Project Gutenberg's The Fairy-Land of Science , by Arabella B. Buckley
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Title: The Fairy-Land of Science
Author: Arabella B. Buckley
Release Date: May, 2004 [EBook #5726]
[Yes, we are more than one year ahead of schedule]
[This file was first posted on August 17, 2002]
Edition: 10
Language: English
*** START OF THE PROJECT GUTENBERG EBOOK THE FAIRY-LAND OF SCIENCE ***
The Fairy-Land of Science
Arabella B. Buckley
TABLE OF CONTENTS
Lecture I The Fairy-Land of Science; How to Enter It;
How to Use It; And How to Enjoy It
Lecture II Sunbeams, and the Work They Do
Lecture III The Aerial Ocean in Which We Live
Lecture IV A Drop of Water on its Travels
Lecture V The Two Great Sculptors - Water and Ice
Lecture VI The Voices of Nature, and How We Hear Them
Lecture VII The Life of a Primrose
Lecture VIII The History of a Piece of Coal
Lecture IX Bees in the Hive
Lecture X Bees and Flowers
Week 1
LECTURE I
HOW TO ENTER IT; HOW TO USE IT; AND HOW TO ENJOY IT
I HAVE promised to introduce you today to the fairy-land of
science - a somewhat bold promise, seeing that most of you
probably look upon science as a bundle of dry facts, while fairy-
land is all that is beautiful, and full of poetry and
imagination. But I thoroughly believe myself, and hope to prove
to you, that science is full of beautiful pictures, of real
poetry, and of wonder-working fairies; and what is more, I
promise you they shall be true fairies, whom you will love just
as much when you are old and greyheaded as when you are young;
for you will be able to call them up wherever you wander by land
or by sea, through meadow or through wood, through water or
through air; and though they themselves will always remain
invisible, yet you will see their wonderful poet at work
everywhere around you.
Let us first see for a moment what kind of tales science has to
tell, and how far they are equal to the old fairy tales we all
know so well. Who does not remember the tale of the "Sleeping
Beauty in the Wood," and how under the spell of the angry fairy
the maiden pricked herself with the spindle and slept a hundred
years? How the horses in the stall, the dogs in the court-yard,
the doves on the roof, the cook who was boxing the scullery boy's
ears in the kitchen, and the king and queen with all their
courtiers in the hall remained spell-bound, while a thick hedge
grew up all round the castle and all within was still as death.
But when the hundred years had passed the valiant prince came,
the thorny hedge opened before him bearing beautiful flowers; and
he, entering the castle, reached the room where the princess lay,
and with one sweet kiss raised her and all around her to life
again.
Can science bring any tale to match this?
Tell me, is there anything in this world more busy and active
than water, as it rushes along in the swift brook, or dashes over
the stones, or spouts up in the fountain, or trickles down from
the roof, or shakes itself into ripples on the surface of the
pond as the wind blows over it? But have you never seen this
water spell-bound and motionless? Look out of the window some
cold frosty morning in winter, at the little brook which
yesterday was flowing gently past the house, and see how still it
lies, with the stones over which it was dashing now held tightly
in its icy grasp. Notice the wind-ripples on the pond; they have
become fixed and motionless. Look up at the roof of the house.
There, instead of living doves merely charmed to sleep, we have
running water caught in the very act of falling and turned into
transparent icicles, decorating the eaves with a beautiful
crystal fringe. On every tree and bush you will catch the water-
drops napping, in the form of tiny crystals; while the fountain
looks like a tree of glass with long down-hanging pointed leaves.
Even the damp of your own breath lies rigid and still on the
window-pane frozen into delicate patterns like fern-leaves of
ice.
All this water was yesterday flowing busily, or falling drop by
drop, or floating invisibly in the air; now it is all caught and
spell-bound - by whom? By the enchantments of the frost-giant
who holds it fast in his grip and will not let it go.
But wait awhile, the deliverer is coming. In a few weeks or
days, or it may be in a few hours, the brave sun will shine down;
the dull-grey, leaden sky will melt before his, as the hedge gave
way before the prince in the fairy tale, and when the sunbeam
gently kisses the frozen water it will be set free. Then the
brook will flow rippling on again; the frost-drops will be shaken
down from the trees, the icicles fall from the roof, the moisture
trickle down the window-pane, and in the bright, warm sunshine
all will be alive again.
Is not this a fairy tale of nature? and such as these it is
which science tells.
Again, who has not heard of Catskin, who came out of a hollow
tree, bringing a walnut containing three beautiful dresses - the
first glowing as the sun, the second pale and beautiful as the
moon, the third spangled like the star-lit sky, and each so fine
and delicate that all three could be packed into a walnut shell;
and each one of these tiny structures is not the mere dress but
the home of a living animal. It is a tiny, tiny shell-palace
made of the most delicate lacework, each pattern being more
beautiful than the last; and what is more, the minute creature
that lives in it has built it out of the foam of the sea, though
he himself is nothing more than a drop of jelly.
Lastly, anyone who has read the 'Wonderful Travellers' must
recollect the man whose sight was so keen that he could hit the
eye of a fly sitting on a tree two miles away. But tell me, can
you see gas before it is lighted, even when it is coming out of
the gas-jet close to your eyes? Yet, if you learn to use that
wonderful instrument the spectroscope, it will enable you to tell
one kind of gas from another, even when they are both ninety-one
millions of miles away on the face of the sun; nay more, it will
read for you the nature of the different gases in the far distant
stars, billions of miles away, and actually tell you whether you
could find there any of the same metals which we have on the
earth.
We might find hundreds of such fairy tales in the domain of
science, but these three will serve as examples, and we much pass
on to make the acquaintance of the science-fairies themselves,
and see if they are as real as our old friends.
Tell me, why do you love fairy-land? what is its charm? Is it
not that things happen so suddenly, so mysteriously, and without
man having anything to do with it? In fairy-land, flowers blow,
houses spring up like Aladdin's palace in a single night, and
people are carried hundreds of miles in an instant by the touch
of a fairy wand.
And then this land is not some distant country to which we can
never hope to travel. It is here in the midst of us, only our
eyes must be opened or we cannot see it. Ariel and Puck did not
live in some unknown region. On the contrary, Ariel's song is
"Where the bee sucks, there suck I;
In a cowslip's bell I lie;
There I couch when owls do cry.
On the bat's back I do fly,
After summer, merrily."
The peasant falls asleep some evening in a wood and his eyes are
opened by a fairy wand, so that he sees the little goblins and
imps dancing around him on the green sward, sitting on mushrooms,
or in the heads of the flowers, drinking out of acorn-cups,
fighting with blades of grass, and riding on grasshoppers.
So, too, the gallant knight, riding to save some poor oppressed
maiden, dashes across the foaming torrent; and just in the
middle, as he is being swept away, his eyes are opened, and he
sees fairy water-nymphs soothing his terrified horse and guiding
him gently to the opposite shore. They are close at hand, these
sprites, to the simple peasant or the gallant knight, or to
anyone who has the gift of the fairies and can see them. but the
man who scoffs at them, and does not believe in them or care for
them, he never sees them. Only now and then they play him an
ugly trick, leading him into some treacherous bog and leaving him
to get out as he may.
Now, exactly all this which is true of the fairies of our
childhood is true too of the fairies of science. There are
forces around us, and among us, which I shall ask you to allow me
to call fairies, and these are ten thousand times more wonderful,
more magical, and more beautiful in their work, than those of the
old fairy tales. They, too, are invisible, and many people live
and die without ever seeing them or caring to see them. These
people go about with their eyes shut, either because they will
not open them, or because no one has taught them how to see.
They fret and worry over their own little work and their own
petty troubles, and do not know how to rest and refresh
themselves, by letting the fairies open their eyes and show them
the calm sweet picture of nature. They are like Peter Bell of
whom Wordsworth wrote:-
"A primrose by a river's brim
A yellow primrose was to him,
And it was nothing more."
But we will not be like these, we will open our eyes and ask,
"What are these forces or fairies, and how can we see them?"
Just go out into the country, and sit down quietly and watch
nature at work. Listen to the wind as it blows, look at the
clouds rolling overhead, and waves rippling on the pond at your
feet. Hearken to the brook as it flows by, watch the flower-buds
opening one by one, and then ask yourself, "How all this is
done?" Go out in the evening and see the dew gather drop by drop
upon the grass, or trace the delicate hoar-frost crystals which
bespangle every blade on a winter's morning. Look at the vivid
flashes of lightening in a storm, and listen to the pealing
thunder: and then tell me, by what machinery is all this
wonderful work done? Man does none of it, neither could he stop
it if he were to try; for it is all the work of those invisible
forces or fairies whose acquaintance I wish you to make. Day and
night, summer and winter, storm or calm, these fairies are at
work, and we may hear them and know them, and make friends of
them if we will.
There is only one gift we must have before we can learn to know
them - we must have imagination. I do not mean mere fancy, which
creates unreal images and impossible monsters, but imagination,
the power of making pictures or images in our mind, of that which
is, though it is invisible to us. Most children have this
glorious gift, and love to picture to themselves all that is told
them, and to hear the same tale over and over again till they see
every bit of it as if it were real. This is why they are sure to
love science it its tales are told them aright; and I, for one,
hope the day may never come when we may lose that childish
clearness of vision, which enables us through the temporal things
which are seen, to realize those eternal truths which are unseen.
If you have this gift of imagination come with me, and in these
lectures we will look for the invisible fairies of nature.
Watch a shower of rain. Where do the drops come from? and why
are they round, or rather slightly oval? In our fourth lecture
we shall se that the little particles of water of which the
raindrops are made, were held apart and invisible in the air by
heat, one of the most wonderful of our forces* or fairies, till
the cold wind passed by and chilled the air. Then, when there
was no longer so much heat, another invisible force, cohesion,
which is always ready and waiting, seized on the tiny particles
at once, and locked them together in a drop, the closest form in
which they could lie. Then as the drops became larger and larger
they fell into the grasp of another invisible force, gravitation,
which dragged them down to the earth, drop by drop, till they
made a shower of rain. Pause for a moment and think. You have
surely heard of gravitation, by which the sun holds the earth and
the planets, and keeps them moving round him in regular order?
Well, it is this same gravitation which is a t work also whenever
a shower of rain falls to the earth. Who can say that he is not
a great invisible giant, always silently and invisibly toiling in
great things and small whether we wake or sleep?
*(I am quite aware of the danger incurred by using this word
"force", especially in the plural; and how even the most modest
little book may suffer at the hands of scientific purists by
employing it rashly. As, however, the better term "energy" would
not serve here, I hope I may be forgiven for retaining the much-
abused term, especially as I sin in very good company.)
Now the shower is over, the sun comes out and the ground is soon
as dry as though no rain had fallen. Tell me; what has become of
the rain-drops? Part no doubt have sunk into the ground, and as
for the rest, why you will say the sun has dried them up. Yes,
but how? The sun is more than ninety-one millions of miles away;
how has he touched the rain-drops? Have you ever heard that
invisible waves are travelling every second over the space
between the sun and us? We shall see in the next lecture how
these waves are the sun's messengers to the earth, and how they
tear asunder the rain-drops on the ground, scattering them in
tiny particles too small for us to see, and bearing them away to
the clouds. Here are more invisible fairies working every moment
around you, and you cannot even look out of the window without
seeing the work they are doing.
If, however, the day is cold and frosty, the water does not fall
in a shower of rain; it comes down in the shape of noiseless
snow. Go out after such a snow-shower, on a calm day, and look
at some of the flakes which have fallen; you will see, if you
choose good specimens, that they are not mere masses of frozen
water, but that each one is a beautiful six-pointed crystal star.
How have these crystals been built up? What power has been at
work arranging their delicate forms? In the fourth lecture we
shall see that up in the clouds another of our invisible fairies,
which, for want of a better name, we call the "force of
crystallization," has caught hold of the tiny particles of water
before "cohesion" had made them into round drops, and there
silently but rapidly, has moulded them into those delicate
crystal starts know as "snowflakes".
And now, suppose that this snow-shower has fallen early in
February; turn aside for a moment from examining the flakes, and
clear the newly-fallen snow from off the flower-bed on the lawn.
What is this little green tip peeping up out of the ground under
the snowy covering? It is a young snowdrop plant. Can you tell
me why it grows? where it finds its food? what makes it spread
out its leaves and add to its stalk day by day? What fairies are
at work here?
First there is the hidden fairy "life," and of her even our
wisest men know but little. But they know something of her way
of working, and in Lecture VII we shall learn how the invisible
fairy sunbeams have been buy here also; how last year's snowdrop
plant caught them and stored them up in it's bulb, and how now in
the spring, as soon as warmth and moisture creep down into the
earth, these little imprisoned sun-waves begin to be active,
stirring up the matter in the bulb, and making it swell and burst
upwards till it sends out a little shoot through the surface of
the soil. Then the sun-waves above-ground take up the work, and
form green granules in the tiny leaves, helping them to take food
out of the air, while the little rootlets below are drinking
water out of the ground. The invisible life and invisible
sunbeams are busy here, setting actively to work another fairy,
the force of "chemical attraction," and so the little snowdrop
plant grows and blossoms, without any help from you or me.
Week 2
One picture more, and then I hope you will believe in my fairies.
From the cold garden, you run into the house, and find the fire
laid indeed in the grate, but the wood dead and the coals black,
waiting to be lighted. You strike a match, and soon there is a
blazing fire. Where does the heat come from? Why do the coals
burn and give out a glowing light? Have you not read of gnomes
buried down deep in the earth, in mines, and held fast there till
some fairy wand has released them, and allowed them to come to
earth again? Well, thousands and millions of years ago, those
coals were plants; and like the snowdrop in the garden of to-day,
they caught the sunbeams and worked them into their leaves. Then
the plants died and were buried deep in the earth and the
sunbeams with them; and like the gnomes they lay imprisoned till
the coals were dug out by the miners, and brought to your grate;
and just now you yourself took hold of the fairy wand which was
to release them. You struck a match, and its atoms clashing with
atoms of oxygen in the air, set the invisible fairies "heat" and
"chemical attraction" to work, and they were soon busy within the
wood and the coals causing their atoms too to clash; and the
sunbeams, so long imprisoned, leapt into flame. Then you spread
out your hands and cried, "Oh, how nice and warm!" and little
thought that you were warming yourself with the sunbeams of ages
and ages ago.
This is no fancy tale; it is literally true, as we shall see in
Lecture VIII, that the warmth of a coal fire could not exist if
the plants of long ago had not used the sunbeams to make their
leaves, holding them ready to give up their warmth again whenever
those crushed leaves are consumed.
Now, do you believe in, and care for, my fairy-land? Can you see
in your imagination fairy 'Cohesion' ever ready to lock atoms
together when they draw very near to each other: or fairy
'Gravitation' dragging rain-drops down to the earth: or the fairy
of 'Crystallization' building up the snow-flakes in the clouds?
Can you picture tiny sunbeam-waves of light and heat travelling
from the sun to the earth? Do you care to know how another
strange fairy, 'Electricity,' flings the lightning across the sky
and causes the rumbling thunder? Would you like to learn how the
sun makes pictures of the world on which he shines, so that we
can carry about with us photographs or sun-pictures of all the
beautiful scenery of the earth? And have you any curiosity about
'Chemical action,' which works such wonders in air, and land, and
sea? If you have any wish to know and make friends of these
invisible forces, the next question is
How are you to enter the fairy-land of science?
There is but one way. Like the knight or peasant in the fairy
tales, you must open you eyes. There is no lack of objects,
everything around you will tell some history if touched with the
fairy wand of imagination. I have often thought, when seeing
some sickly child drawn along the street, lying on its back while
other children romp and play, how much happiness might be given
to sick children at home or in hospitals, if only they were told
the stories which lie hidden in the things around them. They
need not even move from their beds, for sunbeams can fall on them
there, and in a sunbeam there are stories enough to occupy a
month. The fire in the grate, the lamp by the bedside, the water
in the tumbler, the fly on the ceiling above, the flower in the
vase on the table, anything, everything, has its history, and can
reveal to us nature's invisible fairies.
Only you must with to see them. If you go through the world
looking upon everything only as so much to eat, to drink, and to
use, you will never see the fairies of science. But if you ask
yourself why things happen, and how the great God above us has
made and governs this world of ours; If you listen to the wind,
and care to learn why it blows; if you ask the little flower why
it opens in the sunshine and closes in the storm; and if when you
find questions you cannot answer, you will take the trouble to
hunt out in books, or make experiments to solve your own
questions, then you will learn to know and love those fairies.
Mind, I do not advise you to be constantly asking questions of
other people; for often a question quickly answered is quickly
forgotten, but a difficulty really hunted down is a triumph for
ever. For example, if you ask why the rain dries up from the
ground, most likely you will be answered, "that the sun dries
it," and you will rest satisfied with the sound of the words.
But if you hold a wet handkerchief before the fire and see the
damp rising out of it, then you have some real idea how moisture
may be drawn up by heat from the earth.
A little foreign niece of mine, only four years old, who could
scarcely speak English plainly, was standing one morning near the
bedroom window and she noticed the damp trickling down the
window-pane. "Auntie," she said, "what for it rain inside?" It
was quite useless to explain to her in words, how our breath had
condensed into drops of water upon the cold glass; but I wiped
the pane clear, and breathed on it several times. When new drops
were formed, I said, "Cissy and auntie have done like this all
night in the room." She nodded her little head and amused
herself for a long time breathing on the window-pane and watching
the tiny drops; and about a month later, when we were travelling
back to Italy, I saw her following the drops on the carriage
window with her little finger, and heard her say quietly to
herself, "Cissy and auntie made you." Had not even this little
child some real picture in her mind of invisible water coming
from her mouth, and making drops upon the window-pane?
Then again, you must learn something of the language of science.
If you travel in a country with no knowledge of its language, you
can learn very little about it: and in the same way if you are to
go to books to find answers to your questions, you must know
something of the language they speak. You need not learn hard
scientific names, for the best books have the fewest of these,
but you must really understand what is meant by ordinary words.
For example, how few people can really explain the difference
between a solid, such as the wood of the table; a liquid, as
water; and a gas, such as I can let off from this gas-jet by
turning the tap. And yet any child can make a picture of this in
his mind if only it has been properly put before him.
All matter in the world is made up of minute parts or particles;
in a solid these particles are locked together so tightly that
you must tear them forcibly apart if you with to alter the shape
of the solid piece. If I break or bend this wood I have to force
the particles to move round each other, and I have great
difficulty doing it. But in a liquid, though the particles are
still held together, they do not cling so tightly, but are able
to roll or glide round each other, so that when you pour water
out of a cup on to a table, it loses its cuplike shape and
spreads itself out flat. Lastly, in a gas the particles are no
longer held together at all, but they try to fly away from each
other; and unless you shut a gas in tightly and safely, it will
soon have spread all over the room.
A solid, therefore, will retain the same bulk and shape unless
you forcibly alter it; a liquid will retain the same bulk, but no
the same shape if it be left free; a gas will not retain either
the same bulk or the same shape, but will spread over as large a
space as it can find wherever it can penetrate. Such simple
things as these you must learn from books and by experiment.
Then you must understand what is meant by chemical attraction;
and though I can explain this roughly here, you will have to make
many interesting experiments before you will really learn to know
this wonderful fairy power. If I dissolve sugar in water, though
it disappears it still remains sugar, and does not join itself to
the water. I have only to let the cup stand till the water
dries, and the sugar will remain at the bottom. There has been
no chemical attraction here.
But now I will put something else in water which will call up the
fairy power. Here is a little piece of the metal potassium, one
of the simple substances of the earth; that is to say, we cannot
split it up into other substances, wherever we find it, it is
always the same. Now if I put this piece of potassium on the
water it does not disappear quietly like the sugar. See how it
rolls round and round, fizzing violently with a blue flame
burning round it, and at last goes off with a pop.
What has been happening here?
You must first know that water is made of two substances,
hydrogen and oxygen, and these are not merely held together, but
are joined to completely that they have lost themselves and have
become water; and each atom of water is made of two atoms of
hydrogen and one of oxygen.
Now the metal potassium is devotedly fond of oxygen, and the
moment I threw it on the water it called the fairy "chemical
attraction' to help it, and dragged the atoms of oxygen out of
the water and joined them to itself. In doing this it also
caught part of the hydrogen, but only half, and so the rest was
left out in the cold. No, not in the cold! for the potassium and
oxygen made such a great heat in clashing together that the rest
of the hydrogen became very hot indeed, and sprang into the air
to find some other companion to make up for what it had lost.
Here it found some free oxygen floating about, and it seized upon
it so violently, that they made a burning flame, while the
potassium with its newly found oxygen and hydrogen sank down
quietly into the water as potash. And so you see we have got
quite a new substance potash in the basin; made with a great deal
of fuss by chemical attraction drawing different atoms together.
When you can really picture this power to yourself it will help
you very much to understand what you read and observe about
nature.
Next, as plants grow around you on every side, and are of so much
importance in the world, you must also learn something of the
names of the different parts of a flower, so that you may
understand those books which explain how a plant grows and lives
and forms its seeds. You must also know the common names of the
parts of an animal, and of your own body, so that you may be
interested in understanding the use of the different organs; how
you breathe, and how your blood flows; how one animal walks,
another flies, and another swims. Then you must learn something
of the various parts of the world, so that you may know what is
meant by a river, a plain, a valley, or a delta. All these
things are not difficult, you can learn them pleasantly from
simple books on physics, chemistry, botany, physiology, and
physical geography; and when you understand a few plain
scientific terms, then all by yourself, if you will open your
eyes and ears, you may wander happily in the fairy-land of
science. Then wherever you go you will find
"Tongues in trees, books in the running brooks
Sermons in stones, and good in everything."
And now we come to the last part of our subject. When you have
reached and entered the gates of science, how are you to use and
enjoy this new and beautiful land?
This is a very important question for you may make a twofold use
of it. If you are only ambitious to shine in the world, you may
use it chiefly to get prizes, to be at the top of your class, or
to pass in examinations; but if you also enjoy discovering its
secrets, and desire to learn more and more of nature and to revel
in dreams of its beauty, then you will study science for its own
sake as well. Now it is a good thing to win prizes and be at the
top of your class, for it shows that you are industrious; it is a
good thing to pass well in examinations , for it show that you
are accurate; but if you study science for this reason only, do
not complain if you find it full, and dry, and hard to master.
You may learn a great deal that is useful, and nature will answer
you truthfully if you ask you questions accurately, but she will
give you dry facts, just such as you ask for. If you do not love
her for herself she will never take you to her heart.
This is the reason why so many complain that science is dry and
uninteresting. They forget that though it is necessary to learn
accurately, for so only we can arrive at truth, it is equally
necessary to love knowledge and make it lovely to those who
learn, and to do this we must get at the spirit which lies under
the facts. What child which loves its mother's face is content
to know only that she has brown eyes, a straight nose, a small
mouth, and hair arranged in such and such a manner? No, it knows
that its mother has the sweetest smile of any woman living; that
her eyes are loving, her kiss is sweet, and that when she looks
grave, then something is wrong which must be put right. And it
is in this way that those who wish to enjoy the fairy-land of
science must love nature.
It is well to know that when a piece of potassium is thrown on
water the change which takes place is expressed by the formula K +
H2O = KHO + H. But it is better still to have a mental picture of
the tiny atoms clasping each other, and mingling so as to make a
new substance, and to feel how wonderful are the many changing
forms of nature. It is useful to be able to classify a flower and
to know that the buttercup belongs to the Family Ranunculaceae,
with petals free and definite, stamens hypogynous and indefinite,
pistil apocarpous. But it is far sweeter to learn about the life
of the little plant, to understand why its peculiar flower is
useful to it, and how it feeds itself, and makes its seed. No one
can love dry facts; we must clothe them with real meaning and love
the truths they tell, if we wish to enjoy science.
Let us take an example to show this. I have here a branch of
white coral, a beautiful, delicate piece of nature's work. We
will begin by copying a description of it from one of those
class-books which suppose children to learn words like parrots,
and to repeat them with just as little understanding.
"Coral is formed by an animal belonging to the kingdom of
Radiates, sub-kingdom Polypes. The soft body of the animal is
attached to a support, the mouth opening upwards in a row of
tentacles. The coral is secreted in the body of the polyp out of
the carbonate of lime in the sea. Thus the coral animalcule
rears its polypidom or rocky structure in warm latitudes, and
constructs reefs or barriers round islands. It is limited in
rage of depth from 25 to 30 fathoms. Chemically considered,
coral is carbonate of like; physiologically, it is the skeleton
of an animal; geographically, it is characteristic of warm
latitudes, especially of the Pacific Ocean." This description is
correct, and even fairly complete, if you know enough of the
subject to understand it. But tell me, does it lead you to love
my piece of coral? Have you any picture in your mind of the
coral animal, its home, or its manner of working?
But now, instead of trying to master this dry, hard passage, take
Mr. Huxley's penny lecture on 'Coral and Coral Reefs,' and with
the piece of coral in your hand try really to learn its history.
You will then be able to picture to yourself the coral animal as
a kind of sea-anemone, something like those which you have often
seen, like red, blue, or green flowers, putting out feelers in
sea-water on our coasts, and drawing in the tiny sea-animals to
digest them in that bag of fluid which serves the sea-anemone as
a stomach. You will learn how this curious jelly animal can
split itself in two, and so form two polyps, or send a bud out of
its side and so grow up into a kind of "tree or bush of polyps,"
or how it can hatch little eggs inside it and throw out young
ones from its mouth, provided with little hairs, by means of
which they swim to new resting-places. You will learn the
difference between the animal which builds up the red coral as
its skeleton, and the group of animals which build up the white;
and you will look with new interest on our piece of white coral,
as you read that each of those little sups on its stem with
delicate divisions like the spokes of a wheel has been the home
of a separate polyp, and that from the sea-water each little
jelly animal has drunk in carbonate of lime as you drink in sugar
dissolved in water, and then has used it grain by grain to build
that delicate cup and add to the coral tree.
We cannot stop to examine all about coral now, we are only
learning how to learn, but surely our specimen is already
beginning to grow interesting; and when you have followed it out
into the great Pacific Ocean, where the wild waves dash
restlessly against the coral trees, and have seen these tiny
drops of jelly conquering the sea and building huge walls of
stone against the rough breakers, you will hardly rest till you
know all their history. Look at that curious circular island in
the picture, covered with palm trees; it has a large smooth lake
in the middle, and the bottom of this lake is covered with blue,
red, and green jelly animals, spreading out their feelers in the
water and looking like beautiful flowers, and all round the
outside of the island similar animals are to be seen washed by
the sea waves. Such islands as this have been build entirely by
the coral animals, and the history of the way in which the reefs
have sunk gradually down, as the tiny creatures added to them
inch by inch, is as fascinating as the story of the building of
any fairy palace in the days of old. Read all this, and then if
you have no coral of your own to examine, go to the British
Museum and see the beautiful specimens in the glass cases there,
and think that they have been built up under the rolling surf by
the tiny jelly animals; and then coral will become a real living
thing to you, and you will love the thoughts it awakens.
But people often ask, what is the use of learning all this? If
you do not feel by this time how delightful it is to fill your
mind with beautiful pictures of nature, perhaps it would be
useless to say more. But in this age of ours, when restlessness
and love of excitement pervade so many lives, is it nothing to be
taken out of ourselves and made to look at the wonders of nature
going on around us? Do you never feel tired and "out of sorts,"
and want to creep away from your companions, because they are
merry and you are not? Then is the time to read about the
starts, and how quietly they keep their course from age to age;
or to visit some little flower, and ask what story it has to
tell; or to watch the clouds, and try to imagine how the winds
drive them across the sky. No person is so independent as he who
can find interest in a bare rock, a drop of water, the foam of
the sea, the spider on the wall, the flower underfoot or the
starts overhead. And these interests are open to everyone who
enters the fairy-land of science.
Moreover, we learn from this study to see that there is a law and
purpose in everything in the Universe, and it makes us patient
when we recognize the quiet noiseless working of nature all
around us. Study light, and learn how all colour, beauty, and
life depend on the sun's rays; note the winds and currents of the
air, regular even in their apparent irregularity, as they carry
heat and moisture all over the world. Watch the water flowing in
deep quiet streams, or forming the vast ocean; and then reflect
that every drop is guided by invisible forces working according
to fixed laws. See plants springing up under the sunlight, learn
the secrets of plant life, and how their scents and colours
attract the insects. Read how insects cannot live without
plants, nor plants without the flitting butterfly or the busy
bee. Realize that all this is worked by fixed laws, and that out
of it (even if sometimes in suffering and pain) springs the
wonderful universe around us. And then say, can you fear for
your own little life, even though it may have its troubles? Can
you help feeling a part of this guided and governed nature? or
doubt that the power which fixed the laws of the stars and of the
tiniest drop of water - that made the plant draw power from the
sun, the tine coral animal its food from the dashing waves; that
adapted the flower to the insect and the insect to the flower -
is also moulding your life as part of the great machinery of the
universe, so that you have only to work, and to wait, and to
love?
We are all groping dimly for the Unseen Power, but no one who
loves nature and studies it can ever feel alone or unloved in the
world. Facts, as mere facts, are dry and barren, but nature is
full of life and love, and her calm unswerving rule is tending to
some great though hidden purpose. You may call this Unseen Power
what you will - may lean on it in loving, trusting faith, or bend
in reverent and silent awe; but even the little child who lives
with nature and gazes on her with open eye, must rise in some
sense or other through nature to nature's God.
Week 3
Lecture II Sunbeams and How They Work
Who does not love the sunbeams, and feel brighter and merrier as
he watches them playing on the wall, sparkling like diamonds on
the ripples of the sea, or making bows of coloured light on the
waterfall? Is not the sunbeam so dear to us that it has become a
household word for all that is merry and gay? and when we want to
describe the dearest, busiest little sprite amongst us, who wakes
a smile on all faces wherever she goes, do we not call her the
"sunbeam of the house"?
And yet how little even the wisest among us know about the nature
and work of these bright messengers of the sun as they dart
across space!
Did you ever wake quite early in the morning, when it was pitch-
dark and you could see nothing, not even your own hand; and then
lie watching as time went on till the light came gradually
creeping in at the window? If you have done this you will have
noticed that you can at first only just distinguish the dim
outline of the furniture; then you can tell the difference
between the white cloth on the table and the dark wardrobe beside
it; then by degrees all the smaller details, the handles of the
drawer, the pattern on the wall, and the different colours of all
the objects in the room become clearer and clearer till at last
you see all distinctly in broad daylight.
What has been happening here? and why have the things in the room
become visible by such slow degrees? We say that the sun is
rising, but we know very well that it is not the sun which moves,
but that our earth has been turning slowly round, and bringing
the little spot on which we live face to face with the great
fiery ball, so that his beams can fall upon us.
Take a small globe, and stick a piece of black plaster over
England, then let a lighted lamp represent the sun, and turn the
globe slowly, so that the spot creeps round from the dark side
away from the lamp, until it catches, first the rays which pass
along the side of the globe, then the more direct rays, and at
last stands fully in the blaze of the light. Just this was
happening to our spot of the world as you lay in bed and saw the
light appear; and we have to learn today what those beams are
which fall upon us and what they do for us.
First we must learn something about the sun itself, since it is
the starting-place of all the sunbeams. If the sun were a dark
mass instead of a fiery one we should have none of these bright
cheering messengers, and though we were turned face to face with
him every day we should remain in one cold eternal night. Now
you will remember we mentioned in the last lecture that it is
heat which shakes apart the little atoms of water and makes them
gloat up in the air to fall again as rain; and that if the day is
cold they fall as snow, and all the water is turned into ice.
But if the sun were altogether dark, think how bitterly cold it
would be; far colder than the most wintry weather ever known,
because in the bitterest night some warmth comes out of the
earth, where it has been stored from the sunlight which fell
during the day. But if we never received any warmth at all, no
water would ever rise up into the sky, no rain ever fall, no
rivers flow, and consequently no plants could grow and no animals
live. All water would be in the form of snow and ice, and the
earth would be one great frozen mass with nothing moving upon it.
