the power of the
moon were entirely suspended, or if the moon were blotted out of
existence, there would still be a tide. The fluctuation between high and
low tide would not be nearly so great as it is at present, but it would
occur at the same time each day, because it would be wholly a product of
the sun.
It will be easily seen that these two forces acting upon the water at
the same time will cause a complicated condition in the movement of the
waters of the ocean. There will come a time once in twenty-eight days
when the sun and the moon will act conjointly, and both will pull in the
same direction at the same time upon the water. This joint action of the
sun and moon produces the highest tide, which is called the "spring"
tide. From this point, however, the tides will grow less each day,
because the relation of the sun and moon is constantly changing, owing
to the fact that it requires 365 days for the sun to complete his
apparent revolution around the earth, while the moon does her actual
course in twenty-eight days. When the sun and moon have changed their
relative positions so that they are at right angles to each other with
reference to the earth--at a quarter-circle apart--the sun and moon will
be pulling against each other; at least this is the point where the moon
is at the greatest disadvantage with reference to its ability to attract
the water.
Because one-quarter around the earth the sun is creating his own tide,
which to that extent counteracts the effect produced by the moon, the
tide under the moon at this point is at its lowest point and is called
the "neap" tide. When the moon has passed on around the earth to a point
where it is opposite to that of the sun--at a half-circle apart--there
will be another spring tide, and then another neap tide when it is on
the last quarter, and from that point the tide will increase daily until
it reaches the point where the sun and moon are in exact line with
reference to the earth's center, when another spring tide occurs. From
this it will be seen that there are two spring tides and two neap tides
in each twenty-eight days. This is the fundamental law governing tides.
There are many other conditions that modify tidal effects. Neither the
sun nor the moon is always at the same distance from the earth. So that
there will be a variation at times in high and low tides. For instance,
it will happen sometimes that when both the sun and moon are acting
conjointly they will both be at their nearest point to the earth, and
when this is the case the spring tide will be much higher than usual.
For many years the writer has observed that artesian wells, made by deep
borings of small diameter into the earth to a water supply, have a daily
period of ebb and flow, as well as a neap and spring tide, the same as
the tides of the ocean, except that the process is reversed. The time of
greatest flow of an artesian well will occur at low tide in the ocean.
This might be accounted for from the fact that when the tide is at its
height the moon is also pulling upon the crust of the earth, which would
tend to take the pressure off the sand rock which lies one or two
thousand feet below the surface and through which the flow of water
comes, and thus slacken the flow. When the moon is in position for low
tide, the crust of the earth would settle back and thus produce a
greater pressure upon the water-bearing rock. This is the only theory
that has suggested itself to the writer that would seem to account for
these phenomena.
Looked at from one standpoint, it is easy to account for tidal action.
But when we attempt to make up a table giving the hour and minute as
well as the height of the tide at that particular time we find that we
have a very complicated mathematical problem. However, tables are made
out so that we know at just what time in the day a tide will occur every
day in the year.
CHAPTER XXI.
WHAT IS A SPONGE?
Before entering upon the great subject of water and ice--two of the most
tremendous factors in world-building--let us consider a small matter, so
far as its permanent effects are concerned, yet one which enters largely
into the comfort and health of mankind, and which, though an animal, may
be discussed where it belongs--under "Water."
There are few things more familiar about the ordinary household than a
piece of sponge, and yet, perhaps, there are but few things about which
there is so little known. The sponge had been in use many, many years
before it was given a place in either the animal or vegetable kingdom.
The casual observer, because he saw it attached to a rock, jumped to the
conclusion that it was of vegetable origin. But after being kicked back
and forth, so to speak, from one kingdom to the other, even by what are
called well-educated people, it has finally been received into the
family of animals; a dignity in which the sponge itself seems to take
but little interest.
The sponge is found in the bottom of the sea; at no very great depth,
however. It is usually attached to a rock or some other substance and it
is due to this fact chiefly that it has been classed as a vegetable. At
least one scientist has attempted to give it a place between the two
kingdoms, but this only adds confusion without giving any satisfactory
explanation of its origin. It seems to belong to a very low order of
animal life. It breathes water instead of air, but probably, like many
other water animals, it absorbs the oxygen from the air which is more or
less contained in the water. There is a process of oxidation going on
within the sponge in a manner somewhat as we find it in ordinary animal
life, and like the animal it expels carbon dioxide. All this, however,
is carried on apparently without any lungs or any digestive organs, or
in fact any of the organs that are common to the animals of the higher
order. The sponge, however, as we see it in our bathrooms, is only the
framework, bony structure, or skeleton of the animal.
The sponge is exceedingly porous and readily absorbs water or any fluid
by the well-known process of capillary attraction. The sponge fiber is
very tough and is not like anything known to exist in the vegetable
kingdom. The substance analyzes almost the same as ordinary silk, which
all know is an animal product. If we burn a piece of sponge it exhibits
very much the same phenomena as the burning of hair or wool, and the
smell is very much the same.
The structure of a piece of sponge when examined under a microscope is a
wonderfully complicated fabric. Under the microscope it shows a network
of interlacing filaments running in every direction in a system of
curved lines intersecting and interlacing with each other in a manner to
leave capillary openings.
It is a wonderful structure, and one that a mechanical engineer could
get many valuable lessons from. It will stand a strain in one direction
as well as another. There are no special laminations or lines of
cleavage; it is very resilient or elastic, and readily yields to
pressure, but as readily comes back to its normal position when the
pressure is relieved. If we examine the body of a sponge we shall notice
that there are occasional large openings into it, but everywhere
surrounded by smaller ones. If we should capture a live sponge and place
it in an aquarium with sea water, where we could study it, we should
find a circulation constantly going on, and that water was constantly
sucked in at the smaller openings all over the outside of the sponge and
as continuously ejected from the large openings. This process
constitutes what corresponds in the higher order of animals to both
respiration and blood circulation, combined. The sponge feeds upon
substances that are gathered up from the sea water, and breathes the air
contained in the same, so that it breathes, eats, and drinks through the
same set of organs.
When we first capture a live sponge from the sea it has a slimy, dirty
appearance, and is very heavy. The sponge is found to be filled with a
glutinous substance that is the fleshy part of the animal. It is very
soft and jelly-like, and after the sponge is dead it is readily squeezed
out, by a process which is called "taking the milk out," which leaves
simply the skeleton, the only useful part as an article of commerce.
This fleshy substance, in life, has somewhat the appearance and
composition of the white of an egg.
The mechanical process by which the sponge takes its nourishment is
exceedingly interesting. There are small globe-shaped cells with
openings through them that are lined with little hairlike projections
that move in such a manner as to suck the water in at one side of the
cell and push it out at the other. These little fibers are technically
called "cilia." We might describe them as little suction pumps that are
located at many points in the sponge, all acting conjointly to produce a
circulation through the finer openings or capillary vessels and finally
discharging into the larger chambers which carry off the residue. If we
should analyze the water as it is sucked into the sponge and that which
issues from it through the larger openings, we should find a difference
between the two. The expelled water would contain more or less carbon
dioxide.
There are many different varieties of sponge, and, while they all
possess certain characteristics in common, they are still very different
in many respects. Some of them are large and coarse, while others are
exceedingly soft and velvety. What is called a single sponge is a colony
of animals rather than a single animal; at least they are so regarded by
zoölogists. This can hardly be true if we regard the sponge itself as a
part of the animal. If the sponge is simply regarded as the house in
which the animal lives then it becomes a great tenement with numerous
occupants. But it is a tenement upon which the life of the sponge
depends, and is a part of it.
The sponge could not breathe without the fibrous structure in the cells
containing the machinery for producing the circulation. It will be seen
that the sponge, while it is an animal, is of the very simplest variety,
so far as its organs are concerned. True, its framework is very
complicated, but the organs for sustaining the life of the animal are
the simplest possible. The little self-acting pumps pull the water into
the sponge through the smaller openings, where it appropriates the food
substance from the water and where a chemical action takes place which
builds up the fleshy substance of the animal, and then expels the
residue which is not needed to support its life.
Simple as it is, however, as a mechanical structure, the life and growth
of the sponge is as mysterious as that of the most highly organized
animal or even the soul of man. We can study out the structure of a
plant or animal; we can analyze it and tell what are the elements of
which it is composed; we can describe the mechanical operations that are
carried on and the chemical combinations that take place, but no man has
ever yet solved the mystery of life, even in the lowest form--whether
animal or vegetable.
The sponge, whether considered as a single or compound animal, has the
power to reproduce itself, and here the mystery of life is as much
hidden as it is in God's highest creation. It has been stated that every
sponge contains a large number of separate cells which carry on the
operation of circulation and respiration, and may be likened to the
heart and lungs of an animal of a higher creation. Zoölogists claim that
each one of these cells represents a separate animal, living in a common
structure. However this may be, it is an interesting fact that the
sponge has the power of secreting ova that grow in large numbers in
little sacks until they have reached a certain stage of progress, when
they are expelled from the mother sponge and turned adrift in the great
ocean to struggle for their own existence. These eggs do not differ much
in their structure and composition from an ordinary hen's egg, except
that there is no shell, only a skin provided with little fibers called
cilia, that project from it, and by the movement of these the embryo
sponge is able to propel itself through the water. It thus lives until
it has reached a certain stage of development, when it seeks out a
pebble or rock, to which it attaches itself at one end--preparation for
which has been made by its peculiar structure during its life when it
was free to float around through the water. It is now a prisoner and
chained to the rock it has selected for the foundation of its home.
Having no longer any use for the little cilia, which enabled it to swim
through the water, it now loses them. Here is a beautiful illustration
of how nature provides for the necessities of the smallest things, and
how when the necessity that demanded a certain condition passes by the
condition passes with it. The embryo begins to show a fibrous
development, which is the beginning of the framework of a new sponge.
Evolution goes on, every step of which is as mysterious as a miracle,
until the growing thing is a full-grown sponge, equipped with the means
for respiration, circulation, feeding, digestion, and reproduction.
