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Astronomy of To-day - A Popular Introduction in Non-Technical Language
by Cecil G. Dolmage
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Also, if there did exist an infinite number of stars, one would expect to find evidence in some direction of an overpoweringly great force,—the centre of gravity of all these bodies.

It is noticed, too, that although the stars increase in number with decrease in magnitude, so that as we descend in the scale we find three times as many stars in each magnitude as in the one immediately above it, yet this progression does not go on after a while. There is, in fact, a rapid falling off in numbers below the twelfth magnitude; which looks as if, at a certain distance from us, the stellar universe were beginning to thin out.

Again, it is estimated, by Mr. Gore and others, that only about 100 millions of stars are to be seen in the whole of the sky with the best optical aids. This shows well the limited extent of the stellar system, for the number is not really great. For instance, there are from fifteen to sixteen times as many persons alive upon the earth at this moment!

Last of all, there appears to be strong photographic evidence that our sidereal system is limited in extent. Two photographs taken by the late Dr. Isaac Roberts of a region rich in stellar objects in the constellation of Cygnus, clearly show what has been so eloquently called the "darkness behind the stars." One of these photographs was taken in 1895, and the other in 1898. On both occasions the state of the atmosphere was practically the same, and the sensitiveness of the films was of the same degree. The exposure in the first case was only one hour; in the second it was about two hours and a half. And yet both photographs show exactly the same stars, even down to the faintest. From this one would gather that the region in question, which is one of the most thickly star-strewn in the Milky Way, is penetrable right through with the means at our command. Dr. Roberts himself in commenting upon the matter drew attention to the fact, that many astronomers seemed to have tacitly adopted the assumption that the stars extend indefinitely through space.

From considerations such as these the foremost astronomical authorities of our time consider themselves justified in believing that the collection of stars around us is finite; and that although our best telescopes may not yet be powerful enough to penetrate to the final stars, still the rapid decrease in numbers as space is sounded with increasing telescopic power, points strongly to the conclusion that the boundaries of the stellar system may not lie very far beyond the uttermost to which we can at present see.

Is it possible then to make an estimate of the extent of this stellar system?

Whatever estimates we may attempt to form cannot however be regarded as at all exact, for we know the actual distances of such a very few only of the nearest of the stars. But our knowledge of the distances even of these few, permits us to assume that the stars close around us may be situated, on an average, at about eight light-years from each other; and that this holds good of the stellar spaces, with the exception of the encircling girdle of the Milky Way, where the stars seem actually to be more closely packed together. This girdle further appears to contain the greater number of the stars. Arguing along these lines, Professor Newcomb reaches the conclusion that the farthest stellar bodies which we see are situated at about between 3000 and 4000 light-years from us.

Starting our inquiry from another direction, we can try to form an estimate by considering the question of proper motions.

It will be noticed that such motions do not depend entirely upon the actual speed of the stars themselves, but that some of the apparent movement arises indirectly from the speed of our own sun. The part in a proper motion which can be ascribed to the movement of our solar system through space is clearly a displacement in the nature of a parallax—Sir William Herschel called it "Systematic Parallax"; so that knowing the distance which we move over in a certain lapse of time, we are able to hazard a guess at the distances of a good many of the stars. An inquiry upon such lines must needs be very rough, and is plainly based upon the assumption that the stars whose distances we attempt to estimate are moving at an average speed much like that of our own sun, and that they are not "runaway stars" of the 1830 Groombridge order. Be that as it may, the results arrived at by Professor Newcomb from this method of reasoning are curiously enough very much on a par with those founded on the few parallaxes which we are really certain about; with the exception that they point to somewhat closer intervals between the individual stars, and so tend to narrow down our previous estimate of the extent of the stellar system.

Thus far we get, and no farther. Our solar system appears to lie somewhere near the centre of a great collection of stars, separated each one from the other, on an average, by some 40 billions of miles; the whole being arranged in the form of a mighty globular cluster. Light from the nearest of these stars takes some four years to come to us. It takes about 1000 times as long to reach us from the confines of the system. This globe of stars is wrapt around closely by a stellar girdle, the individual stars in which are set together more densely than those in the globe itself. The entire arrangement appears to be constructed upon a very regular plan. Here and there, as Professor Newcomb points out, the aspect of the heavens differs in small detail; but generally it may be laid down that the opposite portions of the sky, whether in the Milky Way itself, or in those regions distant from it, show a marked degree of symmetry. The proper motions of stars in corresponding portions of the sky reveal the same kind of harmony, a harmony which may even be extended to the various colours of the stars. The stellar system, which we see disposed all around us, appears in fine to bear all the marks of an organised whole.

The older astronomers, to take Sir William Herschel as an example, supposed some of the nebulae to be distant "universes." Sir William was led to this conclusion by the idea he had formed that, when his telescopes failed to show the separate stars of which he imagined these objects to be composed, he must put down the failure to their stupendous distance from us. For instance, he thought the Orion Nebula, which is now known to be made up of glowing gas, to be an external stellar system. Later on, however, he changed his mind upon this point, and came to the conclusion that "shining fluid" would better account both for this nebula, and for others which his telescopes had failed to separate into component stars.

The old ideas with regard to external systems and distant universes have been shelved as a consequence of recent research. All known clusters and nebulae are now firmly believed to lie within our stellar system.

This view of the universe of stars as a sort of island in the immensities, does not, however, give us the least idea about the actual extent of space itself. Whether what is called space is really infinite, that is to say, stretches out unendingly in every direction, or whether it has eventually a boundary somewhere, are alike questions which the human mind seems utterly unable to picture to itself.

[35] The Ptolemaic idea dies hard!

[36] Even the Milky Way itself is far from being a blaze of light, which shows that the stars composing it do not extend outwards indefinitely.

[37] Mr. Gore has recently made some remarkable deductions, with regard to the amount of light which we get from the stars. He considers that most of this light comes from stars below the sixth magnitude; and consequently, if all the stars visible to the naked eye were to be blotted out, the glow of the night sky would remain practically the same as it is at present. Going to the other end of the scale, he thinks also that the combined light which we get from all the stars below the seventeenth magnitude is so very small, that it may be neglected in such an estimation. He finds, indeed, that if there are stars so low as the twentieth magnitude, one hundred millions of them would only be equal in brightness to a single first-magnitude star like Vega. On the other hand, it is possible that the light of the sky at night is not entirely due to starlight, but that some of it may be caused by phosphorescent glow.



