Art. XV.—On the Genesis of Worlds and Systems.
[Read before the Philosophical Institute of Canterbury, 3rd April, 1879.]*
After much consideration, I have decided to depart from the custom of giving a general view of the advance of science, feeling that the stupendous strides of the last few years are more fitting a course of lectures than a short address. I shall therefore devote the time at my disposal to one branch of science, viz., astronomy, which, from our occupying the southern portion of the globe, is one of the few physical sciences which possess local interest.
A new country, with its strange fauna and flora, is the naturalist's paradise. But the isolation, the want of differentiation in his studies and laboratory work, must ever render it a desert to the experimental physicist. The impossibility of ascertaining fully the progress of any branch of science by the few intellectual rays which reach so far from the focus of intelligence, will also tell in preventing much original research. But of course locally characteristic natural phenomena, if any exist, form an exception to this rule. This is the position of stellar astronomy: a circle of the heavens is hidden from the view of the great men of Europe, and, as it happens, a circle singularly rich in phenomena, containing, as it does, that magnificent region of the galaxy about the Southern Cross and the two Magellanic Clouds.
It is true that the harvest of this work was reaped by Herschel with his great reflector at the Cape. But there is still work for the gleaner, and in a large field of research it may be considered that his observations were only seed sown, the harvest of which may be reaped by future observers—I refer to all those phenomena in which the effect of time gives the chief interest.
As the study of astronomy has thus an undoubted claim upon our consideration, I shall not apologize for offering to you a brief account of a new cosmical hypothesis which has occupied a considerable portion of the Society's time lately. An hypothesis which appears to offer a possible explanation of many of the more peculiar among celestial phenomena. It certainly suggests many definite fields of astronomical research, the results of which, even if unfavourable to the hypothesis, cannot fail to be of value to science.
To the mathematician, also, it offers many novel problems. In fact, if this theory should attract attention so far as to pass into that first stage of success as to be called fallacious in principle, impracticable in detail, and absurd on the face of it; or, better still, should it succeed so well as to promote rational discussion worth answering, or obtain that highest eulogy the world knows how to give—of being discovered not to be new, it is probable
[Footnote] * President's Anniversary Address.
that the problems it offers will be fertile ground for the new calculus of vectors to take root in and expand itself, for both are apparently just fitted for each other.
This being a popular gathering, I propose giving a rapid sketch of the progress of astronomy and its present position, especially of the phenomena which this theory purports to link together and bring under the domain of recognized scientific law. This will also enable the extension of our ideas, which the theory suggests, to be better understood. I need not tell you that this sketch must be a very hasty one, as from the opposition which has generally attended progress in astronomy, every step would require much space to discuss it fully.
It is certainly not now necessary to demonstrate that the Earth is not the centre of the Universe, although we all know the amount of prejudice and obstruction which had to be overcome to get even this much admitted. But the whole view of the Universe and the utterly insignificant position the Earth occupies in it has been achieved only by very hard steady work, in the face of the most virulent opposition, and probably even now some would not be prepared to concede all the ground claimed by astronomers.