Sponges grow in the bottom of the sea at different depths. They are
obtained by divers who make a business of gathering them. The best
sponges are called the Turkish sponge, which are very soft and velvety,
and may be bleached until they are nearly white by subjecting them to
the action of certain acids. The divers become very expert, but they do
not have the modern equipments of a diving suit. The Syrian divers in
the Mediterranean go down naked with a rope attached to their waists and
a stone attached to the rope to cause them to sink, together with a bag
for carrying the sponges. They have trained themselves until they can
remain under water from a minute to a minute and a half, and in that
time can gather from one to three dozen sponges. The ordinary depth to
which they descend is from eight to twelve fathoms. But a very expert
diver will go down as far as forty fathoms. The better class of sponges
are said to grow in the deeper waters. The coarse inferior sponges are
called the Bahama sponge. This sponge is of a peculiar shape, growing
more like a brush, with long bristly fiber.
The trade in sponges is quite large. The consumption in Great Britain
alone amounts to about $1,000,000 per annum.
The sponge as an animal possesses many advantages over his more
aristocratic neighbor, man. He breathes but he has no lungs, and
therefore cannot have pneumonia. He digests his food, but he has no
stomach, and therefore never has dyspepsia, gastritis, or any of the
many ailments that belong to that much abused organ. He has no
intestines, and therefore cannot have appendicitis or Asiatic cholera or
any of the long train of diseases incident to those complicated organs.
He has no nervous system--oh, happy sponge!--therefore he cannot have
nervous prostration, hysteria, or epilepsy. He has no use for doctors,
and therefore has no unpleasant discussions with his neighbors about the
relative merits of the different schools of medicine. If he has any
predilections in the way of "pathies" we should say that he is a
hydropath. While he is a great drinker, he is not at all convivial--he
drinks only water, and takes that in solitary silence. He sows all his
wild oats when he is very young, while he has the freedom to roam at
will. He soon tires of this, however, for he selects the rock that is to
be the foundation of his future home and there settles down for life,
"wrapt in the solitude of his own originality." He is not troubled with
wars or rumors of wars. His eyes are never startled or his nerves shaken
by the scare headlines of yellow journalism. The one sensation of his
life, if sensation he ever has, is when a great ugly creature of some
Oriental clime comes down to his home and tears him away from his native
rock, carries him to the surface, and there literally "squeezes the life
out of him." He finally dies of the "grip," and here he sinks to the
level of his more aristocratic neighbor.
But there is another side to our philosophy. If the sponge is exempt
from all these ills that we have enumerated it is because he is
incapable of suffering and is therefore incapable of enjoyment. Those
beings that have the ability to suffer most have also the ability to
enjoy most. The higher the type of civilization the greater
possibilities it offers for real enjoyment--also for real misery. This
being true, it should be the aim of highly civilized people to eliminate
as far as possible those things that make for misery, and cultivate
those things that make for happiness in the highest and best sense.
CHAPTER XXII.
WATER AND ICE.
We now have entered upon a subject that is of intense interest, studied
from the standpoint of facts as they exist to-day and of history as we
read it in the rocks and bowlders that we find distributed over the face
of the earth.
The whole northern part of the United States extending to a point south
of Cincinnati was at one time covered with a great ice-sheet, traces of
which are plainly visible to anyone who has made anything of a study of
this subject. The glaciers now to be seen in British Columbia and
Alaska, great as they seem to one viewing them to-day, are by comparison
with what once existed simply microscopic specks of ice. Glaciers, like
rivers, flow by gravity, following the lowest bed and lines of least
resistance; the difference being that in the one case the flow is rapid,
while in the other it is scarcely visible, except by measurement from
day to day. Before entering upon a description of the law that governs
the flow of glaciers, let us stop and give a little study to the
phenomena of water as exhibited when it is at the freezing point. Water
is such a large factor in the make-up of our globe and the air that
surrounds it that it becomes a very interesting and important study to
anyone who wishes to understand the phenomena of nature that are closely
related to it.
As all know, pure water is a compound of two gases, oxygen and hydrogen,
combined in the proportion of two atoms of hydrogen and one of oxygen.
Let us now study this fluid in its relation to heat. The reader is
referred to the chapters on heat in Vol. II., where it is stated that
heat is a mode of motion. It is also stated that heat is a form of
energy, and that energy is indestructible, that an unvarying amount of
it exists in some form or another throughout the universe. It is not
always manifested as heat or electricity, although both of these are
always in evidence as active agents of force. Much of the energy is
simply stored--all the time possessing the ability to do work or to be
converted into any of its known forms, such as heat, light, electricity,
or mechanical motion. A weight that is wound up has required a certain
amount of energy to elevate it to the position that it occupies. While
in its elevated position it possesses energy, although not active.
Energy in this form is called potential (possible) energy, and has the
power to do work if released. Active energy is called kinetic (moving)
energy, and the sum of these two energies is a constant quantity.
We will now study energy as it is related to water in the form of heat.
There is a kind of heat called "latent heat," which is not heat at all,
but stored energy, waiting to be turned into heat, or light, or some
other active form. Properly speaking, heat is a movement of the atoms of
matter, the intensity of which is measurable in degrees, and called its
temperature. To use the term latent heat as meaning concealed heat,
which must reappear as heat, is a misnomer and is very misleading. If it
is proper to call a wound-up spring or weight latent heat then its
present use is a correct one. What was formerly termed latent heat is
simply a form of potential energy. When sensible heat that is
measurable, as temperature, disappears in the performance of some sort
of work, especially in connection with certain phenomena relating to
water, we call it--or rather miscall it--latent heat: but the phrase
would better be "stored energy."
The action of water under heat is very peculiar, and in order to get a
correct understanding of the phenomena exhibited in glacial action we
also need to understand the phenomena of water at the freezing point. As
is well known, fresh water freezes at 32 degrees Fahrenheit, and at the
moment of freezing there is a sudden expansion to such an extent that a
cubic foot of ice will occupy a much larger space than it will in the
form of water; and because it occupies so much larger space it is
lighter than the same bulk of water would be, and therefore it floats in
water.
At the point of freezing, the thermometer if placed on the ice will
register 32 degrees. If the ice is allowed to melt, the water at the
moment of liquefaction would be found to register the same degree of
temperature as the ice when first frozen. And yet there has been a vast
expenditure of energy between the points of liquefaction and
congelation, notwithstanding the temperature of ice may be lowered,
after it is formed, many degrees, which is measurable by the
thermometer. Suppose we take a piece of ice which is 10 degrees below
the freezing point and insert in it a thermometer. If now we apply heat
to this ice the thermometer will gradually rise until it reaches the
melting point at 32 degrees Fahrenheit, where it will stand until all
the ice is melted. The application of heat is going on steadily, but
there are no indications of movement in the mercury until the last trace
of ice with which it is in contact has been liquefied. After the ice is
all melted, if the application of heat to the body of liquefied ice be
continued, the column of mercury will resume its movement upward until
it reaches the boiling point, where it is again arrested. And no matter
how much heat is applied to the boiling water, if in an open vessel, the
thermometer remains the same until all the water is evaporated. Here are
two curious facts, and they are facts that, if we can master them, will
serve as a key to the understanding of much that is mysterious in
nature.
It will be our endeavor to give the reader a mental picture of what is
taking place during the time the ice is melting and the thermometer is
stationary. Do not suppose that you can understand this, even so far as
it is understandable, by a casual reading without thought. No man was
ever yet able to present a picture to the mind of another, however
clearly and simply it may be done, unless that other mind is receptive.
When a photographer trains his camera upon an object, however intense
the light may be and however clean-cut the picture that is thrown upon
the plate in the camera, unless that plate is properly sensitized so
that the picture may be impressed upon it, all of the other conditions
are in vain. The reader is always a part of the book he is reading.
CHAPTER XXIII.
STORED ENERGY IN WATER.
In our last chapter we traced the upward movement in the mercury of the
thermometer from 10 degrees below the freezing point up to the boiling
point of water. We found that the thermometer was arrested at 32 degrees
and remained stationary at that point until all the ice was melted,
notwithstanding the fact that heat was being constantly applied. After
the ice is all melted the mercury moves upward until it reaches the
boiling point of water, where the movement is again arrested, and
although the heat is being continuously applied, it remains stationary
until all the water is evaporated. If we push the process still further,
with a sufficient application of energy we can separate the vapor
molecules into their original elements, oxygen and hydrogen.
Let us go back now to the freezing point of water and see what is
becoming of the heat that is consumed in melting the cake of ice, and
still does not produce any effect upon the mercury in the thermometer.
Sensible heat, as before stated, is a movement of the atoms of matter,
and temperature, as it affects the thermometer, is a measure of the
intensity of motion exhibited by these atoms.
In the experiment of the block of ice that in the beginning is 10
degrees below the freezing point, as shown by the thermometer, the
molecules have a definite intensity of motion. The intensity of this
motion increases when heat is applied until it reaches 32 degrees, when
it remains stationary until all of the ice is melted. At this point
there is a rearrangement of the molecules of water as it assumes the
liquid state. To perform this rearrangement requires a certain amount of
work done, which is analogous to the winding up of a weight to a certain
distance. There has been energy used in winding up the weight, but that
energy now is not destroyed, nor still in the form of heat, but is in
the potential state--ready to do some other kind of work. So, the heat
that has been applied to the melting ice has been utilized during the
process of its liquefaction in rearranging the water molecules and
putting them in a state of strain, so to speak, like the weight that is
wound up to a certain height. There is a certain amount of potential
energy that is stored in the molecules of water that will be given up
and become active energy in the form of heat, if the water is again
frozen. To melt a cubic foot of ice requires as much heat as it would
to raise a cubic foot of water 144 degrees Fahrenheit. But, as we have
seen, while all of this energy is absorbed as heat, it is not lost as
energy. It ceases to be kinetic or active and becomes potential energy.