So you see it becomes very interesting for us to learn what the
sun is, and how he sends us his beams. How far away from us do
you think he is? On a fine summer's day when we can see him
clearly, it looks as if we had only to get into a balloon and
reach him as he sits in the sky, and yet we know roughly that he
is more than ninety-one millions of miles distant from our earth.
These figures are so enormous that you cannot really grasp them.
But imagine yourself in an express train, travelling at the
tremendous rate of sixty miles an hour and never stopping. At
that rate, if you wished to arrive at the sun today you would
have been obliged to start 171 years ago. That is, you must have
set off in the early part of the reign of Queen Anne, and you
must have gone on, never, never resting, through the reigns of
George I, George ii, and the long reign of George III, then
through those of George IV, William IV, and Victoria, whirling on
day and night at express speed, and at last, today, you would
have reached the sun!
And when you arrived there, how large do you think you would find
him to be? Anaxagoras, a learned Greek, was laughed at by all
his fellow Greeks because he said that the sun was as large as
the Peloponne-sus, that is about the size of Middlesex. How
astonished they would have been if they could have known that not
only is he bigger than the whole of Greece, but more than a
million times bigger than the whole world!
Our world itself is a very large place, so large that our own
country looks only like a tiny speck upon it, and an express
train would take nearly a month to travel round it. Yet even our
whole globe is nothing in size compared to the sun, for it only
measures 8000 miles across, while the sun measures more the
852,000.
Imagine for a moment that you could cut the sun and the earth
each in half as you would cut an apple; then if you were to lay
the flat side of the half-earth on the flat side of the half sun
it would take 106 such earths to stretch across the face of the
sun. One of these 106 round spots on the diagram represents the
size which our earth would look if placed on the sun; and they
are so tiny compared to him that they look only like a string of
minute beads stretched across his face. Only think, then, how
many of these minute dots would be required to fill the whole of
the inside of Fig. 4, if it were a globe.
One of the best ways to form an idea of the whole size of the sun
is to imagine it to be hollow, like an air-ball, and then see how
many earths it would take to fill it. You would hardly believe
that it would take one million, three hundred and thirty-one
thousand globes the size of our world squeezed together. Just
think, if a huge giant could travel all over the universe and
gather worlds, all as big as ours, and were to make first a heap
of merely ten such worlds, how huge it would be! Then he must
have a hundred such heaps of ten to make a thousand world; and
then he must collect again a thousand times that thousand to make
a million, and when he had stuffed them all into the sun-ball he
would still have only filled three-quarters of it!
After hearing this you will not be astonished that such a monster
should give out an enormous quantity of light and heat; so
enormous that it is almost impossible to form any idea of it.
Sir John Herschel has, indeed, tried to picture it for us. He
found that a ball of lime with a flame of oxygen and hydrogen
playing round it (such as we use in magic lanterns and call oxy-
hydrogen light) becomes so violently hot that it gives the most
brilliant artificial light we can get - such that you cannot put
your eye near it without injury. Yet if you wanted to have a
light as strong as that of our sun, it would not be enough to
make such a lime-ball as big as the sun is. No, you must make it
as big as 146 suns, or more than 146,000,000 times as big as our
earth, in order to get the right amount of light. Then you would
have a tolerably good artificial sun; for we know that the body
of the sun gives out an intense white light, just as the lime-
ball does, and that , like it, it has an atmosphere of glowing
gases round it.
But perhaps we get the best idea of the mighty heat and light of
the sun by remembering how few of the rays which dart out on all
sides from this fiery ball can reach our tiny globe, and yet how
powerful they are. Look at the globe of a lamp in the middle of
the room, and see how its light pours out on all sides and into
every corner; then take a grain of mustard-seed, which will very
well represent the comparative size of our earth, and hold it up
at a distance from the lamp. How very few of all those rays
which are filling the room fall on the little mustard-seed, and
just so few does our earth catch of the rays which dart out from
the sun. And yet this small quantity (1/2000-millionth part of
the whole) does nearly all the work of our world. (These and the
preceding numerical statements will be found worked out in Sir J.
Herschel's 'Familiar Lectures on Scientific Subjects,' 1868, from
which many of the facts in the first part of the lecture are
taken.)
In order to see how powerful the sun's rays are, you have only to
take a magnifying glass and gather them to a point on a piece of
brown paper, for they will set the paper alight. Sir John
Herschel tells us that at the Cape of Good Hope the heat was even
so great that he cooked a beefsteak and roasted some eggs by
merely putting them in the sun, in a box with a glass lid!
Indeed, just as we should all be frozen to death if the sun were
sold, so we should all be burnt up with intolerable heat if his
fierce rays fell with all their might upon us. But we have an
invisible veil protecting us, made - of what do you think? Of
those tiny particles of water which the sunbeams draw up and
scatter in the air, and which, as we shall see in Lecture IV, cut
off part of the intense heat and make the air cool and pleasant
for us.
Week 4
We have now learnt something of the distance, the size, the
light, and the heat of the sun - the great source of the
sunbeams. But we are as yet no nearer the answer to the
question, What is a sunbeam? how does the sun touch our earth?
Now suppose I with to touch you from this platform where I stand,
I can do it in two ways. Firstly, I can throw something at you
and hit you - in this case a thing will have passed across the
space from me to you. Or, secondly, if I could make a violent
movement so as to shake the floor of the room, you would feel a
quivering motion; and so I should touch you across the whole
distance of the room. But in this case no thing would have
passed from me to you but a movement or wave, which passed along
the boards of the floor. Again, if I speak to you, how does the
sound reach you ear? Not by anything being thrown from my mouth
to your ear, but by the motion of the air. When I speak I
agitate the air near my mouth, and that makes a wave in the air
beyond, and that one, another, and another (as we shall see more
fully in Lecture VI) till the last wave hits the drum of your
ear.
Thus we see there are two ways of touching anything at a
distance; 1st, by throwing some thing at it and hitting it; 2nd,
by sending a movement of wave across to it, as in the case of the
quivering boards and the air.
Now the great natural philosopher Newton thought that the sun
touched us in the first of these ways, and that sunbeams were
made of very minute atoms of matter thrown out by the sun, and
making a perpetual cannonade on our eyes. It is easy to
understand that this would make us see light and feel heat, just
as a blow in the eye makes us see starts, or on the body makes it
feel hot: and for a long time this explanation was supposed to be
the true one. But we know now that there are many facts which
cannot be explained on this theory, though we cannot go into them
here. What we will do, is to try and understand what now seems
to be the true explanation of the sunbeam.
About the same time that Newton wrote, a Dutchman, named
Huyghens, suggested that light comes from the sun in tiny waves,
travelling across space much in the same way as ripples travel
across a pond. The only difficulty was to explain in what
substance these waves could be travelling: not through water, for
we know that there is no water in space - nor through air, for
the air stops at a comparatively short distance from our earth.
There must then be something filling all space between us and the
sun, finer than either water or air.
And now I must ask you to use all you imagination, for I want you
to picture to yourselves something quite as invisible as the
Emperor's new clothes in Andersen's fairy-tale, only with this
difference, that our invisible something is very active; and
though we can neither see it nor touch it we know it by its
effects. You must imagine a fine substance filling all space
between us and the sun and the starts. A substance so very
delicate and subtle, that not only is it invisible, but it can
pass through solid bodies such as glass, ice, or even wood or
brick walls. This substance we call "ether." I cannot give you
here the reasons why we must assume that it is throughout all
space; you must take this on the word of such men as Sir John
Herschel or Professor Clerk-Maxwell, until you can study the
question for yourselves.
Now if you can imagine this ether filling every corner of space,
so that it is everywhere and passes through everything, ask
yourselves, what must happen when a great commotion is going on
in one of the large bodies which float in it? When the atoms of
the gases round the sun are clashing violently together to make
all its light and heat, do you not think they must shake this
ether all around them? And then, since the ether stretches on
all sides from the sun to our earth and all other planets, must
not this quivering travel to us, just as the quivering of the
boards would from me to you? Take a basin of water to represent
the ether, and take a piece of potassium like that which we used
in our last lecture, and hold it with a pair of nippers in the
middle of the water. You will see that as the potassium hisses
and the flame burns round it, they will make waves which will
travel all over the water to the edge of the basin,, and you can
imagine how in the same way waves travel over the ether from the
sun to us.
Straight away from the sun on all sides, never stopping, never
resting, but chasing after each other with marvellous quickness,
these tiny waves travel out into space by night and by day. When
our spot of the earth where England lies is turned away from them
and they cannot touch us, then it is night for us, but directly
England is turned so as to face the sun, then they strike on the
land, and the water, and warm it; or upon our eyes, making the
nerves quiver so that we see light. Look up at the sun and
picture to yourself that instead of one great blow from a fist
causing you to see starts for a moment, millions of tiny blows
from these sun-waves are striking every instant on you eye; then
you will easily understand that his would cause you to see a
constant blaze of light.
But when the sun is away, if the night is clear we have light
from the starts. Do these then too make waves all across the
enormous distance between them and us? Certainly they do, for
they too are suns like our own, only they are so far off that the
waves they send are more feeble, and so we only notice them when
the sun's stronger waves are away.
But perhaps you will ask, if no one has ever seen these waves not
the ether in which they are made, what right have we to say they
are there? Strange as it may seem, though we cannot see them we
have measured them and know how large they are, and how many can
go into an inch of space. For as these tiny waves are running on
straight forward through the room, if we put something in their
way, they will have to run round it; and if you let in a very
narrow ray of light through a shutter and put an upright wire in
the sunbeam, you actually make the waves run round the wire just
as water runs round a post in a river; and they meet behind the
wire, just as the water meets in a V shape behind the post. Now
when they meet, they run up against each other, and here it is we
catch them. Fir if they meet comfortably, both rising up in a
good wave, they run on together and make a bright line of light;
but if they meet higgledy-piggledy, one up and the other down,
all in confusion, they stop each other, and then there is no
light but a line of darkness. And so behind your piece of wire
you can catch the waves on a piece of paper, and you will find
they make dark and light lines one side by side with the other,
and by means of these bands it is possible to find out how large
the waves must be. This question is too difficult for us to work
it out here, but you can see that large waves will make broader
light and dark bands than small ones will, and that in this way
the size of the waves may be measured.
And now how large do you think they turn out to be? so very,
very tiny that about fifty thousand waves are contained in a
single inch of space! I have drawn on the board the length of an
inch, and now I will measure the same space in the air between my
finger and thumb. Within this space at this moment there are
fifty thousand tiny waves moving up and down. I promised you we
would find in science things as wonderful as in fairy tales. Are
not these tiny invisible messengers coming incessantly from the
sun as wonderful as any fairies? and still more so when, as we
shall see presently, they are doing nearly all the work of our
world.
We must next try to realize how fast these waves travel. You
will remember that an express train would take 171 years to reach
us from the sun; and even a cannon-ball would take from ten to
thirteen years to come that distance. Well, these tiny waves
take only seven minutes and a half to come the whole 91 millions
of miles. The waves which are hitting your eye at this moment
are caused by a movement which began at the sun only 7 1/2
minutes ago. And remember, this movement is going on
incessantly, and these waves are always following one after the
other so rapidly that they keep up a perpetual cannonade upon the
pupil of your eye. So fast do they come that about 608 billion
waves enter your eye in one single second.* I do not ask you to
remember these figures; I only ask you to try and picture to
yourselves these infinitely tiny and active invisible messengers
from the sun, and to acknowledge that light is a fairy thing.
(*Light travels at the rate of 190,000 miles, or 12,165,120,000
inches in a second. Taking the average number of wave-lengths in
an inch at 50,000, then 12,165,120,000 X 50,000 =
608,256,000,000,000.)
But we do not yet know all about our sunbeams. See, I have here
a piece of glass with three sides, called a prism. If I put it
in the sunlight which is streaming through the window, what
happens? Look! on the table there is a line of beautiful
colours. I can make it long or short, as I turn the prism, but
the colours always remain arranged in the same way. Here at my
left hand is the red, beyond it orange, then yellow, green, blue,
indigo or deep blue, and violet, shading one into the other all
along the line. We have all seen these colours dancing on the
wall when the sun has been shining brightly on the cut-glass
pendants of the chandelier, and you may see them still more
distinctly if you let a ray of light into a darkened room, and
pass it through the prism as in the diagram (Fig. 7). What are
these colours? Do they come from the glass? No; for you will
remember to have seen them in the rainbow, and in the soap-
bubble, and even in a drop of dew or the scum on the top of a
pond. This beautiful coloured line is only our sunbeam again,
which has been split up into many colours by passing through the
glass, as it is in the rain-drops of the rainbow and the bubbles
of the scum of the pond.
Week 5
Till now we have talked of the sunbeam as if it were made of only
one set of waves of different sizes, all travelling along
together from the sun. These various waves have been measured,
and we know that the waves which make up red light are larger and
more lazy than those which make violet light, so that there are
only thirty-nine thousand red waves in an inch, while there are
fifty-seven thousand violet waves in the same space.
How is it then, that if all these different waves making
different colours, hit on our eye, they do not always make us see
coloured light? Because, unless they are interfered with, they
all travel along together, and you know that all colours, mixed
together in proper proportion, make white.
I have here a round piece of cardboard, painted with the seven
colours in succession several times over. When it is still you
can distinguish them all apart, but when I whirl it quickly round
- see! - the cardboard looks quite white, because we see them all
so instantaneously that they are mingled together. In the same
way light looks white to you, because all the different coloured
waves strike on your eye at once. You can easily make on of
these card for yourselves only the white will always look dirty,
because you cannot get the colours pure.
Now, when the light passes through the three-sided glass or
prism, the waves are spread out, and the slow, heavy, red waves
lag behind and remain at the lower end R of the coloured line on
the wall (Fig. 7), while the rapid little violet waves are bent
more out of their road and run to V at the farther end of the
line; and the orange, yellow, green, blue, and indigo arrange
themselves between, according to the size of their waves.
And now you are very likely eager to ask why the quick waves
should make us see one colour, and the slow waves another. This
is a very difficult question, for we have a great deal still to
learn about the effect of light on the eye. But you can easily
imagine that colour is to our eye much the same as music is to
our ear. You know we can distinguish different notes when the
air-waves play slowly or quickly upon the drum of the ear (as we
shall see in Lecture VI) and somewhat in the same way the tiny
waves of the ether play on the retina or curtain at the back of
our eye, and make the nerves carry different messages to the
brain: and the colour we see depends upon the number of waves
which play upon the retina in a second.
Do you think we have now rightly answered the question - What is
a sunbeam? We have seen that it is really a succession of tiny
rapid waves, travelling from the sun to us across the invisible
substance we call "ether", and keeping up a constant cannonade
upon everything which comes in their way. We have also seen
that, tiny as these waves are, they can still vary in size, so
that one single sunbeam is made up of myriads of different-sized
waves, which travel all together and make us see white light;
unless for some reason they are scattered apart, so that we see
them separately as red, green, blue, or yellow. How they are
scattered, and many other secrets of the sun-waves, we cannot
stop to consider not, but must pass on to ask -
What work do the sunbeams do for us?
They do two things - they give us light and heat. It is by means
of them alone that we see anything. When the room was dark you
could not distinguish the table, the chairs, or even the walls of
the room. Why? Because they had no light-waves to send to your
eye. But as the sunbeams began to pour in at the window, the
waves played upon the things in the room, and when they hit them
they bounded off them back to your eye, as a wave of the sea
bounds back from a rock and strikes against a passing boat.
Then, when they fell upon your eye, they entered it and excited
the retina and the nerves, and the image of the chair or the
table was carried to your brain. Look around at all the things
in this room. Is it not strange to think that each one of them
is sending these invisible messengers straight to your eye as you
look at it; and that you see me, and distinguish me from the
table, entirely by the kind of waves we each send to you?
Some substances send back hardly any waves of light, but let them
all pass through them, and thus we cannot see them. A pane of
clear glass, for instance, lets nearly all the light-waves pass
through it, and therefore you often cannot see that the glass is
there, because no light-messengers come back to you from it.
Thus people have sometimes walked up against a glass door and
broken it, not seeing it was there. Those substances are
transparent which, for some reason unknown to us, allow the ether
waves to pass through them without shaking the atoms of which the
substance is made. In clear glass, for example, all the light-
waves pass through without affecting the substance of the glass;
while in a white wall the larger part of the rays are reflected
back to your eye, and those which pass into the wall, by giving
motion to its atoms lose their own vibrations.
Into polished shining metal the waves hardly enter at all, but
are thrown back from the surface; and so a steel knife or a
silver spoon are very bright, and are clearly seen. Quicksilver
is put at the back of looking-glasses because it reflects so many
waves. It not only sends back those which come from the sun, but
those, too, which come from your face. So, when you see yourself
in a looking-glass, the sun-waves have first played on your face
and bounded off from it to the looking-glass; then, when they
strike the looking-glass, they are thrown back again on to the
retina of your eye, and you see your own face by means of the
very waves you threw off from it an instant before.
But the reflected light-waves do more for us than this. They not
only make us see things, but they make us see them in different
colours. What, you will ask, is this too the work of the
sunbeams? Certainly; for if the colour we see depends on the
size of the waves which come back to us, then we must see things
coloured differently according to the waves they send back. For
instance, imagine a sunbeam playing on a leaf: part of its waves
bound straight back from it to our eye and make us see the
surface of the leaf, but the rest go right into the leaf itself,
and there some of them are used up and kept prisoners. The red,
orange, yellow, blue, and violet waves are all useful to the
leaf, and it does not let them go again. But it cannot absorb
the green waves, and so it throws them back, and they travel to
your eye and make you see a green colour. So when you say a leaf
is green, you mean that the leaf does not want the green waves of
the sunbeam, but sends them back to you. In the same way the
scarlet geranium rejects the red waves; this table sends back
brown waves; a white tablecloth sends back nearly the whole of
the waves, and a black coat scarcely any. This is why, when
there is very little light in the room, you can see a white
tablecloth while you would not be able to distinguish a black
object, because the few faint rays that are there, are all sent
back to you from a white surface.
Is it not curious to think that there is really no such thing as
colour in the leaf, the table, the coat, or the geranium flower,
but we see them of different colours because, for some reason,
they send back only certain coloured waves to our eye?
Wherever you look, then, and whatever you see, all the beautiful
tints, colours, lights, and shades around you are the work of the
tiny sun-waves.
Again, light does a great deal of work when it falls upon plants.
Those rays of light which are caught by the leaf are by no means
idle; we shall see in Lecture VII that the leaf uses them to
digest its food and make the sap on which the plant feeds.
Week 6
We all know that a plant becomes pale and sickly if it has not
sunlight, and the reason is, that without these light-waves it
cannot get food out of the air, nor make the sap and juices which
it needs. When you look at plants and trees growing in the
beautiful meadows; at the fields of corn, and at the lovely
landscape, you are looking on the work of the tiny waves of
light, which never rest all through the day in helping to give
life to every green thing that grows.
So far we have spoken only of light; but hold your hand in the
sun and feel the heat of the sunbeams, and then consider if the
waves of heat do not do work also. There are many waves in a
sunbeam which move too slowly to make us see light when they hit
our eye, but we can feel them as heat, though we cannot see them
as light. The simplest way of feeling heat-waves is to hold a
warm iron near your face. You know that no light comes from it,
yet you can feel the heat-waves beating violently against your
face and scorching it. Now there are many of these dark heat-
rays in a sunbeam, and it is they which do most of the work in
the world.
In the first place, as they come quivering to the earth, it is
they which shake the water-drops apart, so that these are carried
up in the air, as we shall see in the next lecture. And then
remember, it is these drops, falling again as rain, which make
the rivers and all the moving water on the earth. So also it is
the heat-waves which make the air hot and light, and so cause it
to rise and make winds and air-currents, and these again give
rise to ocean-currents. It is these dark rays, again, which
strike upon the land and give it the warmth which enables plants
to grow. It is they also which keep up the warmth in our own
bodies, both by coming to us directly from the sun, and also in a
very roundabout way through plants. You will remember that
plants use up rays of light and heat in growing; then either we
eat the plants, or animals eat the plants and we eat the animals;
and when we digest the food, that heat comes back in our bodies,
which the plants first took from the sunbeam. Breathe upon your
hand, and feel how hot your breath is; well, that heat which you
feel, was once in a sunbeam, and has travelled from it through
the food you have eaten, and has now been at work keeping up the
heat of your body.
But there is still another way in which these plants may give out
the heat-waves they have imprisoned. You will remember how we
learnt in the first lecture that coal is made of plants, and that
the heat they give out is the heat these plants once took in.
Think how much work is done by burning coals. Not only are our
houses warmed by coal fires and lighted by coal gas, but our
steam-engines and machinery work entirely by water which has been
turned into steam by the heat of coal and coke fire; and our
steamboats travel all over the world by means of the same power.
In the same way the oil of our lamps comes either from olives,
which grow on trees; or from coal and the remains of plants and
animals in the earth. Even our tallow candles are made of mutton
fat, and sheep eat grass; as so, turn which way we will, we find
that the light and heat on our earth, whether it comes from
fires, or candles, or lamps, or gas, and whether it moves
machinery, or drives a train, or propels a ship, is equally the
work of the invisible waves of ether coming from the sun, which
make what we call a sunbeam.
Lastly, there are still some hidden waves which we have not yet
mentioned, which are not useful to us either as light or heat,
and yet they are not idle.
Before I began this lecture, I put a piece of paper, which had
been dipped in nitrate of silver, under a piece of glass; and
between it and the glass I put a piece of lace. Look what the
sun has been doing while I have been speaking. It has been
breaking up the nitrate of silver on the paper and turning it
into a deep brown substance; only where the threads of the lace
were, and the sun could not touch the nitrate of silver, there
the paper has remained light-coloured, and by this means I have a
beautiful impression of the lace on the paper. I will now dip
the impression into water in which some hyposulphite of soda is
dissolved, and this will "fix" the picture, that is, prevent the
sun acting upon it any more; then the picture will remain
distinct, and I can pass it round to you all. Here, again,
invisible waves have been at work, and this time neither as light
nor as heat, but as chemical agents, and it is these waves which
give us all our beautiful photographs. In any toyshop you can
buy this prepared paper, and set the chemical waves at work to
make pictures. Only you must remember to fix it in the solution
afterwards, otherwise the chemical rays will go on working after
you have taken the lace away, and all the paper will become brown
and your picture will disappear.
And now, tell me, may we not honestly say, that the invisible
waves which make our sunbeams, are wonderful fairy messengers as
they travel eternally and unceasingly across space, never
resting, never tiring in doing the work of our world? Little as
we have been able to learn about them in one short hour, do they
not seem to you worth studying and worth thinking about, as we
look at the beautiful results of their work? The ancient Greeks
worshipped the sun, and condemned to death one of their greatest
philosophers, named Anaxagoras, because he denied that it was a
god. We can scarcely wonder at this when we see what the sun
does for our world; but we know that it is a huge globe made of
gases and fiery matter and not a god. We are grateful for the
sun instead of to him, and surely we shall look at him with new
interest, now that we can picture his tiny messengers, the
sunbeams, flitting over all space, falling upon our earth, giving
us light to see with, and beautiful colours to enjoy, warming the
air and the earth, making the refreshing rain, and, in a word,
filling the world with life and gladness.
Week 7
LECTURE III The Aerial Ocean in Which We Live
Did you ever sit on the bank of a river in some quiet spot where
the water was deep and clear, and watch the fishes swimming
lazily along? When I was a child this was one of my favourite
occupations in the summertime on the banks of the Thames, and
there was one question which often puzzled me greatly, as I
watched the minnows and gudgeon gliding along through the water.
Why should fishes live in something and be often buffeted about
by waves and currents, while I and others lived on the top of the
earth and not in anything? I do not remember ever asking anyone
about this; and if I had, in those days people did not pay much
attention to children's questions, and probably nobody would have
told me, what I now tell you, that we do live in something quite
as real and often quite as rough and stormy as the water in which
the fishes swim. The something in which we live is air, and the
reason that we do not perceive it, is that we are in it, and that
it is a gas, and invisible to us; while we are above the water in
which the fishes live, and it is a liquid which our eyes can
perceive.
But let us suppose for a moment that a being, whose eyes were so
made that he could see gases as we see liquids, was looking down
from a distance upon our earth. He would see an ocean of air, or
aerial ocean, all round the globe, with birds floating about in
it, and people walking along the bottom, just as we see fish
gliding along the bottom of a river. It is true, he would never
see even the birds come near to the surface, for the highest-
flying bird, the condor, never soars more than five miles from
the ground, and our atmosphere, as we shall see, is at least 100
miles high. So he would call us all deep-air creatures, just as
we talk of deep-sea animals; and if we can imagine that he fished
in this air-ocean, and could pull one of us out of it into space,
he would find that we should gasp and die just as fishes do when
pulled out of the water.
He would also observe very curious things going on in our air-
ocean; he would see large streams and currents of air, which we
call winds, and which would appear to him as ocean-currents do to
us, while near down to the earth he would see thick mists forming
and then disappearing again, and these would be our clouds. From
them he would see rain, hail and snow falling to the earth, and
from time to time bright flashes would shoot across the air-
ocean, which would be our lightning. Nay even the brilliant
rainbow, the northern aurora borealis, and the falling stars,
which seem to us so high up in space, would be seen by him near
to our earth, and all within the aerial ocean.
But as we know of no such being living in space, who can tell us
what takes place in our invisible air, and we cannot see it
ourselves, we must try by experiments to see it with our
imagination, though we cannot with our eyes.
First, then, can we discover what air is? At one time it was
thought that it was a simple gas and could not be separated into
more than one kind. But we are now going to make an experiment
by which it has been shown that air is made of two gases mingled
together, and that one of these gases, called oxygen, is used up
when anything burns, while the other nitrogen is not used, and
only serves to dilute the minute atoms of oxygen. I have here a
glass bell-jar, with a cork fixed tightly in the neck, and I
place the jar over a pan of water, while on the water floats a
plate with a small piece of phosphorus upon it. You will see
that by putting the bell-jar over the water, I have shut in a
certain quantity of air, and my object now is to use up the
oxygen out of this air and leave only nitrogen behind. To do
this I must light the piece of phosphorus, for you will remember
it is in burning that oxygen is used up. I will take the cork
out, light the phosphorus, and cork up the jar again. See! as
the phosphorus burns white fumes fill the jar. These fumes are
phosphoric acid which is a substance made of phosphorous and the
oxygen of the air together.
Now, phosphoric acid melts in water just as sugar does, and in a
few minutes these fumes will disappear. They are beginning to
melt already, and the water from the pan is rising up in the
bell-jar. Why is this? Consider for a moment what we have done.
First, the jar was full of air, that is, of mixed oxygen and
nitrogen; then the phosphorus used up the oxygen making white
fumes; afterwards, the water sucked up these fumes; and so, in
the jar now nitrogen is the only gas left, and the water has
risen up to fill all the rest of the space that was once taken up
with oxygen.
We can easily prove that there is no oxygen now in the jar. I
take out the cork and let a lighted taper down into the gas. If
there were any oxygen the taper would burn, but you see it goes
out directly proving that all the oxygen has been used up by the
phosphorous. When this experiment is made very accurately, we
find that for every pint of oxygen in air there are four pints of
nitrogen, so that the active oxygen-atoms are scattered about,
floating in the sleepy, inactive nitrogen.
It is these oxygen-atoms which we use up when we breathe. If I
had put a mouse under the bell-jar, instead of the phosphorus,
the water would have risen just the same, because the mouse would
have breathed in the oxygen and used it up in its body, joining
it to carbon and making a bad gas, carbonic acid, which would
also melt in the water, and when all the oxygen was used, the
mouse would have died.
Do you see now how foolish it is to live in rooms that are
closely shut up, or to hide your head under the bedclothes when
you sleep? You use up all the oxygen-atoms, and then there are
none left for you to breathe; and besides this, you send out of
your mouth bad fumes, though you cannot see them, and these, when
you breathe them in again, poison you and make you ill.
Perhaps you will say, If oxygen is so useful, why is not the air
made entirely of it? But think for a moment. If there was such
an immense quantity of oxygen, how fearfully fast everything
would burn! Our bodies would soon rise above fever heat from the
quantity of oxygen we should take in, and all fires and lights
would burn furiously. In fact, a flame once lighted would spread
so rapidly that no power on earth could stop it, and everything
would be destroyed. So the lazy nitrogen is very useful in
keeping the oxygen-atoms apart; and we have time, even when a
fire is very large and powerful, to put it out before it has
drawn in more and more oxygen from the surrounding air. Often,
if you can shut a fire into a closed space, as in a closely-shut
room or the hold of a ship, it will go out, because it has used
up all the oxygen in the air.
So, you see, we shall be right in picturing this invisible air
all around us as a mixture of two gases. But when we examine
ordinary air very carefully, we find small quantities of other
gases in it, besides oxygen and nitrogen. First, there is
carbonic acid gas. This is the bad gas which we give out of our
mouths after we have burnt up the oxygen with the carbon of our
bodies inside our lungs; and this carbonic acid is also given out
from everything that burns. If only animals lived in the world,
this gas would soon poison the air; but plants get hold of it,
and in the sunshine they break it up again, as we shall see in
Lecture VII, and use up the carbon, throwing the oxygen back into
the air for us to use. Secondly, there are very small quantities
of ammonia, or the gas which almost chokes you in smelling-salts,
and which, when liquid is commonly called "spirits of hartshorn."
This ammonia is useful to plants, as we shall see by and by.
Lastly, there is a great deal of water in the air, floating about
as invisible vapour or water-dust, and this we shall speak of in
the next lecture. Still, all these gases and vapours in the
atmosphere are in very small quantities, and the bulk of the air
is composed of oxygen and nitrogen.
Having now learned what air is, the next question which presents
itself is, Why does it stay round our earth? You will remember
we saw in the first lecture, that all the little atoms of a gas
are trying to fly away from each other, so that if I turn on this
gas-jet the atoms soon leave it, and reach you at the farther end
of the room, and you can smell the gas. Why, then, do not all
the atoms of oxygen and nitrogen fly away from our earth into
space, and leave us without any air?
Ah! here you must look for another of our invisible forces.
Have you forgotten our giant force, "gravitation," which draws
things together from a distance? This force draws together the
earth and the atoms of oxygen and nitrogen; and as the earth is
very big and heavy, and the atoms of air are light and easily
moved, they are drawn down to the earth and held there by
gravitation. But for all that, the atmosphere does not leave off
trying to fly away; it is always pressing upwards and outwards
with all its might, while the earth is doing its best to hold it
down.
The effect of this is, that near the earth, where the pull
downward is very strong, the air-atoms are drawn very closely
together, because gravitation gets the best of the struggle. But
as we get farther and farther from the earth, the pull downward
becomes weaker, and then the air-atoms spring farther apart, and
the air becomes thinner. Suppose that the lines in this diagram
represent layers of air. Near the earth we have to represent
them as lying closely together, but as they recede from the earth
they are also farther apart.
But the chief reason why the air is thicker or denser nearer the
earth, is because the upper layers press it down. If you have a
heap of papers lying one on the top of the other, you know that
those at the bottom of the heap will be more closely pressed
together than those above, and just the same is the case with the
atoms of the air. Only there is this difference, if the papers
have lain for some time, when you take the top ones off, the
under ones remain close together. But it is not so with the air,
because air is elastic, and the atoms are always trying to fly
apart, so that directly you take away the pressure they spring up
again as far as they can.
Week 8
I have here an ordinary pop-gun. If I push the cork in very
tight, and then force the piston slowly inwards, I can compress
the air a good deal. Now I am forcing the atoms nearer and
nearer together, but at last they rebel so strongly against being
more crowded that the cork cannot resist their pressure. Out it
flies, and the atoms spread themselves out comfortably again in
the air all around them. Now, just as I pressed the air together
in the pop-gun, so the atmosphere high up above the earth presses
on the air below and keeps the atoms closely packed together.
And in this case the atoms cannot force back the air above them
as they did the cork in the pop-gun; they are obliged to submit
to be pressed together.
