Astronomy of To-day Part 23

Lastly, such a discovery as that the ninth satellite of Saturn revolves in a _retrograde_ direction--that is to say, in a direction contrary to the other revolutions and rotations in our solar system--appears directly to contradict the hypothesis.

Although Laplace's hypothesis seems to break down under the keen criticism to which it has been subjected, yet astronomers have not relinquished the idea that our solar system has probably had its origin from a nebulous ma.s.s. But the apparent failure of the Laplacian theory is emphasised by the fact, that _not a single example of a nebula, in the course of breaking up into concentric rings, is known to exist in the entire heaven_. Indeed, as we saw in Chapter XXIV., there seems to be no reliable example of even a "ring" nebula at all. Mr. Gore has pointed this out very succinctly in his recently published work, _Astronomical Essays_, where he says:--"To any one who still persists in maintaining the hypothesis of ring formation in nebulae, it may be said that the whole heavens are against him."

The conclusions of Keeler already alluded to, that the spiral is the normal type of nebula, has led during the past few years to a new theory by the American astronomers, Professors Chamberlin and Moulton. In the detailed account of it which they have set forth, they show that those anomalies which were stumbling-blocks to Laplace's theory do not contradict theirs. To deal at length with this theory, to which the name of "Planetesimal Hypothesis" has been given, would not be possible in a book of this kind. But it may be of interest to mention that the authors of the theory in question remount the stream of time still further than did Laplace, and seek to explain the _origin_ of the spiral nebulae themselves in the following manner:--

Having begun by a.s.suming that the stars are moving apparently in every direction with great velocities, they proceed to point out that sooner or later, although the lapse of time may be extraordinarily long, collisions or near approaches between stars are bound to occur. In the case of collisions the chances are against the bodies striking together centrally, it being very much more likely that they will hit each other rather towards the side. The nebulous ma.s.s formed as a result of the disintegration of the bodies through their furious impact would thus come into being with a spinning movement, and a spiral would ensue.

Again, the stars may not actually collide, but merely approach near to each other. If very close, the interaction of gravitation will give rise to intense strains, or tides, which will entirely disintegrate the bodies, and a spiral nebula will similarly result. As happens upon our earth, two such tides would rise opposite to each other; and, consequently, it is a noticeable fact that spiral nebulae have almost invariably two opposite branches (see Plate XXII., p 314). Even if not so close, the gravitational strains set up would produce tremendous eruptions of matter; and in this case, a spiral movement would also be generated. On such an a.s.sumption the various bodies of the solar system may be regarded as having been ejected from parent ma.s.ses.

The acceptance of the Planetesimal Hypothesis in the place of the Hypothesis of Laplace will not, as we have seen, by any means do away with the probability that our solar system, and similar systems, have originated from a nebulous ma.s.s. On the contrary it puts that idea on a firmer footing than before. The spiral nebulae which we see in the heavens are on a vast scale, and may represent the formation of stellar systems and globular cl.u.s.ters. Our solar system may have arisen from a small spiral.

We will close these speculations concerning the origin of things with a short sketch of certain investigations made in recent years by Sir George H. Darwin, of Cambridge University, into the question of the probable birth of our moon. He comes to the conclusion that at least fifty-four millions of years ago the earth and moon formed one body, which had a diameter of a little over 8000 miles. This body rotated on an axis in about five hours, namely, about five times as fast as it does at present. The rapidity of the rotation caused such a tremendous strain that the ma.s.s was in a condition of, what is called, unstable equilibrium; very little more, in fact, being required to rend it asunder. The gravitational pull of the sun, which, as we have already seen, is in part the cause of our ordinary tides, supplied this extra strain, and a portion of the ma.s.s consequently broke off, which receded gradually from the rest and became what we now know as the moon. Sir George Darwin holds that the gravitational action of the sun will in time succeed in also disturbing the present apparent harmony of the earth-moon system, and will eventually bring the moon back towards the earth, so that after the lapse of great ages they will re-unite once again.