This (let us repeat) has been called latent heat. The term grew out of
the old idea that heat was a fluid and that when it became latent it hid
itself away somewhere in the interatomic spaces of matter and ceased to
be longer sensible heat. It came into existence in the same manner and
occupies the same place in the science of heat that the word "current"
does in the science of electricity: both of them are misnomers.
When the ice is all melted potential energy is no longer stored, but is
manifested in the sensible heating of water, the degree of which is
measurable by the thermometer, until it reaches the boiling point, where
it is again arrested. All of the surplus heat above that temperature is
consumed in rending the liquid water into moisture globules that float
away into the air, each one of them charged with a store of potential
energy. Let us follow this vapor spherule as it floats into the upper
regions of the atmosphere. Myriads of its fellows travel with it until
it reaches a point where condensation takes place, when it collapses and
unites with other vapor particles to form water again. In doing this the
heat that was expended upon it to disengage it (whether the heat was
artificial or that of the sun's rays) now reappears either as sensible
heat or as electricity, or both. And this is what is meant in
meteorology by latent heat becoming sensible heat at the time of
condensation; in fact, it is stored or "potential" energy becoming
active or kinetic, and assumes the form of heat or electricity, as
before stated. We have thus reviewed the matter of the foregoing chapter
in order to follow the course of the stored energy from the melting of
the ice to the vapor, and back again to water: to doubly impress the
fact that the energy used was not consumed, but still exists and is
ready for further work.
During the progress of a hailstorm, it has been stated, one of the
factors that is active to produce this phenomenon is the intense
ascensional force that is given to the moisture-laden air, caused by
intense heat at the surface of the earth. This condition forces the
moisture vapor to higher regions of the atmosphere than is the case with
the ordinary thunderstorm. Another factor that is undoubtedly active in
producing hail under these circumstances is that when condensation takes
place in the higher regions, and is therefore more energetic on account
of the intenser cold, the potential energy that is set free by the
moisture spherules takes, in a larger degree, the form of electricity
rather than heat, as is the case under more ordinary circumstances.
While in the end this electrical energy becomes active heat, it does not
for the time being, and thus favors the ready congelation of the
condensed moisture into hailstones. Hailstorms are always attended by
incessant thunder and lightning, and this fact favors the theory
advanced above.
It will be easily seen from a study of the foregoing what a wonderful
factor evaporation (which is a product of the sun's rays) is, in the
play of celestial dynamics. It ascends from the surface of the earth or
ocean laden with a stored energy, the power of which no man can compute,
and beside which gravitation is a mere point. In the upper regions of
atmosphere this potential force under certain conditions is released and
becomes an active factor, not only in the formation of cloud and the
precipitation of rain, hail, and snow, but it disturbs the equilibrium
of the air and sets that in motion.
Certain physicists deny that evaporation has anything to do with
atmospheric electricity. They tell us that it is caused by the arrest of
the energy of the sunbeam by the clouds and vapor in the upper
atmosphere. We admit that a part of the energy is so arrested, and is
stored, for the time, in moisture globules by a process of cloud
evaporation to transparent vapor again. Yet this does not hinder the
same process from going on at the surface of the earth wherever there is
water or moisture. But they tell us that the electroscope does not show
any signs of electrification in the evaporated moisture. Of course it
does not. The electroscope is not made to detect the presence of energy
except when set free as electricity.
A wound-up spring does not seem to be electrified, but if it is released
the energy stored in it will be transformed into electricity if the
conditions are right. Just so, the energy required to put the moisture
spherule into a state of strain is latent until some power releases it,
when it reappears as active energy of some form.
We have now followed the relation of heat to water from a point 10
degrees below freezing up to where it was forced into its original
gases, oxygen and hydrogen. These gases have stored in them a wonderful
amount of potential energy. When one pound of hydrogen and eight pounds
of oxygen unite to form water the mechanical value of the energy given
up at that time in the form of heat is represented by 47,000,000 pounds
raised to one foot in height. And this is the measure of the energy that
was put into nine pounds of water to force it from a state of vapor into
its constituent gases. After the combination of the gases into a state
of vapor the temperature sinks to that of boiling water. The amount of
energy given up in condensing the nine pounds of vapor into nine pounds
of water is equal to 6,720,000 foot-pounds. If this nine pounds of water
is now cooled from the boiling point to 32 degrees Fahrenheit we come to
the final fall, where the potential energy that is stored in the
operation of melting ice is given up suddenly at the moment of freezing,
which in nine pounds of water is 993,546 foot pounds.
Professor Tyndall, in speaking of the amount of energy that is given up
between the points where the constituent gases unite to form nine pounds
of water and the point where it congeals as ice, says: "Our nine pounds
of water, at its origin and during its progress, falls down three
precipices--the first fall is equivalent in energy to the descent of a
ton weight down a precipice 22,320 feet high-over four miles; the second
fall is equal to that of a ton down a precipice 2900 feet high, and the
third is equal to a fall of a ton down a precipice 433 feet high. I have
seen the wild stone avalanches of the Alps, which smoke and thunder down
the declivities with a vehemence almost sufficient to stun the observer.
I have also seen snowflakes descending so softly as not to hurt the
fragile spangles of which they are composed. Yet to produce from aqueous
vapor a quantity which a child could carry of that tender material
demands an exertion of energy competent to gather up the shattered
blocks of the largest stone avalanche I have ever seen and pitch them to
twice the height from which they fell."
When we contemplate the foregoing facts as related to so small an amount
of water as nine pounds, and multiply this result by the amount of snow-
and rainfall each year and the amount of ice that is congealed and again
liquefied by the power of the sun's rays, we are appalled, and shrink
from the task of attempting to reduce the amount of energy expended in a
single year to measurable units.
Having considered water in its relation to heat in the preceding
chapters, we will now take up the subject of water in its relation to
ice and snowfall and the phenomena exhibited in ice rivers, commonly
called glaciers.
When water is under pressure the freezing point is reduced several
degrees below 32 degrees Fahrenheit. This fact has been determined by
confining water in a close vessel and putting it under pressure and
subjecting it to a freezing mixture, and by this means determining the
freezing point under such conditions. By putting a bullet or something
of that nature into the water that is subjected to pressure one can tell
by shaking it when the freezing point is reached. If water is put under
pressure and cooled to a point below 32 degrees, and yet still remains
in the liquid state, it may be suddenly congealed by taking off the
pressure; this shows that the pressure helps to hold the molecules in
the position necessary for the liquid state, and prevents the
rearrangement of them that takes place at the moment of freezing. When
the water molecules are arranged for the liquid condition they may be
compared to a spring that is wound up and held in position by the heat
energy that is stored in the water. And when this energy is given up to
a certain degree the power that holds the spring wound up is suddenly
released, when it unwinds and occupies a larger space. There is a force
that we may call polar force, which is constantly tending to push the
molecules of water into an arrangement such as we see when
crystallization takes place--as it always does in the act of freezing.
These polar forces cannot act so long as the energy in the form of heat
is sufficient to hold the water in the fluid state. But the moment this
energy, which tends to hold it in the fluid state, falls below that
which tends to rearrange it into the crystalline form, it is overcome by
the superior power of the latter force, and we have the phenomenon of
solidified water.
A very interesting experiment may be performed with a block of ice by
anyone when the ice is near the melting point. If a wire is put around
the ice and a sufficient weight is suspended to it, the pressure of the
wire on the ice will gradually liquefy that portion immediately under
the wire, which allows it to sink into the ice slowly, and as this
process goes on the ice freezes together again behind the wire, so that
in time the wire will pass entirely through the block and leave it still
a solid block, as it was before the experiment began.
This is an interesting fact which it will be well to remember when we
come to explain glacial action, or rather the law that governs glacial
action. If we take two pieces of melting ice and bring them together
they immediately congeal at the point of contact. This phenomenon is
called "regelation." Ice has some of the properties of a viscous
substance. It will yield slowly to pressure, especially when near the
melting point, but if put under a tensional strain it will break, as any
brittle substance will, so that it has the properties of both viscosity
and brittleness. Ordinarily we are in the habit of treating water as a
fluid and ice as a solid, but from what has gone before the reader must
understand that in a certain sense ice should be treated as having
semi-fluidic properties.
CHAPTER XXIV.
WHY DOES ICE FLOAT?
Nature is full of surprises. By a long series of experimental
investigations you think you have established a law that is as
unalterable as those of the Medes and Persians. But once in a while you
stumble upon phenomena that seem to contradict all that has gone before.
These, however, may be only the exceptions that prove the rule. It is
recognized as a fundamental law that heat expands and cold contracts;
that the atom when in a state of intense motion (which is the condition
producing the effect that we call "heat") requires more room than when
its motions are of a less amplitude. In other words, an increase in the
amplitude of atomic motion is heating, while a decrease is cooling. It
follows from the above statement that the colder a body becomes the
smaller will be its dimensions. There are two or three, and perhaps
more, exceptions to this rule, and the most notable one is that of
water. Water follows the same law that all other substances do under the
action of heat and cold, within certain limits only. If we take water,
say, at 50 degrees Fahrenheit and subject it to cold it will gradually
contract in bulk until it reaches 39 degrees Fahrenheit. At this point,
very curiously, contraction ceases, and here we find the maximum density
of water. If the temperature is still lowered we find the bulk is
gradually increasing instead of diminishing (as is the rule with other
fluids), and when it reaches the freezing point there is a sudden and
marked expansion, so much so that a cubic foot of ice, which is
solidified water, will not weigh as much as a cubic foot of water before
it freezes--hence it floats.
