Part 18

Beyond the fact that the existence of some repulsive force in the sun, a “negative gravity” actually existent, not in fancy, but in fact, seems pointed at, astronomers can offer little but conjecture here; and while some conceive this force as of an electrical nature, others strenuously deny it. We ought to admit that up to the present time we really know nothing about it, except that it exists.

At this date (October 9th) the comet had made nearly its closest approach to the earth, and the general outline has been compared to that of the wing of some bird, while the actual size was so vast that even at the distance from which it was seen it filled an angle more than half of that from the zenith to the horizon.

All the preceding drawings have been from naked-eye views; but if the reader would like to look more closely, he can see on page 217 one taken on the night of October 5th through the great telescope at Cambridge, Mass. We will leave this to tell its own story, only remarking that it is not possible to reproduce the phantom-like faintness of the original spur, here also distinctly seen, or indeed to indicate fairly the infinite tenuity of the tail itself. Though millions of miles thick, the faintest star is yet perceptibly undimmed by it, and in estimating the character and quantity of matter it contains, after noting that it is not self-luminous, but shines only like the moon by reflected sunlight, we may recall the acute observation of Sir Isaac Newton where he compares the brightness of a comet’s tail with that of the light reflected from the particles in a sunbeam an inch or two thick, in a darkened room, and, after observing that if a little sphere of common air one inch in diameter were rarified to the degree which must obtain at only four thousand miles from the earth’s surface it would fill all the regions of the planets to far beyond the orbit of Saturn, suggests the excessively small quantity of vapor that is really requisite to create this prodigious phantom.

The writer has had occasion for many years to make a special study of the reflection of light from the sky; and if such studies may authorize him to express any opinion of his own, he would give his adhesion to the remark of Sir John Herschel, that the actual weight of matter in such a cometary tail may be conceivably only an affair of pounds or even ounces. But if this is true of the tail, it does not follow of the nucleus, just seen in this picture, but of which the engraving on page 205 gives a much more magnified view. It is a sketch of the head alone, taken from a telescopic view on the 24th of September. Here the direction of the comet is still toward the sun (which must be supposed to be some indefinite distance beyond the upper part of the drawing), and we see that the lucid matter appears to be first jetted up, and then forced backward on either side, as if by a wind from the sun, to form the tail, presenting successive crescent-shaped envelopes of decreasing brightness, which are not symmetrical, but one-sided, while sometimes the appearance is that of spurts of luminous smoke, wavering as if thrown out of particular parts of the internal nucleus “like a squib not held fast.” Down the centre of the tail runs a wonderfully straight black line, like a shadow cast from the nucleus. Only the nucleus itself still evades us, and even in this, the most magnified view which the most powerful telescope till lately in existence could give, remains a point.

Considering the distance of the comet and the other optical conditions, this is still perfectly consistent with the possibility that it may have an actual diameter of a hundred miles or more. It “may” have, observe, not it “has,” for in fact we know nothing about it; but that it is at any rate less than some few hundred miles in diameter, and it may, for anything we can positively say, not be more than a very large stone, in which case our atmosphere would probably act as an efficient buffer if it struck us; or it may have a mass which, coupled with its terrible speed, would cause the shock of its contact not so much to pulverize the region it struck, as dissipate it and everything on it instantly into vapor.

Of the remarkable investigations of the spectroscope on comets, we have only room left to say that they inform us that the most prominent cometary element seems to be carbon,--carbon, which Newton two hundred years before the spectroscope, and before the term “carbonic-acid gas” was coined, by some guess or divination had described in other words as possibly brought to us by comets to keep up the carbonic-acid-gas supply in our air,--carbon, which we find in our own bodies, and of which, according to this view, the comets are original sources.

That we may be partly made of old and used-up comets,--surely it might seem that a madder fancy never came from the brain of a lunatic at the full of the moon!

Science may easily be pardoned for not giving instant reception to such an idea, but let us also remember, first, that it is a consequence of that of Sir Isaac Newton, and that in the case of such a man as he we should not be hasty to think we understand his ignorance, when we may be “ignorant of his understanding;” and, second, that it has been rendered at least debatable by Dr. Hunt’s recent researches whether it is possible to account for the perennial supply of carbon from the earth’s atmosphere, without looking to some means of renewal external to the planet.