CHAPTER XXVI

THE STELLAR UNIVERSE—continued

It is very interesting to consider the proper motions of stars with reference to such an isolated stellar system as has been pictured in the previous chapter. These proper motions are so minute as a rule, that we are quite unable to determine whether the stars which show them are moving along in straight lines, or in orbits of immense extent. It would, in fact, take thousands of years of careful observation to determine whether the paths in question showed any degree of curving. In the case of the more distant stars, the accurate observations which have been conducted during the last hundred years have not so far revealed any proper motions with regard to them; but one cannot escape the conclusion that these stars move as the others do.

If space outside our stellar system is infinite in extent, and if all the stars within that system are moving unchecked in every conceivable direction, the result must happen that after immense ages these stars will have drawn apart to such a distance from each other, that the system will have entirely disintegrated, and will cease to exist as a connected whole. Eventually, indeed, as Professor Newcomb points out, the stars will have separated so far from each other that each will be left by itself in the midst of a black and starless sky. If, however, a certain proportion of stars have a speed sufficiently slow, they will tend under mutual attraction to be brought to rest by collisions, or forced to move in orbits around each other. But those stars which move at excessive speeds, such, for instance, as 1830 Groombridge, or the star in the southern constellation of Pictor, seem utterly incapable of being held back in their courses by even the entire gravitative force of our stellar system acting as a whole. These stars must, therefore, move eventually right through the system and pass out again into the empty spaces beyond. Add to this; certain investigations, made into the speed of 1830 Groombridge, furnish a remarkable result. It is calculated, indeed, that had this star been falling through infinite space for ever, pulled towards us by the combined gravitative force of our entire system of stars, it could not have gathered up anything like the speed with which it is at present moving. No force, therefore, which we can conjure out of our visible universe, seems powerful enough either to have impressed upon this runaway star the motion which it now has, or to stay it in its wild course. What an astounding condition of things!

Speculations like this call up a suspicion that there may yet exist other universes, other centres of force, notwithstanding the apparent solitude of our stellar system in space. It will be recollected that the idea of this isolation is founded upon such facts as, that the heavens do not blaze with light, and that the stars gradually appear to thin out as we penetrate the system with increasing telescopic power. But perchance there is something which hinders us from seeing out into space beyond our cluster of stars; which prevents light, in fact, from reaching us from other possible systems scattered through the depths beyond. It has, indeed, been suggested by Mr. Gore[38] that the light-transmitting ether may be after all merely a kind of "atmosphere" of the stars; and that it may, therefore, thin off and cease a little beyond the confines of our stellar system, just as the air thins off and practically ceases at a comparatively short distance from the earth. A clashing together of solid bodies outside our atmosphere could plainly send us no sound, for there is no air extending the whole way to bear to our ears the vibrations thus set up; so light emitted from any body lying beyond our system of stars, would not be able to come to us if the ether, whose function it is to convey the rays of light, ceased at or near the confines of that system.

Perchance we have in this suggestion the key to the mystery of how our sun and the other stellar bodies maintain their functions of temperature and illumination. The radiations of heat and light arriving at the limits of this ether, and unable to pass any further, may be thrown back again into the system in some altered form of energy.

But these, at best, are mere airy and fascinating speculations. We have, indeed, no evidence whatever that the luminiferous ether ceases at the boundary of the stellar system. If, therefore, it extends outwards infinitely in every direction, and if it has no absorbing or weakening effect on the vibrations which it transmits, we cannot escape from the conclusion that practically all the rays of light ever emitted by all the stars must chase one another eternally through the never-ending abysses of space.

[38] Planetary and Stellar Studies, by John Ellard Gore, F.R.A.S., M.R.I.A., London, 1888.



CHAPTER XXVII

THE BEGINNING OF THINGS

LAPLACE'S NEBULAR HYPOTHESIS

Dwelling upon the fact that all the motions of revolution and rotation in the solar system, as known in his day, took place in the same direction and nearly in the same plane, the great French astronomer, Laplace, about the year 1796, put forward a theory to account for the origin and evolution of that system. He conceived that it had come into being as a result of the gradual contraction, through cooling, of an intensely heated gaseous lens-shaped mass, which had originally occupied its place, and had extended outwards beyond the orbit of the furthest planet. He did not, however, attempt to explain how such a mass might have originated! He went on to suppose that this mass, in some manner, perhaps by mutual gravitation among its parts, had acquired a motion of rotation in the same direction as the planets now revolve. As this nebulous mass parted with its heat by radiation, it contracted towards the centre. Becoming smaller and smaller, it was obliged to rotate faster and faster in order to preserve its equilibrium. Meanwhile, in the course of contraction, rings of matter became separated from the nucleus of the mass, and were left behind at various intervals. These rings were swept up into subordinate masses similar to the original nebula. These subordinate masses also contracted in the same manner, leaving rings behind them which, in turn, were swept up to form satellites. Saturn's ring was considered, by Laplace, as the only portion of the system left which still showed traces of this evolutionary process. It is even probable that it may have suggested the whole of the idea to him.

Laplace was, however, not the first philosopher who had speculated along these lines concerning the origin of the world.

Nearly fifty years before, in 1750 to be exact, Thomas Wright, of Durham, had put forward a theory to account for the origin of the whole sidereal universe. In his theory, however, the birth of our solar system was treated merely as an incident. Shortly afterwards the subject was taken up by the famous German philosopher, Kant, who dealt with the question in a still more ambitious manner, and endeavoured to account in detail for the origin of the solar system as well as of the sidereal universe. Something of the trend of such theories may be gathered from the remarkable lines in Tennyson's Princess:—

"This world was once a fluid haze of light, Till toward the centre set the starry tides, And eddied into suns, that wheeling cast The planets."

The theory, as worked out by Kant, was, however, at the best merely a tour de force of philosophy. Laplace's conception was much less ambitious, for it did not attempt to explain the origin of the entire universe, but only of the solar system. Being thus reasonably limited in its scope, it more easily obtained credence. The arguments of Laplace were further founded upon a mathematical basis. The great place which he occupied among the astronomers of that time caused his theory to exert a preponderating influence on scientific thought during the century which followed.

A modification of Laplace's theory is the Meteoritic Hypothesis of Sir Norman Lockyer. According to the views of that astronomer, the material of which the original nebula was composed is presumed to have been in the meteoric, rather than in the gaseous, state. Sir Norman Lockyer holds, indeed, that nebulae are, in reality, vast swarms of meteors, and the light they emit results from continual collisions between the constituent particles. The French astronomer, Faye, also proposed to modify Laplace's theory by assuming that the nebula broke up into rings all at once, and not in detail, as Laplace had wished to suppose.

The hypothesis of Laplace fits in remarkably well with the theory put forward in later times by Helmholtz, that the heat of the sun is kept up by the continual contraction of its mass. It could thus have only contracted to its present size from one very much larger.

