When a river has so adjusted its slope that it neither deepens its bed

in the upper portion of its course, nor deposits materials, it is said

to have acquired its "regimen," and in such a case if the character of

the soil remains the same, the velocity must also be uniform. The

enlargement of the bed of a river is not, however, in proportion to the

increase of its waters as it approaches the sea. If, therefore, the

slope did not diminish, the regimen would be destroyed, and the river

would again commence to eat out its bed. Hence as rivers enlarge, the

slope diminishes, and consequently every river tends to assume some such

"regimen" as that shown in Fig. 46.

Now, suppose that the fall of the river is again increased, either by a

fresh elevation, or locally by the removal of a barrier. Then once more

the river regains its energy. Again it cuts into its old bed, deepening

the valley, and leaving the old plain as a terrace high above its new

course. In many valleys several such terraces may be seen, one above the

other. In the case of a river running in a transverse valley, that is to

say of a valley lying at right angles to the "strike" or direction of

the strata (such, for instance, as the Reuss), the water acts more

effectively than in longitudinal valleys running along the strike. Hence

the lateral valleys have been less deeply excavated than that of the

Reuss itself, and the streams from them enter the main valley by rapids

or cascades. Again, rivers running in transverse valleys cross rocks

which in many cases differ in hardness, and of course they cut down the

softer strata more rapidly than the harder ones; each ridge of harder

rock will therefore form a dam and give rise to a rapid, or cataract. We

often as we ascend a river, after a comparatively flat plain, find

ourselves in a narrow defile, down which the water rushes in an

impetuous torrent, but at the summit of which, to our surprise, we find

another broad flat valley.

Another lesson which we learn from the study of river valleys, is that,

just as geological structure was shown by Sir C. Lyell to be no evidence

of cataclysms, but the result of slow action; so also the excavation of

valleys is due mainly to the regular flow of rivers; and floods, though

their effects are more sudden and striking, have had, after all,

comparatively little part in the result.

The mouths of rivers fall into two principal classes. If we look at any

map we cannot but be struck by the fact that some rivers terminate in a

delta, some in an estuary. The Thames, for instance, ends in a noble

estuary, to which London owes much of its wealth and power. It is

obvious that the Thames could not have excavated this estuary while the

coast was at its present level. But we know that formerly the land stood

higher, that the German Ocean was once dry land, and the Thames, after

joining the Rhine, ran northwards, and fell eventually into the Arctic

Ocean. The estuary of the Thames, then, dates back to a period when the

south-east of England stood at a higher level than the present, and even

now the ancient course of the river can be traced by soundings under

what is now sea. The sites of present deltas, say of the Nile, were also

once under water, and have been gradually reclaimed by the deposits of

the river.

It would indeed be a great mistake to suppose that rivers always tend

to deepen their valleys. This is only the case when the slope exceeds a

certain angle. When the fall is but slight they tend on the contrary to

raise their beds by depositing sand and mud brought down from higher

levels. Hence in the lower part of their course many of the most

celebrated rivers--the Nile, the Po, the Mississippi, the Thames,

etc.--run upon embankments, partly of their own creation.

[Illustration: Fig. 48.--Diagrammatic section of a valley (exaggerated)

_R R_, rocky basis of valley; _A A_, sedimentary strata; _B_, ordinary

level of river; _C_, flood level.]

The Reno, the most dangerous of all the Apennine rivers, is in some

places as much as 30 feet above the adjoining country. Rivers under such

conditions, when not interfered with by Man, sooner or later break

through their banks, and leaving their former bed, take a new course

along the lowest part of their valley, which again they gradually raise

above the rest. Hence, unless they are kept in their own channels by

human agency, such rivers are continually changing their course.

If we imagine a river running down a regularly inclined plane in a more

or less straight line; any inequality or obstruction would produce an

oscillation, which when once started would go on increasing until the

force of gravity drawing the water in a straight line downwards equals

that of the force tending to divert its course. Hence the radius of the

curves will follow a regular law depending on the volume of water and

the angle of inclination of the bed. If the fall is 10 feet per mile and

the soil homogeneous, the curves would be so much extended that the

course would appear almost straight. With a fall of 1 foot per mile the

length of the curve is, according to Fergusson, about six times the

width of the river, so that a river 1000 feet wide would oscillate once

in 6000 feet. This is an important consideration, and much labour has

been lost in trying to prevent rivers from following their natural law

of oscillation. But rivers are very true to their own laws, and a change

at any part is continued both upwards and downwards, so that a new

oscillation in any place cuts its way through the whole plain of the

river both above and below.

The curves of the Mississippi are, for instance, for a considerable part

of its course so regular that they are said to have been used by the

Indians as a measure of distance.

If the country is flat a river gradually raises the level on each side,

the water which overflows during floods being retarded by reeds, bushes,

trees, and a thousand other obstacles, gradually deposits the solid

matter which it contains, and thus raising the surface, becomes at

length suspended, as it were, above the general level. When this

elevation has reached a certain point, the river during some flood

bursts its banks, and deserting its old bed takes a new course along the

lowest accessible level. This then it gradually fills up, and so on;

coming back from time to time if permitted, after a long cycle of

years, to its first course.

In evidence of the vast quantity of sediment which rivers deposit, I may

mention that the river-deposits at Calcutta are more than 400 feet in

thickness.

In addition to temporary "spates," due to heavy rain, most rivers are

fuller at one time of year than another, our rivers, for instance, in

winter, those of Switzerland, from the melting of the snow, in summer.

The Nile commences to rise towards the beginning of July; from August to

October it floods all the low lands, and early in November it sinks

again. At its greatest height the volume of water sometimes reaches

twenty times that when it is lowest, and yet perhaps not a drop of rain

may have fallen. Though we now know that this annual variation is due to

the melting of the snow and the fall of rain on the high lands of

Central Africa, still when we consider that the phenomenon has been

repeated annually for thousands of years it is impossible not to regard

it with wonder. In fact Egypt itself may be said to be the bed of the

Nile in flood time.

Some rivers, on the other hand, offer no such periodical differences.

The lower Rhone, for instance, below the junction with the Saône, is

nearly equal all through the year, and yet we know that the upper

portion is greatly derived from the melting of the Swiss snows. In this

case, however, while the Rhone itself is on this account highest in

summer and lowest in winter, the Saône, on the contrary, is swollen by

the winter's rain, and falls during the fine weather of summer. Hence

the two tend to counterbalance one another.

Periodical differences are of course comparatively easy to deal with. It

is very different with floods due to irregular rainfall. Here also,

however, the mere quantity of rain is by no means the only matter to be

considered. For instance a heavy rain in the watershed of the Seine,

unless very prolonged, causes less difference in the flow of the river,

say at Paris, than might at first have been expected, because the height

of the flood in the nearer affluents has passed down the river before

that from the more distant streams has arrived. The highest level is

reached when the rain in the districts drained by the various affluents

happens to be so timed that the different floods coincide in their

arrival at Paris.

FOOTNOTES:

[52] Darwin's _Voyage of a Naturalist_.

[53] _Geol. Jour._, 1863.

[54] Favre, _Rech. Geol. de la Savoie._

[55] _Growth and Structure of the Alps._

CHAPTER IX

THE SEA

There is a pleasure in the pathless woods,

There is a rapture on the lonely shore,

There is society, where none intrudes,

By the deep Sea, and music in its roar:

I love not Man the less, but Nature more,

From these our interviews, in which I steal

From all I may be, or have been before,

To mingle with the Universe, and feel

What I can ne'er express, yet cannot all conceal.

Roll on, thou deep and dark-blue Ocean--roll!

BYRON.

[Illustration: THE LAND'S END. _To face page 337._]

CHAPTER IX

THE SEA

When the glorious summer weather comes, when we feel that by a year's

honest work we have fairly won the prize of a good holiday, how we turn

instinctively to the Sea. We pine for the delicious smell of the sea

air, the murmur of the waves, the rushing sound of the pebbles on the

sloping shore, the cries of the sea-birds; and long to

Linger, where the pebble-paven shore,

Under the quick, faint kisses of the Sea,

Trembles and sparkles as with ecstasy.[56]

How beautiful the sea-coast is! At the foot of a cliff, perhaps of pure

white chalk, or rich red sandstone, or stern grey granite, lies the

shore of gravel or sand, with a few scattered plants of blue Sea Holly,

or yellow-flowered Horned Poppies, Sea-kale, Sea Convolvulus, Saltwort,

Artemisia, and Sea-grasses; the waves roll leisurely in one by one, and

as they reach the beach, each in turn rises up in an arch of clear,

cool, transparent, green water, tipped with white or faintly pinkish

foam, and breaks lovingly on the sands; while beyond lies the open Sea

sparkling in the sunshine.

... O pleasant Sea

Earth hath not a plain

So boundless or so beautiful as thine.[57]

The Sea is indeed at times overpoweringly beautiful. At morning and

evening a sheet of living silver or gold, at mid-day deep blue; even

Too deeply blue; too beautiful; too bright;

Oh, that the shadow of a cloud might rest

Somewhere upon the splendour of thy breast

In momentary gloom.[58]

There are few prettier sights than the beach at a seaside town on a fine

summer's day; the waves sparkling in the sunshine, the water and sky

each bluer than the other, while the sea seems as if it had nothing to

do but to laugh and play with the children on the sands; the children

perseveringly making castles with spades and pails, which the waves then

run up to and wash away, over and over and over again, until evening

comes and the children go home, when the Sea makes everything smooth and

ready for the next day's play.

Many are satisfied to admire the Sea from shore, others more ambitious

or more free prefer a cruise. They feel with Tennyson's voyager:

We left behind the painted buoy

That tosses at the harbour-mouth;

And madly danced our hearts with joy,

As fast we fleeted to the South:

How fresh was every sight and sound

On open main or winding shore!

We knew the merry world was round,

And we might sail for evermore.

Many appreciate both. The long roll of the Mediterranean on a fine day

(and I suppose even more of the Atlantic, which I have never enjoyed),

far from land in a good ship, and with kind friends, is a joy never to

be forgotten.