Even a short distance from the earth, however, at the top of a
high mountain, the air becomes lighter, because it has less
weight of atmosphere above it, and people who go up in balloons
often have great difficulty in breathing, because the air is so
thin and light. In 1804 a Frenchman, named Gay-Lussac, went up
four miles and a half in a balloon, and brought down some air;
and he found that it was much less heavy than the same quantity
of air taken close down to the earth, showing that it was much
thinner, or rarer, as it is called;* and when, in 1862, Mr.
Glaisher and Mr. Coxwell went up five miles and a half, Mr.
Glaisher's veins began to swell, and his head grew dizzy, and he
fainted. The air was too thin for him to breathe enough in at a
time, and it did not press heavily enough on the drums of his
ears and the veins of his body. He would have died if Mr.
Coxwell had not quickly let off some of the gas in the balloon,
so that it sank down into denser air. (*100 cubic inches near the
earth weighed 31 grains, while the same quantity taken at four
and a half miles up in the air weighed only 12 grains, or two-
fifths of the weight.)
And now comes another very interesting question. If the air gets
less and less dense as it is farther from the earth, where does
it stop altogether? We cannot go up to find out, because we
should die long before we reached the limit; and for a long time
we had to guess about how high the atmosphere probably was, and
it was generally supposed not to be more than fifty miles. But
lately, some curious bodies, which we should have never suspected
would be useful to us in this way, have let us into the secret of
the height of the atmosphere. These bodies are the meteors, or
falling stars.
Most people, at one time or another, have seen what looks like a
star shoot right across the sky, and disappear. On a clear
starlight night you may often see one or more of these bright
lights flash through the air; for one falls on an average in
every twenty minutes, and on the nights of August 9th and
November 13th there are numbers in one part of the sky. These
bodies are not really stars; they are simply stones or lumps of
metal flying through the air, and taking fire by clashing against
the atoms of oxygen in it. There are great numbers of these
masses moving round and round the sun, and when our earth comes
across their path, as it does especially in August and November,
they dash with such tremendous force through the atmosphere that
they grow white-hot, and give out light, and then disappear,
melted into vapour. Every now and then one falls to the earth
before it is all melted away, and thus we learn that these stones
contain tin, iron, sulphur, phosphorus, and other substances.
It is while these bodies are burning that they look to us like
falling stars, and when we see them we know that hey must be
dashing against our atmosphere. Now if two people stand a
certain known distance, say fifty miles, apart on the earth and
observe these meteors and the direction in which they each see
them fall, they can calculate (by means of the angle between the
two directions) how high they are above them when they first see
them, and at that moment they must have struck against the
atmosphere, and even travelled some way through it, to become
white-hot. In this way we have learnt that meteors burst into
light at least 100 miles above the surface of the earth, and so
the atmosphere must be more than 100 miles high.
Our next question is as to the weight of our aerial ocean. You
will easily understand that all this air weighing down upon the
earth must be very heavy, even though it grows lighter as it
ascends. The atmosphere does, in fact, weigh down upon land at
the level of the sea as much as if a 15-pound weight were put
upon every square inch of land. This little piece of linen
paper, which I am holding up, measures exactly a square inch, and
as it lies on the table, it is bearing a weight of 15 lbs. on its
surface. But how, then, comes it that I can lift it so easily?
Why am I not conscious of the weight?
To understand this you must give all your attention, for it is
important and at first not very easy to grasp. you must
remember, in the first place, that the air is heavy because it is
attracted to the earth, and in the second place, that since air
is elastic all the atoms of it are pushing upwards against this
gravitation. And so, at any point in air, as for instance the
place where the paper now is as I hold it up, I feel no pressure
because exactly as much as gravitation is pulling the air down,
so much elasticity is resisting and pushing it up. So the
pressure is equal upwards, downwards, and on all sides, and I can
move the paper with equal ease any way.
Even if I lay the paper on the table this is still true, because
there is always some air under it. If, however, I could get the
air quite away from one side of the paper, then the pressure on
the other side would show itself. I can do this by simply
wetting the paper and letting it fall on the table, and the water
will prevent any air from getting under it. Now see! if I try to
lift it by the thread in the middle, I have great difficulty,
because the whole 15 pounds' weight of the atmosphere is pressing
it down. A still better way of making the experiment is with a
piece of leather, such as the boys often amuse themselves with in
the streets. This piece of leather has been well soaked. I drop
it on the floor and see! it requires all my strength to pull it
up. (In fastening the string to the leather the hole must be
very small and the know as flat as possible, and it is even well
to put a small piece of kid under the knot. When I first made
this experiment, not having taken these precautions, it did not
succeed well, owing to air getting in through the hole.) I now
drop it on this stone weight, and so heavily is it pressed down
upon it by the atmosphere that I can lift the weight without its
breaking away from it.
Have you ever tried to pick limpets off a rock? If so, you know
how tight they cling. the limpet clings to the rock just in the
same way as this leather does to the stone; the little animal
exhausts the air inside it's shell, and then it is pressed
against the rock by the whole weight of the air above.
Perhaps you will wonder how it is that if we have a weight of 15
lbs. pressing on every square inch of our bodies, it does not
crush us. And, indeed, it amounts on the whole to a weight of
about 15 tons upon the body of a grown man. It would crush us if
it were not that there are gases and fluids inside our bodies
which press outwards and balance the weight so that we do not
feel it at all.
This is why Mr. Glaisher's veins swelled and he grew giddy in
thin air. The gases and fluids inside his body were pressing
outwards as much as when he was below, but the air outside did
not press so heavily, and so all the natural condition of his
body was disturbed.
I hope we now realize how heavily the air presses down upon our
earth, but it is equally necessary to understand how, being
elastic, it also presses upwards; and we can prove this by a
simple experiment. I fill this tumbler with water, and keeping a
piece of card firmly pressed against it, I turn the whole upside-
down. When I now take my hand away you would naturally expect
the card to fall, and the water to be spilt. But no! the card
remains as if glued to the tumbler, kept there entirely by the
air pressing upwards against it. (The engraver has drawn the
tumbler only half full of water. The experiment will succeed
quite as well in this way if the tumbler be turned over quickly,
so that part of the air escapes between the tumbler and the card,
and therefore the space above the water is occupied by air less
dense than that outside.)
And now we are almost prepared to understand how we can weigh the
invisible air. One more experiment first. I have here what is
called a U tube, because it is shaped like a large U. I pour
some water in it till it is about half full, and you will notice
that the water stands at the same height in both arms of the
tube, because the air presses on both surfaces alike. Putting my
thumb on one end I tilt the tube carefully, so as to make the
water run up to the end of one arm, and then turn it back again.
But the water does not now return to its even position, it
remains up in the arm on which my thumb rests. Why is this?
Because my thumb keeps back the air from pressing at that end,
and the whole weight of the atmosphere rests on the water at the
other end. And so we learn that not only has the atmosphere real
weight, but we can see the effects of this weight by making it
balance a column of water or any other liquid. In the case of
the wetted leather we felt the weight of the air, here we see its
effects.
Now when we wish to see the weight of the air we consult a
barometer, which works really just in the same way as the water
in this tube. An ordinary upright barometer is simply a straight
tube of glass filled with mercury or quicksilver, and turned
upside-down in a small cup of mercury. The tube is a little more
than 30 inches long, and though it is quite full of mercury
before it is turned up, yet directly it stands in the cup the
mercury falls, till there is a height of about 30 inches between
the surface of the mercury in the cup, and that of the mercury in
the tube. As it falls it leaves an empty space above the mercury
which is called a vacuum, because it has no air in it. Now, the
mercury is under the same conditions as the water was in the U
tube, there is no pressure upon it at the top of the tube, while
there is a pressure of 15 lbs. upon it in the bowl, and therefore
it remains held up in the tube.
Week 9
But why will it not remain more than 30 inches high in the tube?
You must remember it is only kept up in the tube at all by the
air which presses on the mercury in the cup. And that column of
mercury now balances the pressure of the air outside, and presses
down on the mercury in the cup at its mouth just as much as the
air does on the rest. So this cup and tube act exactly like a
pair of scales. The air outside is the thing to be weighed at
one end as it presses on the mercury, the column answers to the
leaden weight at the other end which tells you how heavy the air
is. Now if the bore of this tube is made an inch square, then
the 30 inches of mercury in it weigh exactly 15 lbs, and so we
know that the weight of the air is 15 lbs. upon every square
inch, but if the bore of the tube is only half a square inch, and
therefore the 30 inches of mercury only weigh 7 1/2 lbs. instead
of 15 lbs., the pressure of the atmosphere will also be halved,
because it will only act upon half a square inch of surface, and
for this reason it will make no difference to the height of the
mercury whether the tube be broad or narrow.
But now suppose the atmosphere grows lighter, as it does when it
has much damp in it. The barometer will show this at once,
because there will be less weight on the mercury in the cup,
therefore it will not keep the mercury pushed so high up in the
tube. In other words, the mercury in the tube will fall.
Let us suppose that one day the air is so much lighter that it
presses down only with a weight of 14 1/2 lbs. to the square inch
instead of 15 lbs. Then the mercury would fall to 29 inches,
because each inch is equal to the weight of half a pound. Now,
when the air is damp and very full of water-vapour it is much
lighter, and so when the barometer falls we expect rain.
Sometimes, however, other causes make the air light, and then,
although the barometer is low, no rain comes,
Again, if the air becomes heavier the mercury is pushed up above
30 to 31 inches, and in this way we are able to weigh the
invisible air-ocean all over the world, and tell when it grows
lighter or heavier. This then, is the secret of the barometer.
We cannot speak of the thermometer today, but I should like to
warn you in passing that it has nothing to do with the weight of
the air, but only with heat, and acts in quite a different way.
And now we have been so long hunting out, testing and weighing
our aerial ocean, that scarcely any time is left us to speak of
its movements or the pleasant breezes which it makes for us in
our country walks. Did you ever try to run races on a very windy
day? Ah! then you feel the air strongly enough; how it beats
against your face and chest, and blows down your throat so as to
take your breath away; and what hard work it is to struggle
against it! Stop for a moment and rest, and ask yourself, what
is the wind? Why does it blow sometimes one way and sometimes
another, and sometimes not at all?
Wind is nothing more than air moving across the surface of the
earth, which as it passes along bends the tops of the trees,
beats against the houses, pushes the ships along by their sails,
turns the windmill, carries off the smoke from cities, whistles
through the keyhole, and moans as it rushes down the valley.
What makes the air restless? why should it not lie still all
round the earth?
It is restless because, as you will remember, its atoms are kept
pressed together near the earth by the weight of the air above,
and they take every opportunity, when they can find more room, to
spread out violently and rush into the vacant space, and this
rush we call a wind.
Imagine a great number of active schoolboys all crowded into a
room till they can scarcely move their arms and legs for the
crush, and then suppose all at once a large door is opened. Will
they not all come tumbling out pell-mell, one over the other,
into the hall beyond, so that if you stood in their way you would
most likely be knocked down? Well, just this happens to the air-
atoms; when they find a space before them into which they can
rush, they come on helter-skelter, with such force that you have
great difficulty in standing against them, and catch hold of
something to support you for fear you should be blown down.
But how come they to find any empty space to receive them? To
answer this we must go back again to our little active invisible
fairies the sunbeams. When the sun-waves come pouring down upon
the earth they pass through the air almost without heating it.
But not so with the ground; there they pass down only a short
distance and then are thrown back again. And when these sun-
waves come quivering back they force the atoms of the air near
the earth apart and make it lighter; so that the air close to the
surface of the heated ground becomes less heavy than the air
above it, and rises just as a cork rises in water. You know that
hot air rises in the chimney; for if you put a piece of lighted
paper on the fire it is carried up by the draught of air, often
even before it can ignite. Now just as the hot air rises from
the fire, so it rises from the heated ground up into higher parts
of the atmosphere. and as it rises it leaves only thin air
behind it, and this cannot resist the strong cold air whose atoms
are struggling and trying to get free, and they rush in and fill
the space.
One of the simplest examples of wind is to be found at the
seaside. there in the daytime the land gets hot under the
sunshine, and heats the air, making it grow light and rise.
Meanwhile the sunshine on the water goes down deeper, and so does
not send back so many heat-waves into the air; consequently the
air on the top of the water is cooler and heavier, and it rushes
in from over the sea to fill up the space on the shore left by
the warm air as it rises. This is why the seaside is so pleasant
in hot weather. During the daytime a light sea-breeze nearly
always sets in from the sea to the land.
When night comes, however, then the land loses its heat very
quickly, because it has not stored it up and the land-air grows
cold; but the sea, which has been hoarding the sun-waves down in
its depths, now gives them up to the atmosphere above it, and the
sea-air becomes warm and rises. For this reason it is now the
turn of the cold air from the land to spread over the sea, and
you have a land-breeze blowing off the shore.
Again, the reason why there are such steady winds, called the
trade winds, blowing towards the equator, is that the sun is very
hot at the equator, and hot air is always rising there and making
room for colder air to rush in. We have not time to travel
farther with the moving air, though its journeys are extremely
interesting; but if, when you read about the trade and other
winds, you will always picture to yourselves warm air made light
by the heat rising up into space and cold air expanding and
rushing in to fill its place, I can promise you that you will not
find the study of aerial currents so dry as many people imagine
it to be.
We are now able to form some picture of our aerial ocean. We can
imagine the active atoms of oxygen floating in the sluggish
nitrogen, and being used up in every candle-flame, gas-jet and
fire, and in the breath of all living beings; and coming out
again tied fast to atoms of carbon and making carbonic acid.
Then we can turn to trees and plants, and see them tearing these
two apart again, holding the carbon fast and sending the
invisible atoms of oxygen bounding back again into the air, ready
to recommence work. We can picture all these air-atoms, whether
of oxygen or nitrogen, packed close together on the surface of
the earth, and lying gradually farther and farther apart, as they
have less weight above them, till they become so scattered that
we can only detect them as they rub against the flying meteors
which flash into light. We can feel this great weight of air
pressing the limpet on to the rock; and we can see it pressing up
the mercury in the barometer and so enabling us to measure its
weight. Lastly, every breath of wind that blows past us tells us
how this aerial ocean is always moving to and fro on the face of
the earth; and if we think for a moment how much bad air and bad
matter it must carry away, as it goes from crowded cities to be
purified in the country, we can see how, in even this one way
alone, it is a great blessing to us.
Yet even now we have not mentioned many of the beauties of our
atmosphere. It is the tiny particles floating in the air which
scatter the light of the sun so that it spreads over the whole
country and into shady places. The sun's rays always travel
straight forward; and in the moon, where there is no atmosphere,
there is no light anywhere except just where the rays fall. But
on our earth the sun-waves hit against the myriads of particles
in the air and glide off them into the corners of the room or the
recesses of a shady lane, and so we have light spread before us
wherever we walk in the daytime, instead of those deep black
shadows which we can see through a telescope on the face of the
moon.
Again, it is electricity playing in the air-atoms which gives us
the beautiful lightning and the grand aurora borealis, and even
the twinkling of the starts is produced entirely by minute
changes in the air. If it were not for our aerial ocean, the
stars would stare at us sternly, instead of smiling with the
pleasant twinkle-twinkle which we have all learned to love as
little children.
All these questions, however, we must leave for the present; only
I hope you will be eager to read about them wherever you can, and
open your eyes to learn their secrets. For the present we must
be content if we can even picture this wonderful ocean of gas
spread round our earth, and some of the work it does for us.
We said in the last lecture that without the sunbeams the earth
would be cold, dark, and frost-ridden. With sunbeams, but
without air, it would indeed have burning heat, side by side with
darkness and ice, but it could have no soft light. our planet
might look beautiful to others, as the moon does to us, but it
could have comparatively few beauties of its own. With the
sunbeams and the air, we see it has much to make it beautiful.
But a third worker is wanted before our planet can revel in
activity and life. This worker is water; and in the next lecture
we shall learn something of the beauty and the usefulness of the
"drops of water" on their travels.
Week 10
LECTURE IV. A DROP OF WATER ON ITS TRAVELS
We are going to spend an hour to-day in following a drop of water
on its travels. If I dip my finger in this basin of water and
lift it up again, I bring with it a small glistening
drop out of the body of water below, and hold it before you. Tell
me, have you any idea where this drop has been? what changes it
has undergone, and what work it has been doing during all the
long ages that water has lain on the face of the earth? It is a
drop now, but it was not so before I lifted it out of the basin;
then it was part of a sheet of water, and will be so again if I
let it fall. Again, if I were to put this basin on the stove till
all the water had boiled away, where would my drop be then? Where
would it go? What forms will it take before it reappears in the
rain-cloud, the river, or the sparkling dew?
These are questions we are going to try to answer to-day; and
first, before we can in the least understand how water travels,
we must call to mind what we have learnt about the sunbeams and
the air. We must have clearly pictured in our imagination those
countless sun-waves which are for ever crossing space, and
especially those larger and slower undulations, the dark heat-
waves; for it is these, you will remember, which force the air-
atoms apart and make the air light, and it is also these which
are most busy in sending water on its travels. But not these
alone. The sun-waves might shake the water-drops as much as they
liked and turn them into invisible vapour, but they could not
carry them over the earth if it were not for the winds and
currents of that aerial ocean which bears the vapour on its
bosom, and wafts it to different regions of the world.
Let us try to understand how these two invisible workers, the
sun-waves and the air, deal with the drops of water. I
have here a kettle (Fig. 18, p. 76) boiling over a spirit-lamp,
and I want you to follow minutely what is going on in it. First,
in the flame of the lamp, atoms of the spirit drawn up from below
are clashing with the oxygen-atoms in the air. This, as you know,
causes heat-waves and light-waves to move rapidly all round the
lamp. The light-waves cannot pass through the kettle, but the
heat-waves can, and as they enter the water inside they agitate
it violently. Quicker, and still more quickly, the particles of
water near the bottom of the kettle move to and fro and are
shaken apart; and as they become light they rise through the
colder water letting another layer come down to be heated in its
turn. The motion grows more and more violent, making the water
hotter and hotter, till at last the particles of which it is
composed fly asunder, and escape as invisible vapour. If this
kettle were transparent you would not see any steam above the
water, because it is in the form of an invisible gas. But as the
steam comes out of the mouth of the kettle you see a cloud. Why
is this? Because the vapour is chilled by coming out into the
cold air, and its particles are drawn together again into tiny,
tiny drops of water, to which Dr. Tyndall has given the
suggestive name of water-dust. If you hold a plate over the steam
you can catch these tiny drops, though they will run into one
another almost as you are catching them.
The clouds you see floating in the sky are made of exactly the
same kind of water-dust as the cloud from the kettle, and I wish
to show you that this is also really the same as the invisible
steam within the kettle. I will do so by an experiment
suggested by Dr. Tyndall. Here is another spirit-lamp, which I
will hold under the cloud of steam - see! the cloud disappears!
As soon as the water-dust is heated the heat-waves scatter it
again into invisible particles, which float away into the room.
Even without the spirit-lamp, you can convince yourself that
water-vapour may be invisible; for close to the mouth of the
kettle you will see a short blank space before the cloud begins.
In this space there must be steam, but it is still so hot that
you cannot see it; and this proves that heat-waves can so shake
water apart as to carry it away invisibly right before your eyes.
Now, although we never see any water travelling from our earth up
into the skies, we know that it goes there, for it comes down
again in rain, and so it must go up invisibly. But where does the
heat come from which makes this water invisible? Not from below,
as in the case of the kettle, but from above, pouring down from
the sun. Wherever the sun-waves touch the rivers, ponds, lakes,
seas, or fields of ice and snow upon our earth, they
carry off invisible water-vapour. They dart down through the top
layers of the water, and shake the water-particles forcibly
apart; and in this case the drops fly asunder more easily and
before they are so hot, because they are not kept down by a great
weight of water above, as in the kettle, but find plenty of room
to spread themselves out in the gaps between the air-atoms of the
atmosphere.
Can you imagine these water-particles, just above any pond or
lake, rising up and getting entangled among the air-atoms? They
are very light, much lighter than the atmosphere; and so, when a
great many of them are spread about in the air which lies just
over the pond, they make it much lighter than the layer of air
above, and so help it to rise, while the heavier layer of air
comes down ready to take up more vapour.
In this way the sun-waves and the air carry off water everyday,
and all day long, from the top of lakes, rivers, pools, springs,
and seas, and even from the surface of ice and snow. Without any
fuss or noise or sign of any kind, the water of our earth is
being drawn up invisibly into the sky.
It has been calculated that in the Indian Ocean three-quarters of
an inch of water is carried off from the surface of the sea in
one day and night; so that as much as 22 feet, or a depth of
water about twice the height of an ordinary room, is silently and
invisibly lifted up from the whole surface of the ocean in one
year. It is true this is one of the hottest parts of the earth,
where the sun-waves are most active; but even in our
own country many feet of water are drawn up in the summer-time.
What, then, becomes of all this water? Let us follow it as it
struggles upwards to the sky. We see it in our imagination first
carrying layer after layer of air up with it from the sea till it
rises far above our heads and above the highest mountains. But
now, call to mind what happens to the air as it recedes from the
earth. Do you not remember that the air-atoms are always trying
to fly apart, and are only kept pressed together by the weight of
air above them? Well, so this water-laden air rises up, its
particles, no longer so much pressed together, begin to separate,
and as all work requires an expenditure of heat, the air becomes
colder, and then you know at once what must happen to the
invisible vapour, -- it will form into tiny water-drops, like the
steam from the kettle. And so, as the air rises and becomes
colder, the vapour gathers into the visible masses, and we can
see it hanging in the sky, and call it clouds. When these clouds
are highest they are about ten miles from the earth, but when
they are made of heavy drops and hang low down, they sometimes
come within a mile of the ground.
Look up at the clouds as you go home, and think that the water of
which they are made has all been drawn up invisibly through the
air. Not, however, necessarily here in London, for we have
already seen that air travels as wind all over the world, rushing
in to fill spaces made by rising air wherever they occur, and so
these clouds may be made of vapour collected in the
Mediterranean, or in the Gulf of Mexico off the coast of America,
or even, if the wind is from the north, of chilly
particles gathered from the surface of Greenland ice and snow,
and brought here by the moving currents of air. Only, of one
thing we may be sure, that they come from the water of our earth.
Sometimes, if the air is warm, these water-particles may travel a
long way without ever forming into clouds; and on a hot,
cloudless day the air is often very full of invisible vapour.
Then, if a cold wind comes sweeping along, high up in the sky,
and chills this vapour, it forms into great bodies of water-dust
clouds, and the sky is overcast. At other times clouds hang
lazily in a bright sky, and these show us that just where they
are (as in Fig. 19) the air is cold and turns the invisible
vapour rising from the ground into visible water-dust, so that
exactly in those spaces we see it as clouds. Such clouds form
often on warm, still summer's day, and they are shaped like
masses of wool, ending in a straight line below. They are not
merely hanging in the sky, they are really resting upon a tall
column of invisible vapour which stretches right up from the
earth; and that straight line under the clouds marks
the place where the air becomes cold enough to turn this
invisible vapour into visible drops of water.
Week 11
And now, suppose that while these or any other kind of clouds are
overhead, there comes along either a very cold wind, or a wind
full of vapour. As it passes through the clouds, it makes them
very full of water, for, if it chills them, it makes the water-
dust draw more closely together; or, if it brings a new load of
water-dust, the air is fuller than it can hold. In either case a
number of water-particles are set free, and our fairy force
"cohesion" seizes upon them at once and forms them into large
water-drops. Then they are much heavier than the air, and so they
can float no longer, but down they come to the earth in a shower
of rain.
There are other ways in which the air may be chilled, and rain
made to fall, as, for example, when a wind laden with moisture
strikes against the cold tops of mountains. Thus the Khasia Hills
in India which face the Bay of Bengal, chill the air which
crosses them on its way from the Indian Ocean. The wet winds are
driven up the sides of the hills, the air expands, and the vapour
is chilled, and forming into drops, falls in torrents of rain.
Sir J. Hooker tells us that as much as 500 inches of rain fell in
these hills in nine months. That is to say, if you could measure
off all the ground over which the rain fell, and spread the whole
nine months' rain over it, it would make a lake 500 inches, or
more than 40 feet deep! You will not be surprised that the
country on the other side of these hills gets hardly any rain,
for all the water has been taken out of the air before
it comes there. Again for example in England, the wind comes to
Cumberland and Westmorland over the Atlantic, full of vapour, and
as it strikes against the Pennine Hills it shakes off its watery
load; so that the lake district is the most rainy in England,
with the exception perhaps of Wales, where the high mountains
have the same effect.
In this way, from different causes, the water of which the sun
has robbed our rivers and seas, comes back to us, after it has
travelled to various parts of the world, floating on the bosom of
the air. But it does not always fall straight back into the
rivers and seas again, a large part of it falls on the land, and
has to trickle down slopes and into the earth, in order to get
back to its natural home, and it is often caught on its way
before it can reach the great waters.
Go to any piece of ground which is left wild and untouched you
will find it covered with grass weeds, and other plants; if you
dig up a small plot you will find innumerable tiny roots creeping
through the ground in every direction. Each of these roots has a
sponge-like mouth by which the plant takes up water. Now, imagine
rain-drops falling on this plot of ground and sinking into the
earth. On every side they will find rootlets thirsting to drink
them in, and they will be sucked up as if by tiny sponges, and
drawn into the plants, and up the stems to the leaves. Here, as
we shall see in Lecture VII., they are worked up into food for
the plant, and only if the leaf has more water than it needs,
some drops may escape at the tiny openings under the
leaf, and be drawn up again by the sun-waves as invisible vapour
into the air.
Again, much of the rain falls on hard rock and stone, where it
cannot sink in, and then it lies in pools till it is shaken apart
again into vapour and carried off in the air. Nor is it idle
here, even before it is carried up to make clouds. We have to
thank this invisible vapour in the air for protecting us from the
burning heat of the sun by day and intolerable frost by night.
Let us for a moment imagine that we can see all that we know
exists between us and the sun. First, we have the fine ether
across which the sunbeams travel, beating down upon our earth
with immense force, so that in the sandy desert they are like a
burning fire. Then we have the coarser atmosphere of oxygen and
nitrogen atoms hanging in this ether, and bending the minute sun-
waves out of their direct path. But they do very little to hinder
them on their way, and this is why in very dry countries the
sun's heat is so intense. The rays beat down mercilessly, and
nothing opposes them. Lastly, in damp countries we have the
larger but still invisible particles of vapour hanging about
among the air-atoms. Now, these watery particles, although they
are very few (only about one twenty-fifth part of the whole
atmosphere), do hinder the sun-waves. For they are very greedy of
heat, and though the light-waves pass easily through them, they
catch the heat-waves and use them to help themselves to expand.
And so, when there is invisible vapour in the air, the sunbeams
come to us deprived of some of their heat-waves, and we
can remain in the sunshine without suffering from the heat.
This is how the water-vapour shields us by day, but by night it
is still more useful. During the day our earth and the air near
it have been storing up the heat which has been poured down on
them, and at night, when the sun goes down, all this heat begins
to escape again. Now, if there were no vapour in the air, this
heat would rush back into space so rapidly that the ground would
become cold and frozen even on a summer's night, and all but the
most hardy plants would die. But the vapour which formed a veil
against the sun in the day, now forms a still more powerful veil
against the escape of the heat by night. It shuts in the heat-
waves, and only allows them to make their way slowly upwards from
the earth - thus producing for us the soft, balmy nights of
summer and preventing all life being destroyed in the winter.
Perhaps you would scarcely imagine at first that it is this screen
of vapour which determines whether or not we shall have dew upon
the ground. Have you ever thought why dew forms, or what power has
been at work scattering the sparkling drops upon the grass?
Picture to yourself that it has been a very hot summer's day, and
the ground and the grass have been well warmed, and that the sun
goes down in a clear sky without any clouds. At once the heat-
waves which have been stored up in the ground, bound back into the
air, and here some are greedily absorbed by the vapour, while
others make their way slowly upwards. The grass, especially, gives
out these heat-waves very quickly, because the blades, being very
thin, are almost all surface. In consequence of this they part
with their heat more quickly than they can draw it up from the
ground, and become cold. Now the air lying just above the grass is
full of invisible vapour, and the cold of the blades, as it
touches them, chills the water- particles, and they are no longer
able to hold apart, but are drawn together into drops on the
surface of the leaves.
We can easily make artificial dew for ourselves. I have here a
bottle of ice which has been kept outside the window. When I
bring it into the warm room a mist forms rapidly outside the
bottle. This mist is composed of water-drops, drawn out of the
air of the room, because the cold glass chilled the air all round
it, so that it gave up its invisible water to form dew-drops.
Just in this same way the cold blades of grass chill the air
lying above them, and steal its vapour.
But try the experiment, some night when a heavy dew is expected,
of spreading a thin piece of muslin over some part of the grass,
supporting it at the four corners with pieces of stick so that it
forms an awning. Though there may be plenty of dew on the grass
all round, yet under this awning you will find scarcely any. The
reason of this is that the muslin checks the heat-waves as they
rise from the grass, and so the grass-blades are not chilled
enough to draw together the water-drops on their surface. If you
walk out early in the summer mornings and look at the fine cobwebs
flung across the hedges, you will see plenty of drops on the
cobwebs themselves sparkling like diamonds; but underneath on the
leaves there will be none, for even the delicate cobweb has been
strong enough to shut in the heat-waves and keep the leaves warm.
Again, if you walk off the grass on to the gravel path, you find
no dew there. Why is this? Because the stones of the gravel can
draw up heat from the earth below as fast as they give it out,
and so they are never cold enough to chill the air which touches
them. On a cloudy night also you will often find little or no dew
even on the grass. The reason of this is that the clouds give
back heat to the earth, and so the grass does not become chilled
enough to draw the water-drops together on its surface. But after
a hot, dry day, when the plants are thirsty and there is little
hope of rain to refresh them, then they are able in the evening
to draw the little drops from the air and drink them in before
the rising sun comes again to carry them away.
But our rain-drop undergoes other changes more strange than
these. Till now we have been imagining it to travel only where
the temperature is moderate enough for it to remain in a liquid
state as water. But suppose that when it is drawn up into the air
it meets with such a cold blast as to bring it to the freezing
point. If it falls into this blast when it is already a drop,
then it will freeze into a hailstone, and often on a hot summer's
day we may have a severe hailstorm, because the rain-drops have
crossed a bitterly cold wind as they were falling, and have been
frozen into round drops of ice.
But if the water-vapour reaches the freezing air while it is still
an invisible gas, and before it has been drawn into a drop, then
its history is very different. The ordinary force of cohesion has
then no power over the particles to make them into watery globes,
but its place is taken by the fairy process of "crystallization,"
and they are formed into beautiful white flakes, to fall in a
snow-shower. I want you to picture this process to yourselves, for
if once you can take an interest in the wonderful power of nature
to build up crystals, you will be astonished how often you will
meet with instances of it, and what pleasure it will add to your
life.
The particles of nearly all substances, when left free and not
hurried, can build themselves into crystal forms. If you melt
salt in water and then let all the water evaporate slowly, you
will get salt-crystals; -- beautiful cubes of transparent salt
all built on the same pattern. The same is true of sugar; and if
you will look at the spikes of an ordinary stick of sugar-candy,
such as I have here, you will see the kind of crystals which
sugar forms. You may even pick out such shapes as these
from the common crystallized brown sugar in the sugar basin, or
see them with a magnifying glass on a lump of white sugar.
But it is not only easily melted substances such as sugar and
salt which form crystals. The beautiful stalactite grottos are
all made of crystals of lime. Diamonds are crystals of carbon,
made inside the earth. Rock-crystals, which you know probably
under the name of Irish diamonds, are crystallized quartz; and
so, with slightly different colourings, are agates, opals,
jasper, onyx, cairngorms, and many other precious stones. Iron,
copper, gold, and sulphur, when melted and cooled slowly build
themselves into crystals, each of their own peculiar form, and we
see that there is here a wonderful order, such as we should never
have dreamt of, if we had not proved it. If you possess a
microscope you may watch the growth of crystals yourself by
melting some common powdered nitre in a little water till you
find that no more will melt in it. Then put a few drops of this
water on a warm glass slide and place it under the microscope. As
the drops dry you will see the long transparent needles of nitre
forming on the glass, and notice how regularly these crystals
grow, not by taking food inside like living beings, but by adding
particle to particle on the outside evenly and regularly.