Nor need we wonder at this. It is natural for all of us to think more highly of anything which immediately concerns us than it probably deserves, and it is necessarily the peculiarity of ignorance to intensify this failing, The stay-at-home resident of a small town grows up thoroughly convinced that it is the undoubted centre around which the world revolves, and for which the metropolis exists as a place for the supply of the town's necessities, and although the disputes of the terrace and the square render it doubtful as to the exact position of the axis, yet the broad fact of its local existence is never questioned. So, the untravelled mind sees in the sun, moon, and stars, ministering lights, having the sole office of rendering this earth a fit habitation for man. But occasionally, amidst the long ages of almost brute-like stupidity, periods of enlightenment have occurred, when men have thrown away this garment of egotism—have looked beyond mere self, and tried earnestly to gauge man's place in nature. Thus we find Democritus teaching that the milky way was a belt of stars. Aristarchus showing the Greeks that the Sun is the centre of the system, and the Earth and planets revolve round it. Eratosthenes measuring the size of the globe and placing meridians and parallels on its surface. Then again, for many ages the cobbler stuck to his last, the practical man to his wooden plough, and the scholar to his traditions. No speculative theorist disturbed the calm, and gradually the world again became flat, and men's ideas stale and unprofitable. But, after many centuries of this hybernation, Tycho Brahe, Kepler, Galileo, led on by Copernicus, with the insane folly of
visionaries, neglected their business, and again went star-gazing. Many others followed the pernicious example of these unpractical dreamers, until the long succession of such lunatics, and the wonderful method of their madness, impelled even the most stolid to look for themselves, and then the astonishing discovery was made that men were not entirely composed of pocket and stomach. In fact, that unless development were to proceed backwards, and the tail again manifest itself, intellectual food was perhaps as essential as corporeal. In this way, after many efforts, the human mind has escaped its leading strings, has travelled, and seen on what a vast scale the Universe has been constructed; has gauged the Sun and seen him to be a million times larger than the Earth, and the millions of stars, suns like himself; has seen the earth sink into a small particle of cosmical dust of insignificant dimensions, compared to even the visible universe.
But do we think less highly of the earth for these extensions of our ideas? Certainly not. Like the travelled man returning to his boyhood's home, it is true the church spire may have lost its relative grandeur and altitude, and he no longer looks in his back garden for the earth's axis, yet he loves the place none the less, and finds the brook as clear and the wild flowers as fragrant as when he left; with all kinds of poetic essences diffused around everything, which it never would have had without the wider knowledge he has brought back with him.
So, whilst the Universe has been made to reveal its myriads of blazing suns and systems of suns, the Earth has unfolded to our eyes an endless diversity of treasures, and thus at once an infinity of massive grandeur and an infinity of detailed beauty have been simultaneously discovered.
But astronomers tell us that among the myriads of ordinary stars or rather suns which form the milky way, there are many erratic members and many bodies altogether unlike the general order. Some ten thousand stars are such close pairs that they appear to form twin suns, sometimes each of the twins have still smaller suns revolving round the larger one. In some places the stars appear so thickly spread that to the naked eye they are mere specks of mist, but the telescope says they are clusters of suns. Over a hundred stars appear to be altogether abnormal in their properties, shining with varying intensity at different times, and at some of their bright periods shining much more intensely than at other times. Quite like a modern belle going through regular short cycles of brilliancy, as each day rolls on, and, like her also, having, as it were, London and country seasons, for, after going through long periods of brilliant dress and undress, it gradually sinks into humdrum country life, scarcely even dressing for dinner. In fact the vagaries of variable stars are so extraordinary that they appear without any law or order; but, as Mrs. Grundy rigidly regu-
lates the apparently giddy proceedings of society's neophyte, so it appears possible on this new hypothesis to show that all this apparent stellar disorder conforms to laws as completely as the most carefully watched young lady.
Besides these variables which have been long out, it occasionally happens that a star blazes forth before the astonished gaze of beholders, and for a time monopolizes all attention. But after a little while, sometimes only a few weeks, sometimes a year or so, this meteor-like sun gradually loses its brilliancy, and passes away altogether, or becomes a very insignificant little star; the temporary star having no longer any existence except in history. The celestial temporaries have one advantage over our earthly stars, they are sufficiently rare that it is seldom any one is out out by the appearance of a rival. Two of these stars have however appeared within the last twelve years.
But there appear several reasons to suppose that there is quite another class of stars, modest retiring suns, of altogether an unobtrusive character. Suns which have put up their shutters, and retired from business. Suns with very little vitality, or perhaps altogether dead suns.