To the Gulf Stream and the Atlantic Ocean Northern Europe owes its mild

climate. The same latitudes on the other side of the Atlantic are much

colder. To find the same average temperature in the United States we

must go far to the south. Immediately opposite us lies Labrador, with an

average temperature the same as that of Greenland; a coast almost

destitute of vegetation, a country of snow and ice, whose principal

wealth consists in its furs, and a scattered population, mainly composed

of Indians and Esquimaux. But the Atlantic would not alone produce so

great an effect. We owe our mild and genial climate mainly to the Gulf

Stream--a river in the ocean, twenty million times as great as the

Rhone--the greatest, and for us the most important, river in the world,

which brings to our shores the sunshine of the West Indies.

The Sea is outside time. A thousand, ten thousand, or a million years

ago it must have looked just as it does now, and as it will ages hence.

With the land this is not so. The mountains and hills, rivers and

valleys, animals and plants are continually changing: but the Sea is

always the same,

Steadfast, serene, immovable, the same

Year after year.

Directly we see the coast, or even a ship, the case is altered. Boats

may remain the same for centuries, but ships are continually being

changed. The wooden walls of old England are things of the past, and the

ironclads of to-day will soon be themselves improved off the face of the

ocean.

The great characteristic of Lakes is peace, that of the Sea is energy,

somewhat restless, perhaps, but still movement without fatigue.

The Earth lies quiet like a child asleep,

The deep heart of the Heaven is calm and still,

Must thou alone a restless vigil keep,

And with thy sobbing all the silence fill.[59]

A Lake in a storm rather gives us the impression of a beautiful Water

Spirit tormented by some Evil Demon; but a storm at Sea is one of the

grandest manifestations of Nature.

Yet more; the billows and the depths have more;

High hearts and brave are gathered to thy breast;

They hear not now the booming waters roar,

The battle thunders will not break their rest.

Keep thy red gold and gems, thou stormy grave;

Give back the true and brave.[60]

The most vivid description of a storm at sea is, I think, the following

passage from Ruskin's _Modern Painters_:

"Few people, comparatively, have ever seen the effect on the

sea of a powerful gale continued without intermission for three

or four days and nights; and to those who have not, I believe

it must be unimaginable, not from the mere force or size of the

surge, but from the complete annihilation of the limit between

sea and air. The water from its prolonged agitation is beaten,

not into mere creaming foam, but into masses of accumulated

yeast, which hangs in ropes and wreaths from wave to wave, and,

where one curls over to break, form a festoon like a drapery

from its edge; these are taken up by the wind, not in

dissipating dust, but bodily, in writhing, hanging, coiling

masses, which make the air white and thick as with snow, only

the flakes are a foot or two long each: the surges themselves

are full of foam in their very bodies underneath, making them

white all through, as the water is under a great cataract; and

their masses, being thus half water and half air, are torn to

pieces by the wind whenever they rise, and carried away in

roaring smoke, which chokes and strangles like actual water.

Add to this, that when the air has been exhausted of its

moisture by long rain, the spray of the sea is caught by it as

described above, and covers its surface not merely with the

smoke of finely divided water, but with boiling mist; imagine

also the low rain-clouds brought down to the very level of the

sea, as I have often seen them, whirling and flying in rags and

fragments from wave to wave; and finally, conceive the surges

themselves in their utmost pitch of power, velocity, vastness,

and madness, lifting themselves in precipices and peaks,

furrowed with their whirl of ascent, through all this chaos,

and you will understand that there is indeed no distinction

left between the sea and air; that no object, nor horizon, nor

any landmark or natural evidence of position is left; and the

heaven is all spray, and the ocean all cloud, and that you can

see no further in any direction than you see through a

cataract."

SEA LIFE

The Sea teems with life. The Great Sea Serpent is, indeed, as much a

myth as the Kraken of Pontoppidan, but other monsters, scarcely less

marvellous, are actual realities. The Giant Cuttle Fish of Newfoundland,

though the body is comparatively small, may measure 60 feet from the tip

of one arm to that of another. The Whalebone Whale reaches a length of

over 70 feet, but is timid and inoffensive. The Cachalot or Sperm Whale,

which almost alone among animals roams over the whole ocean, is as

large, and much more formidable. It is armed with powerful teeth, and is

said to feed mainly on Cuttle Fish, but sometimes on true fishes, or

even Seals. When wounded it often attacks boats, and its companions do

not hesitate to come to the rescue. In one case, indeed, an American

ship was actually attacked, stove in, and sunk by a gigantic male

Cachalot.

The Great Roqual is still more formidable, and has been said to attain a

length of 120 feet, but this is probably an exaggeration. So far as we

know, the largest species of all is Simmond's Whale, which reaches a

maximum of 85 to 90 feet.

In former times Whales were frequent on our coasts, so that, as Bishop

Pontoppidan said, the sea sometimes appeared as if covered with smoking

chimneys, but they have been gradually driven further and further north,

and are still becoming rarer. As they retreated man followed, and to

them we owe much of our progress in geography. Is it not, however, worth

considering whether they might not also be allowed a "truce of God,"

whether some part of the ocean might not be allotted to them where they

might be allowed to breed in peace? As a mere mercantile arrangement the

maritime nations would probably find this very remunerative. The

reckless slaughter of Whales, Sea Elephants, Seals, and other marine

animals is a sad blot, not only on the character, but on the common

sense, of man.

The monsters of the ocean require large quantities of food, but they are

supplied abundantly. Scoresby mentions cases in which the sea was for

miles tinged of an olive green by a species of Medusa. He calculates

that in a cubic mile there must have been 23,888,000,000,000,000, and

though no doubt the living mass did not reach to any great depth, still,

as he sailed through water thus discoloured for many miles, the number

must have been almost incalculable.

This is, moreover, no rare or exceptional case. Navigators often sail

for leagues through shoals of creatures, which alter the whole colour of

the sea, and actually change it, as Reclus says, into "une masse

animée."

Still, though the whole ocean teems with life, both animals and plants

are most abundant near the coast. Air-breathing animals, whether mammals

or insects, are naturally not well adapted to live far from dry land.

Even Seals, though some of them make remarkable migrations, remain

habitually near the shore. Whales alone are specially modified so as to

make the wide ocean their home. Of birds the greatest wanderer is the

Albatross, which has such powers of flight that it is said even to sleep

on the wing.

Many Pelagic animals--Jelly-fishes, Molluscs, Cuttle-fishes, Worms,

Crustacea, and some true fishes--are remarkable for having become

perfectly transparent; their shells, muscles, and even their blood have

lost all colour, or even undergone the further modification of having

become blue, often with beautiful opalescent reflections. This obviously

renders them less visible, and less liable to danger.

The sea-shore, wherever a firm hold can be obtained, is covered with

Sea-weeds, which fall roughly into two main divisions, olive-green and

red, the latter colour having a special relation to light. These

Sea-weeds afford food and shelter to innumerable animals.

The clear rocky pools left by the retiring tide are richly clothed with

green sea-weeds, while against the sides are tufts of beautiful filmy

red algæ, interspersed with Sea-anemones,--white, creamy, pink, yellow,

purple, with a coronet of blue beads, and of many mixed colours;

Sponges, Corallines, Starfish, Limpets, Barnacles, and other shell-fish;

feathery Zoophytes and Annelides expand their pink or white disks, while

here and there a Crab scuttles across; little Fish or Shrimps timidly

come out from crevices in the rocks, or from among the fronds of the

sea-weeds, or hastily dart from shelter to shelter; each little pool is,

in fact, a miniature ocean in itself, and the longer one looks the more

and more one will see.

The dark green and brown sea-weeds do not live beyond a few--say about

15--fathoms in depth. Below them occur delicate scarlet species, with

Corallines and a different set of shells, Sea-urchins, etc. Down to

about 100 fathoms the animals and plants are still numerous and varied.

But they gradually diminish in numbers, and are replaced by new forms.

To appreciate fully the extreme loveliness of marine animals they must

be seen alive. "A tuft of Sertularia, laden with white, or brilliantly

tinted Polypites," says Hincks, "like blossoms on some tropical tree, is

a perfect marvel of beauty. The unfolding of a mass of Plumularia, taken

from amongst the miscellaneous contents of the dredge, and thrown into a

bottle of clear sea-water, is a sight which, once seen, no dredger will

forget. A tree of Campanularia, when each one of its thousand

transparent calycles--itself a study of form--is crowned by a circlet of

beaded arms, drooping over its margin like the petals of a flower,

offers a rare combination of the elements of beauty.

"The rocky wall of some deep tidal pool, thickly studded with the long

and slender stems of Tubularia, surmounted by the bright rose-coloured

heads, is like the gay parterre of a garden. Equally beautiful is the

dense growth of Campanularia, covering (as I have seen it in Plymouth

Sound) large tracts of the rock, its delicate shoots swaying to and fro

with each movement of the water, like trees in a storm, or the colony of

Obelia on the waving frond of the tangle looking almost ethereal in its

grace, transparency, and delicacy, as seen against the coarse dark

surface that supports it."

Few things are more beautiful than to look down from a boat into

transparent water. At the bottom wave graceful sea-weeds, brown, green,

or rose-coloured, and of most varied forms; on them and on the sands or

rocks rest starfishes, mollusca, crustaceans, Sea-anemones, and

innumerable other animals of strange forms and varied colours; in the

clear water float or dart about endless creatures; true fishes, many of

them brilliantly coloured; Cuttle-fishes like bad dreams; Lobsters and

Crabs with graceful, transparent Shrimps; Worms swimming about like

living ribbons, some with thousands of coloured eyes, and Medusæ like

living glass of the richest and softest hues, or glittering in the

sunshine with all the colours of the rainbow.

And on calm, cool nights how often have I stood on the deck of a ship

watching with wonder and awe the stars overhead, and the sea-fire below,

especially in the foaming, silvery wake of the vessel, where often

suddenly appear globes of soft and lambent light, given out perhaps

from the surface of some large Medusa.

"A beautiful white cloud of foam," says Coleridge, "at momently

intervals coursed by the side of the vessel with a roar, and little

stars of flame danced and sparkled and went out in it; and every now and

then light detachments of this white cloud-like foam darted off from the

vessel's side, each with its own small constellation, over the sea, and

scoured out of sight like a Tartar troop over a wilderness."

Fish also are sometimes luminous. The Sun-fish has been seen to glow

like a white-hot cannon-ball, and in one species of Shark (Squalus

fulgens) the whole surface sometimes gives out a greenish lurid light

which makes it a most ghastly object, like some great ravenous spectre.

THE OCEAN DEPTHS

The Land bears a rich harvest of life, but only at the surface. The

Ocean, on the contrary, though more richly peopled in its upper layers,

which swarm with such innumerable multitudes of living creatures that

they are, so to say, almost themselves alive--teems throughout with

living beings.

