The Outline of Science, Vol. 1 (of 4)

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The largest telescopes at present in existence are _reflectors_. It is
much easier to construct a very large mirror than to construct a very
large lens; it is also cheaper. A mirror is more likely to get out of
order than is a lens, however, and any irregularity in the shape of a
mirror produces a greater distorting effect than in a lens. A refractor
is also more convenient to handle than is a reflector. For these reasons
great refractors are still made, but the largest of them, the great
Yerkes' refractor, is much smaller than the greatest reflector, the one
on Mount Wilson, California. The lens of the Yerkes' refractor measures
three feet four inches in diameter, whereas the Mount Wilson reflector
has a diameter of no less than eight feet four inches.

[Illustration: THE YERKES 40-INCH REFRACTOR

(The largest _refracting_ telescope in the world. Its big lens weighs
1,000 pounds, and its mammoth tube, which is 62 feet long, weighs about
12,000 pounds. The parts to be moved weigh approximately 22 tons.

The great _100-inch reflector_ of the Mount Wilson reflecting
telescope--the largest _reflecting_ instrument in the world--weighs
nearly 9,000 pounds and the moving parts of the telescope weigh about
100 tons.

The new _72-inch reflector_ at the Dominion Astrophysical Observatory,
near Victoria, B. C., weighs nearly 4,500 pounds, and the moving parts
about 35 tons.)]

[Illustration: _Photo: H. J. Shepstone._

THE DOUBLE-SLIDE PLATE HOLDER ON YERKES 40-INCH REFRACTING TELESCOPE

The smaller telescope at the top of the picture acts as a "finder"; the
field of view of the large telescope is so restricted that it is
difficult to recognise, as it were, the part of the heavens being
surveyed. The smaller telescope takes in a larger area and enables the
precise object to be examined to be easily selected.]

[Illustration: MODERN DIRECT-READING SPECTROSCOPE

(_By A. Hilger, Ltd._)

The light is brought through one telescope, is split up by the prism,
and the resulting spectrum is observed through the other telescope.]

But there is a device whereby the power of these giant instruments,
great as it is, can be still further heightened. That device is the
simple one of allowing the photographic plate to take the place of the
human eye. Nowadays an astronomer seldom spends the night with his eye
glued to the great telescope. He puts a photographic plate there. The
photographic plate has this advantage over the eye, that it builds up
impressions. However long we stare at an object too faint to be seen, we
shall never see it. With the photographic plate, however, faint
impressions go on accumulating. As hour after hour passes, the star
which was too faint to make a perceptible impression on the plate goes
on affecting it until finally it makes an impression which can be made
visible. In this way the photographic plate reveals to us phenomena in
the heavens which cannot be seen even through the most powerful
telescopes.

Telescopes of the kind we have been discussing, telescopes for exploring
the heavens, are mounted _equatorially_; that is to say, they are
mounted on an inclined pillar parallel to the axis of the earth so that,
by rotating round this pillar, the telescope is enabled to follow the
apparent motion of a star due to the rotation of the earth. This motion
is effected by clock-work, so that, once adjusted on a star, and the
clock-work started, the telescope remains adjusted on that star for any
length of time that is desired. But a great official observatory, such
as Greenwich Observatory or the Observatory at Paris, also has _transit_
instruments, or telescopes smaller than the equatorials and without the
same facility of movement, but which, by a number of exquisite
refinements, are more adapted to accurate measurements. It is these
instruments which are chiefly used in the compilation of the _Nautical
Almanac_. They do not follow the apparent motions of the stars. Stars
are allowed to drift across the field of vision, and as each star
crosses a small group of parallel wires in the eye-piece its precise
time of passage is recorded. Owing to their relative fixity of position
these instruments can be constructed to record the _positions_ of stars
with much greater accuracy than is possible to the more general and
flexible mounting of equatorials. The recording of transit is
comparatively dry work; the spectacular element is entirely absent;
stars are treated merely as mathematical points. But these observations
furnish the very basis of modern mathematical astronomy, and without
them such publications as the _Nautical Almanac_ and the _Connaissance
du Temps_ would be robbed of the greater part of their importance.