In addition to all these varieties of stars there is a very wonderful class of bodies called nebulæ. These are delicate luminous clouds, probably consisting of masses of glowing gas. Some of them are of very definite structure, spherical, spindle-shaped, spiral, comet-like, and frequently strewn all over with brilliant stars. Some of them are so large that the size of our whole Solar System would be hardly a sufficient unit to measure them with. Most of these nebulæ are spread out in two sheets covering a large part of the celestial sphere at the poles of the galactic circle.
As in the human family so with the stellar inhabitant of space, many are associated into well-marked groups; as we have families, tribes, nations, and the whole race, so we have our solar family, our multiple star-system, and probably, by the recent researches of Proctor, the whole visible heavens is a definite and connected system, consisting chiefly of a vast ring of stars, with nebular caps at both its poles.
All of these bodies appear to be moving indiscriminately about, without common direction or purpose, although certain pairs and groups seem to have considerable community of motion. But they move fast in those celestial regions, they quite out-do our Canterbury snail ways, a thousand times as fast as our fastest railway train is only a walking star, and I feel afraid to tell you how fast some can run. And every star is pulling hard at all its near neighbours. The nearest star to our sun must have a velocity of sixty miles an hour to escape the sun's attraction.
But amidst all this flying about, this indescribable hurry, these powerful attractions, surely you will say there must occasionally be collisions. The
hypothesis I am about to describe suggests that this is the case, but especially says further, that if they do knock against each other the blow may be a mere graze of the two outsides, or sometimes a large piece of each may be struck off, and in extremely rare cases they may meet fair; but as this latter is so extremely rare, the other cases are those chiefly considered, and so the theory is called Partial Impact. I shall now try and show you what a perfect Aladdin's lamp of possibilities this theory possesses.
A gentleman who was present at a bombardment told me that he had seen the cannon balls strike pieces off the cannon and travel on in space. But the energy of each particle of a star at collision is hundreds of thousands of times greater than in a cannon ball, so the stars also will strike a piece off each where they strike one another, the remainder passing on in space. The proportional resistance to motion produced by impact in the escaping parts, would be thousands of times less than if a cannon ball of butter just grazed the top of an iron wall; in fact, the large pieces not coming into collision will be certain to travel on. So the effect of the collision of our two stars will be to strike a piece off each other where they touch each other, and each star will travel on, with a slice cut off its side. The parts of each which met will be left behind by both the retreating bodies, and will probably remain where the collision occurred. But, owing to the way it has been struck off, the two sides being impelled in opposite directions, it cannot help revolving, and it is not unlikely that nearly all the thousands of rotating bodies and systems in the Universe may have thus been set spinning by partial impact. At least, although we do not know what other agencies may ultimately be found to be capable of producing rotation, at present indirect impact seems to be the only one known.
Everyone, now-a-days, knows that heat is a kind of motion, and that ordinary motion destroyed, produces heat. An axle, screw, or gimblet—without grease—gets hot if quickly used. A rifle bullet makes a flash of light on striking the target, and often melts. A particle of matter plunges into our atmosphere and becomes so hot that it forms a shooting star. A school-boy takes his caning, and speaks of it as a warming. We rub the little cold hands of the wee ones who have been playing with the snow, and we stamp our feet when the thermometer sinks below zero. So if stars come into collision they will develope heat in the part struck off as striking a flint and steel strikes off a spark. In fact, our two stars may be considered as flint and steel meeting one another, striking off a spark, and passing on in space. Any student of heat will tell you that if the motion of a piece of iron be destroyed, he can calculate the temperature produced, if he knows its speed, and that the heat does not depend on the size of the
iron, only on its velocity. So when our dead suns come into impact, the temperature will not depend on the size of the spark cut off, only on the velocity destroyed. But if the piece cut off be small, it has but little attractive power to keep it together, and the particles are so hot—or moving so fast—that every single molecule flies completely away and disappears into space. Does it not look extremely likely that here we have our temporary stars, bursting forth when the collision occurs, and disappearing when its particles travel away into space? It certainly appears very likely.