The deepest abysses have a fauna of their own, which makes up for the

comparative scantiness of its numbers, by the peculiarity and interest

of their forms and organisation. The middle waters are the home of

various Fishes, Medusæ, and animalcules, while the upper layers swarm

with an inexhaustible variety of living creatures.

It used to be supposed that the depths of the Ocean were destitute of

animal life, but recent researches, and especially those made during our

great national expedition in the "Challenger," have shown that this is

not the case, but that the Ocean depths have a wonderful and peculiar

life of their own. Fish have been dredged up even from a depth of 2750

fathoms.

The conditions of life in the Ocean depths are very peculiar. The light

of the sun cannot penetrate beyond about two hundred fathoms; deeper

than this complete darkness prevails. Hence in many species the eyes

have more or less completely disappeared.

Sir Wyville Thomson mentions a kind of Crab (Ethusa granulata), which

when living near the surface has well developed eyes; in deeper water,

100 to 400 fathoms, eyestalks are present, but the animal is apparently

blind, the eyes themselves being absent; while in specimens from a depth

of 500-700 fathoms the eyestalks themselves have lost their special

character, and have become fixed, their terminations being combined into

a strong, pointed beak.

In other deep sea creatures, on the contrary, the eyes gradually become

more and more developed, so that while in some species the eyes

gradually dwindle, in others they become unusually large.

Many of the latter species may be said to be a light to themselves,

being provided with a larger or smaller number of curious luminous

organs. The deep sea fish are either silvery, pink, or in many cases

black, sometimes relieved with scarlet, and when the luminous organs

flash out must present a very remarkable appearance.

We have still much to learn as to the structure and functions of these

organs, but there are cases in which their use can be surmised with some

probability. The light is evidently under the will of the fish.[61] It

is easy to imagine a Photichthys (Light Fish) swimming in the black

depths of the Ocean, suddenly flashing out light from its luminous

organs, and thus bringing into view any prey which may be near; while,

if danger is disclosed, the light is again at once extinguished. It may

be observed that the largest of these organs is in this species situated

just under the eye, so that the fish is actually provided with a bull's

eye lantern. In other cases the light may rather serve as a defence,

some having, as, for instance, in the genus Scopelus, a pair of large

ones in the tail, so that "a strong ray of light shot forth from the

stern-chaser may dazzle and frighten an enemy."

In other cases they appear to serve as lures. The "Sea-devil" or

"Angler" of our coasts has on its head three long, very flexible,

reddish filaments, while all round its head are fringed appendages,

closely resembling fronds of sea-weed. The fish conceals itself at the

bottom, in the sand or among sea-weed, and dangles the long filaments in

front of its mouth. Little fishes, taking these filaments for worms,

unsuspectingly approach, and thus fall victims.

Several species of the same family live at great depths, and have very

similar habits. A mere red filament would be invisible in the dark and

therefore useless. They have, however, developed a luminous organ, a

living "glow-lamp," at the end of the filament, which doubtless proves a

very effective lure.

In the great depths, however, fish are comparatively rare. Nor are

Molluscs much more abundant. Sea-urchins, Sea Slugs, and Starfish are

more numerous, and on one occasion 20,000 specimens of an Echinus were

brought up at a single haul. True corals are rare, nor are Hydrozoa

frequent, though a giant species, allied to the little Hydra of our

ponds but upwards of 6 feet in height, has more than once been met

with. Sponges are numerous, and often very beautiful. The now well known

Euplectella, "Venus's Flower-basket," resembles an exquisitely delicate

fabric woven in spun silk; it is in the form of a gracefully curved

tube, expanding slightly upwards and ending in an elegant frill. The

wall is formed of parallel bands of glassy siliceous fibres, crossed by

others at right angles, so as to form a square meshed net. These sponges

are anchored on the fine ooze by wisps of glassy filaments, which often

attain a considerable length. Many of these beautiful organisms,

moreover, glow when alive with a soft diffused light, flickering and

sparkling at every touch. What would one not give to be able to wander a

while in these wonderful regions!

It is curious that no plants, so far as we know, grow in the depths of

the Ocean, or, indeed, as far as our present information goes, at a

greater depth than about 100 fathoms.

As regards the nature of the bottom itself, it is in the neighbourhood

of land mainly composed of materials, brought down by rivers or washed

from the shore, coarser near the coast, and tending to become finer and

finer as the distance increases and the water deepens. The bed of the

Atlantic from 400 to 2000 fathoms is covered with an ooze, or very fine

chalky deposit, consisting to a great extent of minute and more or less

broken shells, especially those of Globigerina. At still greater depths

the carbonate of lime gradually disappears, and the bottom consists of

fine red clay, with numerous minute particles, some of volcanic, some of

meteoric, origin, fragments of shooting stars, over 100,000,000 of which

are said to strike the surface of our earth every year. How slow the

process of deposition must be, may be inferred from the fact that the

trawl sometimes brings up many teeth of Sharks and ear-bones of Whales

(in one case no less than 600 teeth and 100 ear-bones), often

semi-fossil, and which from their great density had remained intact for

ages, long after all the softer parts had perished and disappeared.

The greatest depth of the Ocean appears to coincide roughly with the

greatest height of the mountains. There are indeed cases recorded in

which it is said that "no bottom" was found even at 39,000 feet. It is,

however, by no means easy to sound at such great depths, and it is now

generally considered that these earlier observations are untrustworthy.

The greatest depth known in the Atlantic is 3875 fathoms--a little to

the north of the Virgin Islands, but the soundings as yet made in the

deeper parts of the Ocean are few in number, and it is not to be

supposed that the greatest depth has yet been ascertained.

CORAL ISLANDS

In many parts of the world the geography itself has been modified by the

enormous development of animal life. Most islands fall into one of three

principal categories:

Firstly, Those which are in reality a part of the continent near which

they lie, being connected by comparatively shallow water, and standing

to the continent somewhat in the relation of planets to the sun; as,

for instance, the Cape de Verde Islands to Africa, Ceylon to India, or

Tasmania to Australia.

Secondly, Volcanic islands; and

Thirdly, Those which owe their origin to the growth of Coral reefs.

[Illustration: Fig. 49.--Whitsunday Island.]

Coral islands are especially numerous in the Indian and Pacific Oceans,

where there are innumerable islets, in the form of rings, or which

together form rings, the rings themselves being sometimes made up of

ringlets. These "atolls" contain a circular basin of yellowish green,

clear, shallow water, while outside is the dark blue deep water of the

Ocean. The islands themselves are quite low, with a beach of white sand

rising but a few feet above the level of the water, and bear generally

groups of tufted Cocoa Palms.

It used to be supposed that these were the summits of submarine

volcanoes on which the coral had grown. But as the reef-making coral

does not live at greater depths than about twenty-five fathoms, the

immense number of these reefs formed an almost insuperable objection to

this theory. The Laccadives and Maldives for instance--meaning literally

the "lac of or 100,000 islands," and the "thousand islands"--are a

series of such atolls, and it was impossible to imagine so great a

number of craters, all so nearly of the same altitude.

In shallow tracts of sea, coral reefs no doubt tend to assume the

well-known circular form, but the difficulty was to account for the

numerous atolls which rise to the surface from the abysses of the ocean,

while the coral-forming zoophytes can only live near the surface.

Darwin showed that so far from the ring of corals resting on a

corresponding ridge of rocks, the lagoons, on the contrary, now occupy

the place which was once the highest land. He pointed out that some

lagoons, as for instance that of Vanikoro, contain an island in the

middle; while other islands, such as Tahiti, are surrounded by a margin

of smooth water separated from the ocean by a coral reef. Now if we

suppose that Tahiti were to sink slowly it would gradually approximate

to the condition of Vanikoro; and if Vanikoro gradually sank, the

central island would disappear, while on the contrary the growth of the

coral might neutralise the subsidence of the reef, so that we should

have simply an atoll with its lagoon. The same considerations explain

the origin of the "barrier reefs," such as that which runs for nearly a

thousand miles, along the north-east coast of Australia. Thus Darwin's

theory explains the form and the approximate identity of altitude of

these coral islands. But it does more than this, because it shows that

there are great areas in process of subsidence, which though slow, is of

great importance in physical geography.

The lagoon islands have received much attention; which "is not

surprising, for every one must be struck with astonishment, when he

first beholds one of these vast rings of coral-rock, often many leagues

in diameter, here and there surmounted by a low verdant island with

dazzling white shores, bathed on the outside by the foaming breakers of

the ocean, and on the inside surrounding a calm expanse of water, which,

from reflection is generally of a bright but pale green colour. The

naturalist will feel this astonishment more deeply after having examined

the soft and almost gelatinous bodies of these apparently insignificant

coral-polypifers, and when he knows that the solid reef increases only

on the outer edge, which day and night is lashed by the breakers of an

ocean never at rest. Well did François Pyrard de Laval, in the year 1605

exclaim, 'C'est une merveille de voir chacun de ces atollons, environné

d'un grand banc de pierre tout autour, n'y ayant point d'artifice

humain.'"[62]

Of the enchanting beauty of the coral beds themselves we are assured

that language conveys no adequate idea. "There were corals," says Prof.

Ball, "which, in their living state, are of many shades of fawn, buff,

pink, and blue, while some were tipped with a magenta-like bloom.

Sponges which looked as hard as stone spread over wide areas, while

sprays of coralline added their graceful forms to the picture. Through

the vistas so formed, golden-banded and metallic-blue fish meandered,

while on the patches of sand here and there Holothurias and various

mollusca and crustaceans might be seen slowly crawling."

Abercromby also gives a very graphic description of a Coral reef. "As we

approached," he says, "the roaring surf on the outside, fingery lumps of

beautiful live coral began to appear of the palest lavender-blue colour;

and when at last we were almost within the spray, the whole floor was

one mass of living branches of coral.