Plausible, however, as Laplace's great hypothesis appears on the surface, closer examination shows several vital objections, a few of those set forth by Professor Moulton being here enumerated—

Although Laplace held that the orbits of the planets were sufficiently near to being in the one plane to support his views, yet later investigators consider that their very deviations from this plane are a strong argument against the hypothesis.

Again, it is thought that if the theory were the correct explanation, the various orbits of the planets would be much more nearly circular than they are.

It is also thought that such interlaced paths, as those in which the asteroids and the little planet Eros move, are most unlikely to have been produced as a result of Laplace's nebula.

Further, while each of the rings was sweeping up its matter into a body of respectable dimensions, its gravitative power would have been for the time being so weak, through being thus spread out, that any lighter elements, as, for instance, those of the gaseous order, would have escaped into space in accordance with the principles of the kinetic theory.

The idea that rings would at all be left behind at certain intervals during the contraction of the nebula is, perhaps, one of the weakest points in Laplace's hypothesis.

Mathematical investigation does not go to show that the rings, presuming they could be left behind during the contraction of the mass, would have aggregated into planetary bodies. Indeed, it rather points to the reverse.

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 mass. 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 assuming 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 mass 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 assumption the various bodies of the solar system may be regarded as having been ejected from parent masses.

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 mass. 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 clusters. 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 mass 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 mass 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 masses, 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 masses of the Old and New Worlds. These masses 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 shores 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 passage:—

"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 anticipated 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 shores 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 pass as incidents almost unnoticed in space. 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 space of its constituent 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 glass-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 space, accompanied by several dark, cold balls 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 passed, 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 masses of comets are so very minute that one can hardly suppose them to contain any large or dense constituent 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 space. 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 orbit, and our globe would quickly pass 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 Hellas 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 shore.

* * * * *

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.



INDEX

Achromatic telescope, 115, 116

Adams, 24, 236, 243

Aerial telescopes, 110, 111

Agathocles, Eclipse of, 85

Agrippa, Camillus, 44

Ahaz, dial of, 85

Air, 166

Airy, Sir G.B., 92

Al gul, 307

Al Sufi, 284, 290, 296, 315

Alcor, 294

Alcyone, 284

Aldebaran, 103, 288, 290, 297

Algol, 307, 309-310, 312, 323, 347

Alpha, Centauri, 52-53, 280, 298-299, 304, 320

Alpha Crucis, 298

Alps, Lunar, 200

Altair, 295

Altitude of objects in sky, 196

Aluminium, 145

Amos viii. 9, 85

Anderson, T.D., 311-312

Andromeda (constellation), 279, 314; Great Nebula in, 314, 316

Andromedid meteors, 272

Anglo-Saxon Chronicle, 87-88

Anighito meteorite, 277

Annular eclipse, 65-68, 80, 92, 99

Annular Nebula in Lyra, 315-316

Annulus, 68

Ansae, 242-243

Anticipation in discovery, 236-237

Apennines, Lunar, 200

Aphelion, 274

Apparent enlargement of celestial objects, 192-196

Apparent size of celestial objects deceptive, 196, 294

Apparent sizes of sun and moon, variations in, 67, 80, 178

Aquila (constellation), 295

Arabian astronomers, 107, 307

Arago, 92, 257

Arc, degrees minutes and seconds of, 60

Arcturus, 280, 282, 290, 295

Argelander, 290

Argo (constellation), 298

Aristarchus of Samos, 171

Aristarchus (lunar crater), 205

Aristophanes, 101

Aristotle, 161, 173, 185

Arrhenius 222, 253-254

Assyrian tablet, 84

Asteroidal zone, analogy of, to Saturn's rings, 238

Asteroids (or minor planets), 30-31, 225-228, 336; discovery of the, 23, 244; Wolf's method of discovering, 226-227

Astrology, 56

Astronomical Essays, 63, 337

Astronomical Society, Royal, 144

Astronomy, Manual of, 166

Atlantic Ocean, parallelism of opposite shores, 340-341

Atlas, the Titan, 18

Atmosphere, absorption by earth's, 129-130; ascertainment of, by spectroscope, 124-125, 212; height of earth's, 167, 267; of asteroids, 226; of earth, 129, 130, 166-169, 218, 222, 267, 346; of Mars, 156, 212, 216; of Mercury, 156; of moon, 70-71, 156, 201-203; of Jupiter, 231; of planets, 125; of Saturn's rings, 239