Let us try an experiment. Take a small glass flask, terminating in a
long neck, say of four to six inches, and of small diameter. Suppose the
water in the glass to be at 50 degrees Fahrenheit. Fill the flask with
water until it stands halfway up the neck at 50 degrees temperature. Now
immerse the flask gradually in hot water, and observe the effect. For a
moment the water will lower in the neck of the tube, but this is due to
the fact that the glass expands before the heat is communicated to the
water and enlarges its capacity. But immediately the water will begin to
rise as the heat is communicated to it, and will continue to expand up
to the boiling point. Now take the flask out of the hot water and
gradually introduce it into a freezing mixture made of broken ice and
salt. Immediately the water will begin to fall in the tube, showing that
it is contracting under the cold, and it will continue to contract until
it reaches a temperature of 39 degrees Fahrenheit, when it will come to
a standstill and then proceed to expand as the temperature of the water
lowers. When it reaches the freezing point the fluid can no longer rise
in the neck of the flask, which is broken by the sudden expansion that
takes place at this point.
To show what an irresistible power resides in the atoms of which the
body is made, let us take an iron flask with walls one-half inch or more
in thickness; fill it with water and seal it up by screwing on the neck
an iron cap; now plunge it into the freezing mixture, and the first
effect will be to contract the water unless it is already below 39
degrees Fahrenheit, but when it reaches that point expansion sets in,
which continues to the freezing point, when a greatly increased
expansion takes place suddenly. The walls of the iron flask, although a
half-inch in thickness, are no longer able to resist the combined
efforts of the billions upon billions of the atoms of which the water is
made up, in their individual clamor for more room, hence the flask is
shivered into pieces.
There are one or two other substances which are exceptions to the
general rule, but we will mention only one, which is the metal bismuth.
If we should melt a sufficient amount to fill an iron flask, such as we
have described, and subject it to the same freezing process, the flask
will be broken the same as in the experiment made with the water.
A query arises, Why this phenomenon? Why does water follow a different
law in cooling from that of nearly all other substances?
This is a case where it is much easier to ask a question than to answer
it. When water solidifies at the moment of freezing, crystallization
sets in. But what is crystallization? Crystallization is a peculiar
arrangement of the molecules of matter, which takes place in some
substances when they pass from the liquid to the solid form. The
molecules assume definite forms and shapes, according to the nature of
the substance. When water assumes the solid form under the action of
cold the molecules arrange themselves according to certain definite and
fixed laws, the result of which is to increase the bulk to a
considerable extent over that which the same number of molecules would
occupy at a temperature of 39 degrees Fahrenheit. Hence, as has been
heretofore stated, a given block of solidified water is lighter than the
same bulk would be in the fluid state, and this is the reason why ice
floats.
What would happen in case nature did not make this exception to the laws
of expansion and contraction by heat and cold, in the case of water?
First, our lakes would freeze from the bottom upward; as soon as the
surface became frozen, or even colder than the water underneath, it
would drop to the bottom, the warmer water below coming up by a
well-known law--that the warmer fluid rises and the colder falls. This
circulation would continue until ice began to form, which would
immediately drop to the bottom, and this process would go on until the
whole mass were frozen solid. In the same way our rivers in the northern
climates would freeze from the bottom, and in time our valleys would
fill up with ice to a thickness that the summer's sun would never melt,
and gradually all north of a certain zone would become a great glacier,
rendering not only the lakes and rivers but also the surface of the
earth unfitted for animal life.
Those who believe that the laws of nature are the creations of a
beneficent and all-wise Intelligence will see in this exception to the
general law in the case of freezing water a striking evidence of design.
But those who have no such belief will say it is a most fortunate though
fortuitous circumstance (a saying they will have to make, regarding
thousands of other things in nature), and go on floundering in the
interminable sea of "I don't know."
The atom when it is acting under the direction of a fixed law is a giant
in strength. And when its individual strength is multiplied by billions
upon billions the combined energy exerted produces a power that is
irresistible. Not only has nature endowed these atoms with this
wonderful power, but she has also willed that they arrange themselves in
lines of beauty. In confirmation of this we need only to study the work
of the frost upon our window panes. As we lie in our beds on a cold
night and exhale moisture from our lungs it settles upon the window
panes of our bedrooms, where Nature--that wonderful artist--forms it
into beautiful pictures that gladden our eyes when we awake:
Most beautiful things; there are flowers and trees,
And bevies of birds, and swarms of bees,
And cities, and temples, and towers, and these
All pictured in silver sheen.
CHAPTER XXV.
GLACIERS.
Glaciers are rivers of ice, and, like other rivers, some of them are
small and some very large. They flow down the gorges from high
mountains, whose peaks are always covered with a blanket of eternal
snow. Summer and winter the snow is precipitated upon these mountains,
and from time to time the heat of the sun's rays softens the snow, when
by its great weight it packs more closely together until it is, in many
cases, formed into solid ice-cakes. If we take a quantity of snow or a
quantity of granulated ice and put it under a sufficient pressure we can
produce clear solid ice, and it is by this process that ice is formed
out of the snow and hail that falls continually upon the tops of these
glacial mountains. We have seen that ice possesses certain viscous or
semi-fluidic properties and that it will yield to pressure, but if we
put it under sufficient tensional strain it snaps like glass or any
other brittle substance. As the snows upon these mountains pile up
higher and higher the pressure becomes greater and greater until it
reaches a point where the mass begins to move gradually down the
mountain side, following the gulches and defiles that furnish a path of
least resistance to its flow.
At the sides and bottom, where there is contact with the earth, the
movement is slower than it is at the surface and in the middle of the
ice stream. If there were no curves in the ravine or gulch through which
it flows the point of greatest movement would be confined to the middle
of its width. But in flowing through a winding gulch the most rapid flow
follow the lines of greatest pressure, and this line is deflected from
side to side, so that the line of greatest flow is more winding than is
the bottom of the valley through which it flows. (The movement is called
a "flow," but it is very sluggish, only a few inches in a day, as will
appear later.)
If the bottom and sides of the valley were straight the surface of the
ice would be comparatively even; I say comparatively, for as compared
with a smooth surface it would be very rough; but there would be none of
the great crevasses or openings now to be found in the ice, which
sometimes are very large and extend to a great depth. If in its downward
course the bottom of the ravine suddenly becomes steeper, the top of the
ice is put under a tensional strain which causes it to break, thus
forming the crevasses.
If at the bottom of the descent the valley curves upward or preserves
the straight line for a considerable distance, these crevasses will
close at the top and perhaps open at the bottom, and the blocks of ice
will freeze together to such an extent that the water caused by the
melting ice will flow on top until it comes to another crevasse, where
it runs through to the bottom or underflow, which is always an attendant
of a glacier.
The glacier continues its flow down the mountain side till in some cases
it reaches quite to the valley below, and in others it stops short, as
the action of the sun is so great that it melts entirely away at this
point as fast as it moves down. In the winter time, however, the glacier
may flow far down into the valley and will accumulate greatly in bulk,
owing to the fact that the ice forms from the precipitation of snow on
top faster than it melts away underneath. If it were not for the fact
that in summer the glaciers melt faster than they form, the whole valley
would in time become a great river of ice. It is the case in Switzerland
that some years the accumulation is greater from snowfall than
diminution from melting. If this condition should continue it would
become a serious matter.
In the downward flow of a glacier--slow as it is--there is an exhibition
of wonderful power; great bowlders are torn from their beds and either
ground to powder or carried down to the end of the glacier, to be
dropped with the other débris that has been carried there by the same
force, forming an accumulation that geologists call the "moraine." Of
these moraines we will speak more fully later on.
It was the privilege of the writer some years since to visit the great
glaciers of Switzerland and to some extent study their action. Some
rivers have their origin chiefly in melting glaciers. They start as ice
rivers and end in rivers of water. The effects during the great ice age
of some of these glacial rivers, which are now extinct, are very
remarkable; we shall have occasion to refer to them when we come to
treat of the glacial period.
There is a glacial river flowing which is fed largely by the great Rhone
glacier in Switzerland. The water from this river is almost as white as
milk, which is occasioned by the grinding action of the great ice blocks
on the rock as it flows down the sides of the mountain. These glacial
rivers are much higher in summer, of course, than in winter, some of
them having not only an annual fluctuation, but a diurnal one. The
former is caused by the cold of winter, and the latter because it
freezes to some extent at night and checks the flow of water. The
difference between day and night in these high altitudes is very marked.
While it is extremely hot in the sun, it is cool the moment we step into
the shade.
I remember walking across one of the glaciers in the Alps, called the
Mer de Glace, one clear day in summer, when I suffered so much from the
heat, although standing upon a sea of ice, that it was necessary to
carry an umbrella. In fact, during my stay there was a case of sunstroke
that occurred upon this same glacier. This intense heat during the day
melts the surface of the ice, which forms streams that run along on the
top of a glacier until they come to a crevasse or riffle in the ice
river, where they plunge down and become a part of the glacial stream
that is flowing underneath the ice.
The speed at which these ice streams flow varies greatly with the size
of the glacier as to width and depth and the steepness of the grade, and
many other conditions. In its movement the glacier is constantly bending
and freezing and being torn asunder by tensional strain, yielding and
liquefying at other points by pressure, only to freeze again when that
pressure is removed. This, taken in connection with the friction of the
great ice bowlders, produces a movement that is exceedingly complicated
in its actions and interactions.
According to Professor Tyndall's investigations, the most rapid movement
observed in the glaciers of Switzerland is thirty-seven inches per day
at the point of greatest movement. From this point each way the motion
gradually diminishes until it reaches the sides of the glacier, where
the motion is not more than two or three inches.
The great North American glaciers move at a much higher rate of speed.
We are indebted to Dr. G. Frederick Wright, author of "The Ice Age in
North America," who spent a month studying the Muir glacier in Alaska,
for many details concerning that great ice river. This glacier empties
into Muir Inlet, which is an offshoot of Glacier Bay. It is situated in
latitude 58 degrees 50 minutes and longitude 136 degrees 40 minutes west
of Greenwich. The bay into which this glacier empties is about thirty
miles long and from eight to twelve miles wide. This bay, with its great
glacier, has a setting of grand mountain peaks. I cannot do better than
to quote the words of Dr. Wright when he describes the location of this
glacier. Dr. Wright lived for a month in a tent on the edge of this bay,
a short distance below the face of the great glacier, where the icebergs
fell off every few minutes into the deep water.