In support of this theory of the terrestrial origin of the moon, Professor W.H. Pickering has put forward a bold hypothesis that our satellite had its origin in the great basin of the Pacific. This ocean is roughly circular, and contains no large land ma.s.ses, except the Australian Continent. He supposes that, prior to the moon's birth, our globe was already covered with a slight crust. In the tearing away of that portion which was afterwards destined to become the moon the remaining area of the crust was rent in twain by the shock; and thus were formed the two great continental ma.s.ses of the Old and New Worlds.

These ma.s.ses floated apart across the fiery ocean, and at last settled in the positions which they now occupy. In this way Professor Pickering explains the remarkable parallelism which exists between the opposite sh.o.r.es of the Atlantic. The fact of this parallelism had, however, been noticed before; as, for example, by the late Rev. S.J. Johnson, in his book _Eclipses, Past and Future_, where we find the following pa.s.sage:--

"If we look at our maps we shall see the parts of one Continent that jut out agree with the indented portions of another. The prominent coast of Africa would fit in the opposite opening between North and South America, and so in numerous other instances. A general rending asunder of the World would seem to have taken place when the foundations of the great deep were broken up."

Although Professor Pickering's theory is to a certain degree antic.i.p.ated in the above words, still he has worked out the idea much more fully, and given it an additional fascination by connecting it with the birth of the moon. He points out, in fact, that there is a remarkable similarity between the lunar volcanoes and those in the immediate neighbourhood of the Pacific Ocean. He goes even further to suggest that Australia is another portion of the primal crust which was detached out of the region now occupied by the Indian Ocean, where it was originally connected with the south of India or the east of Africa.

Certain objections to the theory have been put forward, one of which is that the parallelism noticed between the opposite sh.o.r.es of the Atlantic is almost too perfect to have remained through some sixty millions of years down to our own day, in the face of all those geological movements of upheaval and submergence, which are perpetually at work upon our globe. Professor Pickering, however, replies to this objection by stating that many geologists believe that the main divisions of land and water on the earth are permanent, and that the geological alterations which have taken place since these were formed have been merely of a temporary and superficial nature.

CHAPTER XXVIII

THE END OF THINGS

We have been trying to picture the beginning of things. We will now try to picture the end.

In attempting this, we find that our theories must of necessity be limited to the earth, or at most to the solar system. The time-honoured expression "End of the World" really applies to very little beyond the end of our own earth. To the people of past ages it, of course, meant very much more. For them, as we have seen, the earth was the centre of everything; and the heavens and all around were merely a kind of minor accompaniment, created, as they no doubt thought, for their especial benefit. In the ancient view, therefore, the beginning of the earth meant the beginning of the universe, and the end of the earth the extinction of all things. The belief, too, was general that this end would be accomplished through fire. In the modern view, however, the birth and death of the earth, or indeed of the solar system, might pa.s.s as incidents almost unnoticed in s.p.a.ce. They would be but mere links in the chain of cosmic happenings.

A number of theories have been forward from time to time prognosticating the end of the earth, and consequently of human life. We will conclude with a recital of a few of them, though which, if any, is the true one, the Last Men alone can know.

Just as a living creature may at any moment die in the fulness of strength through sudden malady or accident, or, on the other hand, may meet with death as a mere consequence of old age, so may our globe be destroyed by some sudden cataclysm, or end in slow processes of decay.

Barring accidents, therefore, it would seem probable that the growing cold of the earth, or the gradual extinction of the sun, should after many millions of years close the chapter of life, as we know it. On the former of these suppositions, the decrease of temperature on our globe might perhaps be accelerated by the thinning of the atmosphere, through the slow escape into s.p.a.ce of its const.i.tuent gases, or their gradual chemical combination with the materials of the earth. The subterranean heat entirely radiated away, there would no longer remain any of those volcanic elevating forces which so far have counteracted the slow wearing down of the land surface of our planet, and thus what water remained would in time wash over all. If this preceded the growing cold of the sun, certain strange evolutions of marine forms of life would be the last to endure, but these, too, would have to go in the end.