"Atmosphere" of the stars, 331

Atmospheric layer and "glass-house" compared, 167, 203

August Meteors (Perseids), 270

Auriga (constellation), 294-296, 306, 311; New Star in, 311

Aurigae, [b] (Beta), 294, 297, 304

Aurora Borealis, 141, 143, 259

Australia, suggested origin of, 340

Axis, 29-30; of earth, 163, 180; small movement of earth's, 180-181

Babylonian tablet, 84

Babylonian idea of the moon, 185

Bacon, Roger, 108

Bacubirito meteorite, 277

Bagdad, 107

Baily, Francis, 92

"Baily's Beads," 69, 70, 91-92, 154

Bailly (lunar crater), 199

Ball, Sir Robert, 271

Barnard, E.E., 31, 224, 232-234, 237, 258

"Bay of Rainbows," 197

Bayer's classification of stars, 289, 291-292

Bayeux Tapestry, 263

Bear, Great (constellation). See Ursa Major; Little, see Ursa Minor

Beehive (Praesepe), 307

Beer, 206

Belopolsky, 304

"Belt" of Orion, 297

Belt theory of Milky Way, 321

Belts of Jupiter, 230

Bergstrand, 314

Berlin star chart, 244

Bessel, 173, 280, 305

Beta ([b]) Lyrae, 307

Beta ([b]) Persei. See Algol

Betelgeux, 297

Bible, eclipses in, 85

Biela's Comet, 256-257, 272-273, 345

Bielids, 270, 272-273

Billion, 51-52

Binary stars, spectroscopic, 301-306, 309; visual, 300, 303-306

"Black Drop," 152-154

"Black Hour," 89

"Black Saturday," 89

Blood, moon in eclipse like, 102

Blue (rays of light), 121, 130

Bode's Law, 22-23, 244-245

Bolometer, 127

Bond, G.P., 236, 257

Bonpland, 270

Booetes (constellation), 295, 314

Bradley, 111

Brahe, Tycho, 290, 311

Bredikhine's theory of comets' tails, 253-254, 256

Bright eclipses of moon, 65, 102

British Association for the Advancement of Science, 318

British Astronomical Association, Journal of, 194

British Museum, 84

Bull (constellation). See Taurus; "Eye" of the, 297; "Head" of the, 297

Burgos, 98

Busch, 93

Caesar, Julius, 85, 110, 180, 259, 262, 291, 293

Calcium, 138, 145

Callisto, 233-234

Cambridge, 24, 91, 119, 243

Campbell, 305

Canali, 214

"Canals" of Mars, 214-222, 224-225

Cancer (constellation), 307

Canes Venatici (constellation), 306, 314

Canis Major (constellation), 289, 296-297; Minor, 296-297

Canopus, 285, 298-299, 320

Capella, 280, 282, 290, 294, 297, 303, 313

Carbon, 145

Carbon dioxide. See Carbonic acid gas

Carbonic acid gas, 166, 213, 221-222

Carnegie Institution, Solar Observatory of, 118

Cassegrainian telescope, 114, 118

Cassini, J.D., 236, 240

"Cassini's Division" in Saturn's ring, 236, 238

Cassiopeia (constellation), 279, 294, 311, 314

Cassiopeiae, [e] (Eta), 303

Cassiopeia's Chair, 294

Cassius, Dion, 86

Castor, 282, 297, 304

Catalogues of stars, 106, 290-291, 311

Centaur. See Centaurus

Centaurus (constellation), 298, 306

Centre of gravity, 42, 283-284, 324

Ceres, diameter of, 30, 225

Ceti, Omicron (or Mira), 307-308

Cetus, or the Whale (constellation), 307

Chaldean astronomers, 74, 76

Challis, 243-244

Chamberlin, 337

"Chambers of the South," 299

Chandler, 308

Charles V., 261

"Charles' Wain," 291

Chemical rays, 127

Chinese and eclipses, 83

Chloride of sodium, 122

Chlorine, 122, 145

Christ, Birth of, 102

Christian Era, first recorded solar eclipse in, 85

Chromatic aberration, 110

Chromosphere, 71-72, 93-94, 130-132, 138-139

Circle, 171-173

Clark, Alvan, & Sons, 117-118, 303

Claudius, Emperor, 86

Clavius (lunar crater), 199

Clerk Maxwell, 237

"Clouds" (of Aristophanes), 101

Clustering power, 325

Clusters of stars, 300, 306, 314, 328

Coal Sacks. See Holes in Milky Way

Coelostat, 119

Coggia's Comet, 254

Colour, production of, in telescopes, 109-111, 115, 121

Collision of comet with earth, 345-346; of dark star with sun, 346-348; of stars, 285, 312

Columbus, 103

Coma Berenices (constellation), 307, 316

Comet, first discovery of by photography, 258; first orbit calculated, 255; first photograph of, 257-258; furthest distance seen, 258; passage of among satellites of Jupiter, 250; passage of earth and moon through tail of, 257, 346

Comet of 1000 A.D., 262; 1066, 262-264; 1680, 255, 265; 1811, 254-255; 1861, 254, 257, 346; 1881, 257-258; 1882, 251, 258, 291; 1889, 258; 1907, 258

Comets, 27-28, 58, Chaps. XIX. and XX., 345-346; ancient view of, 259-261; captured, 251-253; Chinese records of, 83-84; composition of, 252; contrasted with planets, 247; families of, 251-252, 256; meteor swarms and, 274; revealed by solar eclipses, 95-96; tails of, 141, 182, 248, 252-254

Common, telescopes of Dr. A.A., 118

Conjunction, 209

Constellations, 105, 278-279, 285, 289

Contraction theory of sun's heat, 128-129, 335

Cook, Captain, 154

Cooke, 118

Copernican system, 20, 107, 149, 170-173, 279, 280

Copernicus, 20, 108, 149, 158, 170-172, 236

Copernicus (lunar crater), 200, 204

Copper, 145

Corder, H., 144

Corona, 70-72, 90, 92-97, 132, 140-141, 270; earliest drawing of, 91; earliest employment of term, 90; earliest mention of, 86; earliest photograph of, 93; illumination given by, 71; possible change in shape of during eclipse, 96-98; structure of, 142-143; variations in shape of, 141

Corona Borealis (constellation), 295

Coronal matter, 142; streamers, 95-96, 141-143

Coronium, 133, 142, 317

Cotes, 91

Coude, equatorial, 119

Cowell, P.H., 255, 264

Crabtree, 152

Crape ring of Saturn, 236-237

Craterlets on Mars, 220

Craters (ring-mountains) on moon, 197-205, 214, 340; suggested origin of, 203-204, 214

Crawford, Earl of, 94

Crecy, supposed eclipse at battle of, 88-89

Crescent moon, 183, 185

Crommelin, A.C.D., 255, 264

Crossley Reflector, 118, 315-316

Crown glass, 115

Crucifixion, darkness of, 86

Crucis, [a] (Alpha), 298

Crux, or "Southern Cross" (constellation), 298-299, 323

Cycle, sunspot, 136-137, 141, 143-144

Cygni, 61, 173, 280

Cygnus, or the Swan (constellation), 295, 325

Daniel's Comet of 1897, 258

Danzig, 111

Dark Ages, 102, 107, 260

Dark eclipses of moon, 65, 102-103

Dark matter in space, 323

Dark meteors, 275-276

Dark stars, 309-310, 312, 323, 346-347

"Darkness behind the stars," 325

Darwin, Sir G.H., 339

Davis, 94

Dawes, 236

Dearborn Observatory, 303

Death from fright at eclipse, 73

Debonnaire, Louis le, 88, 261

Deimos, 223

Deity, symbol of the, 87

"Demon star." See Algol

Denebola, 296

Denning, W.F., 269

Densities of sun and planets, 39

Density, 38

Deslandres, 140

Diameters of sun and planets, 31

Disappearance of moon in lunar eclipse, 65, 102-103

Disc, 60

"Disc" theory. See "Grindstone" theory

Discoveries, independent, 236

Discovery, anticipation in, 236-237; indirect methods of, 120

"Dipper," the, 291; the "Little," 294

Distance of a celestial body, how ascertained, 56-58; of sun from earth, how determined, 151, 211

Distances of planets from sun, 47

Distances of sun and moon, relative, 68

Dog, the Greater. See Canis Major; the Lesser, see Canis Minor

"Dog Star," 289, 297

Dollond, John, 115-116

Donati's Comet, 254, 257

Doppler's method, 125, 136, 282, 301-302

Dorpat, 117

Double canals of Mars, 214-215, 218-220

Double planet, earth and moon a, 189

Double stars, 300

Douglass, 233

"Dreams, Lake of," 197

Dumb-bell Nebula, 316

Earth, 20, 22, 31, 39, 48, 64, Chap. XV., 267; cooling of, 343; diameter of, 31; interior of, 166; mean distance of from sun, 47; rigidity of, 181; rotation of, 30, 33, 161-165, 170; shape of, 165; "tail" to, 182