The old dread of comets is passing away, and all that science has to tell us of them indicates that, though still fruitful sources of curiosity and indeed of wonder, they need no longer be objects of terror. Though there be, as Kepler said, more comets in the sky than fish in the ocean, the encounter of the earth with a comet’s tail would be like the encounter with a shadow, and the chance of a collision with the nucleus is remote indeed. We may sleep undisturbed even if a new comet is announced every month, though it is true that here as elsewhere lie remote possibilities of evil.

The consideration of the unfamiliar powers certainly latent in Nature, such as belong to a little tremor of the planet’s surface or such as was shown in that scene I have described, when the comparatively insignificant effect of the few tons of dynamite was to make solid buildings unrealities, which vanished away as quickly as magic-lantern pictures from a screen, may help us to understand that the words of the great poet are but the possible expression of a physical fact, and that “the cloud-capped towers, the gorgeous palaces, the solemn temples,”--and we with them,--may indeed conceivably some day vanish as the airy nothings at the touch of Prospero’s wand, and without the warning to us of a single instant that the security of our ordinary lives is about to be broken. We concede this, however, in the present case only as an abstract possibility; for the advance of astronomical knowledge is much more likely to show that the kernel of the comet is but of the bigness of some large meteorite, against which our air is an efficient shield, and the chance of evil is in any case most remote,--in any case only such as may come in any hour of our lives from any quarter, not alone from the earthquake or the comet, but from “the pestilence that walketh in darkness;” from the infinitely little below and within us, as well as from the infinite powers of the universe without.

VIII.

THE STARS.

In the South Kensington Museum there is, as everybody knows, an immense collection of objects, appealing to all tastes and all classes, and we find there at the same time people belonging to the wealthy and cultivated part of society lingering over the Louis Seize cabinets or the old majolica, and the artisan and his wife studying the statements as to the relative economy of baking-powders, or admiring Tippoo Saib’s wooden tiger.

There is one shelf, however, which seems to have some attraction common to all social grades, for its contents appear to be of equal interest to the peer and the costermonger. It is the representation of a man resolved into his chemical elements, or rather an exhibition of the materials of which the human body is composed. There is a definite amount of water, for instance, in our blood and tissues, and there on the shelf are just so many gallons of water in a large vessel. Another jar shows the exact quantity of carbon in us; smaller bottles contain our iron and our phosphorus in just proportion, while others exhibit still other constituents of the body, and the whole reposes on the shelf as if ready for the coming of a new Frankenstein to re-create the original man and make him walk about again as we do. The little vials that contain the different elements which we all bear about in small proportions are more numerous, and they suggest, not merely the complexity of our constitutions, but the identity of our elements with those we have found by the spectroscope, not alone in the sun, but even in the distant stars and nebulæ; for this wonderful instrument of the New Astronomy can find the traces of poison in a stomach or analyze a star, and its conclusions lead us to think that the ancients were nearly right when they called man a microcosm, or little universe. We have literally within our own bodies samples of the most important elements of which the great universe without is composed; and you and I are not only like each other, and brothers in humanity, but children of the sun and stars in a more literal sense, having bodies actually made in large part of the same things that make Sirius and Aldebaran. They and we are near relatives.

But if near in kind, we are distant relatives in another way, for the sun, whose remoteness we have elsewhere tried to give an idea of, is comparatively close at hand; quite at hand, one may say, for if his distance, which we have found so enormous, be represented by that of a man standing so close beside us that our hand may rest on his shoulder, to obtain the proportionate distance of one of the nearest stars, like Sirius, for instance, we should need to send the man over a hundred miles away. It is probably impossible to give to any one an adequate idea of the extent of the sidereal universe; but it certainly is especially hard for the reader who has just realized with difficulty the actual immensity of the distance of the sun, and who is next told that this distance is literally a physical point as seen from the nearest star. The jaded imagination can be spurred to no higher flight, and the facts and the enormous numbers that convey them will not be comprehended.

Look down at one of the nests of those smallest ants, which are made in our paths. To these little people, we may suppose, the other side of the gravel walk is the other side of the world, and the ant who has been as far as the gate, a greater traveller than a man who comes back from the Indies. It is very hard to think not only of ourselves as relatively far smaller than such insects, but that, less than such an ant-hill is to the whole landscape, is our solar system itself in comparison with the new prospect before us; yet so it is.