He says: "To the south the calm surface of the bay opened outward into
Cross Sound twenty-five miles away. The islands dotting the smooth
surface of the waters below us seemed but specks, and the grand vista of
snowclad mountains guarding either side of Chatham Strait seemed
gradually to come to a point on the southern horizon. Westward toward
the Pacific was the marvelous outline of the southern portion of the St.
Elias Alps. The lofty peaks of Crillon, 15,900 feet high, and Fair
Weather, 15,500 feet high, about twenty-five miles away and about the
same distance apart, stood as sentinels over the lesser peaks."
The Muir glacier might be likened to a great inland sea of ice fed by
many tributaries or ice rivers. It narrows up at the point where it
empties into Muir Inlet to 10,664 feet, or a little over two miles. An
enormous pressure is exerted at this point, which causes the ice to flow
in the central portion at the rate of about seventy feet per day. There
is a continual booming, like the firing of a cannon, going on, caused by
the bursting of some great iceberg either before it takes its final leap
into the water or at the moment of its fall. At the point where these
great icebergs drop off into the water they stand like a solid wall 300
feet above its surface. Dr. Wright says: "From this point there is a
constant succession of falls of ice into the water, accompanied by loud
reports. Scarcely ten minutes, either night or day, passed during the
whole month without our being startled with such reports; and frequently
they were like thunder claps or the booming of cannon at the
bombardment of a besieged city, and this though our camp was two and
one-half miles below the ice front.... Repeatedly I have seen vast
columns of ice extending up to the full height of the front topple over
and fall into the water. How far these columns extended below the water
could not be told accurately, but I have seen bergs floating away which
were certainly 500 feet in length."
It is estimated that the cubical contents of some of these icebergs are
equal to 40,000,000 feet. This great glacier is fed by the constant
precipitation of snow upon the sides and peaks of the high mountains
that surround its vast amphitheater, which is floored with icebergs.
Wonderful as this seems to us to-day, it is scarcely a microscopic speck
of what existed during the ice age all over the northern part of North
America.
There are many other great glaciers in the mountains of the Pacific
coast. Some years ago I saw one of these immense glaciers in British
Columbia, from a point called Glacier Station, in the Selkirk Mountains,
on the Canadian Pacific Railroad. It was during the month of August,
when all of the region was pervaded by a dense smoke occasioned by
burning forests. This glacier is a very showy one, owing to the
steepness of the side of the mountain and its great breadth. All the
glaciers that exist to-day are gradually receding, and are destined
eventually to entirely disappear, unless there is a change in
meteorological conditions, which some scientists claim will be the case
if we only wait long enough, when again all this northern country will
be covered with a great ice sheet. There is no doubt in regard to the
facts concerning a glacial period that must have existed in the ages
past. To anyone who has made a study of the subject there is not wanting
abundant evidence to prove that this northern country was at one time
enveloped with a great ice sheet of enormous thickness. The conditions
that existed to bring about such a state of things have been the subject
of much speculation by philosophers, but no one, as yet, has arrived at
any very satisfactory conclusion. Many theories have been advanced, some
of them not worth considering, while others have many things that give
them a show of plausibility. But all of them have what is said of the
Darwinian theory, "a missing link." It will be interesting, however, and
also instructive, to know what can be said in favor of a set of
conditions that would produce such momentous results.
CHAPTER XXVI.
EVIDENCES AND THEORIES OF AN ICE AGE.
There is abundant and unassailable evidence that at one time, ages ago,
a vast ice sheet covered the whole of the northern part of North
America, extending south in Illinois to a point between latitudes 37 and
38. This is the most southerly point to which the ice sheet reached.
From this point the line of extreme flow runs off in a northeasterly and
northwesterly direction. The northeasterly line is through southeastern
Ohio and Pennsylvania, striking the Atlantic Ocean about at New York,
thence through Long Island and up the coast of Massachusetts.
Northwesterly it follows the Mississippi River to its junction with the
Missouri, which it crosses at a point some miles west of this junction,
following the general course of this river a little south of it through
the States of Missouri, Nebraska, Dakota, and Montana. The lines,
especially the northeasterly one, are very irregular, shooting out into
curves and then receding. This line of extreme ice flow is marked by
glacial drift so prominently that no one who has studied glacial action
can doubt for a moment what was the cause of these deposits. The line
is called the "terminal moraine." By examining a map of North America
and tracing the line of the moraine as we have described it, it will be
seen that about two-thirds of North America was at one time covered with
ice to a greater or less depth. How deep, is simply a matter of
conjecture, but in the central portions of the great glacier, where was
the bulk of snowfall, it must have reached a depth of several miles to
account for the enormous pressure that would be required to carry the
ice so far southward.
But let us go back and define what is meant by a moraine. A moraine is a
name given to the deposits that are of stone, gravel, and earth that
have been carried along by the movement of the glaciers and deposited at
their margins, sometimes piled up to great depths. The composition of
these moraines is determined of course by the nature of the country over
which the stream of ice is flowing. Bowlders of enormous size have been
carried for hundreds of miles, and the experienced geologist is able to
examine any one of them and tell us where its home was before the
glacial period. Moraines are divided into different classes according to
their position and constitution. The moraine found at the extreme limit
of ice-flow is called the "terminal" moraine, as before mentioned. Those
that are found inside of this line and between two flows are called
"medial" moraines. There is a subdivision called "kettle" or "gravel"
moraines, which are very prominent in northern Illinois and southern
Wisconsin, and may be said to culminate in the vicinity of Madison. This
moraine is a great deposit of gravelly soil. Where this moraine exists
the face of the country is covered with "kettle holes" of all sizes and
shapes, and in some of them there are small lakes, while others are dry.
The great chain of inland lakes that are found in southern Wisconsin and
northern Illinois were formed by deposits of ice that had been covered
by glacial drift, gravel and otherwise, brought down and deposited upon
these masses of ice which gradually melted away, leaving a depression at
the points where they lay, while the drift that was piled around them
loomed up and became the shores of the lake. This is substantially Dr.
Wright's theory, who studied the formation of these "kettle holes" at
the mouth of the Muir glacier. This enthusiastic glacialist has spent
many summers tracing the terminal moraine with its fringe along the
lines heretofore indicated. He is, therefore, entitled to speak with
authority on matters of glacial action.
The part of the country that has been plowed over by these glaciers is
called the glaciated area and the rest the unglaciated. The whole of
North America north of the line of the terminal moraine that we have
traced is a glacial region, with the exception of a few hundred square
miles chiefly in Wisconsin, where the ice seemed to have parted and
passed around this area, coming together again on the south side of it.
The ice probably did not reach the extreme limit that shows glacial
deposit, but undoubtedly the effects of it are seen for some distance to
the south, owing to the fact that during the time it was melting great
quantities of water flowed away from the extreme edge of the ice,
carrying with it more or less of the glacial drift, which was deposited
for some distance to the south. When the ice receded it undoubtedly
paused at different points, where it remained stationary for a long
period of time. I mean stationary at its edges, for the flow of ice was
continually moving, but in its progress southward it came to a point
where the heat was sufficient to melt the ice as fast as it arrived at
that point. The on-moving ice was continually bringing with it the
débris that it had gathered up at different points on its journey, so
that it is easy to see how these moraines could accumulate to a greater
or less depth at the margin of the ice flow, which would be determined
by the duration of the period it remained stationary. This, however, is
only one factor, as the surface of the earth in some parts of the
country would be more easily picked up and carried than in others;
therefore, the drift accumulated much more rapidly in some sections than
in others.
Another factor that was active in the more rapid accumulation at certain
points was the speed at which the ice moved, and this would be
determined by the pressure that was behind it, and there would always be
lines of unequal pressure existing in such a great glacier as must have
existed when these moraines were formed.
As an instance of the difference in the glacial deposits that are made
in different periods during the time of the melting of the great ice
sheet we may compare the Kettle Moraines of Wisconsin with the clay
deposit mixed with broken gravel that we find along the west coast of
Lake Michigan. Those whose homes are situated between Winnetka and
Waukegan on the lake shore have the foundations of their houses set in
glacial drift that was shoved into position by the ice during the
glacial period.
Anyone who makes an examination of the bluffs along the shore of this
lake will notice that there is no stratification whatever to the deposit
such as will always be found in an unglaciated region. Going west from
the bluff a few miles we come down to the prairie level, where we find
the soil of an entirely different nature. The soil of the prairies of
Illinois and Iowa is probably to a great extent a water deposit. It is
the kind we find in the bottom of a pond that has stood for many years,
and it would seem that at some period all this prairie country with the
black soil was the bottom of a great lake.
The facts of a glacial period are beyond question, but when it occurred,
and how it occurred are questions that many have tried to answer. So
far, all that we can say of them is that some of them are shrewd
guesses. The evidences adduced for determining the time, are the erosion
caused by rivers and streams since the ice subsided. Some of the rivers
and outlets of lakes had their courses changed by the action of the ice,
so that when it subsided new water courses were formed, and the erosion
that they have produced from that time to the present furnishes the data
for determining the time since the subsidence of the ice at any
particular point. For instance, Niagara Falls was undoubtedly at one
time situated at Queenstown, a number of miles below its present
position. And the time that it has taken to grind out the great gorge
that exists between that point and the present falls is approximately a
measure of the time that has elapsed since the subsidence of the ice at
that point. Various estimates have been made to determinate the rate of
erosion. The earlier ones put the time at about 35,000 years. But there
are later investigators who make the time much shorter, not over 10,000
years.
So much for the time; but you ask What about the occasion, or cause?
This is a question that many have attempted to answer, there having been
eight or ten theories promulgated with regard to the cause of the
glacial period, but no one of them is entirely satisfactory, and only
two or three of them are deserving of much discussion. It is always
interesting to know what people think, however, even if we do not agree
with them.