"Earthlight," or "Earthshine," 186

Earth's axis, Precessional movement of, 175-177, 295, 298-299

Earth's shadow, circular shape of, 64, 160

Eclipse, 61

Eclipse knowledge, delay of, 74

Eclipse party, work of, 73

Eclipse of sun, advance of shadow in total, 69; animal and plant life during, 71; earliest record of total, 84; description of total, 69-73; duration of total, 69, 72; importance of total, 68

Eclipses, ascertainment of dates of past, 74; experience a necessity in solar, 73-74; of moon, 63-65, Chap. IX., 203; photography in, 93; prediction of future, 74; recurrence of, 74-80

Eclipses of sun, 25, 65-74, Chap. VIII., 201-202, 234; 1612 A.D., 90; 1715, 88, 91; 1724, 88, 91; 1836, 92; 1842, 92-93; 1851, 81, 93; 1868, 93; 1870, 94; 1871, 94; 1878, 95; 1882, 95; 1883, 95-96; 1893, 95-96; 1896, 96, 99; 1898, 96, 98; 1900, 97; 1905, 75-76, 80-81, 97-98; 1907, 98; 1908, 98; 1914, 99; 1927, 92, 99-100

Eclipses, Past and Future, 340

Egenitis, 272

Electric furnace, 128

Electric light, spectrum of, 122

Elements composing sun, 144-145

Ellipses, 32, 66, 172-173, 177-178

Elliptic orbit, 66, 177

Ellipticity, 32

Elongation, Eastern, 147, 149; Western, 147, 149

Encke's Comet, 253, 256

"End of the World," 342

England, solar eclipses visible in, 87-88, 91-92

Epsilon, ([e]) Lyrae, 302

Equator, 48

Equatorial telescope, 226

Equinoxes. See Precession of

Eros, 210-211, 223, 226-227; discovery of, 24, 210, 227; importance of, 211; orbit of, 32, 37, 210, 336

Eruptive prominences, 139

Esclistre, 89

Ether, 322-323, 331-332

Europa, 233, 235

Evans, J.E., 219

Evening star, 149-150, 241

Everest, Mount, 200

Evershed, 182

Eye-piece, 110

Fabricius, 307

Faculae, 136, 143

Fauth, 205

Faye, 335

Fin du Monde, 346

First quarter, 183

"Fixed stars," 280

Flagstaff, 215-216, 220

Flammarion, Camille, 346

Flamsteed, 90

"Flash spectrum," 137

"Flat," 112

Flint glass, 115

Focus, 66, 177

"Forty-foot Telescope," 115

Foster, 102

Fraunhofer, 117

French Academy of Sciences, 115

Froissart, 89

"Full moon" of Laplace, 190

Galaxy. See Milky Way.

Galilean telescope, 109

Galileo, 55, 109, 172, 197, 206, 232-235, 242

Galle, 24, 211, 244

Ganymede, 233-234

Gas light, spectrum of, 122

Gegenschein, 181-182

"Gem" of meteor ring, 271

Gemini, or the Twins (constellation), 22, 296-297

Geminorum, [z] (Zeta), 304

Geometrical groupings of stars, 292

"Giant" planet, 230, 238-239

Gibbous, 183, 185

Gill, Sir David, 211, 258, 291, 317-318

Gold, 145

Goodricke, 307

Gore, J.E., 63, 285, 303, 307-308, 310, 323-324, 331, 337, 347

Granulated structure of photosphere, 134

Gravitation (or gravity), 39, 41-45, 128, 306

Greek ideas, 18, 158, 161-162, 171, 186, 197

Green (rays of light), 121

Greenwich Observatory, 143-144, 232, 255, 303

Gregorian telescope, 113-114

Grimaldi (lunar crater), 199

"Grindstone" theory, 319-322

"Groombridge, 1830," 281-282, 326, 330

Groups of stars, 306-307

Grubb, Sir Howard, 118

Gulliver's Travels, 224

Hale, G.E., 119, 140

Half moon, 183, 185

Hall, Asaph, 223

Hall, Chester Moor, 115

Halley, Edmund, 91, 255, 264-265, 306

Halley's Comet, 255, 264-265

Haraden Hill, 91

Harvard, 118, 302

Harvest moon, 190-192

Hawaii, 221

Heat rays, 127

Heidelberg, 226, 232

Height of lunar mountains, how determined, 201

Height of objects in sky, estimation of, 196

Helium, 138, 145, 182

Helmholtz, 128, 335

Hercules (constellation), 295

Herod the Great, 101-102

Herodotus, 84

Herschel, A.S., 269

Herschel, Sir John, 92, 322

Herschel, Sir William, 22, 36, 114-115, 204, 213, 235, 283, 292, 308, 319-320, 326-328

Herschelian telescope, 114, 119

Hesper, 109

Hesperus, 150

Hevelius, 111

Hezekiah, 85

Hi, 83

Hindoos, 18

Hipparchus, 106, 177, 290, 311

Ho, 83

Holes in Milky Way, 321-323

Holmes, Oliver Wendell, 213

Homer, 223

Horace, Odes of, 106

Horizon, 159

Horizontal eclipse, 169

Horrox, 44, 151-152

Hour Glass Sea, 212

Huggins, Sir William, 94, 125, 317

Humboldt, 270

"Hunter's moon," 192

Huyghens, 111-112, 240, 242-243

Hyades, 296-297, 307

Hydrocarbon gas, 254

Hydrogen, 94, 131, 138, 140, 144, 156, 182, 254

Ibrahim ben Ahmed, 270

Ice-layer theory: Mars, 219; moon, 205, 219

Illusion theory of Martian canals, 219

Imbrium, Mare, 197

Inclination of orbits, 36-37

Indigo (rays of light), 121

Inferior conjunction, 147, 149

Inferior planets, 20, 22, Chap. XIV., 229

Instruments, pre-telescopic, 106-107, 172

International photographic survey of sky, 290-291

Intra-Mercurial planet, 25-26

Introduction to Astronomy, 31

Inverted view in astronomical telescope, 116-117

Io, 233-234

Iridum, Sinus, 197

Iron, 145, 254

Is Mars Habitable? 221

Jansen, 108

Janssen, 94, 236, 258

Japetus, 240

Jessenius, 89

Job, Book of, 299

Johnson, S.J., 103, 340

Josephus, 101, 262

Juno, 225

Jupiter, 20, 22-23, 31, 34, 37, 42, 227-228, 230-236, 241, 272, 311; comet family of, 251-253, 256; discovery of eighth satellite, 26, 232; eclipse of, by satellite, 234; without satellites, 234-235