Sec. 2

The Spectroscope

We have already learnt something of the principles of the spectroscope,
the instrument which, by making it possible to learn the actual
constitution of the stars, has added a vast new domain to astronomy. In
the simplest form of this instrument the analysing portion consists of a
single prism. Unless the prism is very large, however, only a small
degree of dispersion is obtained. It is obviously desirable, for
accurate analytical work, that the dispersion--that is, the separation
of the different parts of the spectrum--should be as great as possible.
The dispersion can be increased by using a large number of prisms, the
light emerging from the first prism, entering the second, and so on. In
this way each prism produces its own dispersive effect and, when a
number of prisms are employed, the final dispersion is considerable. A
considerable amount of light is absorbed in this way, however, so that
unless our primary source of light is very strong, the final spectrum
will be very feeble and hard to decipher.

Another way of obtaining considerable dispersion is by using a
_diffraction grating_ instead of a prism. This consists essentially of a
piece of glass on which lines are ruled by a diamond point. When the
lines are sufficiently close together they split up light falling on
them into its constituents and produce a spectrum. The modern
diffraction grating is a truly wonderful piece of work. It contains
several thousands of lines to the inch, and these lines have to be
spaced with the greatest accuracy. But in this instrument, again, there
is a considerable loss of light.

We have said that every substance has its own distinctive spectrum, and
it might be thought that, when a list of the spectra of different
substances has been prepared, spectrum analysis would become perfectly
straightforward. In practice, however, things are not quite so simple.
The spectrum emitted by a substance is influenced by a variety of
conditions. The pressure, the temperature, the state of motion of the
object we are observing, all make a difference, and one of the most
laborious tasks of the modern spectroscopist is to disentangle these
effects from one another. Simple as it is in its broad outlines,
spectroscopy is, in reality, one of the most intricate branches of
modern science.

BIBLIOGRAPHY

(The following list of books may be useful to readers wishing to pursue
further the study of Astronomy.)

BALL, _The Story of the Heavens_.
BALL, _The Story of the Sun_.
FORBES, _History of Astronomy_.
HINCKS, _Astronomy_.
KIPPAX, _Call of the Stars_.
LOWELL, _Mars and Its Canals_.
LOWELL, _Evolution of Worlds_.
MCKREADY, _A Beginner's Star-Book_.
NEWCOMB, _Popular Astronomy_.
NEWCOMB, _The Stars: A Study of the Universe_.
OLCOTT, _Field Book of the Stars_.
PRICE, _Essence of Astronomy_.
SERVISS, _Curiosities of the Skies_.
WEBB, _Celestial Objects for Common Telescopes_.
YOUNG, _Text-Book of General Astronomy_.

II

THE STORY OF EVOLUTION

INTRODUCTORY

THE BEGINNING OF THE EARTH--MAKING A HOME FOR LIFE--THE FIRST LIVING
CREATURES

Sec. 1

The Evolution-idea is a master-key that opens many doors. It is a
luminous interpretation of the world, throwing the light of the past
upon the present. Everything is seen to be an antiquity, with a history
behind it--a _natural history_, which enables us to understand in some
measure how it has come to be as it is. We cannot say more than
"understand in some measure," for while the _fact_ of evolution is
certain, we are only beginning to discern the _factors_ that have been
at work.

The evolution-idea is very old, going back to some of the Greek
philosophers, but it is only in modern times that it has become an
essential part of our mental equipment. It is now an everyday
intellectual tool. It was applied to the origin of the solar system and
to the making of the earth before it was applied to plants and animals;
it was extended from these to man himself; it spread to language, to
folk-ways, to institutions. Within recent years the evolution-idea has
been applied to the chemical elements, for it appears that uranium may
change into radium, that radium may produce helium, and that lead is the
final stable result when the changes of uranium are complete. Perhaps
all the elements may be the outcome of an inorganic evolution. Not less
important is the extension of the evolution-idea to the world within as
well as to the world without. For alongside of the evolution of bodies
and brains is the evolution of feelings and emotions, ideas and
imagination.

Organic evolution means that the present is the child of the past and
the parent of the future. It is not a power or a principle; it is a
process--a process of becoming. It means that the present-day animals
and plants and all the subtle inter-relations between them have arisen
in a natural knowable way from a preceding state of affairs on the whole
somewhat simpler, and that again from forms and inter-relations simpler
still, and so on backwards and backwards for millions of years till we
lose all clues in the thick mist that hangs over life's beginnings.