"But it is only when venturing as far as is prudent into the water, over

the outward edge of the great sea wall, that the true character of the

reef and all the beauties of the ocean can be really seen. After

walking over a flat uninteresting tract of nearly bare rock, you look

down and see a steep irregular wall, expanding deeper into the ocean

than the eye can follow, and broken into lovely grottoes and holes and

canals, through which small resplendent fish of the brightest blue or

gold flit fitfully between the lumps of coral. The sides of these

natural grottoes are entirely covered with endless forms of

tender-coloured coral, but all beautiful, and all more or less of the

fingery or branching species, known as madrepores. It is really

impossible to draw or describe the sight, which must be taken with all

its surroundings as adjuncts."[63]

The vegetation of these fairy lands is also very lovely; the Coral tree

(Erythrina) with light green leaves and bunches of scarlet blossoms, the

Cocoa-nut always beautiful, the breadfruit, the graceful tree ferns, the

Barringtonia, with large pink and white flowers, several species of

Convolvulus, and many others unknown to us even by name.

THE SOUTHERN SKIES

In considering these exquisite scenes, the beauty of the Southern skies

must not be omitted. "From the time we entered the torrid zone," says

Humboldt, "we were never wearied with admiring, every night, the beauty

of the southern sky, which, as we advanced towards the south, opened new

constellations to our view. We feel an indescribable sensation, when, on

approaching the equator, and particularly on passing from one hemisphere

to the other, we see those stars which we have contemplated from our

infancy, progressively sink, and finally disappear. Nothing awakens in

the traveller a livelier remembrance of the immense distance by which he

is separated from his country, than the aspect of an unknown firmament.

The grouping of the stars of the first magnitude, some scattered nebulæ

rivalling in splendour the milky way, and tracts of space remarkable for

their extreme blackness, give a particular physiognomy to the southern

sky. This sight fills with admiration even those, who, uninstructed in

the branches of accurate science, feel the same emotions of delight in

the contemplation of the heavenly vault, as in the view of a beautiful

landscape, or a majestic river. A traveller has no need of being a

botanist to recognise the torrid zone on the mere aspect of its

vegetation; and, without having acquired any notion of astronomy, he

feels he is not in Europe, when he sees the immense constellation of the

Ship, or the phosphorescent clouds of Magellan, arise on the horizon.

The heaven and the earth, in the equinoctial regions, assume an exotic

character."

"The sunsets in the Eastern Archipelago," says H. O. Forbes,[64] "were

scenes to be remembered for a lifetime. The tall cones of Sibissie and

Krakatoa rose dark purple out of an unruffled golden sea, which

stretched away to the south-west, where the sun went down; over the

horizon gray fleecy clouds lay in banks and streaks, above them pale

blue lanes of sky, alternating with orange bands, which higher up gave

place to an expanse of red stretching round the whole heavens.

Gradually as the sun retreated deeper and deeper, the sky became a

marvellous golden curtain, in front of which the gray clouds coiled

themselves into weird forms before dissolving into space...."

THE POLES

The Arctic and Antarctic regions have always exercised a peculiar

fascination over the human mind. Until now every attempt to reach the

North Pole has failed, and the South has proved even more inaccessible.

In the north, Parry all but reached lat. 83; in the south no one has

penetrated beyond lat. 71.11. And yet, while no one can say what there

may be round the North Pole, and some still imagine that open water

might be found there, we can picture to ourselves the extreme South with

somewhat more confidence.

Whenever ships have sailed southwards, except at a few places where land

has been met with, they have come at last to a wall of ice, from fifty

to four hundred feet high. In those regions it snows, if not

incessantly, at least very frequently, and the snow melts but little. As

far as the eye can reach nothing is to be seen but snow. Now this snow

must gradually accumulate, and solidify into ice, until it attains such

a slope that it will move forward as a glacier. The enormous Icebergs of

the Southern Ocean, moreover, show that it does so, and that the snow of

the extreme south, after condensing into ice, moves slowly outward and

at length forms a wall of ice, from which Icebergs, from time to time,

break away. We do not exactly know what, under such circumstances, the

slope would be; but Mr. Croll points out that if we take it at only half

a degree, and this seems quite a minimum, the Ice cap at the South Pole

must be no less than twelve miles in thickness. It is indeed probably

even more, for some of the Southern tabular icebergs attain a height of

eight hundred, or even a thousand feet above water, indicating a total

thickness of the ice sheet even at the edge, of over a mile.

Sir James Ross mentions that--"Whilst measuring some angles for the

survey near Mount Lubbock an island suddenly appeared, which he was

quite sure was not to be seen two or three hours previously. He was much

astonished, but it eventually turned out to be a large iceberg, which

had turned over, and so exposed a new surface covered with earth and

stones."

The condition of the Arctic regions is quite different. There is much

more land, and no such enormous solid cap of ice. Spitzbergen, the land

of "pointed mountains," is said to be very beautiful. Lord Dufferin

describes his first view of it as "a forest of thin lilac peaks, so

faint, so pale, that had it not been for the gem-like distinctness of

their outline one could have deemed them as unsubstantial as the spires

of Fairyland."

It is, however, very desolate; scarcely any vegetation excepting a dark

moss, and even this goes but a little way up the mountain side. Scoresby

ascended one of the hills near Horn Sound, and describes the view as

"most extensive and grand. A fine sheltered bay was seen to the east of

us, an arm of the same on the north-east, and the sea, whose glassy

surface was unruffled by a breeze, formed an immense expanse on the

west; the glaciers, rearing their proud crests almost to the tops of

mountains between which they were lodged, and defying the power of the

solar beams, were scattered in various directions about the sea-coast

and in the adjoining bays. Beds of snow and ice filling extensive

hollows, and giving an enamelled coat to adjoining valleys, one of

which, commencing at the foot of the mountain where we stood, extended

in a continual line towards the north, as far as the eye could

reach--mountain rising above mountain, until by distance they dwindled

into insignificance, the whole contrasted by a cloudless canopy of

deepest azure, and enlightened by the rays of a blazing sun, and the

effect, aided by a feeling of danger, seated as we were on the pinnacle

of a rock almost surrounded by tremendous precipices--all united to

constitute a picture singularly sublime."

One of the glaciers of Spitzbergen is 11 miles in breadth when it

reaches the sea-coast, the highest part of the precipitous front

adjoining the sea being over 400 feet, and it extends far upwards

towards the summit of the mountain. The surface forms an inclined plane

of smooth unsullied snow, the beauty and brightness of which render it a

conspicuous landmark on that inhospitable shore. From the perpendicular

face great masses of ice from time to time break away,

Whose blocks of sapphire seem to mortal eye

Hewn from cærulean quarries of the sky.[65]

Field ice is comparatively flat, though it may be piled up perhaps as

much as 50 feet. It is from glaciers that true icebergs, the beauty and

brilliance of which Arctic travellers are never tired of describing,

take their origin.

The attempts to reach the North Pole have cost many valuable lives;

Willoughby and Hudson, Behring and Franklin, and many other brave

mariners; but yet there are few expeditions more popular than those to

"the Arctic," and we cannot but hope that it is still reserved for the

British Navy after so many gallant attempts at length to reach the North

Pole.

FOOTNOTES:

[56] Shelley.

[57] Campbell.

[58] Holmes.

[59] Bell.

[60] Hemans.

[61] Gunther, _History of Fishes_.

[62] Darwin, _Coral Reefs_.

[63] Abercromby, _Seas and Skies in many Latitudes_.

[64] _A Naturalist's Wanderings in the Eastern Archipelago._

[65] Montgomery.

CHAPTER X

THE STARRY HEAVENS

A man can hardly lift up his eyes towards the heavens without

wonder and veneration, to see so many millions of radiant

lights, and to observe their courses and revolutions, even

without any respect to the common good of the

Universe.--SENECA.

CHAPTER X

THE STARRY HEAVENS

Many years ago I paid a visit to Naples, and ascended Vesuvius to see

the sun rise from the top of the mountain. We went up to the Observatory

in the evening and spent the night outside. The sky was clear; at our

feet was the sea, and round the bay the lights of Naples formed a lovely

semicircle. Far more beautiful, however, were the moon and the stars

overhead; the moon throwing a silver path over the water, and the stars

shining in that clear atmosphere with a brilliance which I shall never

forget.

For ages and ages past men have admired the same glorious spectacle, and

yet neither the imagination of Man nor the genius of Poetry had risen to

the truer and grander conceptions of the Heavens for which we are

indebted to astronomical Science. The mechanical contrivances by which

it was attempted to explain the movements of the heavenly bodies were

clumsy and prosaic when compared with the great discovery of Newton.

Ruskin is unjust I think when he says "Science teaches us that the

clouds are a sleety mist; Art, that they are a golden throne." I should

be the last to disparage the debt we owe to Art, but for our knowledge,

and even more, for our appreciation, feeble as even yet it is, of the

overwhelming grandeur of the Heavens, we are mainly indebted to Science.

There is scarcely a form which the fancy of Man has not sometimes

detected in the clouds,--chains of mountains, splendid cities, storms at

sea, flights of birds, groups of animals, monsters of all kinds,--and

our superstitious ancestors often terrified themselves by fantastic

visions of arms and warriors and battles which they regarded as portents

of coming calamities. There is hardly a day on which Clouds do not

delight and surprise us by their forms and colours. They belong,

however, to our Earth, and I must now pass on to the heavenly bodies.

[Illustration: THE MOON.

_To face page 377._]

THE MOON

The Moon is the nearest, and being the nearest, appears to us, with the

single exception of the Sun, the largest, although it is in reality one

of the smallest, of the heavenly bodies. Just as the Earth goes round

the Sun, and the period of revolution constitutes a year, so the Moon

goes round the Earth approximately in a period of one month. But while

we turn on our axis every twenty-four hours, thus causing the

alternation of light and darkness--day and night--the Moon takes a month

to revolve on hers, so that she always presents the same, or very nearly

the same, surface to us.

Seeing her as we do, not like the Sun and Stars, by light of her own,

but by the reflected light of the Sun, her form appears to change,

because the side upon which the Sun shines is not always that which we

see. Hence the "phases" of the Moon, which add so much to her beauty

and interest.

Who is there who has not watched them with admiration? "We first see her

as an exquisite crescent of pale light in the western sky after sunset.

Night after night she moves further and further to the east, until she

becomes full, and rises about the same time that the Sun sets. From the

time of full moon the disc of light begins to diminish, until the last

quarter is reached. Then it is that the Moon is seen high in the heavens

in the morning. As the days pass by, the crescent shape is again

assumed. The crescent wanes thinner and thinner as the Moon draws closer

to the Sun. Finally, she becomes lost in the overpowering light of the

Sun, again to emerge as the new moon, and again to go through the same

cycle of changes."[66]

But although she is so small the Moon is not only, next to the Sun, by

far the most beautiful, but also for us the most important, of the

heavenly bodies. Her attraction, aided by that of the Sun, causes the

tides, which are of such essential service to navigation. They carry

our vessels in and out of port, and, indeed, but for them many of our

ports would themselves cease to exist, being silted up by the rivers

running into them. The Moon is also of invaluable service to sailors by

enabling them to determine where they are, and guiding them over the

pathless waters.

