of which I have been working for some time. It is this: _The ascending
air is chilled by its expansion_. Indeed this chilling is one source
of the coldness of the higher atmospheric regions. And now fix your
eye upon those mixed currents of air and aqueous vapor which rise from
the warm tropical ocean. They start with plenty of heat to preserve
the vapor as vapor; but as they rise they come into regions already
chilled, and they are still further chilled by their own expansion.
The consequence might be foreseen. The load of vapor is in great part
precipitated, dense clouds are formed, their particles coalesce to
rain-drops, which descend daily in gushes so profuse that the word
"torrential" is used to express the copiousness of the rainfall. I
could show you this chilling by expansion, and also the consequent
precipitation of clouds.
Thus long before the air from the equator reaches the poles its vapor
is in great part removed from it, having redescended to the earth as
rain. Still a good quantity of the vapor is carried forward, which
yields hail, rain, and snow in northern and southern lands.
Mountain Condensers.
To complete our view of the process of atmospheric precipitation we
must take into account the action of mountains. Imagine a south-west
wind blowing across the Atlantic towards Ireland. In its passage it
charges itself with aqueous vapor. In the south of Ireland it
encounters the mountains of Kerry: the highest of these is
Magillicuddy's Reeks, near Killarney. Now the lowest stratum of this
Atlantic wind is that which is most fully charged with vapor. When it
encounters the base of the Kerry Mountains it is tilted up and flows
bodily over them. Its load of vapor is therefore carried to a height,
it expands on reaching the height, it is chilled in consequence of
the expansion, and comes down in copious showers of rain. From this,
in fact, arises the luxuriant vegetation of Killarney; to this,
indeed, the lakes owe their water supply. The cold crests of the
mountains also aid in the work of condensation.
Note the consequence. There is a town called Cahirciveen to the
south-west of Magillicuddy's Reeks, at which observations of the
rainfall have been made, and a good distance farther to the
north-east, right in the course of the south-west wind there is
another town, called Portarlington, at which observations of rainfall
have also been made. But before the wind reaches the latter station it
has passed over the mountains of Kerry and left a great portion of its
moisture behind it. What is the result? At Cahirciveen, as shown by
Dr. Lloyd, the rainfall amounts to fifty-nine inches in a year, while
at Portarlington it is only twenty-one inches.
Again, you may sometimes descend from the Alps when the fall of rain
and snow is heavy and incessant, into Italy, and find the sky over the
plains of Lombardy blue and cloudless, the wind at the same time
_blowing over the plain towards the Alps_. Below the wind is hot
enough to keep its vapor in a perfectly transparent state; but it
meets the mountains, is tilted up, expanded, and chilled. The cold of
the higher summits also helps the chill. The consequence is that the
vapor is precipitated as rain or snow, thus producing bad weather upon
the heights, while the plains below, flooded with the same air, enjoy
the aspect of the unclouded summer sun. Clouds blowing _from_ the
Alps are also sometimes dissolved over the plains of Lombardy.
In connection with the formation of clouds by mountains, one
particularly instructive effect may be here noticed. You frequently
see a streamer of cloud many hundred yards in length drawn out from an
Alpine peak. Its steadiness appears perfect, though a strong wind may
be blowing at the same time over the mountain head. Why is the cloud
not blown away? It _is_ blown away; its permanence is only apparent.
At one end it is incessantly dissolved; at the other end it is
incessantly renewed: supply and consumption being thus equalized, the
cloud appears as changeless as the mountain to which it seems to
cling. When the red sun of the evening shines upon these
cloud-streamers they resemble vast torches with their flames blown
through the air.
Architecture of Snow.
We now resemble persons who have climbed a difficult peak, and thereby
earned the enjoyment of a wide prospect. Having made ourselves masters
of the conditions necessary to the production of mountain snow, we are
able to take a comprehensive and intelligent view of the phenomena of
glaciers.
[Illustration: SNOW CRYSTALS.]
A few words are still necessary as to the formation of snow. The
molecules and atoms of all substances, when allowed free play, build
themselves into definite and, for the most part, beautiful forms
called crystals. Iron, copper, gold, silver, lead, sulphur, when
melted and permitted to cool gradually, all show this crystallizing
power. The metal bismuth shows it in a particularly striking manner,
and when properly fused and solidified, self-built crystals of great
size and beauty are formed of this metal.