All greatness and littleness are relative. When the traveller from the great star Sirius (where, according to the author of “Micromegas,” all the inhabitants are proportionately tall and proportionately long-lived), discovered our own little solar system, and lighted on what we call the majestic planet Saturn, he was naturally astonished at the pettiness of everything compared with the world he had left. That the Saturnian inhabitants were in his eyes a race of mere dwarfs (they were only a mile high, instead of twenty-four miles like himself) did not make them contemptible to his philosophic mind, for he reflected that such little creatures might still think and reason; but when he learned that these puny beings were also correspondingly short-lived, and passed but fifteen thousand years between the cradle and the grave, he could not but agree that this was like dying as soon as one was born, that their life was but a span, and their globe an atom. Yet it seems that when one of these very Saturnian dwarfs came afterward with him to our own little ball, and by the aid of a microscope discovered certain animalculæ on its surface, and even held converse with two of them, he could not in turn make up his own mind that intelligence could inhere in such invisible insects, till one of them (it was an astronomer with his sextant) measured his height to an inch, and the other, a divine, expounded to him the theology of some of these mites, according to which all the heavenly host, including Saturn and Sirius itself, were created for them.

Do not let us hold this parable as out of place here, for what use is it to write down a long series of figures expressing the magnitude of other worlds, if it leave us with the old sense of the importance to creation of our own; and what use to describe their infinite number to a human mite who reads, and remains of the opinion that he is the object they were all created for?

Above us are millions of suns like ours. The Milky Way (shown on page 225) spreads among them, vague and all-surrounding, as a type of the infinities yet unexplored, and of the world of nebulæ of which we still know so little. Let us say at once that it is impossible here to undertake the description of the discoveries of the New Astronomy in this region, for we can scarcely indicate the headings of the chapters which would need to be written to describe what is most important.

The first of these chapters (if we treated our subjects in the order of distance) would be one on space itself, and our changed ideas of the void which separates us from the stars. Of this we will only say in passing, that the old term “the temperature of space” has been nearly abrogated; for while it used to be supposed that more than half of the heat which warmed the earth came from this mysterious “space” or from the stars, it is now recognized that the earth is principally warmed only by the sun. Of the contents of the region between the earth and the stars, we have, it must be admitted, still little but conjecture; though perhaps that conjecture turns more than formerly to the idea that the void is not a real void, but that it is occupied by something which, if highly attenuated, is none the less matter, and something other and more than the mere metaphysical conception of a vehicle to transmit light to us.

Of the stars themselves, we should need another chapter to tell what has been newly learned as to their color and light, even by the old methods, that is, by the eye and the telescope alone; but if we cannot dwell on this, we must at least refer, however inadequately, to what American astronomers are doing in this department of the New Astronomy, and first in the photometry of the stars, which has assumed a new importance of late years, owing to the labors carried on in this department at Cambridge.

That one star differs from another star in glory we have long heard, but our knowledge of physical things depends largely on our ability to answer the question, “how much?” and the value of this new work lies in the accuracy and fulness of its measures; for in this case the whole heavens visible from Cambridge to near the southern horizon have been surveyed, and the brightness of every naked-eye star repeatedly measured, so that all future changes can be noted. This great work has taxed the resources of a great observatory, and its results are only to be adequately valued by other astronomers; but Professor Pickering’s own investigations on variable stars have a more popular interest. It is surely an amazing fact that suns as large or larger than our own should seem to dwindle almost to extinction, and regain their light within a few days or even hours; yet the fact has long been known, while the cause has remained a mystery. A mystery, in most cases, it remains still; but in some we have begun to get knowledge, as in the well-known instance of Algol, the star in the head of Medusa. Here it has always been thought probable that the change was due to something coming between us and the star; but it is on this very account that the new investigation is more interesting, as showing how much can be done on an old subject by fresh reasoning alone, and how much valuable ore may lie in material which has already been sifted. The discussion of the subject by Professor Pickering, apart from its elevated aim, has if, in its acute analysis only, the interest belonging to a story where the reader first sees a number of possible clews to some mystery, and then the gradual setting aside, one by one, of those which are only loose ends, and the recognition of the real ones which lead to the successful solution. The skill of the novelist, however, is more apparent than real, since the riddle he solves for us is one he has himself constructed, while here the enigma is of Nature’s propounding; and if the solution alone were given us, the means by which it is reached would indeed seem to be inexplicable.