The geography of the Moon, so far as concerns the side turned towards

us, has been carefully mapped and studied, and may almost be said to be

as well known as that of our own earth. The scenery is in a high degree

weird and rugged; it is a great wilderness of extinct volcanoes, and,

seen with even a very moderate telescope, is a most beautiful object.

The mountains are of great size. Our loftiest mountain, Mount Everest,

is generally stated as about 29,000 feet in height. The mountains of the

Moon reach an altitude of over 42,000, but this reckons to the lowest

depression, and it must be remembered that we reckon the height of

mountains to the sea level only. Several of the craters on the Moon have

a diameter of 40 or 50--one of them even as much as 78--miles. Many

also have central cones, closely resembling those in our own volcanic

regions. In some cases the craters are filled nearly to the brim with

lava. The volcanoes seem, however, to be all extinct; and there is not a

single case in which we have conclusive evidence of any change in a

lunar mountain.

[Illustration: Fig. 50.--A group of Lunar Volcanoes.]

The Moon, being so much smaller than the earth, cooled, of course, much

more rapidly, and it is probable that these mountains are millions of

years old--much older than many of our mountain chains. Yet no one can

look at a map of the Moon without being struck with the very rugged

character of its mountain scenery. This is mainly due to the absence of

air and water. To these two mighty agencies, not merely "the

cloud-capped towers, the gorgeous palaces, the solemn temples," but the

very mountains themselves, are inevitable victims. Not merely storms and

hurricanes, but every gentle shower, every fall of snow, tends to soften

our scenery and lower the mountain peaks. These agencies are absent from

the Moon, and the mountains stand to-day just as they were formed

millions of years ago.

But though we find on our own globe (see, for instance, Fig. 21)

volcanic regions closely resembling those of the Moon, there are other

phenomena on the Moon's surface for which our earth presents as yet no

explanation. From Tycho, for instance, a crater 17,000 feet high and 50

miles across, a number of rays or streaks diverge, which for hundreds,

or in some cases two or three thousand, miles pass straight across

plains, craters, and mountains. The true nature of these streaks is not

yet understood.

THE SUN

The Sun is more than 400 times as distant as the Moon; a mighty glowing

globe, infinitely hotter than any earthly fiery furnace, 300,000 times

as heavy, and 1,000,000 times as large as the earth. Its diameter is

865,000 miles, and it revolves on its axis in between 25 and 26 days.

Its distance is 92,500,000 miles. And yet it is only a star, and by no

means one of the first magnitude.

The surface of the Sun is the seat of violent storms and tempests. From

it gigantic flames, consisting mainly of hydrogen, flicker and leap.

Professor Young describes one as being, when first observed, 40,000

miles high. Suddenly it became very brilliant, and in half an hour

sprang up 40,000 more. For another hour it soared higher and higher,

reaching finally an elevation of no less than 350,000 miles, after which

it slowly faded away, and in a couple of hours had entirely disappeared.

This was no doubt an exceptional case, but a height of 100,000 miles is

not unusual, and the velocity frequently reaches 100 miles in a second.

The proverbial spots on the Sun in many respects resemble the

appearances which would be presented if a comparatively dark central

mass was here and there exposed by apertures through the more brilliant

outer gases, but their true nature is still a matter of discussion.

During total eclipses it is seen that the Sun is surrounded by a

"corona," or aureola of light, consisting of radiant filaments, beams,

and sheets of light, which radiate in all directions, and the true

nature of which is still doubtful.

Another stupendous problem connected with the Sun is the fact that, as

geology teaches us, it has given off nearly the same quantity of light

and heat for millions of years. How has this come to pass? Certainly not

by any process of burning such as we are familiar with. Indeed, if the

heat of the Sun were due to combustion it would be burnt up in 6000

years. It has been suggested that the meteors, which fall in showers on

to the Sun, replace the heat which is emitted. To some slight extent

perhaps they do so, but the main cause seems to be the slow condensation

of the Sun itself. Mathematicians tell us that a contraction of about

220 feet a year would account for the whole heat emitted, and as the

present diameter of the Sun is about 860,000 miles, the potential store

of heat is still enormous.

To the Sun we owe our light and heat; it is not only the centre of our

planetary system, it is the source and ruler of our lives. It draws up

water from the ocean, and pours it down in rain to fill the rivers and

refresh the plants; it raises the winds, which purify the air and waft

our ships over the seas; it draws our carriages and drives our

steam-engines, for coal is but the heat of former ages stored up for our

use; animals live and move by the Sun's warmth; it inspires the song of

birds, paints the flowers, and ripens the fruit. Through it the trees

grow. For the beauties of nature, for our food and drink, for our

clothing, for our light and life, for the very possibility of our

existence, we are indebted to the Sun.

What is the Sun made of? Comte mentioned as a problem, which it was

impossible that man could ever solve, any attempt to determine the

chemical composition of the heavenly bodies. "Nous concevons," he said,

"la possibilité de déterminer leurs formes, leurs distances, leurs

grandeurs, et leurs mouvements, tandis que nous ne saurions jamais

étudier par aucun moyen leur composition chimique ou leur structure

minéralogique." To do so might well have seemed hopeless, and yet the

possibility has been proved, and a beginning has been made. In the early

part of this century Wollaston observed that the bright band of colours

thrown by a prism, and known as the spectrum, was traversed by dark

lines, which were also discovered, and described more in detail, by

Fraunhofer, after whom they are generally called "Fraunhofer's lines."

The next step was made by Wheatstone, who showed that the spectrum

formed by incandescent vapours was formed of bright lines, which

differed for each substance, and might, therefore, be used as a

convenient mode of analysis. In fact, by this process several new

substances have actually been discovered. These bright lines were found

on comparison to coincide with the dark lines in the spectrum, and to

Kirchhoff and Bunsen is due the credit of applying this method of

research to astronomical science. They arranged their apparatus so that

one-half was lighted by the Sun, the other by the incandescent gas they

were examining. When the vapour of sodium was treated in this way they

found that the bright line in the flame of soda exactly coincided with a

line in the Sun's spectrum. The conclusion was obvious; there is sodium

in the Sun. It must, indeed, have been a glorious moment when the

thought flashed upon them; and the discovery, with its results, is one

of the greatest triumphs of human genius.

The Sun has thus been proved to contain hydrogen, sodium, barium,

magnesium, calcium, aluminium, chromium, iron, nickle, manganese,

titanium, cobalt, lead, zinc, copper, cadmium, strontium, cerium,

uranium, potassium, etc., in all 36 of our terrestrial elements, while

as regards some others the evidence is not conclusive. We cannot as yet

say that any of our elements are absent, nor though there are various

lines which cannot as yet be certainly referred to any known substance,

have we clear proof that the Sun contains any element which does not

exist on our earth. On the whole, then, the chemical composition of the

Sun appears closely to resemble that of our earth.

THE PLANETS

The Syrian shepherds watching their flocks by night long ago

noticed--and they were probably not the first--that there were five

stars which did not follow the regular course of the rest, but,

apparently at least, moved about irregularly. These they appropriately

named Planets, or wanderers.

Further observations have shown that this irregularity of their path is

only apparent, and that, like our own Earth, they really revolve round

the Sun. To the five first observed--Mercury, Venus, Mars, Jupiter, and

Saturn--two large ones, Uranus and Neptune, and a group of minor bodies,

have since been added.

The following two diagrams give the relative orbits of the Planets.

[Illustration: Fig. 51.--Orbits of the inner Planets.]

MERCURY

It is possible, perhaps probable, that there may be an inner Planet,

but, so far as we know for certain, Mercury is the one nearest to the

Sun, its average distance being 36,000,000 miles. It is much smaller

than the Earth, its weight being only about 1/24th of ours. Mercury is a

shy though beautiful object, for being so near the Sun it is not easily

visible; it may, however, generally be seen at some time or other during

the year as a morning or evening star.

[Illustration: Fig. 52.--Relative distances of the Planets from the

Sun.]

VENUS

The true morning or evening star, however, is Venus--the peerless and

capricious Venus.

Venus, perhaps, "has not been noticed, not been thought of, for many

months. It is a beautifully clear evening; the sun has just set. The

lover of nature turns to admire the sunset, as every lover of nature

will. In the golden glory of the west a beauteous gem is seen to

glisten; it is the evening star, the planet Venus. A week or two later

another beautiful sunset is seen, and now the planet is no longer a

glistening point low down; it has risen high above the horizon, and

continues a brilliant object long after the shades of night have

descended. Again a little longer and Venus has gained its full

brilliancy and splendour. All the heavenly host--even Sirius and

Jupiter--must pale before the splendid lustre of Venus, the unrivalled

queen of the firmament."[67]

Venus is about as large as our Earth, and when at her brightest

outshines about fifty times the most brilliant star. Yet, like all the

other planets, she glows only with the reflected light of the Sun, and

consequently passes through phases like those of the Moon, though we

cannot see them with the naked eye. To Venus also owe we mainly the

power of determining the distance, and consequently the magnitude, of

the Sun.

THE EARTH

Our own Earth has formed the subject of previous chapters. I will now,

therefore, only call attention to her movements, in which, of course,

though unconsciously, we participate. In the first place, the Earth

revolves on her axis in 24 hours. Her circumference at the tropics is

24,000 miles. Hence a person at the tropics is moving in this respect at

the rate of 1000 miles an hour, or over 16 miles a minute.

But more than this, astronomers have ascertained that the whole solar

system is engaged in a great voyage through space, moving towards a

point on the constellation of Hercules at the rate of at least 20,000

miles an hour, or over 300 miles a minute.[68]

But even more again, we revolve annually round the Sun in a mighty orbit

580,000,000 miles in circumference. In this respect we are moving at the

rate of no less than 60,000 miles an hour, or 1000 miles a minute--a

rate far exceeding of course, in fact by some 100 times, that of a

cannon ball.

How few of us know, how little we any of us realise, that we are rushing

through space with such enormous velocity.

MARS

To the naked eye Mars appears like a ruddy star of the first magnitude.