[Illustration: SNOW-STAR.]
[Illustration: SNOW-STAR.]
If you dissolve salt-petre in water, and allow the solution to
evaporate slowly, you may obtain large crystals, for no portion of the
salt is converted into vapor. The water of our atmosphere is fresh
though it is derived from the salt sea. Sugar dissolved in water, and
permitted to evaporate, yields crystals of sugar-candy. Alum readily
crystallizes in the same way. Flints dissolved, as they sometimes are
in nature, and permitted to crystallize, yield the prisms and pyramids
of rock crystal. Chalk dissolved and crystallized yields Iceland spar.
The diamond is crystallized carbon. All our precious stones, the
ruby, sapphire, beryl, topaz, emerald, are all examples of this
crystallizing power.
[Illustration: SNOW-STAR.]
You have heard of the force of gravitation, and you know that it
consists of an attraction of every particle of matter for every other
particle. You know that planets and moons are held in their orbits by
this attraction. But gravitation is a very simple affair compared to
the force, or rather forces, of crystallization. For here the ultimate
particles of matter, inconceivably small as they are, show themselves
possessed of attractive and repellent poles, by the mutual action of
which the shape and structure of the crystal are determined. In the
solid condition the attracting poles are rigidly locked together; but
if sufficient heat be applied the bond of union is dissolved, and in
the state of fusion the poles are pushed so far asunder as to be
practically out of each other's range. The natural tendency of the
molecules to build themselves together is thus neutralized.
This is the case with water, which as a liquid is to all appearance
formless. When sufficiently cooled the molecules are brought within
the play of the crystallizing force, and they then arrange themselves
in forms of indescribable beauty. When snow is produced in calm air,
the icy particles build themselves into beautiful stellar shapes, each
star possessing six rays. There is no deviation from this type, though
in other respects the appearances of the snow-stars are infinitely
various. In the polar regions these exquisite forms were observed by
Dr. Scoresby, who gave numerous drawings of them. I have observed them
in mid-winter filling the air, and loading the slopes of the Alps. But
in England they are also to be seen, and no words of mine could convey
so vivid an impression of their beauty as the annexed drawings of a
few of them, executed at Greenwich by Mr. Glaisher.
[Illustration: SNOW-STAR.]
It is worth pausing to think what wonderful work is going on in the
atmosphere during the formation and descent of every snow-shower; what
building power is brought into play! and how imperfect seem the
productions of human minds and hands when compared with those formed
by the blind forces of nature!
But who ventures to call the forces of nature blind? In reality, when
we speak thus we are describing our own condition. The blindness is
ours; and what we really ought to say, and to confess, is that our
powers are absolutely unable to comprehend either the origin or the
end of the operations of nature.
But while we thus acknowledge our limits, there is also reason for
wonder at the extent to which science has mastered the system of
nature. From age to age, and from generation to generation, fact has
been added to fact, and law to law, the true method and order of the
Universe being thereby more and more revealed. In doing this science
has encountered and overthrown various forms of superstition and
deceit, of credulity and imposture. But the world continually produces
weak persons and wicked persons; and as long as they continue to exist
side by side, as they do in this our day, very debasing beliefs will
also continue to infest the world.
Atomic Poles.
"What did I mean when, a few moments ago I spoke of attracting and
repellent poles?" Let me try to answer this question. You know that
astronomers and geographers speak of the earth's poles, and you have
also heard of magnetic poles, the poles of a magnet being the points
at which the attraction and repulsion of the magnet are as it were
concentrated.
Every magnet possesses two such poles; and if iron filings be
scattered over a magnet, each particle becomes also endowed with two
poles. Suppose such particles devoid of weight and floating in our
atmosphere, what must occur when they come near each other? Manifestly
the repellent poles will retreat from each other, while the attractive
poles will approach and finally lock themselves together. And
supposing the particles, instead of a single pair, to possess several
pairs of poles arranged at definite points over their surfaces; you
can then picture them, in obedience to their mutual attractions and
repulsions, building themselves together to form masses of definite
shape and structure.