But what about the two large pieces (the two wounded stars); a slice has been cut off each, and the hotter interior exposed; friction has also developed heat, and so when they become round again they will be hotter on one side than on the other. As they revolve they must almost certainly form a variable star, and the struggle of the two rotations will make this variation pass through long cycles, just as a spinning top oscillates if it has a kick. But as it would seem that two variable stars must be often produced together, the lists were searched to see if any pairs could be found, and a chart has been made from Chambers' list, and it shows sixteen well-marked pairs, or thirty-two connected stars out of one hundred and twenty. Unless we suppose this spotted condition to be a disease and catching, it is difficult, except on this view, to account for the pairs. Not only do we thus find these pairs existing, but some variable stars are close to the places where old temporary stars formerly existed, and also variable stars have become ordinary stars, as we should expect them to do when the temperature became uniform; and doubtless when the whole are carefully matched, many will be found to be gradually approaching the state of uniformity exhibited by ordinary stars. But it is not necessary to suppose thate th piece struck off each should always be such an excessively small ratio as to be projected into space, although the temperature produced by the collision will be almost always high enough to make gas of the coalesced part. This part may have mass enough to remain a permanent nebula. In this case reasons have been urged that render it probable that at first this gas would tend to take a spindle shape. Afterwards many possibilities present themselves according to the varying circumstances of the collision, for it is perfectly evident that these may be very numerous indeed. As the bodies may vary from cold dense solid bodies to rare masses of hot diffused gas, they may originally be moving very fast or very slowly; they may have been spinning with great velocity or hardly rotating at all; they may be nearly the same size, or a very unequal pair; and it does not need a Newton to see that any of these states will influence the result attained at collision and afterwards. The only effects which appear absolutely certain to follow partial impact are that rotation must ensue, that the matter will tend to
spread out more or less in a plane, with frequently gas at the poles, and that the middle body produced by the collision will generally be very hot, proportional to the mass.
In the papers presented to the Institute, the possible conditions of impact under which the different kinds of nebulæ may have been produced have been discussed. Thus it is suggested that the spiral nebulæ may have been produced by the collision of two previously existing nebulous masses, otherwise it appears that the extreme pressure would have destroyed the central part of the spiral. Singularly enough these nebulæ are found in the nebulous portion of the celestial sphere. Such, evidence as this gives great probability to this theory. It is suggested that the comet-like nebulæ are masses with a high resultant velocity; that the planetary nebulæ are gaseous shells produced by the outrushing gas leaving the position of impact, and travelling outwards in every direction into space. Reasons based on the dynamical theory of gases have been urged why the heavier chemical molecules should return, and form the star which is very often seen at the centre of these bodies. Anyone who has followed this speculation must see that if this theory does represent the birth of nebulæ, they must be changing their shape, and sometimes new ones will be formed and old ones die out, and this is really the case. They vary; many new nebulæ have not only been found, but some have disappeared again, and many that used to exist are lost.