It has two satellites, which have been happily named Phobos and

Deimos--Fear and Dismay. It is little more than half as large as the

Earth, and, though generally far more distant, it sometimes approaches

us within 35,000,000 miles. This has enabled us to study its physical

structure. It seems very probable that there is water in Mars, and the

two poles are tipped with white, as if capped by ice and snow. It

presents also a series of remarkable parallel lines, the true nature of

which is not yet understood.

THE MINOR PLANETS

A glance at Figs. 51 and 52 will show that the distances of the Planets

from the Sun follow a certain rule.

If we take the numbers 0, 3, 6, 12, 24, 48, 96, each one (after the

second) the double of that preceding, and add four, we have the series.

4 7 10 16 28 52 100

Now the distances of the Planets from the Sun are as follow:--

Mercury. Venus. Earth. Mars. Jupiter. Saturn.

3.9 7.2 10 15.2 52.9 95.4

For this sequence, which was first noticed by Bode, and is known as

Bode's law, no explanation can yet be given. It was of course at once

observed that between Mars and Jupiter one place is vacant, and it has

now been ascertained that this is occupied by a zone of Minor Planets,

the first of which was discovered by Piazzi on January 1, 1801, a worthy

prelude to the succession of scientific discoveries which form the glory

of our century. At present over 300 are known, but certainly these are

merely the larger among an immense number, some of them doubtless mere

dust.

JUPITER

Beyond the Minor Planets we come to the stupendous Jupiter, containing

300 times the mass, and being 1200 times the size of our Earth--larger

indeed than all the other planets put together. It is probably not

solid, and from its great size still retains a large portion of the

original heat, if we may use such an expression. Jupiter usually shows a

number of belts, supposed to be due to clouds floating over the surface,

which have a tendency to arrange themselves in belts or bands, owing to

the rotation of the planet. Jupiter has four moons or satellites.

SATURN

[Illustration: Fig. 53.--Saturn.]

Next to Jupiter in size, as in position, comes Saturn, which, though far

inferior in dimensions, is much superior in beauty. To the naked eye

Saturn appears as a brilliant star, but when Galileo first saw it

through a telescope it appeared to him to be composed of three bodies in

a line, a central globe with a small one on each side. Huyghens in 1655

first showed that in reality Saturn was surrounded by a series of rings

(see Fig. 53). Of these there are three, the inner one very faint, and

the outer one divided into two by a dark line. These rings are really

enormous shoals of minute bodies revolving round the planet, and

rendering it perhaps the most marvellous and beautiful of all the

heavenly bodies.

While we have one Moon, Mars two, and Jupiter four, Saturn has no less

than eight satellites.

URANUS

Saturn was long supposed to be the outermost body belonging to the solar

system. In 1781, however, on the 13th March, William Herschel was

examining the stars in the constellation of the Twins. One struck him

because it presented a distinct disc, while the true fixed stars,

however brilliant, are, even with the most powerful telescope, mere

points of light. At first he thought it might be a comet, but careful

observations showed that it was really a new planet. Though thus

discovered by Herschel it had often been seen before, but its true

nature was unsuspected. It has a diameter of about 31,700 miles.

Four satellites of Uranus have been discovered, and they present the

remarkable peculiarity that while all the other planets and their

satellites revolve nearly in one plane, the satellites of Uranus are

nearly at right angles, indicating the presence of some local and

exceptional influence.

NEPTUNE

The study of Uranus soon showed that it followed a path which could not

be accounted for by the influence of the Sun and the other then known

planets. It was suspected, therefore, that this was due to some other

body not yet discovered. To calculate where such a body must be so as to

account for these irregularities was a most complex and difficult, and

might have seemed almost a hopeless, task. It was, however, solved

almost simultaneously and independently by Adams in this country, and Le

Verrier in France.

Neptune, so far as we yet know the out-most of our companions, is 35,000

miles in diameter, and its mean distance from the Sun is 2,780,000,000

miles.

ORIGIN OF THE PLANETARY SYSTEM

The theory of the origin of the Planetary System known as the "Nebular

Hypothesis," which was first suggested by Kant, and developed by

Herschel and Laplace, may be fairly said to have attained a high degree

of probability. The space now occupied by the solar system is supposed

to have been filled by a rotating spheroid of extreme tenuity and

enormous heat, due perhaps to the collision of two originally separate

bodies. The heat, however, having by degrees radiated into space, the

gas cooled and contracted towards a centre, destined to become the Sun.

Through the action of centrifugal force the gaseous matter also

flattened itself at the two poles, taking somewhat the form of a disc.

For a certain time the tendency to contract, and the centrifugal force,

counterbalanced one another, but at length a time came when the latter

prevailed and the outer zone detached itself from the rest of the

sphere. One after another similar rings were thrown off, and then

breaking up, formed the planets and their satellites.

That each planet and satellite did form originally a ring we still have

evidence in the wonderful and beautiful rings of Saturn, which, however,

in all probability will eventually form spherical satellites like the

rest. Thus then our Earth was originally a part of the Sun, to which

again it is destined one day to return. M. Plateau has shown

experimentally that by rotating a globe of oil in a mixture of water and

spirit having the same density this process may be actually repeated in

miniature.

This brilliant, and yet simple, hypothesis is consistent with, and

explains many other circumstances connected with the position,

magnitude, and movements of the Planets and their satellites.

The Planets, for instance, lie more or less in the same plane, they

revolve round the Sun and rotate on their own axis in the same

direction--a series of coincidences which cannot be accidental, and for

which the theory would account. Again the rate of cooling would of

course follow the size; a small body cools more rapidly than a large

one. The Moon is cold and rigid; the Earth is solid at the surface, but

intensely hot within; Jupiter and Saturn, which are immensely larger,

still retain much of their original heat, and have a much lower density

than the Earth; and astronomers tell us on other grounds that the Sun

itself is still contracting, and that to this the maintenance of its

temperature is due.

Although, therefore, the Nebular Theory cannot be said to have been

absolutely proved, it has certainly been brought to a high state of

probability, and is, in its main features, generally accepted by

astronomers.

The question has often been asked whether any of the heavenly bodies are

inhabited, and as yet it is impossible to give any certain answer. It

seems _à priori_ probable that the millions of suns which we see as

stars must have satellites, and that some at least of them may be

inhabited. So far as our own system is concerned the Sun is of course

too hot to serve as a dwelling-place for any beings with bodies such as

ours. The same may be said of Mercury, which is at times probably ten

times as hot as our tropics. The outer planets appear to be still in a

state of vapour. The Moon has no air or water.

Mars is in a condition which most nearly resembles ours. All, however,

that can be said is that, so far as we can see, the existence of living

beings on Mars is not impossible.

COMETS

The Sun, Moon, and Stars, glorious and wonderful as they are, though

regarded with great interest, and in some cases worshipped as deities,

excited the imagination of our ancestors less than might have been

expected, and even now attract comparatively little attention, from the

fact that they are always with us. Comets, on the other hand, both as

rare and occasional visitors, from their large size and rapid changes,

were regarded in ancient times with dread and with amazement.

Some Comets revolve round the Sun in ellipses, but many, if not the

majority, are visitors indeed, for having once passed round the Sun

they pass away again into space, never to return.

The appearance which is generally regarded as characteristic of a Comet

is that of a head with a central nucleus and a long tail. Many, however,

of the smaller ones possess no tail, and in fact Comets present almost

innumerable differences. Moreover the same Comet changes rapidly, so

that when they return, they are identified not in any way by their

appearance, but by the path they pursue.

Comets may almost be regarded as the ghosts of heavenly bodies. The

heads, in some cases, may consist of separate solid fragments, though on

this astronomers are by no means agreed, but the tails at any rate are

in fact of almost inconceivable tenuity. We know that a cloud a few

hundred feet thick is sufficient to hide, not only the stars, but even

the Sun himself. A Comet is thousands of miles in thickness, and yet

even extremely minute stars can be seen through it with no appreciable

diminution of brightness. This extreme tenuity of comets is moreover

shown by their small weight. Enormous as they are I remember Sir G. Airy

saying that there was probably more matter in a cricket ball than there

is in a comet. No one, however, now doubts that the weight must be

measured in tons; but it is so small, in relation to the size, as to be

practically inappreciable. If indeed they were comparable in mass even

to the planets, we should long ago have perished. The security of our

system is due to the fact that the planets revolve round the Sun in one

direction, almost in circles, and very nearly in the same plane. Comets,

however, enter our system in all directions, and at all angles; they are

so numerous that, as Kepler said, there are probably more Comets in the

sky than there are fishes in the sea, and but for their extreme tenuity

they would long ago have driven us into the Sun.

When they first come in sight Comets have generally no tail; it grows as

they approach the Sun, from which it always points away. It is no mere

optical illusion; but while the Comet as a whole is attracted by the

Sun, the tail, how or why we know not, is repelled. When once driven

off, moreover, the attraction of the Comet is not sufficient to recall

it, and hence perhaps so many Comets have now no tails.

Donati's Comet, the great Comet of 1858, was first noticed on the 2d

June as a faint nebulous spot. For three months it remained quite

inconspicuous, and even at the end of August was scarcely visible to the

naked eye. In September it grew rapidly, and by the middle of October

the tail extended no less than 40 degrees, after which it gradually

disappeared.

Faint as is the light emitted by Comets, it is yet their own, and

spectrum analysis has detected the presence in them of carbon, hydrogen,

nitrogen, sodium, and probably of iron.

Comets then remain as wonderful, and almost as mysterious, as ever, but

we need no longer regard "a comet as a sign of impending calamity; we

may rather look upon it as an interesting and a beautiful visitor, which

comes to please us and to instruct us, but never to threaten or to

destroy."[69] We are free, therefore, to admire them in peace, and

beautiful, indeed, they are.