Imagine the molecules of water in calm cold air to be gifted with
poles of this description, which compel the particles to lay
themselves together in a definite order, and you have before your
mind's eye the unseen architecture which finally produces the visible
and beautiful crystals of the snow. Thus our first notions and
conceptions of poles are obtained from the sight of our eyes in
looking at the effects of magnetism; and we then transfer these
notions and conceptions to particles which no eye has ever seen. The
power by which we thus picture to ourselves effects beyond the range
of the senses is what philosophers call the Imagination, and in the
effort of the mind to seize upon the unseen architecture of crystals,
we have an example of the "scientific use" of this faculty. Without
imagination we might have _critical_ power, but not _creative_ power
in science.
Architecture of Lake Ice.
We have thus made ourselves acquainted with the beautiful snow-flowers
self-constructed by the molecules of water in calm, cold air. Do the
molecules show this architectural power when ordinary water is frozen?
What, for example, is the structure of the ice over which we skate in
winter? Quite as wonderful as the flowers of the snow. The observation
is rare, if not new, but I have seen in water slowly freezing
six-rayed ice-stars formed, and floating free on the surface. A
six-rayed star, moreover, is typical of the construction of all our
lake ice. It is built up of such forms wonderfully interlaced.
Take a slab of lake ice and place it in the path of a concentrated
sunbeam. Watch the track of the beam through the ice. Part of the beam
is stopped, part of it goes through; the former produces internal
liquefaction, the latter has no effect whatever upon the ice. But the
liquefaction is not uniformly diffused. From separate spots of the ice
little shining points are seen to sparkle forth. Every one of those
points is surrounded by a beautiful liquid flower with six petals.
Ice and water are so optically alike that unless the light fall
properly upon these flowers you cannot see them. But what is the
central spot? A vacuum. Ice swims on water because, bulk for bulk, it
is lighter than water; so that when ice is melted it shrinks in size.
Can the liquid flowers then occupy the whole space of the ice melted?
Plainly no. A little empty space is formed with the flowers, and this
space, or rather its surface, shines in the sun with the lustre of
burnished silver.
In all cases the flowers are formed parallel to the surface of
freezing. They are formed when the sun shines upon the ice of every
lake; sometimes in myriads, and so small as to require a magnifying
glass to see them. They are always attainable, but their beauty is
often marred by internal defects of the ice. Every one portion of the
same piece of ice may show them exquisitely, while a second portion
shows them imperfectly.
Annexed is a very imperfect sketch of these beautiful figures.
Here we have a reversal of the process of crystallization. The
searching solar beam is delicate enough to take the molecules down
without deranging the order of their architecture. Try the experiment
for yourself with a pocket-lens on a sunny day. You will not find the
flowers confused; they all lie parallel to the surface of freezing. In
this exquisite way every bit of the ice over which our skaters glide
in winter is put together.
I said that a portion of the sunbeam was stopped by the ice and
liquefied it. What is this portion? The dark heat of the sun. The
great body of the light waves and even a portion of the dark ones,
pass through the ice without losing any of their heating power. When
properly concentrated on combustible bodies, even after having passed
through the ice, their burning power becomes manifest.
[Illustration: LIQUID FLOWERS IN LAKE ICE.]
And the ice itself may be employed to concentrate them. With an
ice-lens in the polar regions Dr. Scoresby has often concentrated the
sun's rays so as to make them burn wood, fire gunpowder, and melt
lead; thus proving that the heating power is retained by the rays,
even after they have passed through so cold a substance.
By rendering the rays of the electric lamp parallel, and then sending
them through a lens of ice, we obtain all the effects which Dr.
Scoresby obtained with the rays of the sun.
[Illustration]
THE ORGANIC WORLD
(FROM THE ELEMENTS OF SCIENCE.)
BY ST. GEORGE MIVART F.R.S.