This is especially so when we remember what a point there is to work on, for the whole system reasoned about, though it may be larger than our own, is at such a distance that it appears, literally and exactly, far smaller to the eye than the point of the finest sewing-needle; and it is a course of accurate reasoning, and reasoning alone, on the character of the observed changing brightness of this point, which has not only shown the existence of some great dark satellite, but indicated its size, its distance from its sun, its time of revolution, the inclination of its orbit, and still more. The existence of dark invisible bodies in space, then, is in one case at least demonstrated, and in this instance the dark body is of enormous size; for, to illustrate by our own solar system, we should probably have to represent it in imagination by a planet or swarm of planetoids hundreds of times the size of Jupiter, and (it may be added) whirling around the sun at less than a tenth the distance of Mercury.

Of a wholly different class of variables are those which have till lately only been known at intervals of centuries, like that new star Tycho saw in 1572. I infer from numerous inquiries that there is such a prevalent popular notion that the “Star of Bethlehem” may be expected to show itself again at about the present time, that perhaps I may be excused for answering these questions in the present connection.

In the first place, the idea is not a new, but a very old one, going back to the time of Tycho himself, who disputed the alleged identity of his star with that which appeared to the shepherds at the Nativity. The evidence relied on is, that bright stars are said to have appeared in this constellation repeatedly at intervals of from three hundred and eight to three hundred and nineteen years (though even this is uncertain); and as the mean of these numbers is about three hundred and fourteen, which again is about one-fifth of 1572 (the then number of years from the birth of Christ), it has been suggested, in support of the old notion, that the Star of Bethlehem might have been a variable, shining out every three hundred and fourteen or three hundred and fifteen years, whose fifth return would fall in with the appearance that Tycho saw, and whose sixth return would come in 1886 or 1887. This is all there is about it, and there is nothing like evidence, either that this was the star seen by the Wise Men, or that it is to be seen again by us. On the other hand, nothing in our knowledge, or rather in our ignorance, authorizes us to say positively it cannot come again; and it may be stated for the benefit of those who like to believe in its speedy return, that if it does come, it will make its appearance some night in the northern constellation of Cassiopeia’s chair, the position originally determined by Tycho at its last appearance, being twenty-eight degrees and thirteen minutes from the pole, and twenty-six minutes in right ascension.

We were speaking of these new stars as having till lately only appeared at intervals of centuries; but it is not to be inferred that if they now appear oftener it is because there are more of them. The reason is, that there are more persons looking for them; and the fact is recognized that, if we have observers enough and look closely enough, the appearance of “new stars” is not so very rare a phenomenon. Every one at all interested in such matters remembers that in 1866 a new star broke out in the Northern Crown so suddenly that it was shining as bright as the Polar Star, where six hours before there had been nothing visible to the eve. Now all stars are not as large as our sun, though some are much larger; but there are circumstances which make it improbable that this was a small or near object, and it is well remembered how the spectroscope showed the presence of abnormal amounts of incandescent hydrogen, the material which is perhaps the most widely diffused in the universe (and which is plentiful, too, in our own bodies), so that there was some countenance to the popular notion that this was a world in flames. We were, at any rate, witnessing a catastrophe which no earthly experience can give us a notion of, in a field of action so remote that the flash of light which brought the news was unknown years on the way, so that all this--strange but now familiar thought--occurred long before we saw it happen. The star faded in a few days to invisibility to the naked eye, though not to the telescope; and, in fact, all these phenomena at present appear rather to be enormous and sudden enlargements of the light of existing bodies than the creation of absolutely new ones; while of these “new stars” the examples may almost be said to be now growing numerous, two having appeared in the last two years.

Not to enlarge, then, on this chapter of photometry, let us add, in reference to another department of stellar astronomical work, that the recognized master in the study of double stars the world over is not an astronomer by profession, at the head of some national observatory in Berlin or Paris, but a stenographer in the Chicago law-courts, Mr. W. S. Burnham, who, after his day’s duties, by nightly labor, prolonged for years with the small means at an amateur’s command, has perhaps added more to our knowledge of his special subject in ten years than all other living astronomers.

We have here only alluded to the spectroscope in its application to stellar research, and we cannot now do more than to note the mere headlines of the chapters that should be written on it.