Week 12
Can we form any idea why the crystals build themselves up so
systematically? Dr. Tyndall says we can, and I hope by the help
of these small bar magnets to show you how he explains it. These
little pieces of steel, which I hope you can see lying
on this white cardboard, have been rubbed along a magnet until
they have become magnets themselves, and I can attract and lift
up a needle with any one of them. But if I try to lift one bar
with another, I can only do it by bringing certain ends together.
I have tied a piece of red cotton (c, Fig. 21) round one end of
each of the magnets, and if I bring two red ends together they
will not cling together but roll apart. If, on the contrary, I
put a red end against an end where there is not cotton, then the
two bars cling together. This is because every magnet has two
poles or points which are exactly opposite in character, and to
distinguish them one is called the positive pole and the other
the negative pole. Now when I bring two red ends, that is, two
positive poles together, they drive each other away. See! the
magnet I am not holding runs away from the other. But if I bring
a red end and a black end, that is, a positive and a negative end
together, then they are attracted and cling. I will make a
triangle (A, Fig. 21) in which a black end and a red end always
come together, and you see the triangle holds together. But now if
I take off the lower bar and turn it (B, Fig. 21) so that two red
ends and two black ends come together, then this bar actually
rolls back from the others down the cardboard. If I were to break
these bars into a thousand pieces, each piece would still have two
poles, and if they were scattered about near each other in such a
way that they were quite free to move, they would arrange
themselves always so two different poles came together.
Now picture to yourselves that all the particles of those
substances which form crystals have poles like our magnets, then
you can imagine that when the heat which held them apart is
withdrawn and the particles come very near together, they will
arrange themselves according to the attraction of their poles and
so build up regular and beautiful patterns.
So, if we could travel up to the clouds where this fairy power of
crystallization is at work, we should find the particles of
water-vapour in a freezing atmosphere being built up into minute
solid crystals of snow. If you go out after a snow-shower and
search carefully, you will see that the snow-flakes are not mere
lumps of frozen water, but beautiful six-pointed crystal stars, so
white and pure that when we want to speak of anything being
spotlessly white, you say that it is "white as snow." Some of
these crystals are simply flat slabs with six sides, others are
stars with six rods or spikes springing from the centre, others
with six spikes each formed like a delicate fern. No less than a
thousand different forms of delicate crystals have been found
among snowflakes, but though there is such a great variety, yet
they are all built on the six-sided and six-pointed plan, and are
all rendered dazzlingly white by the reflection of the light from
the faces of the crystals and the tiny air-bubbles built up within
them. This, you see, is why, when the snow melts, you have only a
little dirty water in your hand; the crystals are gone and there
are no more air-bubbles held prisoners to act as looking-glasses
to the light. Hoar-frost is also made up of tiny water-crystals,
and is nothing more than frozen dew hanging on the blades of grass
and from the trees.
But how about ice? Here, you will say, is frozen water, and yet
we see no crystals, only a clear transparent mass. Here, again,
Dr. Tyndall helps us. He says (and as I have proved it true, so
may you for yourselves, if you will) that if you take a
magnifying glass, and look down on the surface of ice on a sunny
day, you will see a number of dark, six-sided stars, looking like
flattened flowers, and in the centre of each a bright spot. These
flowers, which are seen when the ice is melting, are our old
friends the crystal stars turning into water, and the
bright spot in the middle is a bubble of empty space, left
because the watery flower does not fill up as much room as the
ice of the crystal star did.
And this leads us to notice that ice always takes up more room
than water, and that this is the reason why our water-pipes burst
in severe frosts; for as the water freezes it expands with great
force, and the pipe is cracked, and then when the thaw comes on ,
and the water melts again, it pours through the crack it has
made.
It is not difficult to understand why ice should take more room;
for we know that if we were to try to arrange bricks end to end
in star-like shapes, we must leave some spaces between, and could
not pack them so closely as if they lay side by side. And so,
when this giant force of crystallization constrains the atoms of
frozen water to grow into star-like forms, the solid mass must
fill more room than the liquid water, and when the star
melts, this space reveals itself to us in the bright spot of the
centre.
We have now seen our drop of water under all its various forms of
invisible gas, visible steam, cloud, dew, hoar-frost, snow, and
ice, and we have only time shortly to see it on its travels, not
merely up and down, as hitherto, but round the world.
We must first go to the sea as the distillery, or the place from
which water is drawn up invisibly, in its purest state, into the
air; and we must go chiefly to the seas of the tropics, because
here the sun shines most directly all the year round, sending
heat-waves to shake the water-particles asunder. It has been
found by experiment that, in order to turn 1 lb. of water into
vapour, as much heat must be used as is required to melt 5 lbs.
of iron; and if you consider for a moment how difficult iron is
to melt, and how we can keep an iron poker in a hot fire and yet
it remains solid, this will help you to realize how much heat the
sun must pour down in order to carry off such a constant supply
of vapour from the tropical seas.
Now, when all this vapour is drawn up into the air, we know that
some of it will form into clouds as it gets chilled high up in
the sky, and then it will pour down again in those tremendous
floods of rain which occur in the tropics.
But the sun and air will not let it all fall down at once, and
the winds which are blowing from the equator to the poles carry
large masses of it away with them. Then, as you know, it will
depend on many things how far this vapour is carried. Some of it,
chilled by cold blasts, or by striking on cold mountain tops, as
it travels northwards, will fall in rain in Europe and Asia, while
that which travels southwards may fall in South America,
Australia, or New Zealand, or be carried over the sea to the South
Pole. Wherever it falls on the land as rain, and is not used by
plants, it will do one of two things; either it will run down in
streams and form brooks and rivers, and so at last find its way
back to the sea, or it will sink deep in the earth till it comes
upon some hard rock through which it cannot get, and then, being
hard pressed by the water coming on behind, it will rise up again
through cracks, and come to the surface as a spring. These
springs, again, feed rivers, sometimes above- ground, sometimes
for long distances under-ground; but one way or another at last
the whole drains back into the sea.
But if the vapour travels on till it reaches high mountains in
cooler lands, such as the Alps of Switzerland; or is carried to
the poles and to such countries as Greenland or the Antarctic
Continent, then it will come down as snow, forming immense snow-
fields. And here a curious change takes place in it. If you make
an ordinary snowball and work it firmly together, it becomes very
hard, and if you then press it forcibly into a mould you can turn
it into transparent ice. And in the same way the snow which falls
in Greenland and on the high mountains of Switzerland becomes
very firmly pressed together, as it slides down into the valleys.
It is like a crowd of people passing from a broad thoroughfare
into a narrow street. As the valley grows narrower and
narrower the great mass of snow in front cannot move down
quickly, while more and more is piled up by the snowfall behind,
and the crowd and crush grow denser and denser. In this way the
snow is pressed together till the air that was hidden in its
crystals, and which gave it its beautiful whiteness, is all
pressed out, and the snow-crystals themselves are squeezed into
one solid mass of pure, transparent ice.
Then we have what is called a "glacier," or river of ice, and
this solid river comes creeping down till, in Greenland, it
reaches the edge of the sea. There it is pushed over the brink of
the land, and large pieces snap off, and we have "icebergs."
These icebergs - made, remember, of the same water which was
first draw up from the tropics - float on the wide sea, and
melting in its warm currents, topple over and over* (A floating
iceberg must have about eight times as much ice under the water
as it has above, and therefore, when the lower part melts in a
warm current, the iceberg loses its balance and tilts over, so as
to rearrange itself round the centre of gravity.) till they
disappear and mix with the water, to be carried back again to the
warm ocean from which they first started. In Switzerland the
glaciers cannot reach the sea, but they move down into the
valleys till they come to a warmer region, and there the end of
the glacier melts, and flows away in a stream. The Rhone and many
other rivers are fed by the glaciers of the Alps; and as these
rivers flow into the sea, our drop of water again finds its way
back to its home.
But when it joins itself in this way to its companions, from whom
it was parted for a time, does it come back clear and transparent
as it left them? From the iceberg it does indeed return pure and
clear; for the fairy Crystallization will have no impurities, not
even salt, in her ice-crystals, and so as they melt they give back
nothing but pure water to the sea. Yet even icebergs bring down
earth and stones frozen into the bottom of the ice, and so they
feed the sea with mud.
But the drops of water in rivers are by no means as pure as when
they rose up into the sky. We shall see in the next lecture how
rivers carry down not only sand and mud all along their course,
but even solid matter such as salt, lime, iron, and flint,
dissolved in the clear water, just as sugar is dissolved, without
our being able to see it. The water, too, which has sunk down
into the earth, takes up much matter as it travels along. You all
know that the water you drink from a spring is very different
from rain-water, and you will often find a hard crust at the
bottom of kettles and in boilers, which is formed of the
carbonate of lime which is driven out of the clear water when it
is boiled. The water has become "hard" in consequence of having
picked up and dissolved the carbonate of lime on its way through
the earth, just in the same way as water would become sweet if
you poured it through a sugar-cask. You will also have heard of
iron-springs, sulphur-springs, and salt-springs, which come out
of the earth, even if you have never tasted any of them, and the
water of all these springs finds its way back at last to the
sea.
And now, can you understand why sea-water should taste
salt and bitter? Every drop of water which flows from the earth
to the sea carries something with it. Generally, there is so
little of any substance in the water that we cannot taste it, and
we call it pure water; but the purest of spring or river-water
has always some solid matter dissolved in it, and all this goes
to the sea. Now, when the sun-waves come to take the water out of
the sea again, they will have nothing but the pure water itself;
and so all these salts and carbonates and other solid substances
are left behind, and we taste them in sea-water.
Some day, when you are at the seaside, take some extra water and
set it on the hob till a great deal has simmered gently away, and
the liquid is very thick. Then take a drop of this liquid, and
examine it under a microscope. As it dries up gradually, you will
see a number of crystals forming, some square - and these will be
crystals of ordinary salt; some oblong - these will be crystals
of gypsum or alabaster; and others of various shapes. Then, when
you see how much matter from the land is contained in sea-water,
you will no longer wonder that the sea is salt; on the contrary,
you will ask, Why does it not grow salter every year?
The answer to this scarcely belongs to our history of a drop of
water, but I must just suggest it to you. In the sea are numbers
of soft-bodied animals, like the jelly animals which form the
coral, which require hard material for their shells or the solid
branches on which they live, and they are greedily watching for
these atoms of lime, of flint, or magnesia, and of other
substances brought down into the sea. It is with lime and magnesia
that the tiny chalk-builders form their beautiful shells, and the
coral animals their skeletons, while another class of builders use
the flint; and when these creatures die, their remains go to form
fresh land at the bottom of the sea; and so, though the earth is
being washed away by the rivers and springs it is being built up
again, out of the same materials, in the depths of the great
ocean.
And now we have reached the end of the travels of our drop of
water. We have seen it drawn up by the fairy "heat," invisible
into the sky; there fairy "cohesion" seized it and formed it into
water-drops and the giant, "gravitation," pulled it down again to
the earth. Or, if it rose to freezing regions, the fairy of
"crystallization" built it up into snow-crystals, again to fall
to the earth, and either to be melted back into water by heat, or
to slide down the valleys by force of gravitation, till it became
squeezed into ice. We have detected it, when invisible, forming a
veil round our earth, and keeping off the intense heat of the
sun's rays by day, or shutting it in by night. We have seen it
chilled by the blades of grass, forming sparkling dew-drops or
crystals of hoar-frost, glistening in the early morning sun; and
we have seen it in the dark underground, being drunk up greedily
by the roots of plants. We have started with it from the tropics,
and travelled over land and sea, watching it forming rivers, or
flowing underground in springs, or moving onwards to the high
mountains or the poles, and coming back again in glaciers and
icebergs. Through all this, while it is being carried
hither and thither by invisible power, we find no trace of its
becoming worn out, or likely to rest from its labours. Ever
onwards it goes, up and down, and round and round the world,
taking many forms, and performing many wonderful feats. We have
seen some of the work that it does, in refreshing the air,
feeding the plants, giving us clear, sparkling water to drink,
and carrying matter to the sea; but besides this, it does a
wonderful work in altering all the face of our earth. This work
we shall consider in the next lecture, on "The two great
Sculptors - Water and Ice."
Week 13
LECTURE V. THE TWO GREAT SCULPTORS - WATER AND ICE.
In our last lecture we saw that water can exist in three forms:--
1st, as an invisible vapour; 2nd, as liquid water; 3rd, as solid
snow and ice.
To-day we are going to take the two last of these
forms, water and ice, and speak of them as sculptors.
To understand why they deserve this name we must first consider
what the work of a sculptor is. If you go into a statuary yard
you will find there large blocks of granite, marble, and other
kinds of stone, hewn roughly into different shapes; but if you
pass into the studio, where the sculptor himself is at work you
will find beautiful statues, more or less finished; and you will
see that out of rough blocks of stone he has been able to cut
images which look like living forms. You can even see by their
faces whether they are intended to be sad, or thoughtful, or
gay, and by their attitude whether they are writhing in pain,
or dancing with joy, or resting peacefully. How has all this
history been worked out from the shapeless stone? It has been
done by the sculptor's chisel. A piece chipped off here, a
wrinkle cut there, a smooth surface rounded off in another place,
so as to give a gentle curve; all these touches gradually shape
the figure and mould it out of the rough stone, first into a
rude shape and afterwards, by delicate strokes, into the form of
a living being.
Now, just in the same way as the wrinkles and curves of a statue
are cut by the sculptor's chisel, so the hills and valleys, the
steep slopes and gentle curves on the face of our earth, giving
it all its beauty, and the varied landscapes we love so well,
have been cut out by water and ice passing over them. It is true
that some of the greater wrinkles of the earth, the lofty
mountains, and the high masses of land which rise above the sea ,
have been caused by earthquakes and shrinking of the
earth. We shall not speak of these to-day, but put them aside as
belonging to the rough work of the statuary yard. But when once
these large masses are put ready for water to work upon, then
all the rest of the rugged wrinkles and gentle slopes which make
the country so beautiful are due to water and ice, and for this
reason I have called them "sculptors."
Go for a walk in the country, or notice the landscape as you
travel on a railway journey. You pass by hills and through
valleys, through narrow steep gorges cut in hard rock, or
through wild ravines up the sides of which you can hardly
scramble. Then you come to grassy slopes and to smooth plains
across which you can look for miles without seeing a hill; or,
when you arrive at the seashore, you clamber into caves and
grottos, and along dark narrow passages leading from one bay to
another. All these - hills, valleys, gorges, ravines, slopes,
plains, caves, grottos, and rocky shores - have been cut out by
the water. Day by day and year by year, while everything seems
to us to remain the same, this industrious sculptor is chipping
away, a few grains here, a corner there, a large mass in another
place, till he gives to the country its own peculiar scenery,
just as the human sculptor gives expression to his statue.
Our work to-day will consist in trying to form some idea of the
way in which water thus carves out the surface of the earth, and
we will begin by seeing how much can be done by our old friends
the rain-drops before they become running streams.
Everyone must have noticed that whenever rain falls on soft
ground it makes small round holes in which it
collects, and then sinks into the ground, forcing its way
between the grains of earth. But you would hardly think that the
beautiful pillars in Fig. 24 have been made entirely in this way
by rain beating upon and soaking into the ground.
Where these pillars stand there was once a solid mass of clay and
stones, into which the rain-drops crept, loosening the earthly
particles; and then when the sun dried the earth again cracks
were formed, so that the next shower loosened it still more, and
carried some of the mud down into the valley below. But here and
there large stones were buried in the clay, and where this
happened the rain could not penetrate, and the stones
became the tops of tall pillars of clay, washed into shape by the
rain beating on its sides, but escaping the general destruction
of the rest of the mud. In this way the whole valley has been
carved out into fine pillars, some still having capping-stones,
while others have lost them, and these last will soon be washed
away. We have no such valleys of earth-pillars here in England,
but you may sometimes see tiny pillars under bridges where the
drippings have washed away the earth between the pebbles, and
such small examples which you can observe for yourselves are
quite as instructive as more important ones.
Another way in which rain changes the surface of the earth is by
sinking down through loose soil from the top of a cliff to a
depth of many feet till it comes to solid rock, and then lying
spread over a wide apace. Here it makes a kind of watery mud,
which is a very unsafe foundation for the hill of earth above
it, and so after a time the whole mass slips down and makes a
fresh piece of land at the foot of the cliff. If you have ever
been at the Isle of Wight you will have seen an undulating strip
of ground, called the Undercliff, at Ventnor and other places,
stretching all along the sea below the high cliffs. This land
was once at the top of the cliff, and came down by succession of
landslips such as we have been describing. A very great landslip
of this kind happened in the memory of living people, at Lyme
Regis, in Dorsetshire, in the year 1839.
You will easily see how in forming earth-pillars and causing
landslips rain changes the face of the country, but
these are only rare effects of water. It is when the rain
collects in brooks and forms rivers that it is most busy in
sculpturing the land. Look out some day into the road or the
garden where the ground slopes a little, and watch what happens
during a shower of rain. First the rain-drops run together in
every little hollow of the ground, then the water begins to flow
along any ruts or channels it can find, lying here and there in
pools, but always making its way gradually down the slope.
Meanwhile from other parts of the ground little rills are
coming, and these all meet in some larger ruts where the ground
is lowest, making one great stream, which at last empties itself
into the gutter or an area, or finds its way down some grating.
Now just this, which we can watch whenever a heavy shower of rain
comes down on the road, happens also all over the world. Up in
the mountains, where there is always a great deal of rain,
little rills gather and fall over the mountain sides, meeting in
some stream below. Then, as this stream flows on, it is fed by
many runnels of water, which come from all parts of the country,
trickling along ruts, and flowing in small brooks and rivulets
down the gentle slope of the land till they reach the big stream,
which at last is important enough to be called a river.
Sometimes this river comes to a large hollow in the land and
there the water gathers and forms a lake; but still at the lower
end of this lake out it comes again, forming a new river, and
growing and growing by receiving fresh streams until at last it
reaches the sea.
The River Thames, which you all know, and whose course you will
find clearly described in Mr. Huxley's 'Physiography,' drains in
this way no less than one-seventh of the whole of England. All the
rain which falls in Berkshire, Oxfordshire, Middlesex,
Hertfordshire, Surrey, the north of Wiltshire and north-west of
Kent, the south of Buckinghamshire and of Gloucestershire, finds
its way into the Thames; making an area of 6160 square miles over
which every rivulet and brook trickle down to the one great river,
which bears them to the ocean. And so with every other area of
land in the world there is some one channel towards which the
ground on all sides slopes gently down, and into this channel all
the water will run, on its way to the sea.
But what has this to do with sculpture or cutting out of valleys?
If you will only take a glass of water out of any river, and let
it stand for some hours, you will soon answer this question for
yourself. For you will find that even from river water which
looks quite clear, a thin layer of mud will fall to the bottom
of the glass, and if you take the water when the river is
swollen and muddy you will get quite a thick deposit. This shows
that the brooks, the streams, and the rivers wash away the land
as they flow over it and carry it from the mountains down to the
valleys, and from the valleys away out into the sea.
But besides earthly matter, which we can see, there is much
matter dissolved in the water of rivers (as we mentioned in the
last lecture), and this we cannot see.
If you use water which comes out of a chalk country you will find
that after a time the kettle in which you have been in the habit
of boiling this water has a hard crust on its bottom and sides,
and this crust is made of chalk or carbonate of lime,
which the water took out of the rocks when it was passing
through them. Professor Bischoff has calculated that the river
Rhine carries past Bonn every year enough carbonate of lime
dissolved in its water to make 332,000 million oyster-shells,
and that if all these shells were built into a cube it would
measure 560 feet.
Week 14
Imagine to yourselves the whole of St. Paul's churchyard filled
with oyster-shells, built up in a large square till they reached
half as high again as the top of the cathedral, then you will
have some idea of the amount of chalk carried invisibly past
Bonn in the water of the Rhine every year.
Since all this matter, whether brought down as mud or dissolved,
comes from one part of the land to be carried elsewhere or out
to sea, it is clear that some gaps and hollows must be left in
the places from which it is taken. Let us see how these gaps are
made. Have you ever clambered up the mountainside, or even up
one of those small ravines in the hillside, which have generally
a little stream trickling through them? If so, you must have
noticed the number of pebbles, large and small, lying in patches
here and there in the stream, and many pieces of broken rock,
which are often scattered along the sides of the ravine; and
how, as you climb, the path grows steeper, and the rocks become
rugged and stick out in strange shapes.
The history of this ravine will tell us a great deal about the
carving of water. Once it was nothing more than a little furrow
in the hillside down which the rain found its way in a thin
thread-like stream. But by and by, as the stream carried down
some of the earth, and the furrow grew deeper and wider, the sides
began to crumble when the sun dried up the rain which had soaked
in. Then in winter, when the sides of the hill were moist with the
autumn rains, frost came and turned the water to ice, and so made
the cracks still larger, and the swollen steam rushing down,
caught the loose pieces of rock and washed them down into its bed.
Here they were rolled over and over, and grated against each
other, and were ground away till they became rounded pebbles, such
as lie in the foreground of the picture (Fig. 25); while the grit
which was rubbed off them was carried farther down by the stream.
And so in time this became a little valley, and as the stream cut
it deeper and deeper, there was room to clamber along the sides of
it, and ferns and mosses began to cover the naked stone, and small
trees rooted themselves along the banks, and this beautiful little
nook sprang up on the hill-side entirely by the sculpturing of
water.
Shall you not feel a fresh interest in all the little valleys,
ravines, and gorges you meet with in the country, if you can
picture them being formed in this way year by year? There are
many curious differences in them which you can study for
yourselves. Some will be smooth, broad valleys and here the
rocks have been soft and easily worn, and water trickling down
the sides of the first valley has cut other channels so as to
make smaller valleys running across it. In other places there
will be narrow ravines, and here the rocks have been hard, so
that they did not wear away gradually, but broke off and fell in
blocks, leaving high cliffs on each side. In some places you
will come to a beautiful waterfall, where the water has tumbled
over a steep cliff, and then eaten its way back, just like a saw
cutting through a piece of wood.
There are two things in particular to notice in a waterfall like
this. First, how the water and spray dash against the bottom of
the cliff down which it falls, and grind the small pebbles
against the rock. In this way the bottom of the cliff is
undermined, and so great pieces tumble down from time to time,
and keep the fall upright instead of its being sloped away at the
top, and becoming a mere steam. Secondly, you may often see
curious cup-shaped holes, called "pot-holes," in the rocks on the
sides of a waterfall, and these also are concerned in its
formation. In these holes you will generally find two or three
small pebbles, and you have here a beautiful example of how water
uses stones to grind away the face of the earth. These holes are
made entirely by the falling water eddying round and round in a
small hollow of the rock, and grinding the pebbles which it has
brought down, against the bottom and sides of this hollow, just as
you grind round a pestle in a mortar. By degrees the hole grows
deeper and deeper and though the first pebbles are probably ground
down to powder, others fall in, and so in time there is a great
hole perforated right through, helping to make the rock break and
fall away.
In this and other ways the water works its way back in a
surprising manner. The Isle of Wight gives us some good
instances of this; Alum Bay Chine and the celebrated Blackgang
Chine have been entirely cut out by waterfalls. But the best
know and most remarkable example is the Niagara Falls, in
America. Here, the River Niagara first wanders through a flat
country, and then reaches the great Lake Erie in a hollow of the
plain. After that, it flows gently down for about fifteen miles,
and then the slope becomes greater and it rushes on to the Falls
of Niagara. These falls are not nearly so high as many people
imagine, being only 165 feet, or about half the height of St.
Paul's Cathedral, but they are 2700 feet or nearly half-a-mile
wide, and no less than 670,000 tons of water fall
over them every minute, making magnificent clouds of spray.
Sir Charles Lyell, when he was at Niagara, came to the conclusion
that, taking one year with another, these falls eat back the
cliff at the rate of about one foot a year, as you can easily
imagine they would do, when you think with what force the water
must dash against the bottom of the falls. In this way a deep
cleft has been cut right back from Queenstown for a distance of
seven miles, to the place where the falls are now. This helps us
a little to understand how very slowly and gradually
water cuts its way; for if a foot a year is about the average of
the waste of the rock, it will have taken more than thirty-five
thousand years for that channel of seven miles to be made.
But even this chasm cut by the falls of Niagara is nothing
compared with the canyons of Colarado. Canyon is a Spanish word
for a rocky gorge, and these gorges are indeed so grand, that if
we had not seen in other places what water can do, we should
never have been able to believe that it could have cut out these
gigantic chasms. For more than three hundred miles the River
Colorado, coming down from the Rocky Mountains, has eaten its way
through a country made of granite and hard beds of limestone and
sandstone, and it has cut down straight through these rocks,
leaving walls from half-a-mile to a mile high, standing straight
up from it. The cliffs of the Great Canyon, as it is called,
stretch up for more than a mile above the river which flows in
the gorge below! Fancy yourselves for a moment in a boat on this
river, as shown in Figure 27, and looking up at these gigantic
walls of rock towering above you. Even half-way up them, a man,
if he could get there, would be so small you could not see him
without a telescope; while the opening at the top between the
two walls would seem so narrow at such an immense distance that
the sky above would have the appearance of nothing more than a
narrow streak of blue. Yet these huge chasms have not been made
by any violent breaking apart of the rocks or convulsion of an
earthquake. No, they have been gradually, silently, and steadily
cut through by the river which now glides quietly in the wider
chasms, or rushes rapidly through the narrow gorges at their feet.
"No description," says Lieutenant Ives, one of the first
explorers of this river, "can convey the idea of the varied and
majestic grandeur of this peerless waterway. Wherever the river
turns, the entire panorama changes. Stately facades, august
cathedrals, amphitheatres, rotundas, castellated walls, and rows
of time-stained ruins, surmounted by every form of tower,
minaret, dome and spire, have been moulded from the cyclopean
masses of rock that form the mighty defile." Who will say, after
this, that water is not the grandest of all sculptors, as it
cuts through hundreds of miles of rock, forming such magnificent
granite groups, not only unsurpassed but unequalled by any of
the works of man?
But we must not look upon water only as a cutting instrument, for
it does more than merely carve out land in one place, it also
carries it away and lays it down elsewhere; and in this it is
more like a modeller in clay, who smooths off the material from
one part of his figure to put it upon another.
Running water is not only always carrying away mud, but at the
same time laying it down here and there wherever it flows. When
a torrent brings down stones and gravel from the mountains, it
will depend on the size and weight of the pieces how long they
will be in falling through the water. If you take a handful of
gravel and throw it into a glass full of water, you will notice
that the stones in it will fall to the bottom at once, the grit
and coarse sand will take longer in sinking, and lastly, the fine
sand will be an hour or two in settling down, so that the water
becomes clear. Now, suppose that this gravel were sinking in the
water of a river. The stones would be buoyed up as long as the
river was very full and flowed very quickly, but they would drop
through sooner than the coarse sand. The coarse sand in its turn
would begin to sink as the river flowed more slowly, and would
reach the bottom while the fine sand was still borne on. Lastly,
the fine sand would sink through very, very slowly, and only
settle in comparatively still water.
From this it will happen that stones will generally lie near to
the bottom of torrents at the foot of the banks from which they
fall, while the gravel will be carried on by the stream after it
leaves the mountains. This too, however, will be laid down when
the river comes into a more level country and runs more slowly.
Or it may be left together with the finer mud in a lake, as in
the lake of Geneva, into which the Rhone flows laden with mud
and comes out at the other end clear and pure. But if no lake
lies in the way the finer earth will still travel on, and the
river will take up more and more as it flows, till at last it
will leave this too on the plains across which it moves
sluggishly along, or will deposit it at its mouth when it joins
the sea.
Week 15
You all know the history of the Nile; how, when the rains fall
very heavily in March and April in the mountains of Abyssinia,
the river comes rushing down and brings with it a load of mud
which it spreads out over the Nile valley in Egypt. This annual
layer of mud is so thin that it takes a thousand years for it to
become 2 or 3 feet thick; but besides that which falls in the
valley a great deal is taken to the mouth of the river and there
forms new land, making what is called the "Delta" of the Nile.
Alexandria, Rosetta, and Damietta, are towns which are all built
on land made of Nile mud which was carried down ages and ages ago,
and which has now become firm and hard like the rest of the
country. You will easily remember other deltas mentioned in books,
and all these are made of the mud carried down from the land to
the sea. The delta of the Ganges and Brahmapootra in India, is
actually as large as the whole of England and Wales, (58,311
square miles.) and the River Mississippi in America drains such a
large tract of country that its delta grows, Mr. Geikie tells us,
at the rate of 86 yards in year.
All this new land laid down in Egypt, in India, in America, and
in other places, is the work of water. Even on the Thames you
may see mud-banks, as at Gravesend, which are made of earth
brought from the interior of England. But at the mouth of the
Thames the sea washes up very strongly every tide, and so it
carries most of the mud away and prevents a delta growing up
there. If you will look about when you are at the seaside, and
notice wherever a stream flows down into the sea, you may even
see little miniature deltas being formed there, though the sea
generally washes them away again in a few hours, unless the
place is well sheltered.
This, then, is what becomes of the earth carried down by rivers.
Either on plains, or in lakes, or in the sea, it falls down to
form new land. But what becomes of the dissolved chalk and other
substances? We have seen that a great deal of it is used by river
and sea animals to build their shells and skeletons, and some of
it is left on the surface of the ground by springs when the water
evaporates. It is this carbonate of lime which forms a hard crust
over anything upon which it may happen to be deposited, and then
these things are called "petrified."
But it is in the caves and hollows of the earth that this
dissolved matter is built up into the most beautiful forms. If
you have ever been to Buxton in Derbyshire, you will probably
have visited a cavern called Poole's Cavern, not far from there,
which when you enter it looks as if it were built up entirely of
rods of beautiful transparent white glass, hanging from the
ceiling, from the walls, or rising up from the floor. In this
cavern, and many others like it,*(See the picture at the head of
the lecture.) water comes dripping through the roof, and as it
falls carbonate of lime forms itself into a thin, white film on
the roof, often making a complete circle, and then, as the water
drips from it day by day, it goes on growing and growing till it
forms a long needle-shaped or tube-shaped rod, hanging like an
icicle. These rods are called stalactites, and they are so
beautiful, as their minute crystals glisten when a light is
taken into the cavern, that one of them near Tenby is called the
"Fairy Chamber." Meanwhile, the water which drips on to the
floor also leaves some carbonate of lime where it falls, and this
forms a pillar, growing up towards the roof, and often the hanging
stalactites and the rising pillars (called stalagmites) meet in
the middle and form one column. And thus we see that underground,
as well as aboveground, water moulds beautiful forms in the crust
of the earth. At Adelsberg, near Trieste, there is a magnificent
stalactite grotto made of a number of chambers one following
another, with a river flowing through them; and the famous Mammoth
Cave of Kentucky, more than ten miles long, is another example of
these wonderful limestone caverns.
But we have not yet spoken of the sea, and this surely is not
idle in altering the shape of the land. Even the waves
themselves in a storm wash against the cliffs and bring down
stones and pieces of rock on to the shore below. And they help
to make cracks and holes in the cliffs, for as they dash with
force against them they compress the air which lies in the joints
of the stone and cause it to force the rock apart, and so larger
cracks are made and the cliff is ready to crumble.
It is, however, the stones and sand and pieces of rock lying at
the foot of the cliff which are most active in wearing it away.
Have you never watched the waves breaking upon a beach in a
heavy storm? How they catch up the stones and hurl them down
again, grinding them against each other! At high tide in such a
storm these stones are thrown against the foot of the cliff, and
each blow does something towards knocking away part of the rock,
till at last, after many storms, the cliff is undermined and large
pieces fall down. These pieces are in their turn ground down to
pebbles which serve to batter against the remaining rock.