The number of all the various kinds of living creatures is so enormous
that it would be impossible to study them profitably, were they not
classified in an orderly manner. Therefore the whole mass has been
divided, in the first place, into two supreme groups, fancifully
termed kingdoms--the "animal kingdom" and the "vegetal kingdom." Each
of these is subdivided into an orderly series of subordinate groups,
successively contained one within the other, and named sub-kingdoms,
classes, orders, families, genera and species. The lowest group but
one is the "genus," which contains one or more different kinds termed
"species," as e.g., the species "wood anemone" and the species "blue
titmouse." The lowest group of all--a species--may be said to consist
of individuals which differ from each other only by trifling
characters, such as characters due to difference of sex, while their
peculiar organization is faithfully reproduced by generation as a
whole, though small individual differences exist in all cases.
The vegetal, or vegetable, kingdom, consists of the great mass of
flowering plants, many of which, however, have such inconspicuous
flowers that they are mistakenly regarded as flowerless, as is often
the case with the grasses, the pines, and the yews. Another mass, or
sub-kingdom, of plants consists of the really flowerless plants, such
as the ferns, horsetails (Fig. 1), lycopods, and mosses. Sea and
fresh-water weeds (_algæ_), and mushrooms, or "moulds," of all kinds
(_fungi_), amongst which are the now famous "bacteria," constitute a
third and lowest set of plants.
[Illustration: FIG. 1. HORSE-TAIL (_Equisetum drummondii_).]
The animal kingdom consists, first, of a sub-kingdom of animals which
possess a spinal column, or backbone, and which are known as
vertebrate animals. Such are all beasts, birds, reptiles, and fishes.
There are also a variety of remotely allied marine organisms known as
tunicates, sea-squirts, or ascidians (Fig. 2). There is, further, an
immense group of arthropods, consisting of all insects, crab-like
creatures, hundred-legs and their allies, with spiders, scorpions,
tics and mites. We have also the sub-kingdom of shell-fish or
molluscs, including cuttle-fishes, snails, whelks, limpets, the
oyster, and a multitude of allied forms. A multitudinous sub-kingdom of
worms also exists, as well as another of star-fishes and their
congeners. There is yet another of zoophytes, or polyps, and another
of sponges, and, finally, we have a sub-kingdom of minute creatures,
or animalculæ, of very varied forms, which may make up the sub-kingdom
of _Protozoa_, consisting of animals which are mostly unicellular.
[Illustration: FIG. 2. A TUNICATE (_Ascidia_).]
Multitudinous and varied as are the creatures which compose this
immense organic world, they nevertheless exhibit a very remarkable
uniformity of composition in their essential structure. Every living
creature from a man to a mushroom, or even to the smallest animalcule
or unicellular plant is always partly fluid, but never entirely so.
Every living creature also consists in part (and that part is the most
active living part) of a soft, viscid, transparent, colorless
substance, termed protoplasm, which can be resolved into the four
elements, oxygen, hydrogen, nitrogen and carbon. Besides these four
elements, living organisms commonly contain sulphur, phosphorus,
chlorine, potassium, sodium, calcium, magnesium and iron.
In the fact that living creatures always consist of the four elements,
oxygen, hydrogen, nitrogen and carbon, we have a fundamental character
whereby the organic and inorganic (or non-living) worlds are to be
distinguished, for as we have seen, inorganic bodies, instead of being
thus uniformly constituted, may consist of the most diverse elements
and sometimes of but two or even of only one.
Again, many minerals, such as crystals, are bounded by plain surfaces,
and, with very few exceptions (spathic and hematite iron and dolomite
are such exceptions) none are bounded by curved lines and surfaces,
while living organisms are bounded by such lines and surfaces.
Yet, again, if a crystal be cut through, its internal structure will
be seen to be similar throughout. But if the body of any living
creature be divided, it will, at the very least, be seen to consist of
a variety of minute distinct particles, called "granules," variously
distributed throughout its interior.
All organisms consist either--as do the simplest, mostly microscopic,
plants and animals--of a single minute mass of protoplasm, or of a
few, or of many, or of an enormous aggregation of such before-mentioned
particles, each of which is one of those bodies named a "cell" (Fig.
3). Cells may, or may not, be enclosed in an investing coat or
"cell-wall." Every cell generally contains within it a denser,
normally spheroidal, body known as the nucleus.