Jupiter, satellites of, 26, 62, 108, 189, 232-235; their eclipses, 234-235; their occultations, 62, 234; their transits, 62, 234

Kant, 334

Kapteyn, 284, 313

Keeler, 315, 337

Kelvin, Lord, 129

Kepler, 44, 152, 172, 237, 242, 245, 253, 311

Kinetic theory, 156, 202, 212, 226, 231, 239, 336

King, L.W., 84

Knowledge, 87

Labrador, 97

Lacus Somniorum, 197

"Lake of Dreams," 197

Lalande, 244, 283

Lampland, 215, 219

Langley, 95, 127

Laplace, 190, 333

Laputa, 224

Le Maire, 115

Le Verrier, 24, 236, 243-244, 275

Lead, 145

Leibnitz Mountains (lunar), 200

Leo (constellation), 270, 295-296

Leonids, 270-272, 274-275

Lescarbault, 25

Lewis, T., 303

Lexell's Comet, 250

Lick Observatory, 31, 98, 117-118, 215, 232, 303, 305, 315; Great Telescope of, 117, 215, 237

"Life" of an eclipse of the moon, 80; of the sun, 77-78

Life on Mars, Lowell's views, 217-218; Pickering's, 221; Wallace's, 221-223

Light, no extinction of, 322-324; rays of, 127; velocity of, 52, 235-236; white, 121

"Light year," 53, 280

Lindsay, Lord, 94

Linne (lunar crater), 205

Liouville, 190

Lippershey, 108

Liquid-filled lenses, 116

Locksley Hall, 296; Sixty Years After, 109

Lockyer, Sir Norman, 73, 94, 236, 335

Loewy, 119, 206

London, eclipses visible at, 87-88, 91-92

Longfellow, 88

Lowell Observatory, 215, 219, 233-234

Lowell, Percival, 155, 212-213, 215-221

Lucifer, 150

Lynn, W.T., 219, 263

Lyra (constellation), 177, 283, 294-295, 307, 315, 347

Maedler, 206, 284

Magellanic Clouds, 317

Magnetism, disturbances of terrestrial, 143, 283

Magnitudes of stars, 287-289

Major planets, 229-230

"Man in the Moon," 197

Manual of Astronomy, 166

Maps of the moon, 206

Mare Imbrium, 197

Mare Serenitatis, 205

Mars, 20, 22-23, 31-32, 34, 37, 109, 155, 210-225, 234; compared with earth and moon, 221, 225; polar caps of, 212-214, 216; satellites of, 26, 223-224; temperature of, 213, 216, 221-222

Mass, 38; of a star, how determined, 305

Masses of celestial bodies, how ascertained, 42; of earth and moon compared, 42; of sun and planets compared, 39

Maunder, E.W., 87, 143, 219

Maunder, Mrs., E.W., 96, 144

Maxwell, Clerk, 237

Mayer, Tobias, 206, 283

McClean, F.K., 98

Mean distance, 46

"Medicean Stars," 232

Mediterranean, eclipse tracks across, 94, 97

Melbourne telescope, 118

Melotte, P., 232

Mercator's Projection, 80-81

Mercury (the metal), 145

Mercury (the planet), 20, 22, 25-26, 31-32, 34, 37, Chap. XIV.; markings on, 156; possible planets within orbit of, 25-26; transit of, 62, 151, 154

Metals in sun, 145

Meteor swarms, 268-269, 271, 274-275

Meteors, 28, 56, 167, 259, Chap. XXI.

Meteors beyond earth's atmosphere, 275-276

Meteorites, 276-277

Meteoritic Hypothesis, 335

Metius, Jacob, 108

Michell, 283, 305

Middle Ages, 102, 260, 264

Middleburgh, 108

Milky Way (or Galaxy), 285, 299, 311, 317, 319-327; penetration of, by photography, 325

Million, 47, 51-52

Minor planets. See Asteroids.

Mira Ceti, 307-308

"Mirk Monday," 89

Mirror (speculum), 111, 116

Mizar, 294, 302

Monck, W.H.S., 275

Mongol Emperors of India, 107

Moon, 26, Chap. XVI.; appearance of, in lunar eclipse, 65, 102-103; diameter of, 189; distance of, how ascertained, 58; distance of, from earth, 48; full, 63, 86, 149, 184, 189, 190, 206; mass of, 200, 202; mountains on, 197-205; how their height is determined, 201; movement of, 40-42; new, 86, 149, 183, 185; origin of, 339-341; plane of orbit of, 63; possible changes on, 204-205, 221; "seas" of, 197, 206; smallest detail visible on, 207; volume of, 200

Morning star, 149-150, 241

Moulton, F.R., 31, 118, 128, 302, 335, 337

Moye, 154

Multiple stars, 300

Musa-ben-Shakir, 44

Mythology, 105

Neap-tides, 179

Nebulae, 314-318, 328, 335, 345; evolution of stars from, 317-318

Nebular Hypothesis of Laplace, 333-338

Nebular hypotheses, Chap. XXVII.

Nebulium, 317

Neison, 206

Neptune, 20, 25, 31, 34, 37, 243-246, 249, 252, 274, 304; discovery of, 23-24, 94, 210, 236, 243-244; Lalande and, 244; possible planets beyond, 25, 252; satellite of, 26, 245; "year" in, 35-36