Professor Geikie tells us that the waves beat in a storm against
the Bell Rock Lighthouse with as much force as if you dashed a
weight of 3 tons against every square inch of the rock, and
Stevenson found stones of 2 tons' weight which had been thrown
during storms right over the ledge of the lighthouse. Think what
force there must be in waves which can lift up such a rock and
throw it, and such force as this beats upon our sea-coasts and
eats away the land.
Fig. 28 is a sketch on the shores of Arbroath which I made some
years ago. You will not find it difficult to picture to
yourselves how the sea has eaten away these cliffs till some of
the strongest pieces which have resisted the waves stand out by
themselves in the sea. That cave in the left-hand corner ends in a
narrow dark passage from which you come out on the other side of
the rocks into another bay. Such caves as these are made chiefly
by the force of the waves and the air, bringing down pieces of
rock from under the cliff and so making a cavity, and then as the
waves roll these pieces over and over and grind them against the
sides, the hole is made larger. There are many places on the
English coast where large pieces of the road are destroyed by the
crumbling down of cliffs when they have been undermined by caverns
such as these.
Thus, you see, the whole of the beautiful scenery of the sea -
the shores, the steep cliffs, the quiet bays, the creeks and
caverns - are all the work of the "sculptor" water; and he works
best where the rocks are hardest, for there they offer him a
good stout wall to batter, whereas in places where the ground is
soft it washes down into a gradual gentle slope, and so the
waves come flowing smoothly in and have no power to eat away the
shore.
And now, what has Ice got to do with the sculpturing of the land?
First, we must remember how much the frost does in breaking up
the ground. The farmers know this, and always plough after a
frost, because the moisture, freezing in the ground, has broken
up the clods, and done half their work for them.
But this is not the chief work of ice. You will remember how we
learnt in our last lecture that snow, when it falls on the
mountains, gradually slides down into the valleys, and is pressed
together by the gathering snow behind until it becomes moulded
into a solid river of ice (see Fig. 29, Frontispiece). In
Greenland and in Norway there are enormous ice-rivers or glaciers,
and even in Switzerland some of them are very large. The Aletsch
glacier, in the Alps, is fifteen miles long, and some are even
longer than this. They move very slowly - on an average about 20
to 27 inches in the centre, and 13 to 19 inches at the sides every
twenty-four hours, in the summer and autumn. How they move, we
cannot stop to discuss now; but if you will take a slab of thin
ice and rest it upon its two ends only, you can prove to yourself
that ice does bend, for in a few hours you will find that its own
weight has drawn it down in the centre, so as to form a curve.
This will help you to picture to yourselves how glaciers can adapt
themselves to the windings of the valley, creeping slowly onwards
until they come down to a point where the air is warm enough to
melt them, and then the ice flows away in a stream of water. It is
very curious to see the number of little rills running down the
great masses of ice at the glacier's mouth, bringing down with
them gravel, and every now and then a large stone, which falls
splashing into the stream below. If you look at the glacier in the
Frontispiece, you will see that these stones come from those long
lines of stones and boulders stretching along the sides and centre
of the glacier. It is easy to understand where the stones at the
side come from; for we have seen that damp and frost cause pieces
to break off the surface of the rocks, and it is natural that
these pieces should roll down the steep sides of the mountains on
to the glacier. But the middle row requires some explanation. Look
to the back of the picture, and you will see that this line of
stones is made of two side rows, which come from the valleys
above. Two glaciers, you see, have there joined into one, and so
made a heap of stones all along their line of junction.
These stones are being continually, though slowly, conveyed by
the glacier, from all the mountains along its sides, down to the
place where it melts. Here it lets them fall, and they are
gradually piled up till they form great walls of stone, which
are called moraines. Some of the moraines left by the larger
glaciers of olden time, in the country near Turin, form high
hills, rising up even to 1500 feet.
Therefore, if ice did no more than carry these stone blocks, it
would alter the face of the country; but it does much more than
this. As the glacier moves along, it often cracks for a
considerable way across its surface, and this crack widens and
widens, until at last it becomes a great gaping chasm, or
crevasse as it is called, so that you can look down it right to
the bottom of the glacier. Into these crevasses large blocks of
rock fall, and when the chasm is closed again as the ice presses
on, these masses are frozen firmly into the bottom of the
glacier, much in the same way as a steel cutter is fixed in the
bottom of a plane. And they do just the same kind of work; for
as the glacier slides down the valley, they scratch and grind the
rocks underneath them, rubbing themselves away, it is true, but
also scraping away the ground over which they move. In this way
the glacier becomes a cutting instrument, and carves out the
valleys deeper and deeper as it passes through them.
You may always know where a glacier has been, even if no trace of
ice remains; for you will see rocks with scratches along them
which have been cut by these stones; and even where the rocks
have not been ground away, you will find them rounded like those
in the left-hand of the Frontispiece, showing that the glacier-
plane has been over them. These rounded rocks are called "roches
moutonnees," because at the distance they look like sheep lying
down.
You have only to look at the stream flowing from the mouth of a
glacier to see what a quantity of soil it has ground off from
the bottom of the valley; for the water is thick, and coloured a
deep yellow by the mud it carries. This mud soon reaches the
rivers into which the streams run; and such rivers as the Rhone
and the Rhine are thick with matter brought down from the Alps.
The Rhone leaves this mud in the Lake of Geneva, flowing out at
the other end quite clear and pure. A mile and a half of land
has been formed at the head of the lake since the time of the
Romans by the mud thus brought down from the mountains.
Thus we see that ice, like water, is always busy carving out the
surface of the earth, and sending down material to make new land
elsewhere. We know that in past ages the glaciers were much
larger than they are in our time; for we find traces of them
over large parts of Switzerland where glaciers do not now exist,
and huge blocks which could only have been carried by ice, and
which are called "erratic blocks," some of them as big as
cottages, have been left scattered over all the northern part of
Europe. These blocks were a great puzzle to scientific men till,
in 1840, Professor Agassiz showed that they must have been brought
by ice all the way from Norway and Russia.
In those ancient days, there were even glaciers in England; for
in Cumberland and in Wales you may see their work, in scratched
and rounded rocks, and the moraines they have left. Llanberis
Pass, so famous for its beauty, is covered with ice-scratches,
and blocks are scattered all over the sides of the valley. There
is one block high up on the right-hand slope of the valley, as
you enter from the Beddgelert side, which is exactly poised upon
another block, so that it rocks to and fro. It must have been
left thus balanced when the ice melted round it. You may easily
see that these blocks were carried by ice, and not by water,
because their edges are sharp, whereas if they had been rolled
in water, they would have been smoothed down.
We cannot here go into the history of that great Glacial Period
long ago, when large fields of ice covered all the north of
England; but when you read it for yourselves and understand the
changes on the earth's surface which we can see being made by
ice now, then such grand scenery as the rugged valleys of Wales,
with large angular stone blocks scattered over them, will tell
you a wonderful story of the ice of bygone times.
And now we have touched lightly on the chief ways in which water
and ice carve out the surface of the earth. We have seen that
rain, rivers, springs, the waves of the sea, frost, and glaciers
all do their part in chiselling out ravines and valleys, and in
producing rugged peaks or undulating plains - here cutting through
rocks so as to form precipitous cliffs, there laying down new land
to add to the flat country - in one place grinding stones to
powder, in others piling them up in gigantic ridges. We cannot go
a step into the country without seeing the work of water around
us; every little gully and ravine tells us that the sculpture is
going on; every stream, with its burden of visible or invisible
matter, reminds us that some earth is being taken away and carried
to a new spot. In our little lives we see indeed but the very
small changes, but by these we learn how greater ones have been
brought about, and how we owe the outline of all our beautiful
scenery, with its hills and valleys, its mountains and plains, its
cliffs and caverns, its quiet nooks and its grand rugged
precipices, to the work of the "Two great sculptors, Water and
Ice."
Week 16
Lecture VI
THE VOICES OF NATURE AND HOW WE HEAR THEM
We have reached to-day the middle point of our course, and here
we will make a new start. All the wonderful histories which we
have been studying in the last five lectures have had little or
nothing to do with living creatures. The sunbeams would strike
on our earth, the air would move restlessly to and fro, the
water-drops would rise and fall, the valleys and ravines would
still be cut out by rivers , if there were no such thing as life
upon the earth. But without living things there could be none of
the beauty which these changes bring about. Without plants, the
sunbeams, the air and the water would be quite unable to clothe
the bare rocks, and without animals and man they could not
produce light, or sound, or feeling of any kind.
In the next five lectures, however, we are going to learn
something of the use living creatures make of the earth; and to-
day we will begin by studying one of the ways in which we are
affected by the changes of nature, and hear her voice.
We are all so accustomed to trust to our sight to guide us in
most of our actions, and to think of things as we see them, that
we often forget how very much we owe to sound. And yet Nature
speaks to us so much by her gentle, her touching, or her awful
sounds, that the life of a deaf person is even more hard to bear
than that of a blind one.
Have you ever amused yourself with trying how many different
sounds you can distinguish if you listen at an open window in a
busy street? You will probably be able to recognize easily the
jolting of the heavy wagon or dray, the rumble of the omnibus,
the smooth roll of the private carriage and the rattle of the
light butcher's cart; and even while you are listening for these,
the crack of the carter's whip, the cry of the costermonger at
his stall, and the voices of the passers-by will strike upon you
ear. Then if you give still more close attention you will hear
the doors open and shut along the street, the footsteps of the
passengers, the scraping of the shovel of the mud-carts; nay, if
he happen to stand near, you may even hear the jingling of the
shoeblack's pence as he plays pitch and toss upon the pavement.
If you think for a moment, does it not seem wonderful that you
should hear all these sounds so that you can recognize each one
distinctly while all the rest are going on around you?
But suppose you go into the quiet country. Surely there will be
silence there. Try some day and prove it for yourself, lie down
on the grass in a sheltered nook and listen attentively. If
there be ever so little wind stirring you will hear it rustling
gently through the trees; or even if there is not this, it will
be strange if you do not hear some wandering gnat buzzing, or
some busy bee humming as it moves from flower to flower. Then a
grasshopper will set up a chirp within a few yards of you, or, if
all living creatures are silent, a brook not far off may be
flowing along with a rippling musical sound. These and a hundred
other noises you will hear in the most quiet country spot; the
lowing of the cattle, the song of the birds, the squeak of the
field-mouse, the croak of the frog, mingling with the sound of
the woodman's axe in the distance, or the dash of some river
torrent. And beside these quiet sounds, there are still other
occasional voices of nature which speak to us from time to time.
The howling of the tempestuous wind, the roar of the sea-waves in
a storm, the crash of thunder, and the mighty noise of the
falling avalanche; such sounds as these tell us how great and
terrible nature can be.
Now, has it ever occurred to you to think what sounds is, and how
it is that we hear all these things? Strange as it may seem, if
there were no creature that could hear upon the earth, there
would be no such thing as sound, though all these movements in
nature were going on just as they are now.
Try and grasp this thoroughly, for it is difficult at first to
make people believe it. Suppose you were stone-deaf, there would
be no such thing as sound to you. A heavy hammer falling on an
anvil would indeed shake the air violently, but since this air
when it reached your ear would find a useless instrument, it
could not play upon it. and it is this play on the drum of your
ear and the nerves within it speaking to your brain which make
sound. Therefore, if all creatures on or around the earth were
without ears or nerves of hearing, there would be no instrument
on which to play, and consequently there would be no such thing
as sound. This proves that two things are needed in order that
we may hear. First, the outside movement which plays on our
hearing instrument; and, secondly, the hearing instrument itself.
First, then, let us try to understand what happens outside our
ears. Take a poker and tie a piece of string to it, and holding
the ends of the string to your ears, strike the poker against the
fender. You will hear a very loud sound, for the blow will set
all the particles of the poker quivering, and this movement will
pass right along the string to the drum of your ear and play upon
it.
Now take the string away from you ears, and hold it with your
teeth. Stop your ears tight, and strike the poker once more
against the fender. You will hear the sound quite as loudly and
clearly as you did before, but this time the drum of your ear has
not been agitated. How, then, has the sound been produced? In
this case, the quivering movement has passed through your teeth
into the bones of your hear, and from them into the nerves, and
so produced sound in your brain. And now, as a final experiment,
fasten the string to the mantelpiece, and hit it again against
the fender. How much feebler the sound is this time, and how
much sooner it stops! Yet still it reaches you, for the movement
has come this time across the air to the drums of your ear.
Here we are back again in the land of invisible workers! We have
all been listening and hearing ever since we were babies, but
have we ever made any picture to ourselves of how sound comes to
us right across a room or a field, when we stand at one end and
the person who calls is at the other?
Since we have studied the "aerial ocean," we know that the air
filling the space between us, though invisible, is something very
real, and now all we have to do is to understand exactly how the
movement crosses this air.
This we shall do most readily by means of an experiment made by
Dr. Tyndall in his lectures on Sound. I have here a number of
boxwood balls resting in a wooden tray which has a bell hung at
the end of it. I am going to take the end ball and roll it
sharply against the rest, and then I want you to notice carefully
what happens. See! the ball at the other end has flow off and
hit the bell, so that you hear it ring. Yet the other balls
remain where they were before. Why is this? It is because each
of the balls, as it was knocked forwards, had one in front of it
to stop it and make it bound back again, but the last one was
free to move on. When I threw this ball from my hand against the
others, the one in front of it moved, and hitting the third ball,
bounded back again; the third did the same to the fourth, the
fourth to the fifth, and so on to the end of the line. Each ball
thus came back to its place, but it passed the shock on to the
last ball, and the ball to the bell. If I now put the balls
close up to the bell, and repeat the experiment, you still hear
the sound, for the last ball shakes the bell as if it were a ball
in front of it.
Now imagine these balls to be atoms of air, and the bell your
ear. If I clap my hands and so hit the air in front of them,
each air-atom hits the next just as the balls did, and though it
comes back to its place, it passes the shock on along the whole
line to the atom touching the drum of your ear, and so you
receive a blow. But a curious thing happens in the air which you
cannot notice in the balls. You must remember that air is
elastic, just as if there were springs between the atoms as in
the diagram, Fig. 31, and so when any shock knocks the atoms
forward, several of them can be crowded together before they push
on those in front. Then, as soon as they have passed the shock
on, they rebound and begin to separate again, and so swing to and
fro till they come to rest. meanwhile the second set will go
through just the same movements, and will spring apart as soon as
they have passed the shock on to a third set, and so you will
have one set of crowded atoms and one set of separated atoms
alternately all along the line, and the same set will never be
crowded two instants together.
You may see an excellent example of this in a luggage train in a
railway station, when the trucks are left to bump each other till
they stop. You will see three or four trucks knock together,
then they will pass the shock on to the four in front, while they
themselves bound back and separate as far as their chains will
let them: the next four trucks will do the same, and so a kind of
wave of crowded trucks passes on to the end of the train, and
they bump to and fro till the whole comes to a standstill. Try
to imagine a movement like this going on in the line of air-
atoms, the drum of your ear being at the end. Those which are
crowded together at that end will hit on the drum of your ear and
drive the membrane which covers it inwards; then instantly the
wave will change, these atoms will bound back, and the membrane
will recover itself again, but only to receive a second blow as
the atoms are driven forwards again, and so the membrane will be
driven in and out till the air has settled down.
This you see is quite different to the waves of light which moves
in crests and hollows. Indeed, it is not what we usually
understand by a wave at all, but a set of crowdings and partings
of atoms of air which follow each other rapidly across the air.
A crowding of atoms is called a condensation, and a parting is
called a rarefaction, and when we speak of the length of a wave
of sound, we mean the distance between two condensations, or
between two rarefactions.
Although each atom of air moves a very little way forwards and
then back, yet, as a long row of atoms may be crowded together
before they begin to part, a wave is often very long. When a man
talks in an ordinary bass voice, he makes sound-waves from 8 to
12 feet long; a woman's voice makes shorter waves, from 2 to 4
feet long, and consequently the tone is higher, as we shall
presently explain.
And now I hope that some one is anxious to ask why, when I clap
my hands, anyone behind me or at the side, can hear it as well or
nearly as well as you who are in front. This is because I give a
shock to the air all round my hands, and waves go out on all
sides, making as it were gloves of crowdings and partings
widening and widening away from the clap as circles widen on a
pond. Thus the waves travel behind me, above me, and on all
sides, until they hit the walls, the ceiling, and the floor of
the room, and wherever you happen to be, they hit upon your ear.
Week 17
If you can picture to yourself these waves spreading out in all
directions, you will easily see why sound grows fainter at the
distance. Just close round my hands when I clap them, there is
a small quantity of air, and so the shock I give it is very
violent, but as the sound-waves spread on all sides they have
more and more air to move, and so the air-atoms are shaken less
violently and strike with less force on your ear.
If we can prevent the sound-wave from spreading, then the sound
is not weakened. The Frenchman Biot found that a low whisper
could be heard distinctly for a distance of half a mile through a
tube, because the waves could not spread beyond the small column
of air. But unless you speak into a small space of some kind,
you cannot prevent the waves going out from you in all
directions.
Try and imagine that you see these waves spreading all round me
now and hitting on your ears as they pass, then on the ears of
those behind you, and on and on in widening globes till they
reach the wall. What will happen when they get there? If the
wall were thin, as a wooden partition is, they would shake it,
and it again would shake the air on the other side, and so anyone
in the next room would have the sound of my voice brought to
their ear.
But something more will happen. In any case the sound-waves
hitting against the wall will bound back from it just as a ball
bounds back when thrown against anything, and so another set of
sound-waves reflected from the wall will come back across the
room. If these waves come to your ear so quickly that they mix
with direct waves, they help to make the sound louder in this
room than you would in the open air, for the "Ha" from my mouth
and a second "Ha" from the wall come to your ear so
instantaneously that they make one sound. This is why you can
often hear better at the far end of a church when you stand
against a screen or a wall, then when you are half-way up the
building nearer to the speaker, because near the wall the
reflected waves strike strongly on your ear and make the sound
louder.
Sometimes, when the sound comes from a great explosion, these
reflected waves are so strong that they are able to break glass.
In the explosion of gunpowder in St. John's Wood, many houses in
the back streets had their windows broken; for the sound-waves
bounded off at angles from the walls and struck back upon them.
Now suppose the wall were so far behind you that the reflected
sound-waves only hit upon your ear after those coming straight
from me had died away; then you would hear the sound twice, "Ha"
from me and "Ha" from the wall, and here you have an echo, "Ha,
ha." In order for this to happen in ordinary air, you must be
standing at least 56 feet away from the point from which the
waves are reflected, for then the second blow will come one-tenth
of a second after the first one, and that is long enough for you
to feel them separately.* Miss C. A. Martineau tells a story of
a dog which was terribly frightened by an echo. Thinking another
dog was barking, he ran forward to meet him, and was very much
astonished, when, as he came nearer the wall, the echo ceased. I
myself once knew a case of this kind, and my dog, when he could
find no enemy, ran back barking, till he was a certain distance
off, and then the echo of course began again. He grew so furious
at last that we had great difficulty in preventing him from
flying at a strange man who happened to be passing at the time.
(*Sound travels 1120 feet in a second, in air of ordinary
temperature, and therefore 112 feet in the tenth of a second.
Therefore the journey of 56 feet beyond you to reach the wall
and 56 feet to return, will occupy the sound-wave one-tenth of
a second and separate the two sounds.)
Sometimes, in the mountains, walls of rock rise at some distance
one behind another, and then each one will send back its echo a
little later than the rock before it, so that the "Ha" which you
give will come back as a peal of laughter. There is an echo in
Woodstock Park which repeats the word twenty times. Again
sometimes, as in the Alps, the sound-waves coming back rebound
from mountain to mountain and are driven backwards and forwards,
becoming fainter and fainter till they die away; these echoes are
very beautiful.
If you are now able to picture to yourselves one set of waves
going to the wall, and another set returning and crossing them,
you will be ready to understand something of that very difficult
question, How is it that we can hear many different sounds at one
time and tell them apart?
Have you ever watched the sea when its surface is much ruffled,
and noticed how, besides the big waves of the tide, there are
numberless smaller ripples made by the wind blowing the surface
of the water, or the oars of a boat dipping in it, or even rain-
drops falling? If you have done this you will have seen that all
these waves and ripples cross each other, and you can follow any
one ripple with you eye as it goes on its way undisturbed by the
rest. Or you may make beautiful crossing and recrossing ripples
on a pond by throwing in two stones at a little distance from
each other, and here too you can follow any one wave on to the
edge of the pond.
Now just in this way the waves of sound, in their manner of
moving, cross and recross each other. You will remember too,
that different sounds make waves of different lengths, just as
the tide makes a long wave and the rain-drops tiny ones.
Therefore each sound falls with its own peculiar wave upon your
ear, and you can listen to that particular wave just as you look
at one particular ripple, and then the sound becomes clear to
you.
All this is what is going on outside your ear, but what is
happening in your ear itself? How do these blows of the air
speak to your brain? By means of the following diagram, Fig. 33,
we will try to understand roughly our beautiful hearing
instrument, the ear.
First, I want you to notice how beautifully the outside shell, or
concha as it is called, is curbed round so that any movement of
the air coming to it from the front is caught in it and reflected
into the hole of the ear. Put your finger round your ear and
feel how the gristly part is curved towards the front of your
head. This concha makes a curve much like the curve a deaf man
makes with his hand behind his ear to catch the sound. Animals
often have to raise their ears to catch the sound well, but ours
stand always ready. When the air-waves have passed in at the
hole of your ear, they move all the air in the passage, which is
called the auditory, or hearing, canal. This canal is lined with
little hairs to keep out insects and dust, and the wax which
collects in it serves the same purpose. But is too much wax
collects, it prevents the air from playing well upon the drum,
and therefore makes you deaf. Across the end of this canal, a
membrane or skin called the tympanum is stretched, like the
parchment over the head of a drum, and it is this membrane which
moves to and fro as the air-waves strike on it. A violent box on
the ear will sometimes break this delicate membrane, or injure
it, and therefore it is very wrong to hit a person violently on
the ear.
On the other side of this membrane, inside the ear, there is air,
which fills the whole of the inner chamber and the tube, which
runs down into the throat behind the nose, and is called the
Eustachian tube after the man who discovered it. This tube is
closed at the end by a valve which opens and shuts. If you
breathe out strongly, and then shut your mouth and swallow, you
will hear a little "click" in your ear. This is because in
swallowing you draw the air out of the Eustachian tube and so
draw in the membrane, which clicks as it goes back again. But
unless you do this the tube and the whole chamber cavity behind
the membrane remains full of air.
Now, as this membrane is driven to and fro by the sound-waves, it
naturally shakes the air in the cavity behind it, and it also
sets moving three most curious little bones. The first of the
bones is fastened to the middle of the drumhead so that it moves
to and fro every time this membrane quivers. The head of this
bone fits into a hole in the next bone, the anvil, and is
fastened to it by muscles, so as to drag it along with it; but,
the muscles being elastic, it can draw back a little from the
anvil, and so give it a blow each time it comes back. This anvil
is in its turn very firmly fixed to the little bone, shaped like
a stirrup, which you see at the end of the chain.
This stirrup rests upon a curious body which looks in the diagram
like a snail-shell with tubes coming out of it. This body, which
is called the labyrinth, is made of bone, but it has two little
windows in it, one covered only by a membrane, while the other
has the head of the stirrup resting upon it.
Now, with a little attention you will understand that when the
air in the canal shakes the drumhead to and fro, this membrane
must drag with it the hammer, the anvil, and the stirrup. Each
time the drum goes in, the hammer will hit the anvil, and drive
the stirrup against the little window; every time it goes out it
will draw the hammer, the anvil, and the stirrup out again, ready
for another blow. Thus the stirrup is always playing upon this
little window. Meanwhile, inside the bony labyrinth there is a
fluid like water, and along the little passages are very fine
hairs, which wave to and fro like reeds; and whenever the stirrup
hits at the little window, the fluid moves these hairs to and
fro, and they irritate the ends of a nerve, and this nerve
carries the message to your brain. There are also some curious
little stones called otoliths, lying in some parts of this fluid,
and they, by their rolling to and fro, probably keep up the
motion and prolong the sound.
You must not imagine we have explained here the many intricacies
which occur in the ear; I can only hope to give you a rough idea
of it, so that you may picture to yourselves the air-waves moving
backwards and forward in the canal of your ear, then the tympanum
vibrating to and fro, the hammer hitting the anvil, the stirrup
knocking at the little window, the fluid waving the fine hairs
and rolling the tiny stones, the ends of the nerve quivering, and
then (how we know not) the brain hearing the message.
Is not this wonderful, going on as it does at every sound you
hear? And yet his is not all, for inside that curled part of the
labyrinth, which looks like a snail-shell and is called the
cochlea, there is a most wonderful apparatus of more than three
thousand fine stretched filaments or threads, and these act like
the strings of a harp, and make you hear different tones. If you
go near to a harp or a piano, and sing any particular note very
loudly, you will hear this note sounding in the instrument,
because you will set just that particular string quivering, which
gives the note you sang. The air-waves set going by your voice
touch that string, because it can quiver in time with them, while
none of the other strings can do so. Now, just in the same way
the tiny instrument of three thousand strings in your ear, which
is called Corti's organ, vibrates to the air-waves, one thread to
one set of waves, and another to another, and according to the
fibre that quivers, will be the sound you hear. Here then at
last, we see how nature speaks to us. All the movements going on
outside, however violent and varied they may be, cannot of
themselves make sound. But here, in the little space behind the
drum of our ear, the air-waves are sorted and sent on to our
brain, where they speak to us as sound.
Week 18
But why then do we not hear all sounds as music? Why are some
mere noise, and others clear musical notes? This depends
entirely upon whether the sound-waves come quickly and regularly,
or by an irregular succession of shocks. For example, when a
load of stones is being shot out of a cart, you hear only a long,
continuous noise, because the stones fall irregularly, some
quicker, some slower, here a number together, and there two or
three stragglers by themselves; each of these different shocks
comes to your ear and makes a confused, noisy sound. But if you
run a stick very quickly along a paling, you will hear a sound
very like a musical not. This is because the rods of the paling
are all at equal distances one from another, and so the shocks
fall quickly one after another at regular intervals upon your
ear. Any quick and regular succession of sounds makes a note,
even though it may be an ugly one. The squeak of a slate pencil
along a slate, and the shriek of a railway whistle are not
pleasant, but they are real notes which you could copy on a
violin.
I have here a simple apparatus which I have had made to show you
that rapid and regular shocks produce a natural musical note.
This wheel (Fig. 34) is milled at the edge like a shilling, and
when I turn it rapidly so that it strikes against the edge of the
card fixed behind it, the notches strike in rapid succession, and
produce a musical sound. We can also prove by this experiment
that the quicker the blows are, the higher the note will be. I
pull the string gently at first, and then quicker and quicker,
and you will notice that the note grows sharper and sharper, till
the movement begins to slacken, when the note goes down again.
This is because the more rapidly the air is hit, the shorter are
the waves it makes, and short waves give a high note.
Let us examine this with two tuning-forks. I strike one, and it
sounds D, the third space in the treble; I strike the other, and
it sounds G, the first leger line, five notes above the C. I
have drawn on this diagram (Fig. 35), an imaginary picture of
these two sets of waves. You see that the G fork makes three
waves, while the C fork makes only two. Why is this? Because
the prong of the G fork moves three times backwards and forwards
while the prong of the C fork only moves twice; therefore the G
fork does not crowd so many atoms together before it draws back,
and the waves are shorter. These two notes, C and G, are a fifth
of an octave apart; if we had two forks, of which one went twice
as fast as the other, making four waves while the other made two,
then that note would be an octave higher.
So we see that all the sounds we hear, - the warning noises which
keep us from harm, the beautiful musical notes with all the tunes
and harmonies that delight us, even the power of hearing the
voices of those we love, and learning from one another that which
each can tell, - all these depend upon the invisible waves of
air, even as the pleasures of light depend on the waves of ether.
It is by these sound-waves that nature speaks to us, and in all
her movements there is a reason why her boice is sharp or tender,
loud or gentle, awful or loving. Take for instance the brook we
spoke of at the beginning of the lecture. Why does it sing so
sweetly, while the wide deep river makes no noise? Because the
little brook eddies and purls round the stones, hitting them as
it passes; sometimes the water falls down a large stone, and
strikes against the water below; or sometimes it grates the
little pebbles together as they lie in its bed. Each of these
blows makes a small globe of sound-waves, which spread and spread
till they fall on your ear, and because they fall quickly and
regularly, they make a low, musical note. We might almost fancy
that the brook wished to show how joyfully it flows along,
recalling Shelley's beautiful lines:-
"Sometimes it fell
Among the moss with hollow harmony,
Dark and profound; now on the polished stones
It danced; like childhood laughing as it went."
The broad deep river, on the contrary, makes none of these
cascades and commotions. The only places against which it rubs
are the banks and the bottom; and here you can sometimes hear it
grating the particles of sand against each other if you listen
very carefully. But there is another reason why falling water
makes a sound, and often even a loud roaring noise in the
cataract and in the breaking waves of the sea. You do not only
hear the water dashing against the rocky ledges or on the beach,
you also hear the bursting of innumerable little bladders of air
which are contained in the water. As each of these bladders is
dashed on the ground, it explodes and sends sound-waves to your
ear. Listen to the sea some day when the waves are high and
stormy, and you cannot fail to be struck by the irregular bursts
of sound.
The waves, however, do not only roar as they dash on the ground;
have you never noticed how they seem to scream as they draw back
down the beach? Tennyson calls it,
"The scream of the madden'd beach dragged down by the wave;" and
it is caused by the stones grating against each other as the
waves drag them down. Dr. Tyndall tells us that it is possible
to know the size of the stones by the kind of noise they make.
If they are large, it is a confused noise, when smaller, a kind
of scream; while a gravelly beach will produce a mere hiss.
Who could be dull by the side of a brook, a waterfall, or the
sea, while he can listen for sounds like these, and picture to
himself how they are being made? You may discover a number of
other causes of sound made by water, if you once pay attention to
them.
Nor is it only water that sings to us. Listen to the wind, how
sweetly it sighs among the leaves. There we hear it, because it
rubs the leaves together, and they produce the sound-waves. But
walk against the wind some day and you can hear it whistling in
your own ear, striking against the curved cup, and then setting
up a succession of waves in the hearing canal of the ear itself.
Why should it sound in one particular tone when all kinds of
sound-waves must be surging about in the disturbed air?
This glass jar will answer our question roughly. If I strike my
tuning-fork and hold it over the jar, you cannot hear it, because
the sound is feeble, but if I fill the jar gently with water,
when the water rises to a certain point you will hear a loud
clear note, because the waves of air in the jar are exactly the
right length to answer to the note of the fork. If I now blow
across the mouth of the jar you hear the same note, showing that
a cavity of a particular length will only sound to the waves
which fit it. do you see now the reason why pan-pipes give
different sounds, or even the hole at the end of a common key
when you blow across it? Here is a subject you will find very
interesting if you will read about it, for I can only just
suggest it to you here. But now you will see that the canal of
your ear also answers only to certain waves, and so the wind
sings in your ear with a real if not a musical note.
Again, on a windy night have you not heard the wind sounding a
wild, sad note down a valley? Why do you think it sounds so much
louder and more musical here than when it is blowing across the
plain? Because air in the valley will only answer to a certain
set of waves, and, like the pan-pipe, gives a particular note as
the wind blows across it, and these waves go up and down the
valley in regular pulses, making a wild howl. You may hear the
same in the chimney, or in the keyhole; all these are waves set
up in the hole across which the wind blows. Even the music in
the shell which you hold to your ear is made by the air in the
shell pulsating to and fro. And how do you think it is set
going? By the throbbing of the veins in your own ear, which
causes the air in the shell to vibrate.