"The most wonderful sight I remember," says Hamerton, "as an effect of

calm, was the inversion of Donati's Comet, in the year 1858, during the

nights when it was sufficiently near the horizon to approach the rugged

outline of Graiganunie, and be reflected beneath it in Loch Awe. In the

sky was an enormous aigrette of diamond fire, in the water a second

aigrette, scarcely less splendid, with its brilliant point directed

upwards, and its broad, shadowy extremity ending indefinitely in the

deep. To be out on the lake alone, in a tiny boat, and let it rest

motionless on the glassy water, with that incomparable spectacle before

one, was an experience to be remembered through a lifetime. I have seen

many a glorious sight since that now distant year, but nothing to equal

it in the association of solemnity with splendour."[70]

SHOOTING STARS

On almost any bright night, if we watch a short time some star will

suddenly seem to drop from its place, and, after a short plunge, to

disappear. This appearance is, however, partly illusory. While true

stars are immense bodies at an enormous distance, Shooting Stars are

very small, perhaps not larger than a paving stone, and are not visible

until they come within the limits of our atmosphere, by the friction

with which they are set on fire and dissipated. They are much more

numerous on some nights than others. From the 9th to the 11th August we

pass through one cluster which is known as the Perseids; and on the 13th

and 14th November a still greater group called by astronomers the

Leonids. The Leonids revolve round the Sun in a period of 33 years, and

in an elliptic orbit, one focus of which is about at the same distance

from the Sun as we are, the other at about that of Uranus. The shoal of

stars is enormous; its diameter cannot be less than 100,000 miles, and

its length many hundreds of thousands. There are, indeed, stragglers

scattered over the whole orbit, with some of which we come in contact

every year, but we pass through the main body three times in a

century--last in 1866--capturing millions on each occasion. One of these

has been graphically described by Humboldt:

"From half after two in the morning the most extraordinary luminary

meteors were seen in the direction of the east. M. Bonpland, who had

risen to enjoy the freshness of the air, perceived them first. Thousands

of bodies and falling stars succeeded each other during the space of

four hours. Their direction was very regular from north to south. They

filled a space in the sky extending from due east 30° to north and

south. In an amplitude of 60° the meteors were seen to rise above the

horizon at east-north-east, and at east, to describe arcs more or less

extended, and to fall towards the south, after having followed the

direction of the meridian. Some of them attained a height of 40°, and

all exceeded 25° or 30°. No trace of clouds was to be seen. M. Bonpland

states that, from the first appearance of the phenomenon, there was not

in the firmament a space equal in extent to three diameters of the moon

which was not filled every instant with bolides and falling stars. The

first were fewer in number, but as they were of different sizes it was

impossible to fix the limit between these two classes of phenomena. All

these meteors left luminous traces from five to ten degrees in length,

as often happens in the equinoctial regions. The phosphorescence of

these traces, or luminous bands, lasted seven or eight seconds. Many of

the falling stars had a very distinct nucleus, as large as the disc of

Jupiter, from which darted sparks of vivid light. The bodies seemed to

burst as by explosion; but the largest, those from 1° to 1° 15' in

diameter, disappeared without scintillation, leaving behind them

phosphorescent bands (trabes), exceeding in breadth fifteen or twenty

minutes. The light of these meteors was white, and not reddish, which

must doubtless be attributed to the absence of vapour and the extreme

transparency of the air."[71]

The past history of the Leonids, which Le Verrier has traced out with

great probability, if not proved, is very interesting. They did not, he

considers, approach the Sun until 126 A.D., when, in their career

through the heavens, they chanced to come near to Uranus. But for the

influence of that planet they would have passed round the Sun, and then

departed again for ever. By his attraction, however, their course was

altered, and they will now continue to revolve round the Sun.

There is a remarkable connection between star showers and comets, which,

however, is not yet thoroughly understood. Several star showers follow

paths which are also those of comets, and the conclusion appears almost

irresistible that these comets are made up of Shooting Stars.

We are told, indeed, that 150,000,000 of meteors, including only those

visible with a moderate telescope, fall on the earth annually. At any

rate, there can be no doubt that every year millions of them are

captured by the earth, thus constituting an appreciable, and in the

course of ages a constantly increasing, part of the solid substance of

the globe.

THE STARS

We have been dealing in the earlier part of this chapter with figures

and distances so enormous that it is quite impossible for us to realise

them; and yet we have still others to consider compared with which even

the solar system is insignificant.

In the first place, the number of the Stars is enormous. When we look at

the sky at night they seem, indeed, almost innumerable; so that, like

the sands of the sea, the Stars of heaven have ever been used as

effective symbols of number. The total number visible to the naked eye

is, however, in reality only about 3000, while that shown by the

telescope is about 100,000,000. Photography, however, has revealed to us

the existence of others which no telescope can show. We cannot by

looking long at the heavens see more than at first; in fact, the first

glance is the keenest. In photography, on the contrary, no light which

falls on the plate, however faint, is lost; it is taken in and stored

up. In an hour the effect is 3600 times as great as in a second. By

exposing the photographic plate, therefore, for some hours, and even on

successive nights, the effect of the light is as it were accumulated,

and stars are rendered visible, the light of which is too feeble to be

shown by any telescope.

The distances and magnitudes of the Stars are as astonishing as their

numbers, Sirius, for instance, being about twenty times as heavy as the

Sun itself, 50 times as bright, and no less than 1,000,000 times as far

away; while, though like other stars it seems to us stationary, it is in

reality sweeping through the heavens at the rate of 1000 miles a minute;

Maia, Electra, and Alcyone, three of the Pleiades, are considered to be

respectively 400, 480, and 1000 times as brilliant as the Sun, Canopus

2500 times, and Arcturus, incredible as it may seem, even 8000 times, so

that, in fact, the Sun is by no means one of the largest Stars. Even the

minute Stars not separately visible to the naked eye, and the millions

which make up the Milky Way, are considered to be on an average fully

equal to the Sun in lustre.

Arcturus is, so far as we know at present, the swiftest, brightest, and

largest of all. Its speed is over 300 miles a second, it is said to be

8000 times as bright as the Sun, and 80 times as large, while its

distance is so great that its light takes 200 years in reaching us.

The distances of the heavenly bodies are ascertained by what is known as

"parallax." Suppose the ellipse (Fig. 54), marked Jan., Apr., July,

Oct., represents the course of the Earth round the Sun, and that A B are

two stars. If in January we look at the star A, we see it projected

against the front of the sky marked 1. Three months later it would

appear to be at 2, and thus as we move round our orbit the star itself

appears to move in the ellipse 1, 2, 3, 4. The more distant star B also

appears to move in a similar, but smaller, ellipse; the difference

arising from the greater distance. The size of the ellipse is inversely

proportional to the distance, and hence as we know the magnitude of the

earth's orbit we can calculate the distance of the star. The difficulty

is that the apparent ellipses are so minute that it is in very few cases

possible to measure them.

[Illustration: Fig. 54.--The Parallactic Ellipse.]

The distances of the Fixed Stars thus tested are found to be enormous,

and indeed generally incalculable; so great that in most cases, whether

we look at them from one end of our orbit or the other--though the

difference of our position, corresponding to the points marked January

and July in Fig. 54, is 185,000,000 miles--no apparent change of

position can be observed. In some, however, the parallax, though very

minute, is yet approximately measurable. The first star to which this

test was applied with success was that known as 61 Cygni, which is thus

shown to be no less than 40 billions of miles away from us--many

thousand times as far as we are from the Sun. The nearest of the Stars,

so far as we yet know, is [Greek: alpha] Centauri, the distance of which

is about 25 billions of miles.

The Pleiades are considered to be at a distance of nearly 1500 billions

of miles.

As regards the chemical composition of the Stars, it is, moreover,

obvious that the powerful engine of investigation afforded us by the

spectroscope is by no means confined to the substances which form part

of our system. The incandescent body can thus be examined, no matter how

great its distance, so long only as the light is strong enough. That

this method was theoretically applicable to the light of the Stars is

indeed obvious, but the practical difficulties are very great. Sirius,

the brightest of all, is, in round numbers, a hundred millions of

millions of miles from us; and, though as bright as fifty of our suns,

his light when it reaches us, after a journey of sixteen years, is at

most one two-thousand-millionth part as bright. Nevertheless, as long

ago as 1815 Fraunhofer recognised the fixed lines in the light of four

of the Stars; in 1863 Miller and Huggins in our own country, and

Rutherford in America, succeeded in determining the dark lines in the

spectrum of some of the brighter Stars, thus showing that these

beautiful and mysterious lights contain many of the material substances

with which we are familiar. In Aldebaran, for instance, we may infer the

presence of hydrogen, sodium, magnesium, iron, calcium, tellurium,

antimony, bismuth, and mercury. As might have been expected, the

composition of the Stars is not uniform, and it would appear that they

may be arranged in a few well-marked classes, indicating differences of

temperature, or perhaps of age.

Thus we can make the Stars teach us their own composition with light,

which started from its source years ago, in many cases long before we

were born.

Spectrum analysis has also thrown an unexpected light on the movements

of the Stars. Ordinary observation, of course, is powerless to inform

us whether they are moving towards or away from us. Spectrum analysis,

however, enables us to solve the problem, and we know that some are

approaching, some receding.

[Illustration: Fig. 55.--Displacement of the hydrogen line in the

spectrum of Rigel.]

If a star, say for instance Sirius, were motionless, or rather if it

retained a constant distance from the earth, Fraunhofer's lines would

occupy exactly the same position in the spectrum as they do in that of

the Sun. On the contrary, if Sirius were approaching, the lines would be

slightly shifted towards the blue, or if it were receding towards the

red. Fig. 55 shows the displacement of the hydrogen line in the spectrum

of Rigel, due to the fact that it is receding from us at the rate of 39

miles a second. The Sun affords us an excellent test of this theory. As

it revolves on its axis one edge is always approaching and the other

receding from us at a known rate, and observation shows that the lines

given by the light of the two edges differ accordingly. So again as

regards the Stars, we obtain a similar test derived from the Earth's

movement. As we revolve in our orbit we approach or recede any given

star, and our rate of motion being known we thus obtain a second test.

The results thus examined have stood their ground satisfactorily, and in

Huggins' opinion may be relied on within about an English mile a second.

The effect of this movement is, moreover, independent of the distance. A

lateral motion, say of 20 miles a second, which in a nearer object would

appear to be a stupendous velocity, becomes in the Stars quite

imperceptible. A motion of the same rapidity, on the other hand, towards

or away from us, displaces the dark lines equally, whatever the distance

of the object may be. We may then affirm that Sirius, for instance, is

receding from us at the rate of about 20 miles a second. Betelgeux,

Rigel, Castor, Regulus, and others are also moving away; while

some--Vega, Arcturus, and Pollux, for example--are approaching us. By

the same process it is shown that some groups of stars are only

apparently in relation to one another. Thus in Charles' Wain some of the

stars are approaching, others receding.