Our solar system was once represented by a nebula of some sort, and we
may speak of the evolution of the sun and the planets. But since it has
been _the same material throughout_ that has changed in its distribution
and forms, it might be clearer to use some word like genesis. Similarly,
our human institutions were once very different from what they are now,
and we may speak of the evolution of government or of cities. But Man
works with a purpose, with ideas and ideals in some measure controlling
his actions and guiding his achievements, so that it is probably clearer
to keep the good old word history for all processes of social becoming
in which man has been a conscious agent. Now between the genesis of the
solar system and the history of civilisation there comes the vast
process of organic evolution. The word development should be kept for
the becoming of the individual, the chick out of the egg, for instance.

Organic evolution is a continuous natural process of racial change, by
successive steps in a definite direction, whereby distinctively new
individualities arise, take root, and flourish, sometimes alongside of,
and sometimes, sooner or later, in place of, the originative stock. Our
domesticated breeds of pigeons and poultry are the results of
evolutionary change whose origins are still with us in the Rock Dove and
the Jungle Fowl; but in most cases in Wild Nature the ancestral stocks
of present-day forms are long since extinct, and in many cases they are
unknown. Evolution is a long process of coming and going, appearing and
disappearing, a long-drawn-out sublime process like a great piece of
music.

[Illustration: _Photo: Rischgitz Collection._

CHARLES DARWIN

Greatest of naturalists, who made the idea of evolution current
intellectual coin, and in his _Origin of Species_ (1859) made the whole
world new.]

[Illustration: _Photo: Rischgitz Collection._

LORD KELVIN

One of the greatest physicists of the nineteenth century. He estimated
the age of the earth at 20,000,000 years. He had not at his disposal,
however, the knowledge of recent discoveries, which have resulted in
this estimate being very greatly increased.]

[Illustration: _Photo: Lick Observatory._

A GIANT SPIRAL NEBULA

Laplace's famous theory was that the planets and the earth were formed
from great whirling nebulae.]

[Illustration: _Photo: Natural History Museum._

METEORITE WHICH FELL NEAR SCARBOROUGH, AND IS NOW TO BE SEEN IN THE
NATURAL HISTORY MUSEUM

It weighs about 56 lb., and is a "stony" meteorite, i.e., an aerolite.]

Sec. 2

The Beginning of the Earth

When we speak the language of science we cannot say "In the beginning,"
for we do not know of and cannot think of any condition of things that
did not arise from something that went before. But we may qualify the
phrase, and legitimately inquire into the beginning of the earth within
the solar system. If the result of this inquiry is to trace the sun and
the planets back to a nebula we reach only a relative beginning. The
nebula has to be accounted for. And even before matter there may have
been a pre-material world. If we say, as was said long ago, "In the
beginning was Mind," we may be expressing or trying to express a great
truth, but we have gone BEYOND SCIENCE.

The Nebular Hypothesis

One of the grandest pictures that the scientific mind has ever thrown
upon the screen is that of the Nebular Hypothesis. According to
Laplace's famous form of this theory (1796), the solar system was once a
gigantic glowing mass, spinning slowly and uniformly around its centre.
As the incandescent world-cloud of gas cooled and its speed of rotation
increased the shrinking mass gave off a separate whirling ring, which
broke up and gathered together again as the first and most distant
planet. The main mass gave off another ring and another till all the
planets, including the earth, were formed. The central mass persisted as
the sun.

Laplace spoke of his theory, which Kant had anticipated forty-one years
before, with scientific caution: "conjectures which I present with all
the distrust which everything not the result of observation or of
calculation ought to inspire." Subsequent research justified his
distrust, for it has been shown that the original nebula need not have
been hot and need not have been gaseous. Moreover, there are great
difficulties in Laplace's theory of the separation of successive rings
from the main mass, and of the condensation of a whirling gaseous ring
into a planet.

So it has come about that the picture of a hot gaseous nebula revolving
as a unit body has given place to other pictures. Thus Sir Norman
Lockyer pointed out (1890) that the earth is gathering to itself
millions of meteorites every day; this has been going on for millions of
years; in distant ages the accretion may have been vastly more rapid and
voluminous; and so the earth has grown! Now the meteoritic contributions
are undoubted, but they require a centre to attract them, and the
difficulty is to account for the beginning of a collecting centre or
planetary nucleus. Moreover, meteorites are sporadic and erratic,
scattered hither and thither rather than collecting into unit-bodies. As
Professor Chamberlin says, "meteorites have rather the characteristics
of the wreckage of some earlier organisation than of the parentage of
our planetary system." Several other theories have been propounded to
account for the origin of the earth, but the one that has found most
favour in the eyes of authorities is that of Chamberlin and Moulton.
According to this theory a great nebular mass condensed to form the sun,
from which under the attraction of passing stars planet after planet,
the earth included, was heaved off in the form of knotted spiral nebulae,
like many of those now observed in the heavens.