Another grand voice of nature is the thunder. People often have
a vague idea that thunder is produced by the clouds knocking
together, which is very absurd, if you remember that clouds are
but water-dust. The most probable explanation of thunder is much
more beautiful than this. You will remember from Lecture III
that heat forces the air-atoms apart. Now, when a flash of
lightning crosses the sky it suddenly expands the air all round
it as it passes, so that globe after globe of sound-waves is
formed at every point across which the lightning travels. Now
light, you remember, travels so wonderfully rapidly (192,000
miles in a second) that a flash of lightning is seen by us and is
over in a second, even when it is two or three miles long. But
sound comes slowly, taking five seconds to travel half a mile,
and so all the sound-waves at each point of the two or three
miles fall on our ear one after the other, and make the rolling
thunder. Sometimes the roll is made even longer by the echo, as
the sound-waves are reflected to and fro by the clouds on their
road; and in the mountains we know how the peals echo and re-echo
till they die away.
We might fill up far more than an hour in speaking of those
voices which come to us as nature is at work. Think of the
patter of the rain, how each drop as it hits the pavement sends
circles of sound-waves out on all sides; or the loud report which
falls on the ear of the Alpine traveller as the glacier cracks on
its way down the valley; or the mighty boom of the avalanche as
the snow slides in huge masses off the side of the lofty
mountain. Each and all of these create their sound-waves, large
or small, loud or feeble, which make their way to your ear, and
become converted into sound.
We have, however, only time now just to glance at life-sounds, of
which there are so many around us. Do you know why we hear a
buzzing, as the gnat, the bee, or the cockchafer fly past? Not
by the beating of their wings against the air, as many people
imagine, and as is really the case with humming birds, but by the
scraping of the under-part of their hard wings against the edges
of their hind legs, which are toothed like a saw. The more
rapidly their wings move the stronger the grating sound becomes,
and you will now see why in hot, thirsty weather the buzzing of
the gnat is so loud, for the more thirsty and the more eager he
becomes, the wilder his movements will be.
Some insects, like the drone-fly (Eristalis tenax), force the air
through the tiny air-passages in their sides, and as these
passages are closed by little plates, the plates vibrate to and
fro and make sound-waves. Again, what are those curious sounds
you may hear sometimes if you rest your head on a trunk in the
forest? They are made by the timber-boring beetles, which saw
the wood with their jaws and make a noise in the world, even
though they have no voice.
All these life-sounds are made by creatures which do not sing or
speak; but the sweetest sounds of all in the woods are the voices
of the birds. All voice-sounds are made by two elastic bands or
cushions, called vocal chords, stretched across the end of the
tube or windpipe through which we breathe, and as we send the air
through them we tighten or loosen them as we will, and so make
them vibrate quickly or slowly and make sound-waves of different
lengths. But if you will try some day in the woods you will find
that a bird can beat you over and over again in the length of his
note; when you are out of breath and forced to stop he will go on
with his merry trill as fresh and clear as if he had only just
begun. This is because birds can draw air into the whole of
their body, and they have a large stock laid up in the folds of
their windpipe, and besides this the air-chamber behind their
elastic bands or vocal chords has two compartments where we have
only one, and the second compartment has special muscles by which
they can open and shut it, and so prolong the trill.
Only think what a rapid succession of waves must quiver through
the air as a tiny lark agitates his little throat and pours forth
a volume of song! The next time you are in the country in the
spring, spend half an hour listening to him, and try and picture
to yourself how that little being is moving all the atmosphere
round him. Then dream for a little while about sound, what it
is, how marvellously it works outside in the world, and inside in
your ear and brain; and then, when you go back to work again, you
will hardly deny that it is well worth while to listen sometimes
to the voices of nature and ponder how it is that we hear them.
Week 19
LECTURE VII THE LIFE OF A PRIMROSE
When the dreary days of winter and the early damp days of spring
are passing away, and the warm bright sunshine has begun to pour
down upon the grassy paths of the wood, who does not love to go
out and bring home posies of violets, and bluebells, and
primroses? We wander from one plant to another picking a flower
here and a bud there, as they nestle among the green
leaves, and we make our rooms sweet and gay with the tender and
lovely blossoms. But tell me, did you ever stop to think, as you
added flower after flower to your nosegay, how the plants which
bear them have been building up their green leaves and their
fragile buds during the last few weeks? If you had visited the
same spot a month before, a few (of) last year's leaves,
withered and dead, would have been all that you would have found.
And now the whole wood is carpeted with delicate green leaves,
with nodding bluebells, and pale-yellow primroses, as if a fairy
had touched the ground and covered it with fresh young life. And
our fairies have been at work here; the fairy "Life," of whom we
know so little, though we love her so well and rejoice in the
beautiful forms she can produce; the fairy sunbeams with their
invisible influence kissing the tiny shoots and warming them into
vigour and activity; the gentle rain-drops, the balmy air, all
these have been working, while you or I passed heedlessly by;
and now we come and gather the flowers they have made, and too
often forget to wonder how these lovely forms have sprung up
around us.
Our work during the next hour will be to consider this question.
You were asked last week to bring with you to-day a primrose-
flower, or a whole plant if possible, in order the better to
follow out with me the "Life of a Primrose." (To enjoy this
lecture, the reader ought to have, if possible, a primrose-
flower, an almond soaked for a few minutes in hot water, and a
piece of orange.) This is a very different kind of subject from
those of our former lectures. There we took world-
wide histories; we travelled up to the sun, or round the earth,
or into the air; now I only ask you to fix your attention on one
little plant, and inquire into its history.
There is a beautiful little poem by Tennyson, which says -
"Flower in the crannied wall,
I pluck you out of the crannies;
Hold you here, root and all, in my hand,
Little flower; but if I could understand
What you are, root and all, and all in all,
I should know what God and man is."
We cannot learn all about this little flower, but we can learn
enough to understand that it has a real separate life of its
own, well worth knowing. For a plant is born, breathes, sleeps,
feeds, and digests just as truly as an animal does, though in a
different way. It works hard both for itself to get its food,
and for others in making the air pure and fit for animals to
breathe. It often lays by provision for the winter. It sends
young plants out, as parents send their children, to fight for
themselves in the world; and then, after living sometimes to a
good old age, it dies, and leaves its place to others.
We will try to follow out something of this life to-day; and
first, we will begin with the seed.
I have here a packet of primrose-seeds, but they are so small
that we cannot examine them; so I have also had given to each
one of you an almond-kernel, which is the seed of the almond-
tree, and which has been soaked, so that it splits in half
easily. From this we can learn about seeds in general, and then
apply it to the primrose.
If you peel the two skins off your almond-seed (the
thick, brown, outside skin, and the thin, transparent one under
it), the two halves of the almond will slip apart quite easily.
One of these halves will have a small dent at the pointed end,
while in the other half you will see a little lump, which fitted
into the dent when the two halves were joined. This little lump
(a b, Fig. 37) is a young plant, and the two halves of the
almond are the seed leaves which hold the plantlet, and feed it
till it can feed itself. The rounded end of the plantlet (b)
sticking out of the almond, is the beginning of the root, while
the other end (a) will in time become the stem. If you look
carefully, you will see two little points at this end, which are
the tips of future leaves. Only think how minute this plantlet
must be in a primrose, where the whole seed is scarcely larger
than a grain of sand! Yet in this tiny plantlet lies hid the
life of the future plant.
When a seed falls into the ground, so long as the earth is cold
and dry, it lies like a person in a trance, as if it were dead;
but as soon as the warm, damp spring comes, and the busy little
sun-waves pierce down into the earth, they wake up the plantlet
and make it bestir itself. They agitate to and fro the particles
of matter in this tiny body, and cause them to seek out for
other particles to seize and join to themselves.
But these new particles cannot come in at the roots,
for the seed has none; nor through the leaves, for they have not
yet grown up; and so the plantlet begins by helping itself to
the store of food laid up in the thick seed-leaves in which it
is buried. Here it finds starch, oils, sugar, and substances
called albuminoids, -- the sticky matter which you notice in
wheat-grains when you chew them is one of the albuminoids. This
food is all ready for the plantlet to use, and it sucks it in,
and works itself into a young plant with tiny roots at one end,
and a growing shoot, with leaves, at the other.
But how does it grow? What makes it become larger? To answer this
you must look at the second thing I asked you to bring - a piece
of orange. If you take the skin off a piece of orange, you will
see inside a number of long-shaped transparent bags, full of
juice. These we call cells, and the flesh of all plants and
animals is made up of cells like these, only of various shapes.
In the pith of elder they are round, large, and easily seen (a,
Fig. 39); in the stalks of plants they are long, and lap over
each other (b, Fig. 39), so as to give the stalk strength to
stand upright. Sometimes many cells growing one on the top of
the other break into one tube and make vessels. But whether
large or small, they are all bags growing one against the other.
In the orange-pulp these cells contain only sweet juice, but in
other parts of the orange-tree or any other plant
they contain a sticky substance with little grains in it. This
substance is called "protoplasm," or the first form of life, for
it is alive and active, and under a microscope you may see in a
living plant streams of the little grains moving about in the
cells.
Now we are prepared to explain how our plant grows. Imagine the
tiny primrose plantlet to be made up of cells filled with active
living protoplasm, which drinks in starch and other food from
the seed-leaves. In this way each cell will grow too full for
its skin, and then the protoplasm divides into two parts and
builds up a wall between them, and so one cell becomes two. Each
of these two cells again breaks up into two more, and so the
plant grows larger and larger, till by the time it has used up
all the food in the seed-leaves, it has sent roots covered with
fine hairs downwards into the earth, and a shoot with beginnings
of leaves up into the air.
Sometimes the seed-leaves themselves come above the ground, as in
the mustard-plant, and sometimes they are left empty behind,
while the plantlet shoots through them.
And now the plant can no longer afford to be idle and
live on prepared food. It must work for itself. Until now it has
been taking in the same kind of food that you and I do; for we
too find many seeds very pleasant to eat and useful to nourish
us. But now this store is exhausted. Upon what then is the plant
to live? It is cleverer than we are in this, for while we cannot
live unless we have food which has once been alive, plants can
feed upon gases and water and mineral matter only. Think over the
substances you can eat or drink, and you will find they are
nearly all made of things which have been alive: meat,
vegetables, bread, beer, wine, milk; all these are made from
living matter, and though you do take in such things as water
and salt, and even iron and phosphorus, these would be quite
useless if you did not eat and drink prepared food which your
body can work into living matter.
But the plant as soon as it has roots and leaves begins to make
living matter out of matter that has never been alive. Through
all the little hairs of its roots it sucks in water, and in this
water are dissolved more or less of the salts of ammonia,
phosphorus, sulphur, iron, lime, magnesia, and even silica, or
flint. In all kinds of earth there is some iron, and we shall see
presently that this is very important to the plant.
Suppose, then, that our primrose has begun to drink in water at
its roots. How is it to get this water up into the stem and
leaves, seeing that the whole plant is made of closed bags or
cells? It does it in a very curious way, which you can prove for
yourselves. Whenever two fluids, one thicker than the other,
such as treacle and water for example, are only separated by a
skin or any porous substance, they will always mix, the thinner
one oozing through the skin into the thicker one. If you tie a
piece of bladder over a glass tube, fill the tube half-full of
treacle, and then let the covered end rest in a bottle of water,
in a few hours the water will get in to the treacle and the
mixture will rise up in the tube till it flows over the top. Now,
the saps and juices of plants are thicker than water, so, directly
the water enters the cells at the root it oozes up into the cells
above, and mixes with the sap. Then the matter in those cells
becomes thinner than in the cells above, so it too oozes up, and
in this way cell by cell the water is pumped up into the leaves.
When it gets there it finds our old friends the sun-beams hard at
work. If you have ever tried to grow a plant in a cellar, you
will know that in the dark its leaves remain white and sickly.
It is only in the sunlight that a beautiful delicate green tint
is given to them, and you will remember from Lecture II. that
this green tint shows that the leaf has used all the sun-waves
except those which make you see green; but why should it do this
only when it has grown up in the sunshine?
The reason is this: when the sunbeam darts into the leaf and sets
all its particles quivering, it divides the protoplasm into two
kinds, collected into different cells. One of these remains
white, but the other kind, near the surface, is altered by the
sunlight and by the help of the iron brought in by the water.
This particular kind of protoplasm, which is called "chlorophyll,"
will have nothing to do with the green waves and throws them back,
so that every little grain of this protoplasm looks green and
gives the leaf its green colour.
It is these little green cells that by the help of the sun-waves
digest the food of the plant and turn the water and gases into
useful sap and juices. We saw in Lecture III. that when we
breathe-in air, we use up the oxygen in it and send back out of
our mouths carbonic acid, which is a gas made of oxygen and
carbon.
Now, every living things wants carbon to feed upon, but plants
cannot take it in by itself, because carbon is solid (the
blacklead in your pencils is pure carbon), and a plant cannot
eat, it can only drink-in fluids and gases. Here the little
green cells help it out of its difficulty. They take in or
absorb out of the air carbonic acid gas which we have given out
of our mouths and then by the help of the sun-waves they tear
the carbon and oxygen apart. Most of the oxygen they throw back
into the air for us to use, but the carbon they keep.
If you will take some fresh laurel-leaves and put them into a
tumbler of water turned upside-down in a saucer of water, and
set the tumbler in the sunshine, you will soon see little bright
bubbles rising up and clinging to the glass. These are bubbles
of oxygen gas, and they tell you that they have been set free by
the green cells which have torn from them the carbon of the
carbonic acid in the water.
But what becomes of the carbon? And what use is made of the water
which we have kept waiting all this time in the leaves? Water,
you already know, is made of hydrogen and oxygen, but perhaps
you will be surprised when I tell you that starch, sugar, and
oil, which we get from plants, are nothing more than hydrogen
and oxygen in different quantities joined to carbon.
It is very difficult at first to picture such a black thing as
carbon making part of delicate leaves and beautiful flowers, and
still more of pure white sugar. But we can make an experiment by
which we can draw the hydrogen and oxygen out of common loaf
sugar, and then you will see the carbon stand out in all its
blackness. I have here a plate with a heap of white sugar in it.
I pour upon it first some hot water to melt and warm it, and then
some strong sulphuric acid. This acid does nothing more than
simply draw the hydrogen and oxygen out. See! in a few moments a
black mass of carbon begins to rise, all of which has come out of
the white sugar you saw just now. *(The common dilute sulphuric
acid of commerce is not strong enough for this experiment, but
pure sulphuric acid can be secured from any chemist. Great care
must be taken in using it, as it burns everything it touches.) You
see, then, that from the whitest substance in plants we can get
this black carbon; and in truth, one-half of the dry part of every
plant is composed of it.
Now look at my plant again, and tell me if we have not already
found a curious history? Fancy that you see the water creeping
in at the roots, oozing up from cell to cell till it reaches the
leaves, and there meeting the carbon which has just come out of
the air, and being worked up with it by the sun-waves into
starch, or sugar, or oils.
But meanwhile, how is new protoplasm to be formed? for without
this active substance none of the work can go on. Here comes
into use a lazy gas we spoke of in Lecture III. There we thought
that nitrogen was of no use except to float oxygen in the air,
but here we shall find it very useful. So far, as we know,
plants cannot take up nitrogen out of the air, but they can get
it out of the ammonia which the water brings in at their roots.
Ammonia, you will remember, is a strong-smelling gas, made of
hydrogen and nitrogen, and which is often almost stifling near a
manure-heap. When you manure a plant you help it to get this
ammonia, but at any time it gets some from the soil and also
from the rain-drops which bring it down in the air. Out of this
ammonia the plant takes the nitrogen and works it up with the
three elements, carbon, oxygen, and hydrogen, to make the
substances called albuminoids, which form a large part of the
food of the plant, and it is these albuminoids which go to make
protoplasm. You will notice that while the starch and other
substances are only made of three elements, the active protoplasm
is made of these three added to a fourth, nitrogen, and it also
contains phosphorus and sulphur.
And so hour after hour and day after day our primrose goes on
pumping up water and ammonia from its roots to its leaves,
drinking in carbonic acid from the air, and using the sun-waves
to work them all up into food to be sent to all parts of its
body. In this way these leaves act, you see, as the stomach of
the plant, and digest its food.
Sometimes more water is drawn up into the leaves than can be
used, and then the leaf opens thousands of little mouths in the
skin of its under surface, which let the drops out just as drops
of perspiration ooze through our skin when we are overheated.
These little mouths, which are called stomates (a, Fig. 42) are
made of two flattened cells, fitting against each other. When
the air is damp and the plant has too much water these lie open
and let it out, but when the air is dry, and the plant wants to
keep as much water as it can, then they are closely shut. There
are as many as a hundred thousand of these mouths under one
apple-leaf, so you may imagine how small they often are.
Plants which only live one year, such as mignonette, the sweet
pea, and the poppy, take in just enough food to supply their
daily wants and to make the seeds we shall speak of presently.
Then, as soon as their seeds are ripe their roots begin to
shrivel, and water is no longer carried up. The green cells can
no longer get food to digest, and they themselves are broken up by
the sunbeams and turn yellow, and the plant dies.
But many plants are more industrious than the stock and
mignonette, and lay by store for another year, and our primrose
is one of these. Look at this thick solid mass below the primrose
leaves, out of which the roots spring. (See the plant in the
foreground of the heading of the lecture.) This is really the
stem of the primrose hidden underground, and all the starch,
albuminoids, &c., which the plant can spare as it grows, are
sent down into this underground stem and stored up there, to lie
quietly in the ground through the long winter, and then when the
warm spring comes this stem begins to send out leaves for a new
plant.
Week 21
We have now seen how a plant springs up, feeds itself, grows,
stores up food, withers, and dies; but we have said nothing yet
about its beautiful flowers or how it forms its seeds. If we
look down close to the bottom of the leaves in a primrose root
in spring-time, we shall always find three or four little green
buds nestling in among the leaves, and day by day we may see the
stalk of these buds lengthening till they reach up into the open
sunshine, and then the flower opens and shows its beautiful pale-
yellow crown.
We all know that seeds are formed in the flower, and that the
seeds are necessary to grow into new plants. But do we know the
history of how they are formed, or what is the use of the
different parts of the bud? Let us examine them all, and then I
think you will agree with me that this is not the least wonderful
part of the plant.
Remember that the seed is the one important thing and then notice
how the flower protects it. First, look at the outside green
covering, which we call the calyx. See how closely it fits in
the bud, so that no insects can creep in to gnaw the flower, nor
any harm come to it from cold or blight. Then, when the calyx
opens, notice that the yellow leaves which form the crown or
corolla, are each alternate with one of the calyx leaves, so that
anything which got past the first covering would be stopped by
the second. Lastly, when the delicate corolla has opened out,
look at those curious yellow bags just at the top of the tube
(b,2, Fig. 43). What is their use?
But I fancy I see two or three little questioning faces which
seem to say, "I see no yellow bags at the top of the tube." Well,
I cannot tell whether you can or not in the specimen you have in
your hand; for one of the most curious things about primrose
flowers is, that some of them have these yellow bags at the top of
the tube and some of them hidden down right in the middle. But
this I can tell you:those of you who have got no yellow bags at
the top will have a round knob there (I a, Fig. 43), and will find
the yellow bags (b) buried in the tube. Those, on the other hand,
who have the yellow bags (2 b, Fig. 43) at the top will find the
knob (a) half-way down the tube.
Now for the use of these yellow bags, which are called the
anthers of the stamens, the stalk on which they grow being
called the filament or thread. If you can manage to split them
open you will find that they have a yellow powder in them,
called pollen, the same as the powder which sticks to your nose
when you put it into a lily; and if you look with a magnifying
glass at the little green knob in the centre of the flower, you
will probably see some of this yellow dust sticking on it (A,
Fig. 43). We will leave it there for a time, and examine the
body called the pistil, to which the knob belongs. Pull off the
yellow corolla (which will come off quite easily), and turn back
the green leaves. You will then see that the knob stands on the
top of a column, and at the bottom of this column there is a
round ball (s v), which is a vessel for holding the seeds. In
this diagram (A, Fig. 43) I have drawn the whole of this curious
ball and column as if cut in half, so that we may see what is in
it. In the middle of the ball, in a cluster, there are a number of
round transparent little bodies, looking something like round
green orange-cells full of juice. They are really cells full of
protoplasm, with one little dark spot in each of them, which
by-and-by is to make our little plantlet that we found in the
seed.
"These, then, are seeds," you will say. Not yet; they are only
ovules, or little bodies which may become seeds. If they were
left as they are they would all wither and die. But those little
grains of pollen, which we saw sticking to the knob at the top,
are coming down to help them. As soon as these yellow grains
touch the sticky knob or stigma, as it is called, they throw out
tubes, which grow down the column until they reach the ovules. In
each one of these they find a tiny hole, and into this they
creep, and then they pour into the ovule all the protoplasm from
the pollen-grain which is sticking above, and this enables it to
grow into a real seed, with a tiny plantlet inside.
This is how the plant forms its seed to bring up new little ones
next year, while the leaves and the roots are at work preparing
the necessary food. Think sometimes when you walk in the woods,
how hard at work the little plants and big trees are, all around
you. You breathe in the nice fresh oxygen they have been
throwing out, and little think that it is they who are making
the country so fresh and pleasant, and that while they look as if
they were doing nothing but enjoying the bright sunshine, they
are really fulfilling their part in the world by the help of
this sunshine; earning their food from the ground working it up;
turning their leaves where they can best get light (and in this it
is chiefly the violet sun-waves that help them), growing, even at
night, by making new cells out of the food they have taken in the
day; storing up for the winter; putting out their flowers and
making their seeds, and all the while smiling so pleasantly in
quiet nooks and sunny dells that it makes us glad to see them.
But why should the primroses have such golden crowns? plain green
ones would protect the seed quite as well. Ah! now we come to a
secret well worth knowing. Look at the two primrose flowers, 1
and 2, Fig. 43, p. 163, and tell me how you think the dust gets
on to the top of the sticky knob or stigma. No. 2 seems easy
enough to explain, for it looks as if the pollen could fall down
easily from the stamens on to the knob, but it cannot fall up,
as it would have to do in No. 1. Now the curious truth is, as Mr.
Darwin has shown, that neither of these flowers can get the dust
easily for themselves, but of the two No. 1 has the least
difficulty.
Look at a withered primrose, and see how it holds its head down,
and after a little while the yellow crown falls off. It is just
about as it is falling that the anthers or bags of stamens burst
open, and then, in No. 1 (Fig. 44), they are dragged over the
knob and some of the grains stick there. But in the other form
of primrose, No. 2, when the flower falls off, the stamens do
not come near the knob, so it has no chance of getting any
pollen; and while the primrose is upright the tube is so narrow
that the dust does not easily fall. But, as I have said, neither
kind gets it very easily, nor is it good for them if they do. The
seeds are much stronger and better if the dust or pollen of one
flower is carried away and left on the knob or stigma of another
flower; and the only way this can be done is by insects flying
from one flower to another and carrying the dust on their legs and
bodies.
If you suck the end of the tube of the primrose flower you will
find it tastes sweet, because a drop of honey has been lying
there. When the insects go in to get this honey, they brush
themselves against the yellow dust-bags, and some of the dust
sticks to them, and then when they go to the next flower they
rub it off on to its sticky knob.
Look at No. 1 and No. 2 (Fig. 43) and you will see at once that
if an insect goes into No. 1 and the pollen sticks to him, when
he goes into No. 2 just that part of his body on which the
pollen is will touch the knob; and so the flowers become what we
call "crossed," that is, the pollen-dust of the one feeds the
ovule of the other. And just the same thing will happen if he
flies from No. 2 to No. 1. There the dust will be just in the
position to touch the knob which sticks out of the flower.
Therefore, we can see clearly that it is good for the primrose
that bees and other insects should come to it, and anything it
can do to entice them will be useful. Now, do you not think that
when an insect once knew that the pale-yellow crown showed where
honey was to be found, he would soon spy these crowns out as he
flew along? or if they were behind a hedge, and he could not see
them, would not the sweet scent tell him where to come and look
for them? And so we see that the pretty sweet-scented corolla is
not only delightful for us to look at and to smell, but it is
really very useful in helping the primrose to make strong
healthy seeds out of which the young plants are to grow next
year.
And now let us see what we have learnt. We began with a tiny
seed, though we did not then know how this seed had been made.
We saw the plantlet buried in it, and learnt how it fed at first
on prepared food, but soon began to make living matter for
itself out of gases taken from the water through the cells to
its stomach - the leaves! And how marvellously the sun-waves
entering there formed the little green granules, and then helped
them to make food and living protoplasm! At this point we might
have gone further, and studied how the fibres and all the
different vessels of the plant are formed, and a wondrous history
it would have been. But it was too long for one hour's lecture,
and you must read it for yourselves in books on botany. We had to
pass on to the flower, and learn the use of the covering leaves,
the gaily coloured crown attracting the insects, the dust-bags
holding the pollen, the little ovules each with the germ of a new
plantlet, lying hidden in the seed- vessel, waiting for the
pollen-grains to grow down to them. Lastly, when the pollen crept
in at the tiny opening we learnt that the ovule had now all it
wanted to grow into a perfect seed.
And so we came back to a primrose seed, the point from which we
started; and we have a history of our primrose from its birth to
the day when its leaves and flowers wither away and it dies down
for the winter.
But what fairies are they which have been at work here? First,
the busy little fairy Life in the active protoplasm; and
secondly, the sun-waves. We have seen that it was by the help of
the sunbeams that the green granules were made, and the water,
carbonic acid, and nitrogen worked up into the living plant. And
in doing this work the sun-waves were caught and their strength
used up, so that they could no longer quiver back into space. But
are they gone for ever? So long as the leaves or the stem or the
root of the plant remain they are gone, but when those are
destroyed we can get them back again. Take a handful of dry
withered plants and light them with a match, then as the leaves
burn and are turned back again to carbonic acid, nitrogen, and
water, our sunbeams come back again in the flame and heat.
And the life of the plant? What is it, and why is this protoplasm
always active and busy? I cannot tell you. Study as we may, the
life of the tiny plant is as much a mystery as your life and
mine. It came, like all things, from the bosom of the Great
Father, but we cannot tell how it came nor what it is. We can
see the active grains moving under the microscope, but we cannot
see the power that moves them. We only know it is a power given
to the plant, as to you and to me, to enable it to live its
life, and to do its useful work in the world.
Week 22
LECTURE VIII
THE HISTORY OF A PIECE OF COAL
I have here a piece of coal (Fig. 45), which, though it has been
cut with some care so as to have a smooth face, is really in no
other way different from any ordinary lump which you can pick for
yourself out of the coal-scuttle. Our work to-day is to relate
the history of this black lump; to learn what it is, what it has
been, and what it will be.
It looks uninteresting enough at first sight, and yet if we
examine it closely we shall find some questions to ask even about
its appearance. Look at the smooth face of this specimen and see
if you can explain those fine lines which run across so close
together as to look like the edges of the leaves of a book. Try
to break a piece of coal, and you will find that it will split
much more easily along those lines than across the other way of
the lump; and if you wish to light a fire quickly you should
always put this lined face downwards so that the heat can force
its way up through these cracks and gradually split up the block.
Then again if you break the coal carefully along one of these
lines you will find a fine film of charcoal lying in the crack,
and you will begin to suspect that this black coal must have been
built up in very thin layers, with a kind of black dust between
them.
The next thing you will call to mind is that this coal burns and
gives flame and heat, and that this means that in some way
sunbeams are imprisoned in it; lastly, this will lead you to
think of plants, and how they work up the strength of the
sunbeams into their leaves, and hide black carbon in even the
purest and whitest substance they contain.
Is coal made of burnt plants, then? Not burnt ones, for if so it
would not burn again; but you may have read how the makers of
charcoal take wood and bake it without letting it burn, and then
it turns black and will afterwards make a very good fire; and so
you will see that it is probable that our piece of coal is made
of plants which have been baked and altered, but which have still
much sunbeam strength bottled up in them, which can be set free
as they burn.
If you will take an imaginary journey with me to a coal-pit near
Newcastle, which I visited many years ago, you will see that we
have very good evidence that coal is made of plants, for in all
coal-mines we find remains of them at every step we take.
Let us imagine that we have put on old clothes which will not
spoil, and have stepped into the iron basket (see Fig. 46) called
by the miners a cage, and are being let down the shaft to the
gallery where the miners are at work. Most of them will probably
be in the gallery b, because a great deal of the coal in a has
been already taken out. But we will stop in a because there we
can see a great deal of the roof and the floor. When we land on
the floor of the gallery we shall find ourselves in a kind of
tunnel with railway lines laid along it and trucks laden with
coal coming towards the cage to be drawn up, while empty ones are
running back to be loaded where the miners are at work. Taking
lamps in our hands and keeping out of the way of the trucks, we
will first throw the light on the roof, which is made of shale or
hardened clay. We shall not have gone many yards before we see
impressions of plants in the shale, like those in this specimen
(Fig. 47), which was taken out of a coal-mine at Neath in
Glamorganshire, a few days ago, and sent up for this lecture.
You will recognize at once the marks of ferns (a), for they look
like those you gather in the hedges of an ordinary country lane,
and that long striped branch (b) does not look unlike a reed, and
indeed it is something of this kind, as we shall see by-and-by.
You will find plenty of these impressions of plants as you go
along the gallery and look up at the roof, and with them there
will be others with spotted stems, or with stems having a curious
diamond pattern upon them, and many ferns of various kinds.
Next look down at your feet and examine the floor. You will not
have to search long before you will almost certainly find a piece
of stone like that represented in Fig. 48, which has also come
from Neath Colliery. This fossil, which is the cast of a piece
of a plant, puzzled those who found it for a very long time. At
last, however, Mr. Binney found the specimen growing to the
bottom of the trunk of one of the fossil trees with spotted
stems, called Sigillaria; and so proved that this curious pitted
stone is a piece of fossil root, or rather underground stem, like
that which we found in the primrose, and that the little pits or
dents in it are scars where the rootlets once were given off.
Whole masses of these root-stems, with ribbon-like roots lying
scattered near them, are found buried in the layer of clay called
the underclay which makes the floor of the coal, and they prove
to us that this underclay must have been once the ground in which
the roots of the coal-plants grew. You will feel still more sure
of this when you find that there is not only one straight gallery
of coal, but that galleries branch out right and left, and that
everywhere you find the coal lying like a sandwich between the
floor and the roof, showing that quite a large piece of country
must be covered by these remains of plants all rooted in the
underclay.
But how about the coal itself? It seems likely, when we find
roots below and leaves and stems above, that the middle is made
of plants, but can we prove it? We shall see presently that it
has been so crushed and altered by being buried deep in the
ground that the traces of leaves have almost been destroyed,
though people who are used to examining with the microscope, can
see the crushed remains of plants in thin slices of coal.
But fortunately for us, perfect pieces of plants have been
preserved even in the coal-bed itself. Do you remember our
learning in Lecture IV, that water with lime in it petrifies
things, that is, leaves carbonate of lime to fill up grain by
grain the fibres of an animal or plant as the living matter
decays, and so keeps an exact representation of the object?
Now, it so happens that in a coal-bed at South Ouram, near
Halifax, as well as in some other places, carbonate of lime
trickled in before the plants were turned into coal, and made
some round nodules in the plant-bed, which look like cannon-
balls. Afterwards, when all the rest of the bed was turned into
coal, these round balls remained crystallized, and by cutting
thin transparent slices across the nodule we can distinctly see
the leaves and stems and curious little round bodies which make
up the coal. Several such sections may be seen at the British
Museum, and when we compare these fragments of plants with those
which we find above and below the coal-bed, we find that they
agree, thus proving that coal is made of plants, and of those
plants whose roots grew in the clay floor, while their heads
reached up far above where the roof now is.
The next question is, what kind of plants were these? Have we
anything like them living in the world now? You might perhaps
think that it would be impossible to decide this question from
mere petrified pieces of plants. But many men have spent their
whole lives in deciphering all the fragments that could be found,
and though the section given in Fig. 49 may look to you quite
incomprehensible, yet a botanist can reed it as we read a book.