Should, however, the actual process be the reverse of this, and the sun cool down the quicker, then man would, as a consequence of his scientific knowledge, tend in all probability to outlive the other forms of terrestrial life. In such a vista we can picture the regions of the earth towards the north and south becoming gradually more and more uninhabitable through cold, and human beings withdrawing before the slow march of the icy boundary, until the only regions capable of habitation would lie within the tropics. In such a struggle between man and destiny science would be pressed to the uttermost, in the devising of means to counteract the slow diminution of the solar heat and the gradual disappearance of air and water. By that time the axial rotation of our globe might possibly have been slowed down to such an extent that one side alone of its surface would be turned ever towards the fast dying sun. And the mind's eye can picture the last survivors of the human race, huddled together for warmth in a gla.s.s-house somewhere on the equator, waiting for the end to come.

The mere idea of the decay and death of the solar system almost brings to one a cold shudder. All that sun's light and heat, which means so much to us, entirely a thing of the past. A dark, cold ball rushing along in s.p.a.ce, accompanied by several dark, cold b.a.l.l.s circling ceaselessly around it. One of these a mere cemetery, in which there would be no longer any recollection of the mighty empires, the loves and hates, and all that teeming play of life which we call History.

Tombstones of men and of deeds, whirling along forgotten in the darkness and silence. _Sic transit gloria mundi._

In that brilliant flight of scientific fancy, the _Time Machine_, Mr.

H.G. Wells has pictured the closing years of the earth in some such long-drawn agony as this. He has given us a vision of a desolate beach by a salt and almost motionless sea. Foul monsters of crab-like form crawl slowly about, beneath a huge hull of sun, red and fixed in the sky. The rocks around are partly coated with an intensely green vegetation, like the lichen in caves, or the plants which grow in a perpetual twilight. And the air is now of an exceeding thinness.

He dips still further into the future, and thus predicts the final form of life:--

"I saw again the moving thing upon the shoal--there was no mistake now that it was a moving thing--against the red water of the sea. It was a round thing, the size of a football perhaps, or it may be bigger, and tentacles trailed down from it; it seemed black against the weltering blood-red water, and it was hopping fitfully about."

What a description of the "Heir of all the Ages!"

To picture the end of our world as the result of a cataclysm of some kind, is, on the other hand, a form of speculation as intensely dramatic as that with which we have just been dealing is unutterably sad.

It is not so many years ago, for instance, that men feared a sudden catastrophe from the possible collision of a comet with our earth. The unreasoning terror with which the ancients were wont to regard these mysterious visitants to our skies had, indeed, been replaced by an apprehension of quite another kind. For instance, as we have seen, the announcement in 1832 that Biela's Comet, then visible, would cut through the orbit of the earth on a certain date threw many persons into a veritable panic. They did not stop to find out the real facts of the case, namely, that, at the time mentioned, the earth would be nearly a month's journey from the point indicated!

It is, indeed, very difficult to say what form of damage the earth would suffer from such a collision. In 1861 it pa.s.sed, as we have seen, through the tail of the comet without any noticeable result. But the head of a comet, on the other hand, may, for aught we know, contain within it elements of peril for us. A collision with this part might, for instance, result in a violent bombardment of meteors. But these meteors could not be bodies of any great size, for the ma.s.ses of comets are so very minute that one can hardly suppose them to contain any large or dense const.i.tuent portions.