"New" (or temporary), stars, 310-314

Newcomb, Simon, 181, 267, 281, 324, 326-327, 329

Newton, Sir Isaac, 40, 44, 91, 111-113, 115, 165, 172, 237, 255

Newtonian telescope, 112, 114, 116, 119

Nineveh Eclipse, 84-85

Nitrogen, 145, 156, 166, 346

Northern Crown, 295

Nova Aurigae, 311

Nova Persei, 312-314

Novae. See New (or temporary) stars

Nubeculae, 317

"Oases" of Mars, 216, 220

Object-glass, 109

Oblate spheroid, 165

Occultation, 61-62, 202, 296

Olaf, Saga of King, 88

Olbers, 227, 253, 256, 271

"Old moon in new moon's arms," 185

Olmsted, 271

Omicron (or "Mira") Ceti, 307-308

Opposition, 209

"Optick tube," 108-109, 232

Orange (rays of light), 121

Orbit of moon, plane of, 63

Orbits, 32, 36-37, 66, 150, 157

Oriental astronomy, 107

Orion (constellation), 195, 279, 296-297, 316; Great Nebula in, 316, 328

Oxford, 139

Oxygen, 145, 156, 166, 346

Pacific Ocean, origin of moon in, 339

Palitzch, 255

Pallas, 225, 227

Parallax, 57, 173, 280, 305, 320, 326

Pare, Ambrose, 264-265

Peal, S.E., 205

Peary, 277

Pegasus (constellation), 306

Penumbra of sunspot, 135

Perennial full moon of Laplace, 190

Pericles, 84

Perrine, C.D., 232-233, 315

Perseids, 270, 273-275

Perseus (constellation), 273, 279, 307, 312

Phases of an inferior planet, 149, 160; of the moon, 149, 160, 183-185

Phlegon, Eclipse of, 85-86

Phobos, 223

Phoebe, retrograde motion of, 240, 250, 336

Phosphorescent glow in sky, 323

Phosphorus (Venus), 150

Photographic survey of sky, international, 290-291

Photosphere, 130-131, 134

Piazzi, 23

Pickering, E.C., 302

Pickering, W.H., 199, 205-206, 220-221, 240, 339-341

Pictor, "runaway star" in constellation of, 281-282, 320, 330

Plane of orbit, 36, 150

Planetary nebulae, 245, 315

Planetary and Stellar Studies, 331

Planetesimal hypothesis, 337-338

Planetoids. See Asteroids

Planets, classification of, 229; contrasted with comets, 247; in Ptolemaic scheme, 171; relative distances of, from sun, 31-32

Plato (lunar crater), 198

Pleiades, 284, 296-297, 307

Pliny, 169, 260

Plough, 284, 291-296, 302

Plutarch, 86, 89, 169, 181

"Pointers," 292

Polaris. See Pole Star

Pole of earth, Precessional movement of, 176-177, 295, 298-299

Pole Star, 33, 163, 177, 292-296, 300-301

Poles, 30, 163-164; of earth, speed of point at, 164

Pollux, 282, 297

Posidonius, 186

Powell, Sir George Baden, 96

Praesepe (the Beehive), 307

Precession of the Equinoxes, 177, 295, 298-299

Pre-telescopic notions, 55

Primaries, 26

Princess, The (Tennyson), 334

Princeton Observatory, 258

Prism, 121

Prismatic colours, 111, 121

Procyon, 284, 290, 297, 303

Prominences, Solar, 72, 93, 131, 139-140, 143; first observation of, with spectroscope, 94, 140, 236

Proper motions of stars, 126, 281-285, 326, 329-330

Ptolemaeus (lunar crater), 198-199, 204

Ptolemaic idea, 319; system, 18, 19, 158, 171-172

Ptolemy, 18, 101, 171, 290, 296

Puiseux, P., 206

Pulkowa telescope, 117

Puppis, V., 310

Quiescent prominences, 139

Radcliffe Observer, 139

"Radiant," or radiant point, 269

Radiation from sun, 130, 134

Radium, 129, 138

Rainbow, 121

"Rainbows, Bay of," 197

Rambaut, A., 139

Ramsay, Sir William, 138

Rays (on moon), 204

Recurrence of eclipses, 74-80

Red (rays of light), 121, 125, 127, 130

Red Spot, the Great, 230

Reflecting telescope, 111-116; future of, 119

Reflector. See Reflecting telescope

Refracting and reflecting telescopes contrasted, 118

Refracting telescope, 109-111, 115-117; limits to size of, 119-120

Refraction, 121, 168-169

Refractor, See Refracting telescope

Regulus, 290, 296

Retrograde motion of Phoebe, 240, 250, 336

"Reversing Layer," 94, 130, 132, 137-138

Revival of learning, 107

Revolution, 30; of earth around sun, 170-173; periods of sun and planets, 35

Riccioli, 198

Rice-grain structure of photosphere, 134

Rigel, 285, 297

Rills (on moon), 204

Ring-mountains of moon. See Craters

"Ring" nebulae, 315, 337

"Ring with wings," 87

Rings of Saturn, 108, 236-239, 241-243, 334

Ritchey, G.W., 118

Roberts, A.W., 308, 310

Roberts, Isaac, 325

"Roche's limit," 238

Roemer, 235

Roman history, eclipses in, 85-86

Romulus, 85

Roentgen, 120

Rosse, great telescope of Lord, 117, 314

Rotation, 30; of earth, 33, 161-165, 170; of sun, 34, 125, 135-136, 231; periods of sun and planets, 35

Royal Society of London, 90-91, 111

Rubicon, Passage of the, 85

"Runaway" stars, 281, 326, 330

Sagittarius (constellation), 316

Salt, spectrum of table, 122

Samarcand, 107

"Saros," Chaldean, 76-78, 84

Satellites, 26-27, 37

Saturn, 20, 22, 34, 37, 108, 236-243, 258; comet family of, 252; a puzzle to the early telescope observers, 241-243; retrograde motion of satellite Phoebe, 240, 250, 336; ring system of, 241; satellites of, 36, 239-240; shadows of planet on rings and of rings on planet, 237

Schaeberle, 95-96, 303, 316

Schiaparelli, 155, 214, 223

Schickhard (lunar crater), 199

Schmidt, 206

Schoenfeld, 290

Schuster, 95

Schwabe, 136

Scotland, solar eclipses visible in, 89-90, 92

Sea of Serenity, 205

"Sea of Showers," 197

"Seas" of moon, 197, 206

Seasons on earth, 174-175; on Mars, 211

Secondary bodies, 26

Seneca, 95, 260

Septentriones, 291

Serenitatis, Mare, 205

"Seven Stars," 291

"Shadow Bands," 69

Shadow of earth, circular shape of, 62-64

Shadows on moon, inky blackness of, 202

Shakespeare, 259, 293

Sheepshanks Telescope, 119

"Shining fluid" of Sir W. Herschel, 328

"Shooting Stars." See Meteors

Short (of Edinburgh), 114

"Showers, Sea of," 197

Sickle of Leo, 270-271, 296

Siderostat, 118

Silver, 145

Silvered mirrors for reflecting telescopes, 116

Sinus Iridum, 197

Sirius, 280, 282, 284-285, 288-290, 297, 303-304, 320; companion of, 303; stellar magnitude of, 289