The first theory named is that the glacial period is due to the decrease
of the original heat in our climate. This theory can be dismissed by
saying that the planet was cooling at the time and has been cooling ever
since, and that the reasons for an ice age are greater now than then, on
that theory. Another theory assumes that at some former period there was
a greater amount of moisture in the atmosphere; while this of course
would be the occasion for greater precipitation of snow, it does not
account for the changing conditions that would produce the ice effect.
That there was a preglacial period there is abundant evidence, in buried
forests, the filling up and changing of river beds, and other evidences
that will be referred to further on. This theory, unmodified and stated
broadly, is not satisfactory. Another way of accounting for the glacial
period is the change in the distribution of land and water, which is
supposed to affect the distribution of heat over the earth's surface.
There is much in this theory that commends itself as plausible. Another
theory supposes that the land in northern Europe and America was
elevated to a higher level at that time than it is now. Others attribute
it to variation of temperature in space and of the amount of heat
radiated by the sun. The final theory for accounting for the ice age is
attributed to what is termed the precession of the equinoxes. In short,
the precession of the equinoxes means that the division between summer
and winter is changing gradually, so that during a period of 10,500
years the summers are growing longer in the northern hemisphere and the
winters shorter. We are now in the period of long summers, but in
another 10,000 years we shall be in the period of short summers and long
winters. This difference of time between the winters and the summers is
supposed to be sufficient to change the thermal conditions sufficiently
to produce an ice age.
It is true that the conditions now are very evenly balanced, so much so
that in Switzerland the glaciers will increase for some years together,
when the conditions will change, causing them to gradually recede.
Several of the theories that have been advanced present evidences that
are entitled to careful consideration, but none of them can be said to
be entirely satisfactory. It is well known that the chief factors in the
production of glaciers are moisture and cold. Cold alone is not
sufficient; neither is moisture, unless we can precipitate it in the
form of snow. Cold is opposed to the production of moisture, and this is
a flaw in the argument presented by the last theory, unless we can
couple with it another set of conditions which we will discuss later.
The solution, if it is ever reached, is perhaps more likely to be found
in the realm of meteorology than geology.
It is unnecessary to change the conditions of temperature or the amount
of moisture now existing in order to produce the great glacier again,
provided this moisture could be precipitated, enough of it, in the right
place as snow. For instance, if in Switzerland, where the conditions are
nearly balanced, the annual precipitation could be slightly increased we
should have a condition that would precipitate more snow in winter than
would melt in summer. And the glaciers would gradually accumulate in
size until they would fill the valleys and gorges to the same extent as
formerly prevailed. There only needs to be such a change in the
meteorological conditions as will cause a greater precipitation in that
part of the globe favorable to glaciers, as, for instance, in the
northern part of North America toward Alaska. This might be produced by
a change in the conditions of the equatorial current, so that
evaporation would be more rapid in the northern Pacific than it now is.
When we consider that evaporation increases in proportion as the heat
increases, we can see that heat is just as important a factor in the
production of glaciers as cold. If evaporation could be increased in the
Pacific Ocean west of Alaska, which would be carried by the wind over
the mountains upon the land, and precipitated as snow, the great
glaciers in that region would begin to grow instead of gradually
receding, as is the case at present, and this without any change in the
temperature of the world as a whole or in the amount of heat received
from the sun. One can readily see how changes in the elevation of the
bottom of the ocean would have such an effect upon the tropical stream
as would either increase or decrease the temperature of the thermal
river that flows up the western coast of Alaska.
Whatever may have been the cause that created the great ice age in North
America, so that a sheet of ice covered considerably more than half of
the continent, there is no doubt in regard to the fact of the existence
of such an age, and it will be interesting to study some of the physical
changes that have been made by the ice at that period on the surface of
the glaciated area.
CHAPTER XXVII.
GLACIAL AND PREGLACIAL LAKES AND RIVERS.
Since the recession of the ice, preglacial lakes have been filled up and
are now dry land, and river beds have been changed so that new channels
have been cut and new lakes have been formed. Even the imagination, that
wonderful architect, with all its tendencies to exaggeration, palls in
its attempt to give expression in measured quantities to the mighty
power exerted by the great glacier or combination of glaciers that
existed in comparatively recent times. I say recent times, because even
10,000 years is only a mere point of time when compared with the actual
age of our globe.
Some years ago, in company with Dr. Wright, author of the "Ice Age in
North America," I visited Devil's Lake near Baraboo, Wis. At this point
are striking evidences of the work of the ice age. Before the glacial
period the Wisconsin River made a detour some miles west of its present
channel through the high hills in the region of Baraboo. The hills on
each side of Devil's Lake are very precipitous and are formed almost
entirely of rocks. The river at that point passed between two of these
hills. When the ice flowed down it surrounded these hills, yet did not
sweep over their tops, but left great piles of glacial drift, both at
the points where the river channel entered the hills and where it
emerges from them. The channel between the hills was protected and not
filled with the débris. Therefore a deep basin was left, which is kept
filled by the watershed furnished by the surrounding hills. This lake
recedes many feet during the summer, but it is again filled up by the
rains and snows of winter. There is no considerable stream either
flowing into or out from it. It is a lake formed by the glaciers, but in
a different way from those in the gravel deposits at other parts of
southern Wisconsin and northern Illinois.
There are hundreds and perhaps thousands of lakes that have been formed
in one way or another through the power of glacial action. These smaller
inland lakes, so many of which are seen in northern Illinois, southern
Wisconsin, and Minnesota, are due almost entirely to the great deposits
of glacial drift that have been transported with the ice. Wherever these
"kettle holes" are found large bodies of ice have become anchored,
while the ice behind it has carried the drift until it is covered over
and piled up at the sides. When these ice mountains melted away
depressions were left which in some cases have resulted in lakes, and in
others simply dry kettle holes. This process has been hinted at in a
former chapter, but we give it here as one of the kinds of lakes formed
during the glacial period. They are found everywhere that glacial action
has prevailed. They are found in great abundance in some parts of New
England on the margin of the terminal moraine. These lakes, however, are
comparatively insignificant as compared with the great inland seas like
Lake Superior and Lake Michigan, that undoubtedly owe their origin
largely to the ice age.
There are other factors, however, that enter into the formation of the
great chain of lakes on the northern boundary of the United States
besides those mentioned, that have brought into existence the smaller
inland lakes.
Glacial lakes may be divided into three classes. Those found in the
"kettle holes" of the terminal or medial moraines, and those that are
formed by the deposition of the glacial drift, as, for instance, Devil's
Lake, and those that are caused by ice forming dams across the valley of
a river that lasted only during the ice age. In some lakes of the
second class erosion undoubtedly entered into their formation as well as
the piling up of glacial drift.
In order, however, that we may understand more fully the formation of
these greater lakes it will be necessary for us to go back and examine
the conditions that seem to have existed before the glacial period.
It is a fact well known that continents have periods of elevation and
depression. There is abundant evidence that the northern portion of the
North American continent was elevated to a much higher level in
preglacial times than it occupies now. This is evidenced in very many
ways by sounding the depths of old river beds now filled with glacial
débris. The old beds show unmistakable evidences of having been worn
down to their present level by the action of running water. They also
prove to be many feet below the present sea-level. This fact seems to be
sufficient to prove the theory of a higher elevation of the North
American continent in preglacial times. It should be said here that
undoubtedly the constant filling up of the ocean with the drift carried
down by the rivers has somewhat raised its level, but hardly to the
extent indicated by the old river beds. The question naturally arises,
Where did all the dirt come from to fill up these great river beds and
change the whole topography of the northern half of the continent? Dr.
Wright estimates that there is not less than 1,000,000 square miles of
territory in North America covered with glacial débris to an average
depth of 50 feet. Of course, the depth varies in different places from a
few inches to several hundred feet. Of the carrying power of these great
glaciers we will speak more fully in a future chapter. In preglacial
times the watershed of the Mississippi and of the great rivers east of
the Alleghany Mountains, the Susquehanna and Hudson, extended probably
farther north than it does to-day. The larger portion of the drainage
area that now finds an outlet through the River St. Lawrence at one time
undoubtedly drained off through the Mississippi Valley into the Gulf and
the Valley of the Mohawk into that of the Hudson.
It is supposed by those who have made this branch of geology a study
that prior to the glacial period a river flowed down through Lake
Superior, which connected with Lake Michigan at a point near its present
outlet at Sault Ste. Marie, the channel of the river passing down
through what is now the bottom of Lake Michigan, which had an outlet at
the head of the lake near Chicago and flowed off into the Mississippi
River. All of the lake bottoms of this great chain, with the exception
of Lake Erie, are now below sea-level. The reason for this exception
will appear further on. Before the ice age there was supposed to be no
connection between Lake Michigan and Lake Huron, as there is now,
through the Straits of Mackinac.
Another preglacial river had its rise in the region of Lake Huron and
flowed through an old river bed extending from the Georgian Bay in a
southeasterly direction through the province of Ontario, and emptied
into the present Lake Ontario. From Lake Ontario there is an old river
bed running through the Valley of the Mohawk which empties into the
Hudson at Troy. Neither of these two rivers, having their sources in the
north, found an outlet through the present St. Lawrence River. During
the time of the glacial period there is evidence that there was more
than one center of snow and ice accumulation and each of these great
centers probably had several subcenters. This theory has color given to
it by the directions of movement shown by the glacial drift.
The rounded appearance of bowlders was caused by the grinding action of
the ice. These bowlders, when they were first torn from their rocky beds
by the irresistible power of ice pressure, were rough and jagged in
shape, the same as any rock would be, torn from a quarry by a blast.
They have been smoothed and rounded by rubbing against the moving ice
and against each other in the progress of their long journey from their
original homes. Where their home was the geologist can immediately tell
upon examination. It is only necessary then to examine the bowlders of
any particular locality to determine the direction of the ice flow at
that point.