The danger, however, from a comet's head might after all be a danger to our atmosphere. It might precipitate, into the air, gases which would asphyxiate us or cause a general conflagration. It is scarcely necessary to point out that dire results would follow upon any interference with the balance of our atmosphere. For instance, the well-known French astronomer, M. Camille Flammarion,[39] has imagined the absorption of the nitrogen of the air in this way; and has gone on to picture men and animals reduced to breathing only oxygen, first becoming excited, then mad, and finally ending in a perfect saturnalia of delirium.

Lastly, though we have no proof that stars eventually become dark and cold, for human time has so far been all too short to give us even the smallest evidence as to whether heat and light are diminishing in our own sun, yet it seems natural to suppose that such bodies must at last cease their functions, like everything else which we know of. We may, therefore, reasonably presume that there are dark bodies scattered in the depths of s.p.a.ce. We have, indeed, a suspicion of at least one, though perhaps it partakes rather of a planetary nature, namely, that "dark" body which continually eclipses Algol, and so causes the temporary diminution of its light. As the sun rushes towards the constellation of Lyra such an extinguished sun may chance to find itself in his path; just as a derelict hulk may loom up out of the darkness right beneath the bows of a vessel sailing the great ocean.

Unfortunately a collision between the sun and a body of this kind could not occur with such merciful suddenness. A tedious warning of its approach would be given from that region of the heavens whither our system is known to be tending. As the dark object would become visible only when sufficiently near our sun to be in some degree illuminated by his rays, it might run the chance at first of being mistaken for a new planet. If such a body were as large, for instance, as our own sun, it should, according to Mr. Gore's calculations, reveal itself to the telescope some fifteen years before the great catastrophe. Steadily its disc would appear to enlarge, so that, about nine years after its discovery, it would become visible to the naked eye. At length the doomed inhabitants of the earth, paralysed with terror, would see their relentless enemy shining like a second moon in the northern skies.

Rapidly increasing in apparent size, as the gravitational attractions of the solar orb and of itself interacted more powerfully with diminishing distance, it would at last draw quickly in towards the sun and disappear in the glare.

It is impossible for us to conceive anything more terrible than these closing days, for no menace of catastrophe which we can picture could bear within it such a certainty of fulfilment. It appears, therefore, useless to speculate on the probable actions of men in their now terrestrial prison. Hope, which so far had buoyed them up in the direst calamities, would here have no place. Humanity, in the fulness of its strength, would await a wholesale execution from which there could be no chance at all of a reprieve. Observations of the approaching body would have enabled astronomers to calculate its path with great exactness, and to predict the instant and character of the impact. Eight minutes after the moment allotted for the collision the resulting tide of flame would surge across the earth's...o...b..t, and our globe would quickly pa.s.s away in vapour.

And what then?

A nebula, no doubt; and after untold ages the formation possibly from it of a new system, rising phoenix-like from the vast crematorium and filling the place of the old one. A new central sun, perhaps, with its attendant retinue of planets and satellites. And teeming life, perchance, appearing once more in the fulness of time, when temperature in one or other of these bodies had fallen within certain limits, and other predisposing conditions had supervened.

"The world's great age begins anew, The golden years return, The earth doth like a snake renew Her winter weeds outworn: Heaven smiles, and faiths and empires gleam Like wrecks of a dissolving dream.

A brighter h.e.l.las rears its mountains From waves serener far; A new Peneus rolls his fountains Against the morning star; Where fairer Tempes bloom, there sleep Young Cyclads on a sunnier deep.

A loftier Argo cleaves the main, Fraught with a later prize; Another Orpheus sings again, And loves, and weeps, and dies; A new Ulysses leaves once more Calypso for his native sh.o.r.e.

Oh cease! must hate and death return?

Cease! must men kill and die?

Cease! drain not to its dregs the urn Of bitter prophecy!

The world is weary of the past,-- Oh might it die or rest at last!"

[39] See his work, _La Fin du Monde_, wherein the various ways by which our world may come to an end are dealt with at length, and in a profoundly interesting manner.

THE END

Printed by BALLANTYNE, HANSON & CO.

Edinburgh & London