For example, at S and L, where stems are cut across, he can learn
exactly how they were build up inside, and compare them with the
stems of living plants, while the fruits cc and the little round
spores lying near them, tell him their history as well as if he
had gathered them from the tree. In this way we have learnt to
know very fairly what the plants of the coal were like, and you
will be surprised when I tell you that the huge trees of the
coal-forests, of which we sometimes find trunks in the coal-mines
from ten to fifty feet long, are only represented on the earth
now by small insignificant plants, scarcely ever more than two
feet, and often not many inches high.
Have you ever seen the little club moss or Lycopodium which grows
all over England, but chiefly in the north, on heaths and
mountains? At the end of each of its branches it bears a cone
made of scaly leaves; and fixed to the inside of each of these
leaves is a case called a sporangium, full of little spores or
moss-seeds, as we may call them, though they are not exactly like
true seeds. In one of these club-mosses called Selaginella, the
cases near the bottom of the cone contain large spores, while
those near the top contain a powdery dust. These spores are full
of resin, and they are collected on the Continent for making
artificial lightning in the theatres, because they flare when
lighted.
Now this little Selaginella is of all living plants the one most
like some of the gigantic trees of the coal-forests. If you look
at this picture of a coal-forest (Fig. 51), you will find it
difficult perhaps to believe that those great trees, with diamond
markings all up the trunk, hanging over from the right to the
left of the picture, and covering all the top with their boughs,
could be in any way relations of the little Selaginella; yet we
find branches of them in the beds above the coal, bearing cones
larger but just like Selaginella cones; and what is most curious,
the spores in these cones are of exactly the same kind and not
any larger than those of the club-mosses.
These trees are called by botanists Lepidodendrons, or scaly
trees; there are numbers of them in all coal-mines, and one trunk
has been found 49 feet long. Their branches were divided in a
curious forked manner and bore cones at the ends. The spores
which fell from these cones are found flattened in the coal, and
they may be seen scattered about in the coal-ball.
Week 23
Another famous tree which grew in the coal-forests was the one
whose roots we found in the floor or underclay of the coal. It
has been called Sigillaria, because it has marks like seals
(sigillum, a seal) all up the trunk, due to the scars left by the
leaves when they fell from the tree. You will see the
Sigillarias on the left-hand side of the coal-forest picture,
having those curious tufts of leaves springing out of them at the
top. Their stems make up a great deal of the coal, and the bark
of their trunks is often found in the clays above, squeezed flat
in lengths of 30, 60, or 70 feet. Sometimes, instead of being
flat the bark is still in the shape of a trunk, and the interior
is filled with sane; and then the trunk is very heavy, and if the
miners do not prop the roof up well it falls down and kills those
beneath it. Stigmaria is the root of the Sigillaria, and is
found in the clays below the coal. Botanists are not yet quite
certain about the seed-cases of this tree, but Mr. Carruthers
believes that they grew inside the base of the leaves, as they do
in the quillwort, a small plant which grows at the bottom of our
mountain lakes.
But what is that curious reed-like stem we found in the piece of
shale (see Fig. 47)? That stem is very important, for it
belonged to a plant called a Calamite, which, as we shall see
presently, helped to sift the earth away from the coal and keep
it pure. This plant was a near relation of the "horsetail," or
Equisetum, which grows in our marshes; only, just as in the case
of the other trees, it was enormously larger, being often 20 feet
high, whereas the little Equisetum, Fig. 52, is seldom more than
a foot, and never more than 4 feet high in England, though in
tropical South America they are much higher. Still, if you have
ever gathered "horsetails," you will see at once that those trees
in the foreground of the picture (Fig. 51), with leaves arranged
in stars round the branches, are only larger copies of the little
marsh-plants; and the seed-vessels of the two plants are almost
exactly the same.
These great trees, the Lepidodendrons, the Sigillarias, and the
Calamites, together with large tree-ferns, are the chief plants
that we know of in the coal-forests. It seems very strange at
first that they should have been so large when their descendants
are now so small, but if you look at our chief plants and trees
now, you will find that nearly all of them bear flowers, and this
is a great advantage to them, because it tempts the insects to
bring them the pollen-dust, as we saw in the last lecture.
Now the Lipidodendrons and their companions had no true flowers,
but only these seed-cases which we have mentioned; but as there
were no flowering plants in their time, and they had the ground
all to themselves, they grew fine and large. By-and-by, however,
when the flowering plants came in, these began to crowd out the
old giants of the coal-forests, so that they dwindled and
dwindled from century to century till their great-great-
grandchildren, thousands of generations after, only lift up their
tiny heads in marshes and on heaths, and tell us that they were
big once upon a time.
And indeed they must have been magnificent in those olden days,
when they grew thick and tall in the lonely marshes where plants
and trees were the chief inhabitants. We find no traces in the
clay-beds of the coal to lead us to suppose that men lived in
those days, nor lions, nor tigers, nor even birds to fly among
the trees; but these grand forests were almost silent, except
when a huge animal something like a gigantic newt or frog went
croaking through the marsh, or a kind of grasshopper chirruped on
the land. But these forms of life were few and far between,
compared to the huge trees and tangled masses of ferns and reeds
which covered the whole ground, or were reflected in the bosom of
the large pools and lakes round about which they grew.
And now, if you have some idea of the plants and trees of the
coal, it is time to ask how these plants became buried in the
earth and made pure coal, instead of decaying away and leaving
behind only a mixture of earth and leaves?
To answer this question, I must ask you to take another journey
with me across the Atlantic to the shores of America, and to land
at Norfolk in Virginia, because there we can see a state of
things something like the marshes of the coal-forests. All round
about Norfolk the land is low, flat, and marshy, and to the south
of the town, stretching far away into North Carolina, is a large,
desolate swamp, no less than forty miles long and twenty-five
broad. The whole place is one enormous quagmire, overgrown with
water-plants and trees. The soil is as black as ink from the
old, dead leaves, grasses, roots, and stems which lie in it; and
so soft, that everything would sink into it, if it were not for
the matted roots of the mosses, ferns, and other plants which
bind it together. You may dig down for ten or fifteen feet, and
find nothing but peat made of the remains of plants which have
lived and died there in succession for ages and ages, while the
black trunks of the fallen trees lie here and there, gradually
being covered up by the dead plants.
The whole place is so still, gloomy, and desolate, that it goes
by the name of the "Great Dismal Swamp," and you see we have here
what might well be the beginning of a bed of coal; for we know
that peat when dried becomes firm and makes an excellent fire,
and that if it were pressed till it was hard and solid it would
not be unlike coal. If, then, we can explain how this peaty bed
has been kept pure from earth, we shall be able to understand how
a coal-bed may have been formed, even though the plants and trees
which grow in this swamp are different from those which grew in
the coal-forests.
The explanation is not difficult; streams flow constantly, or
rather ooze into the Great Dismal Swamp from the land that lies
to the west, but instead of bringing mud in with them as rivers
bring to the sea, they bring only clear, pure water, because, as
they filter for miles through the dense jungle of reeds, ferns,
and shrubs which grow round the marsh, all the earth is sifted
out and left behind. In this way the spongy mass of dead plants
remains free from earthy grains, while the water and the shade of
the thick forest of trees prevent the leaves, stems, etc., from
being decomposed by the air and sun. And so year after year as
the plants die they leave their remains for other plants to take
root in, and the peaty mass grows thicker and thicker, while tall
cedar trees and evergreens live and die in these vast, swampy
forests, and being in loose ground are easily blown down by the
wind, and leave their trunks to be covered up by the growing moss
and weeds.
Now we know that there were plenty of ferns and of large
Calamites growing thickly together in the coal-forests, for we
find their remains everywhere in the clay, so we can easily
picture to ourselves how the dense jungle formed by these plants
would fringe the coal-swamp, as the present plants do the Great
Dismal Swamp, and would keep out all earthy matter, so that year
after year the plants would die and form a thick bed of peat,
afterwards to become coal.
Week 24
The next thing we have to account for is the bed of shale or
hardened clay covering over the coal. Now we know that from time
to time land has gone slowly up and down on our globe so as in
some places to carry the dry ground under the sea, and in others
to raise the sea-bed above the water. Let us suppose, then, that
the great Dismal Swamp was gradually to sink down so that the sea
washed over it and killed the reeds and shrubs. Then the streams
from the west would not be sifted any longer but would bring down
mud, and leave it, as in the delta of the Nile or Mississippi, to
make a layer over the dead plants. You will easily understand
that this mud would have many pieces of dead trees and plants in
it, which were stifled and died as it covered them over; and thus
the remains would be preserved like those which we find now in
the roof of the coal-galleries.
But still there are the thick sandstones in the coal-mine to be
explained. How did they come there? To explain them, we must
suppose that the ground went on sinking till the sea covered the
whole place where once the swamp had been, and then sea-sand
would be thrown down over the clay and gradually pressed down by
the weight of new sand above, till it formed solid sandstone and
our coal-bed became buried deeper and deeper in the earth.
At last, after long ages, when the thick mass of sandstones above
the bed b (Fig. 46) had been laid down, the sinking must have
stopped and the land have risen a little, so that the sea was
driven back; and then the rivers would bring down earth again and
make another clay-bed. Then a new forest would spring up, the
ferns, Calamites, Lepidodendrons, and Sigillarias would gradually
form another jungle, and many hundred of feet above the buried
coal-bed b, a second bed of peat and vegetable matter would begin
to accumulate to form the coal-bed a.
Such is the history of how the coal which we now dig out of the
depths of the earth once grew as beautiful plants on the surface.
We cannot tell exactly all the ground over which these forests
grew in England, because some of the coal they made has been
carried away since by rivers and cut down by the waves of the
sea, but we can say that wherever there is coal now, there they
must have been then.
Try and picture to yourselves that on the east coast of
Northumberland and Durham, where all is now black with coal-
dust, and grimy with the smoke of furnaces; and where the noise
of hammers and steam-engines, and of carts and trucks hurrying to
and fro, makes the country re-echo with the sound of labour;
there ages ago in the silent swamp shaded with monster trees, one
thin layer of plants after another was formed, year after year,
to become the coal we now value so much. In Lancashire, busy
Lancashire, the same thing was happening, and even in the middle
of Yorkshire and Derbyshire the sea must have come up and washed
a silent shore where a vast forest spread out over at least 700
or 800 square miles. In Stafford-shire, too, which is now almost
the middle of England, another small coal-field tells the same
story, while in South Wales the deep coal-mines and number of
coal-seams remind us how for centuries and centuries forests must
have flourished and have disappeared over and over again under
the sand of the sea.
But what is it that has changed these beds of dead plants into
hard, stony coal? In the first place you must remember they have
been pressed down under an enormous weight of rocks above them.
We can learn something about this even from our common lead
pencils. At one time the graphite or pure carbon, of which the
blacklead (as we wrongly call it) of our pencils is made, was dug
solid out of the earth. but so much has now been used that they
are obliged to collect the graphite dust, and press it under a
heavy weight, and this makes such solid pieces that they can cut
them into leads for ordinary cedar pencils.
Now the pressure which we can exert by machinery is absolutely
nothing compared to the weight of all those hundreds of feet of
solid rock which lie over the coal-beds, and which has pressed
them down for thousands and perhaps millions of years; and
besides this, we know that parts of the inside of the earth are
very hot, and many of the rocks in which coal is found are
altered by heat. So we can picture to ourselves that the coal
was not only squeezed into a solid mass, but often much of the
oil and gas which were in the leaves of the plants was driven out
by heat, and the whole baked, as it were, into one substance.
The difference between coal which flames and coal which burns
only with a red heat, is chiefly that one has been baked and
crushed more than the other. Coal which flames has still got in
it the tar and the gas and the oils which the plant stored up in
its leaves, and these when they escape again give back the
sunbeams in a bright flame. The hard stone coal, on the contrary,
has lost a great part of these oils, and only carbon remains,
which seizes hold of the oxygen of the air and burns without
flame. Coke is pure carbon, which we make artificially by driving
out the oils and gases from coal, and the gas we burn is part of
what is driven out.
We can easily make coal-gas here in this room. I have brought a
tobacco-pipe, the bowl of which is filled with a little powdered
coal, and the broad end cemented up with Stourbridge clay. When
we place this bowl over a spirit-lamp and make it very hot, the
gas is driven out at the narrow end of the pipe and lights easily
(see Fig. 53). This is the way all our gas is made, only that
furnaces are used to bake the coal in, and the gas is passed into
large reservoirs till it is wanted for use.
You will find it difficult at first to understand how coal can be
so full of oil and tar and gases, until you have tried to think
over how much of all these there is in plants, and especially in
seeds - think of the oils of almonds, of lavender, of cloves, and
of caraways; and the oils of turpentine which we get from the
pines, and out of which tar is made. When you remember these and
many more, and also how the seeds of the club-moss now are
largely charged with oil, you will easily imagine that the large
masses of coal-plants which have been pressed together and broken
and crushed, would give out a great deal of oil which, when made
very hot, rises up as gas. You may often yourself see tar oozing
out of the lumps of coal in a fire, and making little black
bubbles which burst and burn. It is from this tar that James
Young first made the paraffin oil we burn in our lamps, and the
spirit benzoline comes from the same source.
From benzoline, again, we get a liquid called aniline, from which
are made so many of our beautiful dyes - mauve, magenta, and
violet; and what is still more curious, the bitter almonds, pear-
drops, and many other sweets which children like to well, are
actually flavoured by essences which come out of coal-tar. Thus
from coal we get not only nearly all our heat and our light, but
beautiful colours and pleasant flavours. We spoke just now of
the plants of the coal as being without beautiful flowers, and
yet we see that long, long after their death they give us lovely
colours and tints as beautiful as any in flower-world now.
Think, then, how much we owe to these plants which lived and died
so long ago! If they had been able to reason, perhaps they might
have said that they did not seem of much use in the world. They
had no pretty flowers, and there was no one to admire their
beautiful green foliage except a few croaking reptiles, and
little crickets and grasshoppers; and they lived and died all on
one spot, generation after generation, without seeming to do much
good to anything or anybody. Then they were covered up and put
out of sight, and down in the dark earth they were pressed all
out of shape and lost their beauty and became only black, hard
coal. There they lay for centuries and centuries, and thousands
and thousands of years, and still no one seemed to want them.
At last, one day, long, long after man had been living on the
earth, and had been burning wood for fires, and so gradually
using up the trees in the forests, it was discovered that this
black stone would burn, and from that time coal has been becoming
every day more and more useful. Without it not only should we
have been without warmth in our houses, or light in our streets
when the stock of forest-wood was used up; but we could never
have melted large quantities of iron-stone and extracted the
iron. We have proof of this in Sussex. The whole country is
full of iron-stone, and the railings of St. Paul's churchyard are
made of Sussex iron. Iron-foundries were at work there as long
as there was wood enough to supply them, but gradually the works
fell into disuse, and the last furnace was put out in the year
1809. So now, because there is no coal in Sussex, the iron lies
idle, while in the North, where the iron-stone is near the coal-
mines, hundreds of tons are melted out every day.
Again, without coal we could have had no engines of any kind, and
consequently no large manufactories of cotton goods, linen goods,
or cutlery. In fact, almost everything we use could only have
been made with difficulty and in small quantities; and even if we
could have made them it would have been impossible to have sent
them so quickly all over the world without coal, for we could
have had no railways or steamships, but must have carried all
goods along canals, and by slow sailing vessels. We ourselves
must have taken days to perform journeys now made in a few hours,
and months to reach our colonies.
In consequence of this we should have remained a very poor
people. Without manufactories and industries we should have had
to live chiefly by tilling the ground, and everyone being obliged
to toil for daily bread, there would have been much less time or
opportunity for anyone to study science, or literature, or
history, or to provide themselves with comforts and refinements
of life.
All this then, those plants and trees of the far-off ages, which
seemed to lead such useless lives, have done and are doing for
us. There are many people in the world who complain that life is
dull, that they do not see the use of it, and that there seems no
work specially for them to do. I would advise such people,
whether they are grown up or little children, to read the story
of the plants which form the coal. These saw no results during
their own short existences, they only lived and enjoyed the
bright sunshine, and did their work, and were content. And now
thousands, probably millions, of years after they lived and died,
England owes her greatness, and we much of our happiness and
comfort, to the sunbeams which those plants wove into their
lives.
They burst forth again in our fires, in our brilliant lights, and
in our engines, and do the greater part of our work; teaching us
"That nothing walks with aimless feet
That not one life shall be destroyed,
Or cast as rubbish to the void,
When God hath made the pile complete."
In Memoriam
Week 25
Lecture IX
Bees in the Hive
I am going to ask you to visit with me to-day one of the most
wonderful cities with no human beings in it, and yet it is
densely populated, for such a city may contain from twenty
thousand to sixty thousand inhabitants. In it you will find
streets, but no pavements, for the inhabitants walk along the
walls of the houses; while in the houses you will see no windows,
for each house just fits its owner, and the door is the only
opening in it. Though made without hands these houses are most
evenly and regularly built in tiers one above the other; and here
and there a few royal palaces, larger and more spacious than the
rest, catch the eye conspicuously as they stand out at the corners
of the streets.
Some of the ordinary houses are used to live in, while others
serve as storehouses where food is laid up in the summer to feed
the inhabitants during the winter, when they are not allowed to
go outside the walls. Not that the gates are ever shut: that is
not necessary, for in this wonderful city each citizen follows
the laws; going out when it is time to go out, coming home at
proper hours, and staying at home when it is his or her duty.
And in the winter, when it is very cold outside, the inhabitants,
having no fires, keep themselves warm within the city by
clustering together, and never venturing out of doors.
One single queen reigns over the whole of this numerous
population, and you might perhaps fancy that, having so many
subjects to work for her and wait upon her, she would do nothing
but amuse herself. On the contrary, she too obeys the laws laid
down for her guidance, and never, except on one or two state
occasions, goes out of the city, but works as hard as the rest in
performing her own royal duties.
From sunrise to sunset, whenever the weather is fine, all is
life, activity, and bustle in this busy city. Though the gates
are so narrow that two inhabitants can only just pass each other
on their way through them, yet thousands go in and out every hour
of the day; some bringing in materials to build new houses, others
food and provisions to store up for the winter; and while all
appears confusion and disorder among this rapidly moving throng,
yet in reality each has her own work to do, and perfect order
reigns over the whole.
Even if you did not already know from the title of the lecture
what city this is that I am describing, you would no doubt guess
that it is a beehive. For where in the whole world, except
indeed upon an anthill, can we find so busy, so industrious, or
so orderly a community as among the bees? More than a hundred
years ago, a blind naturalist, Francois Huber, set himself to
study the habits of these wonderful insects and with the help of
his wife and an intelligent manservant managed to learn most of
their secrets. Before his time all naturalists had failed in
watching bees, because if they put them in hives with glass
windows, the bees, not liking the light, closed up the windows
with cement before they began to work. But Huber invented a hive
which he could open and close at will, putting a glass hive
inside it, and by this means he was able to surprise the bees at
their work. Thanks to his studies, and to those of other
naturalists who have followed in his steps, we now know almost
as much about the home of bees as we do about our own; and if we
follow out to-day the building of a bee-city and the life of its
inhabitants, I think you will acknowledge that they are a
wonderful community, and that it is a great compliment to anyone
to say that he or she is "as busy as a bee."
In order to begin at the beginning of the story, let us suppose
that we go into a country garden one fine morning in May when
the sun is shining brightly overhead, and that we see hanging
from the bough of an old apple-tree a black object which looks
very much like a large plum-pudding. On approaching it, however,
we see that it is a large cluster or swarm of bees clinging to
each other by their legs; each bee with its two fore-legs
clinging to the two hinder legs of the one above it. In this way
as many as 20,000 bees may be clinging together, and yet they
hang so freely that a bee, even from quite the centre of the
swarm, can disengage herself from her neighbours and pass
through to the outside of the cluster whenever she wishes.
If these bees were left to themselves, they would find a home
after a time in a hollow tree, or under the roof of a house, or
in some other cavity, and begin to build their honeycomb there.
But as we do not wish to lose their honey we will bring a hive,
and, holding it under the swarm, shake the bough gently so that
the bees fall into it, and cling to the sides as we turn it over
on a piece of clean linen, on the stand where the hive is to be.
And now let us suppose that we are able to watch what is going on
in the hive. Before five minutes are over the industrious little
insects have begun to disperse and to make arrangements in their
new home. A number (perhaps about two thousand) of large,
lumbering bees of a darker colour than the rest, will it is true,
wander aimlessly about the hive, and wait for the others to feed
them and house them; but these are the drones, or male bees (3,
Fig. 54), who never do any work except during one or two days in
their whole lives. But the smaller working bees (1, Fig. 54) begin
to be busy at once. Some fly off in search of honey. Others walk
carefully all round the inside of the hive to see if there are any
cracks in it; and if there are, they go off to the horse-chestnut
trees, poplars, hollyhocks, or other plants which have sticky
buds, and gather a kind of gum called "propolis," with which they
cement the cracks and make them air-tight. Others again, cluster
round one bee (2, Fig. 54) blacker than the rest and having a
longer body and shorter wings; for this is the queen-bee, the
mother of the hive, and she must be watched and tended.
But the largest number begin to hang in a cluster from the roof
just as they did from the bough of the apple tree. What are they
doing there? Watch for a little while and you will soon see one
bee come out from among its companions and settle on
the top of the inside of the hive, turning herself round and
round, so as to push the other bees back, and to make a space in
which she can work. Then she will begin to pick at the under
part of her body with her fore-legs, and will bring a scale of
wax from a curious sort of pocket under her abdomen. Holding
this wax in her claws, she will bite it with her hard, pointed
upper jaws, which move to and fro sideways like a pair of
pincers, then, moistening it with her tongue into a kind of
paste, she will draw it out like a ribbon and plaster it on the
top of the hive.
After that she will take another piece; for she has eight of
these little wax-pockets, and she will go on till they are all
exhausted. Then she will fly away out of the hive, leaving a
small lump on the hive ceiling or on the bar stretched across
it; then her place will be taken by another bee who will go
through the same manoeuvres. This bee will be followed by
another, and another, till a large wall of wax has been built,
hanging from the bar of the hive as in Fig. 55, only that it
will not yet have cells fashioned in it.
Meanwhile the bees which have been gathering honey out of doors
begin to come back laden. But they cannot store their honey, for
there are no cells made yet to put it in; neither can
they build combs with the rest, for they have no wax in their
wax-pockets. So they just go and hang quietly on to the other
bees, and there they remain for twenty-four hours, during which
time they digest the honey they have gathered, and part of it
forms wax and oozes out from the scales under their body. Then
they are prepared to join the others at work and plaster wax on
to the hive.
Week 26
And now, as soon as a rough lump of wax is ready, another set of
bees come to do their work. These are called the nursing bees,
because they prepare the cells and feed the young ones. One of
these bees, standing on the roof of the hive, begins to force
her head into the wax, biting with her jaws and moving her head
to and fro. Soon she has made the beginning of a round hollow,
and then she passes on to make another, while a second bee takes
her place and enlarges the first one. As many as twenty bees
will be employed in this way, one after another, upon each hole
before it is large enough for the base of a cell.
Meanwhile another set of nursing bees have been working just in
the same way on the other side of the wax, and so a series of
hollows are made back to back all over the comb. Then the bees
form the walls of the cells and soon a number of six-sided
tubes, about half an inch deep, stand all along each side of the
comb ready to receive honey or bee-eggs.
You can see the shape of these cells in c,d, Fig. 56, and notice
how closely they fit into each other. Even the ends are so
shaped that, as they lie back to back, the bottom of one cell
(B, Fig. 56) fits into the space between the ends of
three cells meeting it from the opposite side (A, Fig. 56),
while they fit into the spaces around it. Upon this plan the
clever little bees fill every atom of space, use the least
possible quantity of wax, and make the cells lie so closely
together that the whole comb is kept warm when the young bees
are in it.
There are some kinds of bees who do not live in hives, but each
one builds a home of its own. These bees - such as the
upholsterer bee, which digs a hole in the earth and lines it
with flowers and leaves, and the mason bee, which builds in
walls - do not make six-sided cells, but round ones, for room is
no object to them. But nature has gradually taught the little
hive-bee to build its cells more and more closely, till they fit
perfectly within each other. If you make a number of round holes
close together in a soft substance, and then squeeze the
substance evenly from all sides, the rounds will gradually take
a six-sided form, showing that this is the closest shape into
which they can be compressed. Although the bee does not know
this, yet as gnaws away every bit of wax that can be
spared she brings the holes into this shape.
As soon as one comb is finished, the bees begin another by the
side of it, leaving a narrow lane between, just broad enough for
two bees to pass back to back as they crawl along, and so the
work goes on till the hive is full of combs.
As soon, however, as a length of about five or six inches of the
first comb has been made into cells, the bees which are bringing
home honey no longer hang to make it into wax, but begin to
store it in the cells. We all know where the bees go to fetch
their honey, and how, when a bee settles on a flower, she
thrusts into it her small tongue-like proboscis, which is really
a lengthened under-lip, and sucks out the drop of honey. This she
swallows, passing it down her throat into a honey-bag or first
stomach, which lies between her throat and her real stomach, and
when she gets back to the hive she can empty this bag and pass
honey back through her mouth again into the honey-cells.
But if you watch bees carefully, especially in the spring-time,
you will find that they carry off something else besides honey.
Early in the morning, when the dew is on the ground, or later in
the day, in moist shady places, you may see a bee rubbing itself
against a flower, or biting those bags of yellow dust or pollen
which we mentioned in Lecture VII. When she has covered herself
with pollen, she will brush it off with her feet, and, bringing
it to her mouth, she will moisten and roll it into a little ball,
and then pass it back from the first pair of legs to the second
and so to the third or hinder pair. Here she will pack it into a
little hairy groove called a "basket" in the joint of one of the
hind legs, where you may see it, looking like a swelled joint, as
she hovers among the flowers. She often fills both hind legs in
this way, and when she arrives back at the hive the nursing bees
take the lumps form her, and eat it themselves, or mix it with
honey to feed the young bees; or, when they have any to spare,
store it away in old honey-cells to be used by-and-by. This is the
dark, bitter stuff called "bee- bread" which you often find in a
honeycomb, especially in a comb which has been filled late in the
summer.
When the bee has been relieved of the bee-bread she goes off to
one of the clean cells in the new comb, and, standing on the
edge, throws up the honey from the honey-bag into the cell. One
cell will hold the contents of many honey-bags, and so the busy
little workers have to work all day filling cell after cell, in
which the honey lies uncovered, being too thick and sticky to
flow out, and is used for daily food - unless there is any to
spare, and then they close up the cells with wax to keep for the
winter.
Meanwhile, a day or two after the bees have settled in the hive,
the queen-bee begins to get very restless. She goes outside the
hive and hovers about a little while, and then comes in again,
and though generally the bees all look very closely after her to
keep her indoors, yet now they let her do as she likes. Again
she goes out, and again back, and then, at last, she soars up
into the air and flies away. But she is not allowed to go alone.
All the drones of the hive rise up after her, forming
a guard of honour to follow her wherever she goes.
In about half-an-hour she comes back again, and then the working
bees all gather round her, knowing that now she will remain
quietly in the hive and spend all her time in laying eggs; for
it is the queen-bee who lays all the eggs in the hive. This she
begins to do about two days after her flight. There are now many
cells ready besides those filled with honey; and, escorted by
several bees, the queen-bee goes to one of these, and, putting
her head into it remains there a second as if she were examining
whether it would make a good home for the young bee. Then,
coming out, she turns round and lays a small, oval, bluish-white
egg in the cell. After this she takes no more notice of it, but
goes on to the next cell and the next, doing the same thing, and
laying eggs in all the empty cells equally on both sides of the
comb. She goes on so quickly that she sometimes lays as many as
200 eggs in one day.
Then the work of the nursing bees begins. In two or three days
each egg has become a tiny maggot or larva, and the nursing bees
put into its cell a mixture of pollen and honey which they have
prepared in their own mouths, thus making a kind of sweet bath
in which the larva lies. In five or six days the larva grows so
fat upon this that it nearly fills the cell, and then the bees
seal up the mouth of the cell with a thin cover of wax, made of
little rings and with a tiny hole in the centre.
As soon as the larva is covered in, it begins to give out from
its under-lip a whitish, silken film, made of two threads of silk
glued together, and with this it spins a covering or cocoon all
round itself, and so it remains for about ten days more. At last,
just twenty-one days after the egg was laid, the young bee is
quite perfect, lying in the cell as in Fig. 57, and she begins to
eat her way through the cocoon and through the waxen lid, and
scrambles out of her cell. Then the nurses come again to her,
stroke her wings and feed her for twenty-four hours, and after
that she is quite ready to begin work, and flies out to gather
honey and pollen like the rest of the workers.
By this time the number of working bees in the hive is becoming
very great, and the storing of honey and pollen-dust goes on
very quickly. Even the empty cells which the young bees have
left are cleaned out by the nurses and filled with honey; and
this honey is darker than that stored in clean cells, and which
we always call "virgin honey" because it is so pure and clear.
At last, after six weeks, the queen leaves off laying worker-
eggs, and begins to lay, in some rather larger cells, eggs from
which drones, or male bees, will grow up in about twenty days.
Meanwhile the worker-bees have been building on the edge of the
cones some very curious cells (q, Fig. 57) which look like
thimbles hanging with the open side upwards, and about every three
days the queen stops in laying drone-eggs and goes to put an egg
in one of these cells. Notice that she waits three days between
each of these peculiar layings, because we shall see presently
that there is a good reason for her doing so.
The nursing bees take great care of these eggs, and instead of
putting ordinary food into the cell, they fill it with a sweet,
pungent jelly, for this larva is to become a princess and a
future queen bee. Curiously enough, it seems to be the peculiar
food and the size of the cell which makes the larva grow into a
mother-bee which can lay eggs, for if a hive has the misfortune
to lose its queen, they take one of the ordinary worker-larvae
and put it into a royal cell and feed it with jelly, and it
becomes a queen-bee. As soon as the princess is shut in like the
others, she begins to spin her cocoon, but she does not quite
close it as the other bees do, but leaves a hole at the top.
Week 27
At the end of sixteen days after the first royal egg was laid,
the eldest princess begins to try to eat her way out of her
cell, and about this time the old queen becomes very uneasy, and
wanders about distractedly. The reason of this is that there can
never be two queen-bees in one hive, and the queen knows that
her daughter will soon be coming out of her cradle and will try
to turn her off her throne. So, not wishing to have to fight for
her kingdom, she makes up her mind to seek a new home and take a
number of her subjects with her. If you watch the hive about this
time you will notice many of the bees clustering together after
they have brought in their honey, and hanging patiently, in order
to have plenty of wax ready to use when they start, while the
queen keeps a sharp look-out for a bright, sunny day, on which
they can swarm: for bees will never swarm on a wet or doubtful day
if they can possibly help it, and we can easily understand why,
when we consider how the rain would clog their wings and spoil the
wax under their bodies.
Meanwhile the young princess grows very impatient, and tries to
get out of her cell, but the worker-bees drive her back, for
they know there would be a terrible fight if the two queens met.
So they close up the hole she has made with fresh wax after
having put in some food for her to live upon till she is
released.
At last a suitable day arrives, and about ten or eleven o'clock
in the morning the old queen leaves the hive, taking with her
about 2000 drones and from 12,000 to 20,000 worker-bees, which
fly a little way clustering round her till she alights on the
bough of some tree, and then they form a compact swarm ready for
a new hive or to find a home of their own.
Leaving them to go their way, we will now return to the old hive.
Here the liberated princess is reigning in all her glory; the
worker-bees crowd round her, watch over her, and feed her as
though they could not do enough to show her honour. But still
she is not happy. She is restless, and runs about as if looking
for an enemy, and she tries to get at the remaining royal cells
where the other young princesses are still shut in. But the
workers will not let her touch them, and at last she stands still
and begins to beat the air with her wings and to tremble all over,
moving more and more quickly, till she makes quite a loud, piping
noise.