Now protoplasm is a very unstable substance--as we have seen many
substances are whereof nitrogen is a component part--and it possesses
active properties which are not present in the non-living, or
inorganic world. In the latter, differences of temperature will
produce motion in the shape of "currents," as we have seen with
respect to masses of air and water. But in a portion of protoplasm,
an internal circulation of currents in definite lines will establish
itself from other causes.
Inorganic bodies, as we have seen, will expand with heat, as they may
also do from imbibing moisture; but living protoplasm has an
apparently spontaneous power of contraction and expansion under
certain external conditions which do not occasion such movements in
inorganic matter.
[Illustration: FIG. 3. CELL FROM A SALAMANDER. _n_, nucleus; _n'_,
nucleolus embedded in the network of chromatin threads; _k_, network
of the cell external to the nucleus; _a_, attraction-sphere or
archoplasm containing minute bodies called centrosomes; _cl_, membrane
enclosing the cell externally, _nl_, membrane surrounding the nucleus;
_c_, centrosomes.]
Under favoring conditions, protoplasm has a power of performing
chemical changes, which result in producing heat far more gently and
continuously than it is produced by the combustion of inorganic
bodies. Thus it is that the heat is produced which makes its presence
evident to us in what we call "warm-blooded animals," the most
warm-blooded of all being birds.
Protoplasm has also the wonderful power of transforming certain
adjacent substances into material like itself--into its own
substance--and so, in a sense, creating a new material. Thus it is
that organisms have the power to nourish themselves and grow. An
animal would vainly swallow the most nourishing food if the ultimate,
protoplasmic particles of its body had not this power of
"transforming" suitable substances brought near them in ways to be
hereinafter noticed.
Without that, no organism could ever "grow." The growth of organisms
is utterly different from the increase in size of inorganic bodies.
Crystals, as we have seen, grow merely by external increment; but
organisms grow by an increment which takes place in the very innermost
substance of the tissues which compose their bodies, and the innermost
substance of the cells which compose such tissues; this peculiar form
of growth is termed _intussusception_.
Protoplasm, after thus augmenting its mass, has a further power of
spontaneous division, whereby the mass of the entire organism whereof
such protoplasm forms a part, is augmented and so growth is brought
about.
The small particles of protoplasm which constitute "cells" are far
indeed from being structureless. Besides the nucleus already mentioned
there is a delicate network of threads of a substance called
_chromatin_ within it, and another network permeating the fluid of the
cell substance, which invest the nucleus often with further
complications. These networks generally perform (or undergo) a most
complex series of changes every time a cell spontaneously divides. In
certain cases, however, it appears that the nucleus divides into two
in a more simple fashion, the rest of the cell contents subsequently
dividing--each half enclosing one part of the previously divided
nucleus. It is by a continued process of cell division that the
complex structures of the most complex organisms is brought about.
The division of a cell, or particle of protoplasm, is indeed a
necessary consequence of its complete nutrition.
For new material can only be absorbed by its surface. But as the cell
grows, the proportion borne by its surface to its mass, continually
decreases; therefore this surface must soon be too small to take in
nourishment enough, and the particle, or cell, must therefore either
die or divide. By dividing, its parts can continue the nutritive
process till their surface, in turn, becomes insufficient, when they
must divide again, and so on. Thus the term "feeding" has two senses.
"To feed a horse," ordinarily means to give it a certain quantity of
hay, oats or what not; and such indeed is one kind of feeding. But
obviously, if the nourishment so taken could not get from the stomach
and intestines into the ultimate particles and cells of the horse's
body, the horse could not be nourished, and still less could it grow.
It is this latter process, called assimilation, which is the real and
essential process of feeding, to which the process ordinarily so
called is but introductory.
Protoplasm has also the power of forming and ejecting from its own
substance, other substances which it has made, but which are of a
different nature to its own. This function, as before said, is termed
secretion; and we know the liver secretes bile, and that the cow's
udder secretes milk.
Here again we have an external and an internal process. The milk is
drawn forth from a receptacle, the udder, into which it finds its way,
and so, in a superficial sense, it may be called an organ of
secretion. Nevertheless the true internal secretion takes place in
the innermost substance of the cells or particles of protoplasm, of
the milk-land, which particles really form that liquid.