I have already mentioned that Sirius, though it seems, like other stars,

so stationary that we speak of them as "fixed," is really sweeping along

at the rate of 1000 miles a minute. Even this enormous velocity is

exceeded in other cases. One, which is numbered as 1830 in Groombridge's

_Catalogue of the Stars_, and is therefore known as "Groombridge's

1830," moves no less than 12,000 miles a minute, and Arcturus 22,000

miles a minute, or 32,000,000 of miles a day; and yet the distances of

the Stars are so great that 1000 years would make hardly any difference

in the appearance of the heavens.

Changes, however, there certainly would be. Even in the short time

during which we have any observations, some are already on record. One

of the most interesting is the fading of the 7th Pleiad, due, according

to Ovid, to grief at the taking of Troy. Again, the "fiery Dogstar," as

it used to be, is now, and has been for centuries, a clear white.

The star known as Nova Cygni--the "new star in the Constellation of the

Swan"--was first observed on the 24th November 1876 by Dr. Schmidt of

Athens, who had examined that part of the heavens only four days before,

and is sure that no such star was visible then. At its brightest it was

a brilliant star of the third magnitude, but this only lasted for a few

days; in a week it had ceased to be a conspicuous object, and in a

fortnight became invisible without a telescope. Its sudden splendour was

probably due to a collision between two bodies, and was probably little,

if at all, less than that of the Sun itself. It is still a mystery how

so great a conflagration can have diminished so rapidly.

But though we speak of some stars as specially variable, they are no

doubt all undergoing slow change. There was a time when they were not,

and one will come when they will cease to shine. Each, indeed, has a

life-history of its own. Some, doubtless, represent now what others

once were, and what many will some day become.

For, in addition to the luminous heavenly bodies, we cannot doubt that

there are countless others invisible to us, some from their greater

distance or smaller size, but others, doubtless, from their feebler

light; indeed, we know that there are many dark bodies which now emit no

light, or comparatively little. Thus in the case of Procyon the

existence of an invisible body is proved by the movement of the visible

star. Again, I may refer to the curious phenomena presented by Algol, a

bright star in the head of Medusa. The star shines without change for

two days and thirteen hours; then in three hours and a half dwindles

from a star of the second to one of the fourth magnitude; and then, in

another three and a half hours, reassumes its original brilliancy. These

changes led astronomers to infer the presence of an opaque body, which

intercepts at regular intervals a part of the light emitted by Algol;

and Vogel has now shown by the aid of the spectroscope that Algol does

in fact revolve round a dark, and therefore invisible, companion. The

spectroscope, in fact, makes known to us the presence of many stars

which no telescope could reveal.

Thus the floor of heaven is not only "thick inlaid with patines of

bright gold," but studded also with extinct stars, once probably as

brilliant as our own Sun, but now dead and cold, as Helmholtz tells us

that our Sun itself will be some seventeen millions of years hence.

Such dark bodies cannot of course be seen, and their existence, though

we cannot doubt it, is a matter of calculation. In one case, however,

the conclusion has received a most interesting confirmation. The

movements of Sirius led mathematicians to conclude that it had also a

mighty and massive neighbour, the relative position of which they

calculated, though no such body had ever been seen. In February 1862,

however, the Messrs. Alvan Clark of Cambridgeport were completing their

18-inch glass for the Chicago Observatory. "'Why, father,'" exclaimed

the younger Clark, "'the star has a companion.' The father looked, and

there was a faint star due east from the bright one, and distant about

ten seconds. This was exactly the predicted direction for that time,

though the discoverers knew nothing of it. As the news went round the

world many observers turned their attention to Sirius; and it was then

found that, though it had never before been noticed, the companion was

really shown under favourable circumstances by any powerful telescope.

It is, in fact, one-half of the size of Sirius, though only 1/10000th of

the brightness."[72]

Stars are, we know, of different magnitudes and different degrees of

glory. They are also of different colours. Most, indeed, are white, but

some reddish, some ruddy, some intensely red; others, but fewer, green,

blue, or violet. It is possible that the comparative rarity of these

colours is due to the fact that our atmosphere especially absorbs green

and blue, and it is remarkable that almost all of the green, blue, or

violet stars are one of the pairs of a Double Star, and in every case

the smaller one of the two, the larger being red, orange, or yellow. One

of the most exquisite of these is [Greek: beta] Cygni, a Double Star, the

larger one being golden yellow, the smaller light blue. With a telescope

the effect is very beautiful, but it must be magnificent if one could

only see it from a lesser distance.

Double Stars occur in considerable numbers. In some cases indeed the

relation may only be apparent, one being really far in front of the

other. In very many cases, however, the association is real, and they

revolve round one another. In some cases the period may extend to

thousands of years; for the distance which separates them is enormous,

and, even when with a powerful telescope it is indicated only by a

narrow dark line, amounts to hundreds of millions of miles. The Pole

Star itself is double. Andromeda is triple, with perhaps a fourth dark

and therefore invisible companion. These dark bodies have a special

interest, since it is impossible not to ask ourselves whether some at

any rate of them may not be inhabited. In [Greek: epsilon] Lyræ there

are two, each again being itself double. [Greek: xi] Cancri, and

probably also [Greek: theta] Orionis, consist of six stars, and from

such a group we pass on to Star Clusters in which the number is very

considerable. The cluster in Hercules consists of from 1000 to 4000. A

stellar swarm in the Southern Cross contains several hundred stars of

various colours, red, green, greenish blue, and blue closely thronged

together, so that they have been compared to a "superb piece of fancy

jewellery."[73]

The cluster in the Sword Handle of Perseus contains innumerable stars,

many doubtless as brilliant as our Sun. We ourselves probably form a

part of such a cluster. The Milky Way itself, as we know, entirely

surrounds us; it is evident, therefore, that the Sun, and of course we

ourselves, actually lie in it. It is, therefore, a Star Cluster, one of

countless numbers, and containing our Sun as a single unit.

It has as yet been found impossible to determine even approximately the

distance of these Star Clusters.

NEBULÆ

From Stars we pass insensibly to Nebulæ, which are so far away that

their distance is at present quite immeasurable. All that we can do is

to fix a minimum, and this is so great that it is useless to express it

in miles. Astronomers, therefore, take the velocity of light as a unit.

It travels at the rate of 180,000 miles a second, and even at this

enormous velocity it must have taken hundreds of years to reach us, so

that we see them not as they now are but as they were hundreds of years

ago.

It is no wonder, therefore, that in many of these clusters it is

impossible to distinguish the separate stars of which they are composed.

As, however, our telescopes are improved, more and more clusters are

being resolved. Photography also comes to our aid, and, as already

mentioned, by long exposure stars can be made visible which are quite

imperceptible to the eye, even with aid of the most powerful telescope.

Spectrum analysis also seems to show that such a nebula as that in

Andromeda, which with our most powerful instruments appears only as a

mere cloud, is really a vast cluster of stellar points.

This, however, by no means applies to all the nebulæ. The spectrum of a

star is a bright band of colour crossed by dark lines; that of a gaseous

nebula consists of bright lines. This test has been made use of, and

indicates that some of the nebulæ are really immense masses of

incandescent and very attenuated gas; very possibly, however, in a

condition of which we have no experience, and arranged in discs, bands,

rings, chains, wisps, knots, rays, curves, ovals, spirals, loops,

wreaths, fans, brushes, sprays, lace, waves, and clouds. Huggins has

shown that many of them are really stupendous masses of glowing gas,

especially of hydrogen, and perhaps of nitrogen, while the spectrum also

shows other lines which perhaps may indicate some of the elements which,

so far as our Earth is concerned, appear to be missing between hydrogen

and lithium. Many of the nebulæ are exquisitely beautiful, and their

colour very varied.

In some cases, moreover, nebulæ seem to be gradually condensing into

groups of stars, and in many cases it is difficult to say whether we

should consider a given group as a cluster of stars surrounded by

nebulous matter or a gaseous nebula condensed here and there into stars.

"Besides the single Sun," says Proctor, "the universe contains groups

and systems and streams of primary suns; there are galaxies of minor

orbs; there are clustering stellar aggregations showing every variety of

richness, of figure, and of distribution; there are all the various

forms of star cloudlets, resolvable and irresolvable, circular,

elliptical, and spiral; and lastly, there are irregular masses of

luminous gas clinging in fantastic convolutions around stars and star

systems. Nor is it unsafe to assert that other forms and varieties of

structure will yet be discovered, or that hundreds more exist which we

may never hope to recognise."

Nor is it only as regards the magnitude and distances of the heavenly

bodies that we are lost in amazement and admiration. The lapse of time

is a grander element in Astronomy even than in Geology, and dates back

long before Geology begins. We must figure to ourselves a time when the

solid matter which now composes our Earth was part of a continuous and

intensely heated gaseous body, which extended from the centre of the Sun

to beyond the orbit of Neptune, and had, therefore, a diameter of more

than 6,000,000,000 miles.

As this slowly contracted, Neptune was detached, first perhaps as a

ring, and then as a spherical body. Ages after this Uranus broke away.

Then after another incalculable period Saturn followed suit, and here

the tendencies to coherence and disruption were so evenly balanced that

to this day a portion circulates as rings round the main body instead of

being broken up into satellites. Again after successive intervals

Jupiter, Mars, the Asteroids, the Earth, Venus, and Mercury all passed

through the same marvellous phases. The time which these changes would

have required must have been incalculable, and they all of course

preceded, and preceded again by another incalculable period, the very

commencement of that geological history which itself indicates a lapse

of time greater than human imagination can realise.

Thus, then, however far we penetrate in time or in space, we find

ourselves surrounded by mystery. Just as in time we can form no idea of

a commencement, no anticipation of an end, so space also extends around

us, boundless in all directions. Our little Earth revolves round the

mighty Sun; the Sun itself and the whole solar system are moving with

inconceivable velocity towards a point in the constellation of Hercules;

together with all the nearer stars it forms a cluster in the heavens,

which appears to our eyes as the Milky Way; while outside our star

cluster again are innumerable others, which far transcend, alike in

magnitude, in grandeur, and in distance, the feeble powers of our finite

imagination.

FOOTNOTES:

[66] Ball, _Story of the Heavens_.

[67] Ball, _Story of the Heavens_.

[68] Some authorities estimate it even higher.

[69] Ball.

[70] Hamerton, _Landscape_.

[71] Humboldt, _Travels_.

[72] Clarke, _System of the Stars_.

[73] Kosmos.

End of Project Gutenberg's The Beauties of Nature, by Sir John Lubbock