But such mere gas as nebulæ must not be allowed to detain us. There are far more solid matters to be discussed yet. Thus it has been suggested that the Solar System is not the kind of family Laplace has pictured it, with the Sun as the parent and Neptune as the eldest brother, down to the youngest, Mercury, or perhaps Vulcan. But it implies that the whole system are twin brothers and sisters, all born together; a deserted family whose severed parents are wildly travelling space. The collision which gave the Sun its heat gave it its rotation, threw off the masses which became planets, set these spinning also, giving them their accompanying masses of cosmical dust we call moons. That same great whirl set all the planets travelling in orbits all in the same direction, and nearly in one plane. The theory also attempts to show how the elliptical orbit became nearly circular;—how the original rotation of the two colliding masses would disturb the exact symmetry of the rotation of the planets. It attempts to account for many things too numerous to speak of here. But you will say the Solar System could not have been born in two different ways. Well, hardly. Then you must dispose of Laplace's nebular rings. Perhaps so; but even Laplace's theory demands a rotary nebula to start with, and it would therefore still seem that he needs partial impact to
provide him with that. But I will tell you, in confidence, that although we have not dared yet to put it in black and white, yet, in our discussions, we have even hinted that Laplace may have been altogether wrong, and have whispered many, many reasons, on modern views of energy and the dynamical theory of gases, why we think so. I will tell you one. According to Laplace, the surface of the nebulous sun should go on getting faster and faster as ring after ring was thrown off; but, as a matter of fact, the sun's energy of rotation is only one fifty-thousandth part of that necessary to throw off a ring, and those among us who believe in the conservation of energy, ask, where is that energy gone? It is thought possible that not only may bodies thus be set travelling around the central mass, but that frequently the resultant velocity left in them may carry them quite away from it altogether. It is suggested that possibly the comets and shooting-stars which illuminate our sky may have been thrown off at the birth of temporary stars or systems, and as they travel through space come accidentally into our Solar System, and are sometimes kept within it by the retarding action of an approaching planet, or by some other cause. Almost certainly they were not born with the Sun and planets; for, of all the comets observed, as many go against the direction of the planets as with it, so we really must consider the comets as foreign intruders, and as such treat them with the contempt they deserve. But you will say millions of millions of meteorites strike the earth each year;—exactly probably scarcely a stellar collision has occurred which did not strew space with millions of homeless particles left to wander recklessly through space, until they met destruction at the hands of some pitying cosmical shark, who sympathized with them in their loneliness and so took them in. But if there is so much dust flying about space, it must interfere seriously with our view when we look at very distant objects, as muddy water is opaque if deep. Struve held manfully to his opinion, based on good evidence, that distant light did suffer extinction; and does this not appear to offer a very good reason for thinking he was right?
But other things may be said of our two wounded stars—flint and steel—whom we left travelling in space. We have seen how a spark was struck off which became a temporary star, a nebula or a system, according to circumstances. We also suggested that flint and steel might become a pair of variable stars, getting more and more distant from each other. It is possible, however, if their original proper motion were small, or if they had much cut off them, that they may return again and form a connected pair, and add another to the many twin suns already existing. It is suggested that probably many of these became connected in this way. It is known that some binaries are variable. It is possible that these stars may come into
collision a second time, and, even as an extreme possibility, more than twice; and it does not appear unlikely that this is really the case with Tycho Brahe's temporary star. There is one thing that makes it likely. All the text-books speak of it as a possible variable with a period of 313 years. Now, it appeared absolutely certain that if such a thing as consecutive collision did happen, it would be longer between the first pair of impacts than between the second pair of impacts; and, on taking the dates given by Herschel, it was found that the first interval was 319 and the second 308 years, thus adding another to the very remarkable series of coincidences which have been found in working out this hypothesis.
But people are never satisfied without trying to ride a hobby to death; and really it does seem going rather to extremes to suggest, as has been done, that nearly all we see in the heavens—all the millions of suns, all the nebulæ—are parts of one great system produced by the impact of two stupendous bodies meeting in free space—a system so extensive, that it would probably take light at least a hundred years to pass through the mass; while of the bodies themselves, some are so big that the number of times our sun would be required to measure their volume must be reckoned by thousands. Thus has the hobby been goaded on, and it is not absolutely certain that it has thrown its riders yet. It is true Proctor has been for years carefully laying down a veritable railroad for just such a hobby; when he was working out his great research on the visible universe, so that it was easy work for it, it ran like a snowball down a hill, gathering speed and proportion as it went. But I must tell you how Proctor did this work. He collected statistics of the number of stars and nebulæ, of star-clusters and star-motion. He and his friends placed all these on charts, and when they were finished, a single undoubted system was seen, which he describes roughly as a ring or spiral of stars, with our solar system at or about the centre, and with two caps of nebulæ covering the poles of this ring. So when the picture of the visible universe, given by Proctor, came to be examined, it was found to be so like that which had been suggested as likely to result from “partial impact,” that it was felt the visible universe itself must be one of its numerous offspring.