Size of celestial bodies, how ascertained, 59

Skeleton telescopes, 110

Sky, international photographic survey of, 290-291; light of the, 323

Slipher, E.C., 213, 222

Smithsonian Institution of Washington, 98

Snow on Mars, 213

Sodium, 122, 124, 254

Sohag, 95

Solar system, 20-21, 29-31; centre of gravity of, 42; decay and death of, 344

Somniorum, Lacus, 197

Sound, 125, 166, 331

South pole of heavens, 163, 285, 298-299

Southern constellations, 298-299

Southern Cross. See Crux

Space, 328

Spain, early astronomy in, 107; eclipse tracks across 93, 97-98

Spectroheliograph, 140

Spectroscope, 120, 122, 124-125, 144-145, 212, 231; prominences first observed with, 94, 140, 236

Spectrum of chromosphere, 132-133; of corona, 133; of photosphere, 132; of reversing layer, 132, 137; solar, 122-123, 127, 132

Speculum, 111, 116; metal, 112

Spherical bodies, 29

Spherical shape of earth, proofs of, 158-161

Spherical shapes of sun, planets, and satellites, 160

Spiral nebulae, 314-316, 337-338

Spring balance, 166

Spring tides, 192

Spy-glass, 108

"Square of the distance," 43-44

Stannyan, Captain, 90

Star, mass of, how determined, 305; parallax of, first ascertained, 173, 280

Stars, the, 20, 124, 126, 278 et seq.; brightness of, 287, 320; distances between, 326-327; distances of some, 173, 280, 320; diminution of, below twelfth magnitude, 324; evolution of, from nebulae, 317-318; faintest magnitude of, 288; number of those visible altogether, 324; number of those visible to naked eye, 288

"Steam cracks," 221

Steinheil, 118

Stellar system, estimated extent of, 325-327; an organised whole, 327; limited extent of, 322-328, 330; possible disintegration of, 329

Stiklastad, eclipse of, 88

Stone Age, 285

Stoney, G.J., 202, 222

Stonyhurst Observatory, 100

Story of the Heavens, 271

Streams of stars, Kapteyn's two, 284

Stroobant, 196

Stukeley, 91

Sulphur, 145

Summer, 175, 178

Sun, Chaps XII. and XIII.; as a star, 124, 278, 289; as seen from Neptune, 246, 304; chemical composition of, 144-145; distance of, how ascertained, 151, 211; equator of, 135-136, 139; gravitation at surface of, 129, 138-139; growing cold of, 343-344; mean distance of, from earth, 47, 211; motion of, through space, 282-286, 326; not a solid body, 136; poles of, 136; radiations from, 130; revolution of earth around, 170-173; stellar magnitude of, 288-289; variation in distance of, 66, 178

Sunspots, 34, 125, 134-137, 140-141, 143-144, 308; influence of earth on, 144

Suns and possible systems, 50, 286

Superior conjunction, 147-149

Superior planets, 22, 146, 209-210, 229

Swan (constellation). See Cygnus

Swift, Dean, 224

"Sword" of Orion, 297, 316

Syrtis Major. See Hour Glass Sea

"Systematic Parallax," 326

Systems, other possible, 50, 286

Tails of comets, 182

Tamerlane, 107

Taurus (constellation), 103, 296-297, 307

"Tears of St. Lawrence," 273

Tebbutt's Comet, 257-258

Telescope, 33, 55, 107-108, 149; first eclipse of moon seen through, 104; of sun, 90

Telescopes, direct view reflecting, 114; gigantic, 111; great constructors of, 117-118; great modern, 117-118

Tempel's Comet, 274

Temperature on moon, 203; of sun, 128

Temporary (or new) stars, 310-314

Tennyson, Lord, 109, 296, 334

Terrestrial planets, 229-230

Terrestrial telescope, 117

Thales, Eclipse of, 84

Themis, 240

"Tidal drag," 180, 188, 208, 344

Tide areas, 179-180

Tides, 178-180, 338-339

Time Machine, 344

Tin, 145

Titan, 240

Titius, 245

Total phase, 71-72

Totality, 72; track of, 66

Trail of a minor planet, 226-227

Transit, 62, 150-154; of Mercury, 62, 151, 154; of Venus, 62, 151-152, 154, 211

Trifid Nebula, 316

Triple stars, 300

Tubeless telescopes, 110-111, 243

Tubes used by ancients, 110

Tuttle's Comet, 274

Twilight, 167, 202

Twinkling of stars, 168

Twins (constellation). See Gemini

Tycho Brahe, 290, 311

Tycho (lunar crater), 204

Ulugh Beigh, 107

Umbra of sunspot, 134-135

Universe, early ideas concerning, 17-18, 158, 177, 342

Universes, possibility of other, 330-331

Uranus, 22-24, 31, 210, 243, 245, 275; comet family of, 252; discovery of, 22, 210, 243; rotation period of 34, 245; satellites of, 26, 245; "year" in, 35-36

Ursa Major (constellation), 279, 281, 291, 295, 314; minor, 177, 279, 293-294

Ursae Majoris, ([z]) Zeta. See Mizar

Variable stars, 307-310

Variations in apparent sizes of sun and moon, 67, 80, 178

Vault, shape of the celestial, 194-196

Vega, 177, 278, 280, 282-283, 285, 290, 294, 302, 307, 323

Vegetation on Mars, 221, 217-218; on moon, 205

Venus, 20, 22, 31, 71, 90, 108-109, 111, Chap. XIV., 246, 311; rotation period of, 34, 155

Very, F.W., 314

Vesta, 225, 227

Violet (rays of light), 121-122, 125

Virgil, 19

Volcanic theory of lunar craters, 203-204, 214

Volume, 38

Volumes of sun and planets compared, 38-39

"Vulcan," 25

Wallace, A.R., on Mars, 220-223

Water, lack of, on moon, 201-202

Water vapour, 202, 213, 222

Wargentin, 103

Warner and Swasey Co., 117

Weather, moon and, 206-207

Weathering, 202

Webb, Rev. T.W., 204

Weight, 43, 165-166

Wells, H.G., 344

Whale (constellation). See Cetus

Whewell, 190

Willamette meteorite, 277

Wilson, Mount, 118

Wilson, W.E., 313

"Winged circle" (or "disc"), 87

Winter, 175, 178

Witt, 227

Wolf, Max, 226-227, 232

Wright, Thomas, 319, 334

Wybord, 89

Xenophon, 101

Year, 35

"Year" in Uranus and Neptune, 35-36

Year, number of eclipses in a, 68

"Year of the Stars," 270

Yellow (rays of light), 121-122, 124

Yerkes Telescope Great, 117, 303

Young, 94, 137, 166

Zenith, 174

Zinc, 145

Zodiacal light, 181

Zone of asteroids, 30-31, 227

THE END

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Edinburgh & London



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ABBOTT, Rev. E.A., D.D.

How to Parse. An English Grammar. Fcap. 8vo, 3s. 6d.

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