There seem to have existed centers of ice accumulation to the north of
all of the great lakes. And when they had grown to a sufficient height
they joined at their edges, making one grand glacier, the movements of
which were the resultant of the combined pressure exerted by these great
centers of power, so that all of North America north of the line of the
terminal moraine, with the exception of a small area (heretofore noted)
chiefly in Wisconsin, became covered with one vast sheet of ice.
The glacier north of Lake Superior widened out the old river bed by a
process of erosion to its present width.
There may have existed something of a lake in preglacial times, through
which the river ran, but it undoubtedly owes its present width to the
grinding action of the irresistible icebergs and the piling up of débris
on the shores. The river bed was filled up by a glacial drift at the
point of its present outlet until the lake was raised in its level much
higher than that of Lake Michigan. Another glacier plowed down through
Lake Michigan, widening it out to its present dimensions, while the
glacial drift was deposited at what is now the head of the lake, filling
up the old outlet and thus making a great dam. The damming up of these
great water courses was another cause for increasing the width of these
lakes. In a similar way Lake Erie was formed. It is supposed, however,
that this lake is entirely the product of glacial action, as there is no
evidence of an old river bed in its bottom; besides, it is much
shallower than the other lakes. The same action that formed Lake Erie
filled up the old river bed running through the province of Ontario, so
that when the ice receded Lake Erie became the new channel for the old
river. The same process filled up the Valley of the Mohawk to more than
100 feet in depth and also raised the Valley of the Hudson. This caused
the new channel to be made through the Niagara River and a new route to
the ocean for the drainage of all the chain of lakes through the St.
Lawrence. It will be seen that the bottoms of all of these great lakes
to a certain extent were worn out by the action of running water, except
Erie. The great glaciers widened them out, and in the case of Lake Erie
scooped it out. At the same time it built great dams across the outlets
which raised the surface of the water to a much higher level and caused
them to form new outlets, thus changing the whole face of the country
over which the ice drifted.
The glaciated region of North America is among the most productive in
the world, and in many respects presents a most pleasing landscape.
Other lakes besides these mentioned have been formed during the ice
period through blocking the course of a river by the ice itself. Dr.
Wright, during the time he traced out the line of the terminal moraine,
discovered that the ice sheet crossed the Ohio River at a point near
Cincinnati, where there is a great bend to the northward in the river.
With the exception of this point and perhaps another point below, the
edge of the great ice sheet kept a little north of the Ohio River. At
this point, however, the ice seems to have filled the valley from hill
to hill, which very naturally would form a great dam or lake in the Ohio
Valley. Of course such a lake could not be permanent, because, when the
ice melted away, it again opened the channel and allowed the water to
flow off.
Some years before this discovery was made there were terraces found
along the banks of the Ohio River and its tributaries that had been the
subject of much speculation. It is well known that by the action of
water from rainfall, earth, gravel, and other débris will wash down the
side of a hill or mountain until it strikes a water level, and there it
will build out a terrace near the level of the water surface. The width
of these terraces will be determined by the time the water has stood at
that level and the extent and nature of the soil from which the débris
comes. The evidences that are cited, pro and con, would fill a small
volume, but it is sufficient to say here that the sum of the evidence
goes to show that there was an ice dam formed at a point near Cincinnati
and that it was maintained for a considerable period of time. Terraces
were formed running up the Ohio and its tributaries corresponding to the
level that the water must have risen to if the valley were filled up
with ice. These facts, taken with the greater fact that the ice sheet
actually did cross the Ohio Valley into Kentucky, as is shown by the
terminal moraine, seems to prove conclusively the existence of such a
lake during the period that the ice rested at its extreme limit. The
fact that in some places successive terraces are found does not disprove
the theory, because it is more than likely that when the ice receded it
did so in successive stages, remaining at different positions for a
considerable length of time. There is abundant proof of this in the
successive moraines and also in the formation of successive terraces.
Some of these terraces could have been formed from other causes.
It does not require any great stretch of the imagination to understand
how numerous lakes, much larger than any at the present day, may have
extended over large portions of the West and Northwest during the period
that the ice was receding. The ice did not stand with an even thickness
over the surface of the glaciated area, but at some points it moved down
in great lobes, which marked the lines of greatest pressure as well as
the greatest accumulation. As the ice melted away, the thick bodies of
ice might be many, many years in melting, and they might block the
outlet to a very extensive drainage area and thus form a great inland
sea from the vast amounts of water that would come from the melting ice.
All of the region about Winnipeg, in the Red River country, covering
great areas of hundreds of miles in extent, is a level plain only
lacking the coloring to give to one passing through it the effect of a
great unruffled sea. There is no doubt but that all of this region was
the bottom of a great lake at some period when the ice was receding. And
this accounts for the great depth of black soil that we find in this and
other regions. The soil was a water deposit, such as may be found in the
bottom of any shallow lake or pond to-day, and thus many thousand years
ago provision was made for the fertile areas which to-day are feeding
the world with wheat.
We can imagine that during this period the water that flowed off
through the great Mississippi must have been of enormous volume as
compared to the present time. A large portion of the delta of the
Mississippi which now is a part of the States of Louisiana and
Mississippi was carried down during the ice-melting period. Dr.
Wright--as we have before stated--has estimated that there are a million
square miles of country that has been covered to an average depth of
fifty feet with glacial drift. A very large amount of the earth that was
spread over the northern portion of the United States by leveling down
hills and mountains in the northern country and scooping out the great
lakes has been carried much farther than to the margin of the ice sheet.
And I have no doubt but that a great portion of Louisiana and western
Mississippi is made of earth carried down largely during the period of
melting ice and deposited in this great delta.
Imagine the effect that would be produced by the giving way of an ice
dam or a great number of them at different periods, that would allow a
body of water as large or larger than Lake Michigan to be drained off in
a comparatively short time. When we think of it in this light the great
delta of the Mississippi is easily accounted for.
There are evidences of a great lake in the Red River country of the
Northwest that is much larger than any of our greatest lakes. The
shores of this lake--the bed of which is now dry land and the heart of a
great agricultural region--are well defined and have been surveyed and
mapped out. When this great body of water was released it was to the
northward. For this reason it was undoubtedly held for a much longer
time than some of the lakes to the southward where the ice melted
sooner.
CHAPTER XXVIII.
SOME EFFECTS OF THE GLACIAL PERIOD.
There is a wonderfully interesting effect produced by the action of
water during the subsidence of a glacier at Lucerne, Switzerland. Some
years ago there was discovered under a pile of glacial drift at the edge
of the town of Lucerne a number of deep holes worn in a great ledge of
rocks that crop out at that point. One of these pot-holes having been
discovered, excavations were continued until a large number of them were
unearthed of various shapes and sizes. I had the pleasure of inspecting
some of them in the year 1881. They are situated within an inclosure
called the Garden of the Glaciers. Some of these holes are twenty to
thirty feet in diameter, and the same depth. There are others that are
smaller in size, but all of them possess the same general
characteristics.
In the bottom of each one was found a bowlder, and in one or two cases
two of them. The action of the water had given these bowlders a gyratory
motion, which gradually wore away the rock underneath until round holes
were formed to the size and depth heretofore mentioned. Where there was
only a single bowlder the holes were almost perfectly round, but where
there was more than one bowlder the holes were sometimes in an oblong
shape. The bowlders were worn down to a very small size in most cases,
and were round and smooth. The probabilities are that when the action
first began these bowlders were large and of irregular shape. They must
have been, in order to do the enormous amount of grinding that some of
them did to produce excavations in the solid rock with a diameter of
thirty feet and a depth about the same. The bottoms were round like an
old-fashioned pot, and the insides polished perfectly smooth. This was
purely an effect of the tumbling about of the bowlders by the running
water from the melting ice of the great glacier that covered that region
some time in the long ago.
There are other effects produced in rocks during the ice flow in North
America that are very interesting. Great grooves are formed in the
rocks, in many cases running for long distances, that have been worn in
by the cutting power of the great ice sheet during the progress of its
movement. There is a great groove to be seen at Kelly's Island in Lake
Erie. It will be remembered that this lake is supposed to have been
formed entirely by the ice of the glacial period. In its movement
across the country which is now covered by the lake the ice encountered
a huge rock formation at Kelly's Island. Great V-shaped grooves were cut
through this rock by the action of the ice, deep enough for a man to
stand in. In other places the rock was planed off in the form of a great
molding, a number of feet wide, with the same smoothness and accuracy as
though done by a machine.
Another effect of the glacial period has been the creation of numerous
waterfalls throughout the glaciated area. The most notable instance is
that of the Falls of Niagara.
In preglacial times the beds of all rivers and water courses had worn
down to an even slope, so that there were very few, if any, waterfalls
such as we have to-day. As we have before stated, Niagara River as well
as the St. Lawrence River is a new outlet for the drainage of the great
lakes. A part of this drainage formerly had its outlet through the
Mohawk Valley into the Hudson, which is now filled up with glacial
drift. The evidence is so conclusive that it is no longer doubted that
the Niagara River dates from the time that the ice receded from that
point. When the water first began to flow through this new channel it
plunged over the high rocky cliff at Queenstown, and from that time to
this it has been wearing its way back to the present position of
Niagara Falls, a distance of about seven miles. A vast amount of
interest centers about this river because it is the best evidence we
have of the time that has expired since the glacial period. A great deal
of study has been given to determine the amount of erosion at the Falls
during a year's time. If this could be accurately determined, then by
measuring the distance from the present falls to Queenstown, we could
easily determine the number of years since the ice period. It is
difficult to determine, for the conditions may have changed; for
instance, the rock at the Falls to-day is said to be harder than it is
further down toward Queenstown. The estimates vary from 35,000 years to
10,000 years--that is, from a rate of erosion of five feet to one foot,
per year.