But what does such an idea of the origin of the universe suggest to our mind of the contents of space generally? Clearly, that if two such bodies, why not many, some almost infinitely large compared to them? Why not go with Kant, and think that as the earth and its moon are part of the Solar System, as this system is part of the galaxy, why not the galaxy a part of a still more imposing system? Anyhow, the idea of space, suggested by this theory, is that it contains an infinite number of masses, varying in size from the particle of hydrogen to the stupendous mass which physicists look forward to as the final condition of the visible universe.
Of all the speculations of modern thought no two ideas have obtained stronger hold upon the human mind than the indestructibility of matter and of energy. But although energy is indestructible, it is generally supposed it will pass into an unavailable form, and although matter cannot be lessened in quantity, yet it is believed it will all be aggregated into one stupendous mass. Consequently our great mathematical physicists look forward to a time when any motion but heat will be impossible, and all life will be extinct. Yet this dreary, this repugnant conclusion, has apparently been the only possible result that could happen from any of the standpoints from which the laws of nature have hitherto been viewed. It is no small recommendation that the theory of “partial impact” offers a possible mode of escape from this melancholy prospect. It suggests that if gravitation does aggregate and tend to drain space, impact produces dispersion. Everything moves more slowly at a distance from an attractive source, so if bodies are moving indiscriminately in all directions, it is clear that where they move most slowly, they will certainly congregate together, thus tending in the opposite way to gravity, and in this way may be kept up a more or less uniform distribution of matter in space. The theory shows that the radiated heat of the sun falls upon the cosmical dust, which shuts us in as a curtain, and it is thus prevented from being lost; it also shows how, from various reasons, we must suppose that inconceivable numbers of particles of cold gas are slowly travelling space, and as these particles touch any part of this heated matter, it uses the heat of the body to project itself at increased velocity into more distant regions of space, there perhaps helping to build up new bodies capable of carrying on anew all the wonderfully complicated functions which matter and energy are playing in the visible universe. In this way we hope that this theory will remove these repulsive blots of dissipated energy and aggregated matter, which deface the otherwise fair and stately structure reared by modern science, so that the intellectual cravings of the human mind may find in it the invigoration and rest which they require.
Thus, the entire picture this hypothesis presents to the mind is that of a Cosmos, infinite and immortal. In it a being travelling through eternity, on the wings of light, would see as little permanent change as does the sea-bird over the restless ocean. He would sometimes be present at the nativity of galaxies, see solar systems in all stages, see suns absorb planet after planet, each time flickering up for a few thousand years, and finally, after having devoured all its family, shrink smaller and smaller, and then become less and less brilliant, until the last faint glimmer had died out, and a vast cinder is all that remains of that former scene of teaming life and brilliant beauty. Then he might watch the approach of dead suns,
and see, Phœnix-like, new suns arise from those cold masses of ashes, and as he watches the amazing flash of the collision, he may see flights of comets and meteors emerge from the flames and start on their long journey. Travelling on, he may see worlds absorb their enveloping nebular curtains, see others solidifying. In some, witness the garment of organized life gradually extending itself and clothing the surface with vitality; and should he stay to take a detailed look, he would probably sometimes see forms of life so strange, so weird, that the animated engines of Erewhon would be commonplace compared to them. Is it possible that in some white hot body he would see viscous silicon building itself into complex protoplasmic molecular skeletons, developing organ after organ, and breathing forth its halogen breath? Perchance he might watch a silicon monster tenderly waiting on a sickly friend, and feeding it with delicately-flavoured molten flint broth. But methinks I hear someone whisper, “I thought so. Undoubtedly he is mad.” So, remembering the fate of Solomon de Caus, and being desirous of retaining my liberty, I conclude by thanking you for the attention with which you have listened to me.