Of great importance were the "knots," for they served as collecting
centres drawing flying matter into their clutches. Whatever part of the
primitive bolt escaped and scattered was drawn out into independent
orbits round the sun, forming the "planetesimals" which behave like
minute planets. These planetesimals formed the food on which the knots
subsequently fed.

The Growth of the Earth

It has been calculated that the newborn earth--the "earth-knot" of
Chamberlin's theory--had a diameter of about 5,500 miles. But it grew
by drawing planetesimals into itself until it had a diameter of over
8,100 miles at the end of its growing period. Since then it has shrunk,
by periodic shrinkages which have meant the buckling up of successive
series of mountains, and it has now a diameter of 7,918 miles. But
during the shrinking the earth became more varied.

A sort of slow boiling of the internally hot earth often forced molten
matter through the cold outer crust, and there came about a gradual
assortment of lighter materials nearer the surface and heavier materials
deeper down. The continents are built of the lighter materials, such as
granites, while the beds of the great oceans are made of the heavier
materials such as basalts. In limited areas land has often become sea,
and sea has often given place to land, but the probability is that the
distinction of the areas corresponding to the great continents and
oceans goes back to a very early stage.

The lithosphere is the more or less stable crust of the earth, which may
have been, to begin with, about fifty miles in thickness. It seems that
the young earth had no atmosphere, and that ages passed before water
began to accumulate on its surface--before, in other words, there was
any hydrosphere. The water came from the earth itself, to begin with,
and it was long before there was any rain dissolving out saline matter
from the exposed rocks and making the sea salt. The weathering of the
high grounds of the ancient crust by air and water furnished the
material which formed the sandstones and mudstones and other sedimentary
rocks, which are said to amount to a thickness of over fifty miles in
all.

Sec. 3

Making a Home for Life

It is interesting to inquire how the callous, rough-and-tumble
conditions of the outer world in early days were replaced by others that
allowed of the germination and growth of that tender plant we call
LIFE. There are very tough living creatures, but the average organism is
ill suited for violence. Most living creatures are adapted to mild
temperatures and gentle reactions. Hence the fundamental importance of
the early atmosphere, heavy with planetesimal dust, in blanketing the
earth against intensities of radiance from without, as Chamberlin says,
and inequalities of radiance from within. This was the first preparation
for life, but it was an atmosphere without free oxygen. Not less
important was the appearance of pools and lakelets, of lakes and seas.
Perhaps the early waters covered the earth. And water was the second
preparation for life--water, that can dissolve a larger variety of
substances in greater concentration than any other liquid; water, that
in summer does not readily evaporate altogether from a pond, nor in
winter freeze throughout its whole extent; water, that is such a mobile
vehicle and such a subtle cleaver of substances; water, that forms over
80 per cent. of living matter itself.

Of great significance was the abundance of carbon, hydrogen, and oxygen
(in the form of carbonic acid and water) in the atmosphere of the
cooling earth, for these three wonderful elements have a unique
_ensemble_ of properties--ready to enter into reactions and relations,
making great diversity and complexity possible, favouring the formation
of the plastic and permeable materials that build up living creatures.
We must not pursue the idea, but it is clear that the stones and mortar
of the inanimate world are such that they built a friendly home for
life.

Origin of Living Creatures upon the Earth

During the early chapters of the earth's history, no living creature
that we can imagine could possibly have lived there. The temperature was
too high; there was neither atmosphere nor surface water. Therefore it
follows that at some uncertain, but inconceivably distant date, living
creatures appeared upon the earth. No one knows how, but it is
interesting to consider possibilities.

[Illustration: _Reproduced from the Smithsonian Report, 1915._

A LIMESTONE CANYON

Many fossils of extinct animals have been found in such rock
formations.]

[Illustration: GENEALOGICAL TREE OF ANIMALS

Showing in order of evolution the general relations of the chief classes
into which the world of living things is divided. This scheme represents
the present stage of our knowledge, but is admittedly provisional.]

[Illustration: DIAGRAM OF AMOEBA

(Greatly magnified.)