Hark! What is that note answering her? It is a low, hoarse sound,
and it comes from the cell of the next eldest princess. Now we
see why the young queen has been so restless. She knows her
sister will soon come out, and the louder and stronger the sound
becomes within the cell, the sooner she knows the fight will
have to begin. And so she makes up her mind to follow her
mother's example and to lead off a second swarm. But she cannot
always stop to choose a fine day, for her sister is growing very
strong and may come out of her cell before she is off. And so
the second, or after swarm, gets ready and goes away. And this
explains why princesses' eggs are laid a few days apart, for if
they were laid all on the same day, there would be no time for
one princess to go off with a swarm before the other came out of
her cell. Sometimes, when the workers are not watchful enough,
two queens do meet, and then they fight till one is killed; or
sometimes they both go off with the same swarm without finding
each other out. But this only delays the fight till they get
into the new hive; sooner or later one must be killed.
And now a third queen begins to reign in the old hive, and she
is just as restless as the preceding ones, for there are still
more princesses to be born. But this time, if no new swarm wants
to start, the workers do not try to protect the royal cells. The
young queen darts at the first she sees, gnaws a hole with her
jaws, and, thrusting in her sting through the hole in the cocoon,
kills the young bee while it is still a prisoner. She then goes to
the next, and the next, and never rests till all the young
princesses are destroyed. Then she is contented, for she knows no
other queen will come to dethrone her. After a few days she takes
her flight in the air with the drones, and comes home to settle
down in the hive for the winter.
Then a very curious scene takes place. The drones are no more
use, for the queen will not fly out again, and these idle bees
will never do any work in the hive. So the worker-bees begin to
kill them, falling upon them, and stinging them to death, and as
the drones have no stings they cannot defend themselves, and in
a few days there is not a drone, nor even a drone-egg, left in
the hive. This massacre seems very sad to us, since the poor
drones have never done any harm beyond being hopelessly idle.
But it is less sad when we know that they could not live many
weeks, even if they were not attacked, and, with winter coming,
the bees cannot afford to feed useless mouths, so a quick death
is probably happier for them than starvation.
And now all the remaining inhabitants of the hive settle down to
feeding the young bees and laying in the winter's store. It is
at this time, after they have been toiling and saving, that we
come and take their honey; and from a well-stocked hive we may
even take 30 lbs. without starving the industrious little
inhabitants. But then we must often feed them in return and give
them sweet syrup in the late autumn and the next early spring when
they cannot find any flowers.
Although the hive has now become comparatively quiet and the work
goes on without excitement, yet every single bee is employed in
some way, either out of doors or about the hive. Besides the
honey collectors and the nurses, a certain number of bees are
told off to ventilate the hive. You will easily understand that
where so many insects are packed closely together the heat will
become very great, and the air impure and unwholesome. And the
bees have no windows that they can open to let in fresh air, so
they are obliged to fan it in from the one opening of the hive.
The way in which they do this is very interesting. Some of the
bees stand close to the entrance, with their faces towards it,
and opening their wings, so as to make them into fans, they wave
them to and fro, producing a current of air. Behind these bees,
and all over the floor of the hive, there stand others, this time
with their backs towards the entrance, and fan in the same
manner, and in this way air is sent into all the passages.
Another set of bees clean out the cells after the young bees are
born, and make them fit to receive honey, while others guard the
entrance of the hive to keep away the destructive wax-moth,
which tries to lay its eggs in the comb so that its young ones
may feed on the honey. All industrious people have to guard
their property against thieves and vagabonds, and the bees have
many intruders, such as wasps and snails and slugs, which creep
in whenever they get a chance. If they succeed in escaping the
sentinel bees, then a fight takes place within the hive, and the
invader is stung to death.
Sometimes, however, after they have killed the enemy, the bees
cannot get rid of his body, for a snail or slug is too heavy to
be easily moved, and yet it would make the hive very unhealthy
to allow it to remain. In this dilemma the ingenious little bees
fetch the gummy "propolis" from the plant-buds and cement the
intruder all over, thus embalming his body and preventing it
from decaying.
And so the life of this wonderful city goes on. Building,
harvesting, storing, nursing, ventilating and cleaning from morn
till night, the little worker-bee lives for about eight months,
and in that time has done quite her share of work in the world.
Only the young bees, born late in the season, live on till the
next year to work in the spring. The queen-bee lives longer,
probably about two years, and then she too dies, after having had
a family of many thousands of children.
We have already pointed out that in our fairy-land of nature all
things work together so as to bring order out of apparent
confusion. But though we should naturally expect winds and
currents, rivers and clouds, and even plants to follow fixed
laws, we should scarcely have looked for such regularity in the
life of the active, independent busy bee. Yet we see that she,
too, has her own appointed work to do, and does it regularly and
in an orderly manner. In this lecture we have been speaking
entirely of the bee within the hive, and noticing how
marvellously her instincts guide her in her daily life. But
within the last few years we have learnt that she performs a most
curious and wonderful work in the world outside her home and that
we owe to her not only the sweet honey to eat, but even in a great
degree the beauty and gay colours of the flowers which she visits
when collecting it. This work will form the subject of our next
lecture, and while we love the little bee for her constant
industry, patience, and order within the hive, we shall, I think,
marvel at the wonderful law of nature which guides her in her
unconscious mission of love among the flowers which grow around
it.
Week 28
Lecture X
BEES AND FLOWERS
Whatever thoughts each one of you may have brought to the
lecture to-day, I want you to throw them all aside and fancy
yourself to be in a pretty country garden on a hot summer's
morning. Perhaps you have been walking, or reading, or playing,
but it is getting too hot now to do anything; and so you have
chosen the shadiest nook under the old walnut-tree, close to the
flower-bed on the lawn, and would almost like to go to sleep if
it were not too early in the day.
As you lie there thinking of nothing in particular, except how
pleasant it is to be idle now and then, you notice a gentle
buzzing close to you, and you see that on the flower-bed close
by, several bees are working busily among the flowers. They do
not seem to mind the heat, nor to wish to rest; and they fly so
lightly and look so happy over their work that it does not tire
you to look at them.
That great humble-bee takes it leisurely enough as she goes
lumbering along, poking her head into the larkspurs, and
remaining so long in each you might almost think she had fallen
asleep. The brown hive-bee on the other hand, moves busily and
quickly among the stocks, sweet peas, and mignonette. She is
evidently out on active duty, and means to get all she can from
each flower, so as to carry a good load back to the hive. In
some blossoms she does not stay a moment, but draws her head back
directly she has popped it in, as if to say "No honey there."
But over the full blossoms she lingers a little, and then
scrambles out again with her drop of honey, and goes off to seek
more in the next flower.
Let us watch her a little more closely. There are plenty of
different plants growing in the flower-bed, but, curiously
enough, she does not go first to one kind and then to another;
but keeps to one, perhaps the mignonette, the whole time till she
flies away. Rouse yourself up to follow her, and you will see
she takes her way back to the hive. She may perhaps stop to
visit a stray plant of mignonette on her way, but no other flower
will tempt her till she has taken her load home.
Then when she comes back again she may perhaps go to another kind
of flower, such as the sweet peas, for instance, and keep to them
during the next journey, but it is more likely that she will be
true to her old friend the mignonette for the whole day.
We all know why she makes so many journeys between the garden and
the hive, and that she is collecting drops of honey from each
flower, and carrying it to be stored up in the honeycomb for
winter's food. How she stores it, and how she also gathers
pollen-dust for her bee-bread, we saw in the last lecture; to-day
we will follow her in her work among the flowers, and see, while
they are so useful to her, what she is doing for them in return.
We have already learnt from the life of a primrose that plants
can make better and stronger seeds when they can get pollen-dust
from another plant, than when they are obliged to use that which
grows in the same flower; but I am sure you will be very much
surprised to hear that the more we study flowers the more we find
that their colours, their scent, and their curious shapes are all
so many baits and traps set by nature to entice insects to come
to the flowers, and carry this pollen-dust from one to the other.
So far as we know, it is entirely for this purpose that the
plants form honey in different parts of the flower, sometimes in
little bags or glands, as in the petals of the buttercup flower,
sometimes in clear drops, as in the tube of the honeysuckle.
This food they prepare for the insects, and then they have all
sorts of contrivances to entice them to come and fetch it.
You will remember that the plants of the coal had no bright or
conspicuous flowers. Now we can understand why this was, for
there were no flying insects at that time to carry the pollen-
dust from flower to flower, and therefore there was no need of
coloured flowers to attract them. But little by little, as
flies, butterflies, moths and bees began to live in the world,
flowers too began to appear, and plants hung out these gay-
coloured signs, as much as to say, "Come to me, and I will give
you honey if you will bring me pollen-dust in exchange, so that
my seeds may grow healthy and strong."
We cannot stop to inquire to-day how this all gradually came
about, and how the flowers gradually put on gay colours and
curious shapes to tempt the insects to visit them; but we will
learn something about the way they attract them now, and how you
may see it for yourselves if you keep your eyes open.
For example, if you watch the different kinds of grasses, sedges
and rushes, which have such tiny flowers that you can scarcely
see them, you will find that no insects visit them. Neither will
you ever find bees buzzing round oak-trees, nut-trees, willows,
elms or birches. But on the pretty and sweet-smelling apple-
blossoms, or the strongly scented lime-trees, you will find bees,
wasps, and plenty of other insects.
The reason of this is that grasses, sedges, rushes, nut-trees,
willow, and the others we have mentioned, have all of them a
great deal of pollen-dust, and as the wind blows them to and fro,
it wafts the dust from one flower to another, and so these plants
do not want the insects, and it is not worth their while to give
out honey, or to have gaudy or sweet-scented flowers to attract
them.
But wherever you see bright or conspicuous flowers you may be
quite sure that the plants want the bees or some other winged
insect to come and carry their pollen for them. Snowdrops
hanging their white heads among their green leaves, crocuses with
their violet and yellow flowers, the gaudy poppy, the large-
flowered hollyhock or the sunflower, the flaunting dandelion, the
pretty pink willow-herb, the clustered blossoms of the mustard
and turnip flowers, the bright blue forget-me-not and the
delicate little yellow trefoil, all these are visited by insects,
which easily catch sight of them as they pass by and hasten to
sip their honey.
Sir John Lubbock has shown that bees are not only attracted by
bright colours, but that they even know one colour from another.
He put some honey on slips of glass with coloured papers under
them, and when he had accustomed the bees to find the honey
always on the blue glass, he washed this glass clean, and put the
honey on the red glass instead. Now if the bees had followed
only the smell of the honey, they would have flown to the red
glass, but they did not. They went first to the blue glass,
expecting to find the honey on the usual colour, and it was only
when they were disappointed that they went off to the red.
Is it not beautiful to think that the bright pleasant colours we
love so much in flowers, are not only ornamental, but that they
are useful and doing their part in keeping up healthy life in our
world?
Neither must we forget what sweet scents can do. Have you never
noticed the delicious smell which comes from beds of mignonette,
thyme, rosemary, mint, or sweet alyssum, from the small hidden
bunches of laurustinus blossom, or from the tiny flowers of the
privet? These plants have found another way of attracting the
insects; they have no need of bright colours, for their scent is
quite as true and certain a guide. You will be surprised if you
once begin to count them up, how many white and dull or dark-
looking flowers are sweet-scented, while gaudy flowers, such as
tulip, foxglove and hollyhock, have little or no scent. And
then, just as in the world we find some people who have
everything to attract others to them, beauty and gentleness,
cleverness, kindliness, and loving sympathy, so we find some
flowers, like the beautiful lily, the lovely rose, and the
delicate hyacinth, which have colour and scent and graceful
shapes all combined.
But we are not yet nearly at an end of the contrivances of
flowers to secure the visits of insects. Have you not observed
that different flowers open and close at different times? The
daisy receives its name day's eye, because it opens at sunrise
and closes at sunset, while the evening primrose (Aenothera
biennis) and the night campion (Silene noctiflora) spread out
their flowers just as the daisy is going to bed.
What do you think is the reason of this? If you go near a bed of
evening primroses just when the sun is setting, you will soon be
able to guess, for they will then give out such a sweet scent
that you will not doubt for a moment that they are calling the
evening moths to come and visit them. The daisy opens by day,
because it is visited by day insects, but those particular moths
which can carry the pollen-dust of the evening primrose, fly only
by night, and if this flower opened by day other insects might
steal its honey, while they would not be the right size or shape
to touch its pollen-bags and carry the dust.
It is the same if you pass by a honeysuckle in the evening; you
will be surprised how much stronger its scent is than in the day-
time. This is because the sphinx hawk-moth is the favourite
visitor of that flower, and comes at nightfall, guided by the
strong scent, to suck out the honey with its long proboscis, and
carry the pollen-dust.
Again, some flowers close whenever rain is coming. The pimpernel
(Anagallis arvensis) is one of these, hence its name of the
"Shepherd's Weather-glass." This little flower closes, no doubt,
to prevent its pollen-dust being washed away, for it has no
honey; while other flowers do it to protect the drop of honey at
the bottom of their corolla. Look at the daisies for example
when a storm is coming on; as the sky grows dark and heavy, you
will see them shrink up and close till the sun shines again.
They do this because in each of the little yellow florets in the
centre of the flower there is a drop of honey which would be
quite spoiled if it were washed by the rain.
And now you will see why cup-shaped flowers so often droop their
heads - think of the harebell, the snowdrop, the lily-of-the-
valley, the campanula, and a host of others; how pretty they look
with their bells hanging so modestly from the slender stalk!
They are bending down to protect the honey-glands within them,
for if the cup became full of rain or dew the honey would be
useless, and the insects would cease to visit them.
Week 29
But it is not only necessary that the flowers should keep their
honey for the insects, they also have to take care and keep it
for the right kind of insect. Ants are in many cases great
enemies to them, for they like honey as much as bees and
butterflies do, yet you will easily see that they are so small
that if they creep into a flower they pass the anthers without
rubbing against them, and so take the honey without doing any
good to the plant. Therefore we find numberless contrivances for
keeping the ants and other creeping insects away. Look for
example at the hairy stalk of the primrose flower; those little
hairs are like a forest to a tiny ant, and they protect the
flower from his visits. The Spanish catchfly (Silene otites), on
the other hand, has a smooth, but very gummy stem, and on this
the insects stick, if they try to climb. Slugs and snails too
will often attack and bite flowers, unless they are kept away by
thorns and bristles, such as we find on the teazel and the
burdock. And so we are gradually learning that everything which
a plant does has its meaning, if we can only find it out, and
that even very insignificant hair has its own proper use, and
when we are once aware of this a flower-garden may become quite a
new world to us if we open our eyes to all that is going on in
it.
But as we cannot wander among many plants to-day, let us take a
few which the bees visit, and see how they contrive not to give
up their honey without getting help in return. We will start
with the blue wood-geranium, because from it we first began to
learn the use of insects to flowers.
More than a hundred years ago a young German botanist, Christian
Conrad Sprengel, noticed some soft hairs growing in the centre of
this flower, just round the stamens, and he was so sure that
every part of a plant is useful, that he set himself to find out
what these hairs meant. He soon discovered that they protected
some small honey-bags at the base of the stamens, and kept the
rain from washing the honey away, just as our eyebrows prevent
the perspiration on our faces from running into our eyes. This
led him to notice that plants take great care to keep their honey
for insects, and by degrees he proved that they did this in order
to tempt the insects to visit them and carry off their pollen.
The first thing to notice in this little geranium flower is that
the purple lines which ornament it all point directly to the
place where the honey lies at the bottom of the stamens, and
actually serve to lead the bee to the honey; and this is true of
the veins and marking of nearly all flowers except of those which
open by night, and in these they would be useless, for the
insects would not see them.
When the geranium first opens, all its ten stamens are lying flat
on the corolla or coloured crown, as in the left-hand flower in
Fig. 58, and then the bee cannot get at the honey. But in a
short time five stamens begin to raise themselves and cling round
the stigma or knob at the top of the seed-vessel, as in the
middle flower. Now you would think they would leave their dust
there. But no! the stigma is closed up so tight that the dust
cannot get on to the sticky part. Now, however, the bee can get
at the honey-glands on the outside of the raised stamens; and as
he sucks it, his back touches the anthers or dust-bags, and he
carries off the pollen. Then, as soon as all their dust is gone,
these five stamens fall down, and the other five spring up.
Still, however, the stigma remains closed, and the pollen of
these stamens, too, may be carried away to another flower. At
last these five also fall down, and then, and not till then, the
stigma opens and lays out its five sticky points, as you may see
in the right-hand flower, Fig. 58.
But its own pollen is all gone, how then will it get any? It
will get it from some bee who has just taken it from another and
younger flower; and thus you see the blossom is prevented from
using its own pollen, and made to use that of another blossom, so
that its seeds may grow healthy and strong.
The garden nasturtium, into whose blossom we saw the humble-bee
poling his head, takes still more care of its pollen-dust. It
hides its honey down at the end of its long spur, and only sends
out one stamen at a time instead of five like the geranium; and
then, when all the stamens have had their turn, the sticky knob
comes out last for pollen from another flower.
All this you may see for yourselves if you find geraniums* in the
hedges, and nasturtiums in you garden. But even if you have not
these, you may learn the history of another flower quite as
curious, and which you can find in any field or lane even near
London. The common dead-nettle (Fig. 59) takes a great deal of
trouble in order that the bee may carry off its pollen. When you
have found one of these plants, take a flower from the ring all
round the stalk and tear it gently open, so that you can see down
its throat. There, just at the very bottom, you will find a
thick fringe of hairs, and you will guess at once that these are
to protect a drop of honey below. Little insects which would
creep into the flower and rob it of its honey without touching
the anthers of the stamens cannot get past these hairs, and so
the drop is kept till the bee comes to fetch it. (*The scarlet
and other bright geraniums of our flower-gardens are not true
geraniums, but pelargoniums. You may, however, watch all these
peculiarities in them if you cannot procure the true wild
geranium.)
Now look for the stamens; there are four of them, two long and
two short, and they are quite hidden under the hood which forms
the top of the flower. How will the bee touch them? If you were
to watch one, you would find that when the bee alights on the
broad lip and thrusts her head down the tube, she first of all
knows her back against the little forked tip. This is the sticky
stigma, and she leaves there any dust she has brought from
another flower; then, as she must push far in to reach the honey,
before she comes out again has carried away the yellow powder on
her back, ready to give it to the next flower.
Do you remember how we noticed at the beginning of the lecture
that a bee always likes to visit the same kind of plant in one
journey? You see now that this is very useful to the flowers.
If the bee went from a dead-nettle to a geranium, the dust would
be lost, for it would be of no use to any other plant but a dead-
nettle. But since the bee likes to get the same kind of honey
each journey, she goes to the same kind of flowers, and places
the pollen-dust just where it is wanted.
There is another flower, called the Salvia, which belongs to the
same family as our dead-nettle, and I think you will agree with
me that its way of dusting the bee's back is most clever. The
Salvia (Fig. 60) is shaped just like the dead-nettle, with a hood
and a broad lip, but instead of four stamens it has only two, the
other two being shrivelled up. The two that are left have a very
strange shape, for the stalk or filament of the stamen is very
short, while the anther, which is in most flowers two little bags
stuck together, has here grown out into a long thread, with a
little dust-bag at one end only. In 1, Fig. 60, you only see
one of these stems, because the flower is cut in half, but in the
whole flower, one stands on each side just within the lip. Now,
when the bee puts her head into the tube to reach the honey, she
passes right between these two swinging anthers, and knocking
against the end pushes it before her and so brings the dust-bag
plump down on her back, scattering the dust there! you can
easily try this by thrusting a pencil into any Salvia flower, and
you will see the anther fall.
You will notice that all this time the be does not touch the
sticky stigma which hangs high above her, but after the anthers
are empty and shrivelled the stalk of the stigma grows longer,
and it falls lower down. By-and-by another bee, having pollen on
her back, comes to look for honey, and as she goes into No. 3,
she rubs against the stigma and leaves upon it the dust from
another flower.
Tell me, has not the Salvia, while remaining so much the same
shape as the dead-nettle, devised a wonderful contrivance to make
use of the visits of the bee?
The common sweet violet (Viola odorata) or the dog violet (Viola
canina), which you can gather in any meadow, give up their
pollen-dust in quite a different way from the Salvia, and yet it
is equally ingenious. Everyone has noticed what an irregular
shape this flower has, and that one of its purple petals has a
curious spur sticking out behind. In the tip of this spur and in
the spur of the stamen lying in it the violet hides its honey,
and to reach it the bee must press past the curious ring of
orange-tipped bodies in the middle of the flower. These bodies
are the anthers, Fig. 61, which fit tightly round the stigma, so
that when the pollen-dust, which is very dry, comes out of the
bags, it remains shut in by the tips as if in a box. Two of
these stamens have spurs which lie in the coloured spur of the
flower, and have honey at the end of them. Now, when the bee
shakes the end of the stigma, it parts the ring of anthers, and
the fine dust falls through upon the insect.
Let us see for a moment how wonderfully this flower is arranged
to bring about the carrying of the pollen, as Sprengel pointed
out years ago. In the first place, it hangs on a thin stalk, and
bends its head down so that the rain cannot come near the honey
in the spur, and also so that the pollen-dust falls forward into
the front of the little box made by the closed anthers. Then the
pollen is quite dry, instead of being sticky as in most plants.
This is in order that it may fall easily through the cracks.
Then the style or stalk of the stigma is very thin and its tip
very broad, so that it quivers easily when the bee touches it,
and so shakes the anthers apart, while the anthers themselves
fold over to make the box, and yet not so tightly but that the
dust can fall through when they are shaken. Lastly, if you look
at the veins of the flower, you will find that they all point
towards the spur where the honey is to be found, so that when the
sweet smell of the flower has brought the bee, she cannot fail to
go in at the right place.
Two more flowers still I want us to examine together, and then I
hope you will care to look at every flower you meet, to try and
see what insects visit it, and how its pollen-dust is carried.
These two flowers are the common Bird's-foot trefoil (Lotus
corniculatus), and the Early Orchis (Orchis mascula), which you
may find in almost any moist meadow in the spring and early
summer.
The Bird's-foot trefoil, Fig. 62, you will find almost anywhere
all through the summer, and you will know it from other flowers
very like it by its leaf, which is not a true trefoil, for behind
the three usual leaflets of the clover and the shamrock leaf, it
has two small leaflets near the stalk. The flower, you will
notice, is shaped very like the flower of a pea, and indeed it
belongs to the same family, called the Papilionaceae or butterfly
family, because the flowers look something like an insect flying.
In all these flowers the top petal stands up like a flag to catch
the eye of the insect, and for this reason botanists call it the
"standard". Below it are two side-petals called the "wings," and
if you pick these off you will find that the remaining two petals
are joined together at the tip in a shape like the keel of a
boat. For this reason they are called the "keel". Notice as we
pass that these two last petals have in them a curious little
hollow or depression, and if you look inside the "wings" you will
notice a little knob that fits into this hollow, and so locks the
two together. We shall see by-and-by that this is important.
Week 30
Next let us look at the half-flower when it is cut open, and see
what there is inside. There are ten stamens in all, enclosed
with the stigma in the keel; nine are joined together and one is
by itself. The anthers of five of these stamens burst open while
the flower is still a bud, but the other stamens go on growing,
and push the pollen-dust, which is very moist and sticky, right
up into the tip of the keel. Here you see it lies right round
the stigma, but as we saw before in the geranium, the stigma is
not ripe and sticky yet, and so it does not use the pollen
grains.
Now suppose that a bee comes to the flower. The honey she has to
fetch lies inside the tube, and the one stamen being loose she is
able to get her proboscis in. but if she is to be of any use to
the flower she must uncover the pollen-dust. See how cunningly
the flower has contrived this. In order to put her head into the
tube the bee must stand upon the wings, and her weight bends them
down. but they are locked to the keel by the knob fitting in the
hole, and so the keel is pushed down too, and the sticky pollen-
dust is uncovered and comes right against the stomach of the bee
and sticks there! As soon as she has done feeding and flies
away, up go the wings and the keel with them, covering up any
pollen that remains ready for next time. Then when the bee goes
to another flower, as she touches the stigma as well as the
pollen, she leaves some of the foreign dust upon it, and the
flower uses that rather than its own, because it is better for
its seeds. If however no bee happens to come to one of these
flowers, after a time the stigma becomes sticky and it uses its
own pollen: and this is perhaps one reason why the bird's-foot
trefoil is so very common, because it can do its own work if the
bee does not help it.
Now we come lastly to the Orchis flower. Mr. Darwin has written
a whole book on the many curious and wonderful ways in which
orchids tempt bees and other insects to fertilize them. We can
only take the simplest, but I think you will say that even this
blossom is more like a conjuror's box than you would have
supposed it possible that a flower could be.
Let us examine it closely. It has sic deep-red covering leaves,
Fig. 62, three belonging to the calyx or outer cup, and three
belonging to the corolla or crown of the flower; but all six are
coloured alike, except that the large on in front, called the
"lip", has spots and lines upon it which will suggest to you at
once that they point to the honey.
But where are the anthers, and where is the stigma? Look just
under the arch made by those three bending flower-leaves, and
there you will see two small slits, and in these some little
club-shaped bodies, which you can pick out with the point of a
needle. One of these enlarged is shown. It is composed of
sticky grains of pollen held together by fine threads on the top
of a thin stalk; and at the bottom of the stalk there is a little
round body. This is all that you will find to represent the
stamens of the flower. When these masses of pollen, or pollinia
as they are called, are within the flower, the knob at the bottom
is covered by a little lid, shutting them in like the lid of a
box, and just below this lid you will see two yellowish lumps,
which are very sticky. These are the top of the stigma, and they
are just above the seed-vessel, which you can see in the lowest
flower in the picture.
Now let us see how this flower gives up its pollen. When a bee
comes to look for honey in the orchis, she alights on the lip,
and guided by the lines makes straight for the opening just in
front of the stigmas. Putting her head into this opening she
pushes down into the spur, where by biting the inside skin she
gets some juicy sap. Notice that she has to bite, which takes
time.
You will see at once that she must touch the stigmas in going in,
and so give them any pollen she has on her head. but she also
touches the little lid and it flies instantly open, bringing the
glands at the end of the pollen-masses against her head. These
glands are moist and sticky, and while she is gnawing the inside
of the spur they dry a little and cling to her head and she
brings them out with her. Darwin once caught a bee with as many
as sixteen of these pollen-masses clinging to her head.
But if the bee went into the next flower with these pollinia
sticking upright, she would simply put them into the same slits
in the next flower, she would not touch them against the stigma.
Nature, however, has provided against this. As the bee flies
along, the glands sticking to its head dry more and more, and as
they dry they curl up and drag the pollen-masses down, so that
instead of standing upright, as in 1, Fig. 63, they point
forwards, as in 2.
And now, when the bee goes into the next flower, she will thrust
them right against the sticky stigmas, and as they cling there
the fine threads which hold the grains together break away, and
the flower is fertilized.
If you will gather some of these orchids during your next spring
walk in the woods, and will put a pencil down the tube to
represent the head of the bee you may see the little box open,
and the two pollen-masses cling to the pencil. Then if you draw
it out you may see them gradually bend forwards, and by thrusting
your pencil into the next flower you may see the grains of pollen
bread away, and you will have followed out the work of a bee.
Do not such wonderful contrivances as these make us long to know
and understand all the hidden work that is going on around us
among the flowers, the insects, and all forms of life? I have
been able to tell you but very little, but I can promise you that
the more you examine, the more you will find marvellous histories
such as these in simple field-flowers.
Long as we have known how useful honey was to the bee, and how it
could only get it from flowers, yet it was not till quite lately
that we have learned to follow out Sprengel's suggestion, and to
trace the use which the bee is to the flower. But now that we
have once had our eyes opened, every flower teaches us something
new, and we find that each plant adapts itself in a most
wonderful way to the insects which visit it, both so as to
provide them with honey, and at the same time to make them
unconsciously do it good service.
And so we learn that even among insects and flowers, those who do
most for others, receive most in return. The bee and the flower
do not either of them reason about the matter, they only go on
living their little lives as nature guides them, helping and
improving each other. Think for a moment how it would be, if a
plant used up all its sap for its own life, and did not give up
any to make the drop of honey in its flower. The bees would soon
find out that these particular flowers were not worth visiting,
and the flower would not get its pollen-dust carried, and would
have to do its own work and grow weakly and small. Or suppose on
the other hand that the bee bit a hole in the bottom of the
flower, and so got at the honey, as indeed they sometimes do;
then she would not carry the pollen-dust, and so would not keep
up the healthy strong flowers which make her daily food.
But this, as you see, is not the rule. On the contrary, the
flower feeds the bee, and the bee quite unconsciously helps the
flower to make its healthy seed. Nay more; when you are able to
read all that has been written on this subject, you will find
that we have good reason to think that the flowerless plants of
the Coal Period have gradually put on the beautiful colours,
sweet scent, and graceful shapes of our present flowers, in
consequence of the necessity of attracting insects, and thus we
owe our lovely flowers to the mutual kindliness of plants and
insects.
And is there nothing beyond this? Surely there is. Flowers and
insects, as we have seen, act without thought or knowledge of
what they are doing; but the law of mutual help which guides them
is the same which bids you and me be kind and good to all those
around us, if we would lead useful and happy lives. And when we
see that the Great Power which rules over our universe makes each
work for the good of all, even in such humble things as bees and
flowers; and that beauty and loveliness come out of the struggle
and striving of all living things; then, if our own life be
sometimes difficult, and the struggle hard to bear, we learn from
the flowers that the best way to meet our troubles is to lay up
our little drop of honey for others, sure that when they come to
sip it they will, even if unconsciously, give us new vigour and
courage in return.
And now we have arrived at the end of those subjects which we
selected out of the Fairy-land of Science. You must not for a
moment imagine, however, that we have in any way exhausted our
fairy domain; on the contrary, we have scarcely explored even the
outskirts of it. The "History of a Grain of Salt," "A
Butterfly's Life," or "The Labours of an Ant," would introduce us
to fairies and wonders quite as interesting as those of which we
have spoken in these Lectures. While "A Flash of Lightning," "An
Explosion in a Coal-mine," or "The Eruption of a Volcano," would
bring us into the presence of terrible giants known and dreaded
from time immemorial.
But at least we have passed through the gates, and have learnt
that there is a world of wonder which we may visit if we will;
and that it lies quite close to us, hidden in every dewdrop and
gust of wind, in every brook and valley, in every little plant or
animal. We have only to stretch out our hand and touch them with
the wand of inquiry, and they will answer us and reveal the fairy
forces which guide and govern them; and thus pleasant and happy
thoughts may be conjured up at any time, wherever we find
ourselves, by simply calling upon nature's fairies and asking
them to speak to us. Is it not strange, then, that people should
pass them by so often without a thought, and be content to grow
up ignorant of all the wonderful powers ever active in the world
around them?
Neither is it pleasure alone which we gain by a study of nature.
We cannot examine even a tiny sunbeam, and picture the minute
waves of which it is composed, travelling incessantly from the
sun, without being filled with wonder and awe at the marvellous
activity and power displayed in the infinitely small as well as
in the infinitely great things of the universe. We cannot become
familiar with the facts of gravitation, cohesion, or
crystallization, without realizing that the laws of nature are
fixed, orderly, and constant, and will repay us with failure or
success according as we act ignorantly or wisely; and thus we
shall begin to be afraid of leading careless, useless, and idle
lives. We cannot watch the working of the fairy "life" in the
primrose or the bee, without learning that living beings as well
as inanimate things are governed by these same laws of nature;
nor can we contemplate the mutual adaptation of bees and flowers
without acknowledging that it teaches the truth that those
succeed best in life who, whether consciously or unconsciously,
do their best for others.
And so our wanderings in the Fairy-land of Science will not be
wasted, for we shall learn how to guide our own lives, while we
cannot fail to see that the forces of nature, whether they are
apparently mechanical, as in gravitation or heat; or intelligent,
as in living beings, are one and all the voice of the Great
Creator, and speak to us of His Nature and His Will.
End of Project Gutenberg's The Fairy-Land of Science , by Arabella B. Buckley
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