Every science is, nearly or remotely, related to every other science. If
we could determine accurately the date of the ice period it would settle
a whole lot of other questions that are related to it, and one of them
is the antiquity of man. Many stone implements such as were made and
used by the aborigines have been found at various times buried deeply
under the glacial drift. These finds have occurred so often that there
no longer remains a doubt but that a race of men existed on this
continent in preglacial times. There are evidences that at a time long
ago the temperate zone extended far north of this, and it is not
impossible that what is now the continent of Asia and that of North
America were joined. In fact, they come very close together to-day at
Bering Strait. If such were the case this continent could have been
inhabited from the old world by an overland route. This, however, is
mere speculation. There are a number of factors that are taken into
account in determining the period of the ice age besides the Niagara
River and the Falls. The Falls of St. Anthony at Minneapolis (which like
the Niagara is a creature of the ice age), the wear of water on the
shores of the great lakes, the newness of the rocks that are piled up on
the terminal moraines, all point to a much shorter period since the ice
age than it used to be supposed, and indicate that the time does not
exceed 10,000 years.
To the ordinary mind the ice age no doubt seems like a myth, but to the
man of science who has made a study of all of these evidences it is as
real as any fact in history, and much more real than some of the history
we read. In the former case we are dealing with evidences that appeal to
our senses, while in the latter we are dealing with the recollections of
men concerning what purport to have been actual transactions, and we
know enough about the human mind to make it difficult sometimes to draw
the line between the actual and the imaginary.
The glacial period is not only closely related to the topography of
North America and parts of Europe in the changing of river beds, the
formation of lakes, the transportation of rock, the grinding down of
mountains and spreading the débris over thousands of miles in extent,
but it is related in an intimate way to many of the sciences, such as
botany and zoölogy. A study of the flight of animals and plants in front
of the great advancing ice sheet is a subject of intense interest. The
migration of great forests would seem to be an impossible thing when
viewed from the standpoint of a casual observer. It is true that
individual trees could not take themselves up and move forward in
advance of the oncoming ice, but they could and did send their children
on ahead, and when the ice had overtaken the children there were still
the children's children ad infinitum.
By an examination of the map it will be seen that the land gathers about
the north pole, while the south pole is surrounded chiefly by great
oceans. As we have hinted before, in preglacial times the temperate zone
extended much farther north than it does to-day, and north of that there
was an arctic zone (which to-day is largely covered with ice sheets),
where forests, plants, and animals flourished that were fitted for an
arctic climate. When the glacial period set in and the ice sheet began
its southern journey this zone or climate was moved southward in front
of the ice, thus forming, as it were, a moving zone whose climatic
conditions were similar to those of the arctic regions (at least so far
as temperature was concerned) in preglacial times. The ice movement was
so gradual that time was given for forests to spring up in advance of it
that moved southward at about the same rate as that of the moving ice.
Undoubtedly the average movement was very slow and was probably
thousands of years reaching its southernmost limit, which is now marked
by the terminal moraine. Thus it will be seen that while the individual
trees and plants could not move, the forest as a whole could. It was
gradually being cut down on its northern limit and as gradually it grew
up on the southern limit of the zone; the ice movement being so slow
that the young tree of to-day on the southern limit becomes a full-grown
king of the forest by the time the relentless icebergs reach it and cut
it down and thus the process went on until the plants, trees, and
animals of the arctic region were driven hundreds of miles south of the
great chain of lakes on the northern boundary of the United States.
Many of the animals of preglacial times were unable to stand the strain
of the ever-changing climatic conditions and have become extinct, but
their fossil remains are left to tell the story to the present and
future ages. Much of the history of those times is a sealed book, but
the persevering energy of the glacialist and archæologist is gradually
turning the leaves of this old book and revealing new chapters of the
wonderful story of the ice.
As the ice receded the arctic zone again traveled northward, and many
animals, plants, and trees that had survived the vicissitudes of the ice
age, traveled back with it. Some of them, however, became acclimated and
by adapting themselves to the new conditions remained behind to live and
grow with the aborigines of preglacial times. Some of the plants and
flowers that grew in profusion immediately under the edge of the great
ice sheet were unable to live under the new conditions of increased
warmth--that came with the retrograde movement of the ice--and either
had to follow closely the receding ice or escape to higher altitudes,
where they found a congenial clime. Thus it is that we have arctic
plants and flowers above the timber line and near the snow line of our
high mountains. In proof of this theory it has been found that these
arctic plants do not exist upon high mountains, such as the Peak of
Teneriffe, where they have been isolated from the glaciated region. The
Peak of Teneriffe is situated on one of the Canary Islands, surrounded
by water, so that there was no possible chance for the arctic plants to
seek refuge on these isolated elevations, such as the continental
mountains furnish.
Thus it will be seen that the progression and recession of the ice have
not only formed great lakes, changed river beds, and covered a million
square miles of area with glacial drift averaging fifty feet in depth,
making many waterfalls and giving variety to the surface of the earth,
besides producing the finest agricultural region in the world, but have
also given variety to our forests and plants wherever this ice sheet has
extended.
CHAPTER XXIX.
DRAINAGE BEFORE THE ICE AGE.
We have already said that during the ice age river-beds were changed,
valleys were filled up, new lakes were made, and waterfalls created.
Great as were the changes made by the carrying power of moving ice,
still greater were those made in preglacial times; not, however, from
the action of moving ice, but from running water. Erosion caused by
running water has, probably, during the life of the world, transported
more material from place to place, from mountain to valley, and from
valley to ocean, than any other agency; chiefly for the reason that it
has been so much longer doing its work.
The valley of the Ohio River, a thousand miles or more in length,
together with the great number of feeders that empty into it, is an
instance of the wonderful erosive power of running water. The valley of
the Ohio River will probably average a mile in width at its upper level
and, deep as it is to-day, it was much deeper in preglacial times. There
is evidence that the whole bed of the river was from 100 to 150 feet
deeper than it is at present. This has been determined by borings at
different points to ascertain the depth of the drift that was lodged
during the glacial period in the trough of the Ohio River. Anyone
traveling up or down the river to-day can readily see that it is a great
sinuous groove cut down through the earth by millions of years of water
erosion, and not only this, but that at some time in its history this
great valley has been partly filled, forming on one or both sides of the
river level areas--called bottom land. These lands are exceedingly
productive, owing to the great depth and richness of the soil.
For many years the writer lived upon one of the rivers tributary to the
Ohio and often made trips by steamboat up and down the Ohio River.
Traveling along this river a close observer will be struck by the
exactness of the stratifications in the rock and in the coal beds to be
seen on each side of the river. They match as perfectly as the grain of
a block of wood when sawn asunder--showing that these coal beds were
formed at an age long before the water cut this sinuous groove. What the
water was doing while these coal beds were forming will be brought out
in some future chapter. All the rivers that are tributary to the Ohio,
such as the Monongahela, the Alleghany, the Muskingum, the Tennessee,
the Cumberland, the Kentucky, the Wabash, the Miami, the Licking, the
Scioto, the Big Sandy, the Kanawha, the Hocking, and the Great Beaver,
besides numerous smaller streams, have their own valleys that have been
worn away by the same process, and to a greater depth than they now
appear to be. All of the material that once filled these valleys has
been carried down by the water filling up the bottom of the ocean and
building out the great delta of the lower Mississippi. Mountains have
been worn down and carried away by the action of the running water until
their height is much lower than in former times. The great lakes, that
were enlarged during the glacial period and in some cases wholly
created--by the scooping out and damming up of the waterways and by
piling glacial drift around their shores--have had some of their outlets
raised to a higher level, and others have been created anew.
The old river beds that formerly carried the water that is now drained
through the St. Lawrence were eroded by the action of running water to a
great depth, as is shown by numerous borings along the valley of the
Mohawk and down the Hudson. The salt wells at Syracuse, N. Y., have been
put down through glacial drifts and the salt water is found in the bed
of the old river. Great bodies of salt are found at that low level,
constantly dissolved by the water percolating through the sand and
gravel of the glacial drift. This salt water is pumped up and
evaporated, leaving the salt--forming one of the important industries of
that region. All of the rivers from the Ohio eastward tell the same
story, which is that at some remote period the land was much higher
above the level of the sea than it is to-day. The bottoms of many of
these old river beds are lower than sea-level, but as they were made by
running water they must have been at one time above that point.
There is abundant evidence that the earth sinks in some places and rises
in others. Along the ridges of some of the eastern mountains are found
in great abundance the products of the bottom of the ocean. These
evidences show that at some period, when the mountains were formed, a
great convulsion of nature raised the bottom of the ocean to thousands
of feet above its level. Evidences of this exist in various parts not
only of the United States, but of the world.
You ask, If this erosion goes on and the mountains and hills are carried
down and filled in to the low places of the ocean, what is the final
destiny of the earth that now appears above the surface of the ocean?
Evidently if the earth should remain without further upheaval, at some
time in the far, far future the land would gradually wear down and be
carried off into the ocean and the ocean would gradually rise, owing to
its restricted area, until it would again cover the whole earth as it
undoubtedly did at one time in the earth's history. This fact need not
occasion any uneasiness on the part of those who are living to-day or
for millions of years to come.
The problem of building a world and then tearing it to pieces is a very
complicated one. There is a constant battle going on between the powers
that build up and those that tear down; and this is as true of
character-building as it is of world-building. The world has never been
exactly alike any two successive days from the time its foundations were
laid to the present moment. It seems to be a fundamental law of all life
and growth, as well as of all decay, that there shall be a constant
change. There is no such thing as rest in nature. The smallest molecules
and atoms of matter are in constant agitation. In the animal and
vegetable world there is a period of life and growth, and a period of
decay and death; and this seems to be the destiny of planets themselves
as well as the things that live and grow upon them. Still, science
teaches us that with all this turmoil and change nothing either of
matter or energy is lost, but that it is simply undergoing one eternal
round of change. Does this law apply to mind and soul? Do we die? Or do
we simply change?
* * * * *
Nature's Miracles:
FAMILIAR TALKS ON SCIENCE.
By PROF. ELISHA GRAY.
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These little volumes convey scientific truth without technical terms,
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