The amoeba is one of the simplest of all animals, and gives us a hint
of the original ancestors. It looks like a tiny irregular speck of
greyish jelly, about 1/100th of an inch in diameter. It is commonly
found gliding on the mud or weeds in ponds, where it engulfs its
microscopic food by means of out-flowing lobes (PS). The food vacuole
(FV) contains ingested food. From the contractile vacuole (CV) the waste
matter is discharged. N is the nucleus, GR, granules.]

From ancient times it has been a favourite answer that the dust of the
earth may have become living in a way which is outside scientific
description. This answer forecloses the question, and it is far too soon
to do that. Science must often say "Ignoramus": Science should be slow
to say "Ignorabimus."

A second position held by Helmholtz, Lord Kelvin, and others, suggests
that minute living creatures may have come to the earth from elsewhere,
in the cracks of a meteorite or among cosmic dust. It must be remembered
that seeds can survive prolonged exposure to very low temperatures; that
spores of bacteria can survive high temperature; that seeds of plants
and germs of animals in a state of "latent life" can survive prolonged
drought and absence of oxygen. It is possible, according to Berthelot,
that as long as there is not molecular disintegration vital activities
may be suspended for a time, and may afterwards recommence when
appropriate conditions are restored. Therefore, one should be slow to
say that a long journey through space is impossible. The obvious
limitation of Lord Kelvin's theory is that it only shifts the problem of
the origin of organisms (i.e. living creatures) from the earth to
elsewhere.

The third answer is that living creatures of a very simple sort may have
emerged on the earth's surface from not-living material, e.g. from some
semi-fluid carbon compounds activated by ferments. The tenability of
this view is suggested by the achievements of the synthetic chemists,
who are able artificially to build up substances such as oxalic acid,
indigo, salicylic acid, caffeine, and grape-sugar. We do not know,
indeed, what in Nature's laboratory would take the place of the clever
synthetic chemist, but there seems to be a tendency to complexity.
Corpuscles form atoms, atoms form molecules, small molecules large
ones.

Various concrete suggestions have been made in regard to the possible
origin of living matter, which will be dealt with in a later chapter. So
far as we know of what goes on to-day, there is no evidence of
spontaneous generation; organisms seem always to arise from pre-existing
organisms of the same kind; where any suggestion of the contrary has
been fancied, there have been flaws in the experimenting. But it is one
thing to accept the verdict "omne vivum e vivo" as a fact to which
experiment has not yet discovered an exception and another thing to
maintain that this must always have been true or must always remain
true.

If the synthetic chemists should go on surpassing themselves, if
substances like white of egg should be made artificially, and if we
should get more light on possible steps by which simple living creatures
may have arisen from not-living materials, this would not greatly affect
our general outlook on life, though it would increase our appreciation
of what is often libelled as "inert" matter. If the dust of the earth
did naturally give rise very long ago to living creatures, if they are
in a real sense born of her and of the sunshine, then the whole world
becomes more continuous and more vital, and all the inorganic groaning
and travailing becomes more intelligible.

Sec. 4

The First Organisms upon the Earth

We cannot have more than a speculative picture of the first living
creatures upon the earth or, rather, in the waters that covered the
earth. A basis for speculation is to be found, however, in the simplest
creatures living to-day, such as some of the bacteria and one-celled
animalcules, especially those called Protists, which have not taken any
very definite step towards becoming either plants or animals. No one can
be sure, but there is much to be said for the theory that the first
creatures were microscopic globules of living matter, not unlike the
simplest bacteria of to-day, but able to live on air, water, and
dissolved salts. From such a source may have originated a race of
one-celled marine organisms which were able to manufacture chlorophyll,
or something like chlorophyll, that is to say, the green pigment which
makes it possible for plants to utilise the energy of the sunlight in
breaking up carbon dioxide and in building up (photosynthesis) carbon
compounds like sugars and starch. These little units were probably
encased in a cell-wall of cellulose, but their boxed-in energy expressed
itself in the undulatory movement of a lash or flagellum, by means of
which they propelled themselves energetically through the water. There
are many similar organisms to-day, mostly in water, but some of
them--simple one-celled plants--paint the tree-stems and even the
paving-stones green in wet weather. According to Prof. A. H. Church
there was a long chapter in the history of the earth when the sea that
covered everything teemed with these green flagellates--the originators
of the Vegetable Kingdom.

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