to have no superior for delicate accuracy in the comparison of the magnitudes and varied colours of the stars, while the other gentlemen were equally eminent for the application of the Spectroscope to the analysis of the nature and sources of stellar light. It is surely far from a sign of the decadence of a country, which like our own, by its natural habits and free institutions, produces a supply of men, who for no fee or reward, but impelled by the love of the thing, and often when their day's proper work is done, set themselves, at the cost of expenditure and tail, to consume the hours of midnight in increasing the knowledge of their fellow men, and in searching into the wonderful works of the Great Creator. We may be thankful that not a few such men exist in England; and among them none are worthier than the three gentlemen whose names have been mentioned above. I shall now proceed to give the results at which Mr. Baxendell arrived in his examination of this remarkable star.. On the 15th of May it had decreased from the second magnitude, which it had attained when observed at Tuam, to nearer the fourth than the third magnitude when first seen by Mr. Baxendell at Manchester. It then continued to diminish with very great rapidity, until on the 26th of June it had sunk to nearly the tenth magnitude, and thus had ceased to be visible excepting in excellent telescopes alone. fyr Thus the intensity of the star's light on the 12th of May was fully five hundred times greater than on the Bth of June! Nor were the variations in colour much less remarkable. When first seen there was a slight nebalsity about it, and there was a bluish tinge, as if the yellow of the star were seen through an overlying film of a blue tint. After the 25th of May this bluish tinge disappeared, and the colour changed through many various tints of orange and yellow. From the 26th of June to the 20th of August, things remained without observable change, but, strange to say, a second outburst of light commenced the latter date. By the 15th of September it had risen two magnitudes, that is to say, its light had again become sixfold. The star then remained apparently tranquil until the 9th of November, when it once more began to decline, and at the present time has nearly diminished to its least observed intensity. Its colour varied from a pretty bright yellow on the 17th of September, to a light orange on November the 6th, and then fading through a dull orange, is now of a dullish white. If the state of our scientific knowledge were now no further advanced than it was about seven years ago, there could be no definite conclusions relative to these two singular outbursts of light, which could safely be drawn, even from the elaborate and' accurate observations of Mr. Baxendell. Nearly all that could be said would be, that we have here one of the most remarkable instances of those variable stars, so many of which have been recorded in the annals of Astronomical science. Our thoughts would naturally be carried back three centuries, to the days of Tycho Brahe, who witnessed the sudden apparition of a new star, in brilliancy exceeding the brightest in the heavens, but which he was sure had not been visible half an hour before. The great Danish astronomer, unfortunately for us, had not the means and appliances which since his day have accumulated in the hands of modern observers, and little else was left for him to do, but to gaze, and to guess, and to be astonished. Science, however, during the last few years has taken one of those sudden bounds which render its annals so fascinating to the student; and especially Astronomical science, owing to many causes, has recently received a strong impulse in a new direction; and no longer finding the grasp of her powers restricted to the weighing of suns and planets, and to the measuring of their distances, she now aspires to a loftier aim, and hopes she is henceforth permitted by the Supreme Wisdom to understand some little of the processes from whence are elaborated the heat and the light of the sun, and what are the sources of even those paler fires which come spangling to us from the more distant stars. The means by which this unexpected accession to our knowledge has been obtained, the long train of ingenious experiments (those questionings of Nature), and the logical deductions therefrom, which enable us to say with undoubting confidence, "In yonder star there exists iron at a burning heat; in another, there is incandescent vapour of lime; in almost all of them there are strong evidences of the existence of magnesia and salt, and the recent outburst in the remarkable star of which we have spoken, was owing, in part at least, to the sudden combustion of hydrogen gas:" these things-we may almost call them wonderful things-we shall now proceed to lay before the reader. In so doing, we fear we shall of necessity make a serious call upon his attention; but, in return, we promise him a rich reward for his exercise of patience. On the other hand, out of the hundreds of thousands who will read these lines, there are probably some few who are as familiar as the writer with the simple but beautiful experiments we shall find it necessary to describe. But, even to these few, it can scarcely fail to be pleasant to travel once again over fields which, after all, present an inexhaustible variety; for there are visions of glory which never satiate, and there are truths the contemplation of whose comprehensive simplicity never palls. Among such, we venture to believe, are the laws of interaction which the Supreme Wisdom has impressed upon the material elements which are scattered in almost unbroken continuity through the universe of things. We strongly advise the great majority of our readers to repeat the experiments we shall detail. With this end in view, we shall describe them simply and fully; and, moreover, we shall in 252 THE ATMOSPHERE OF A WORLD ON FIRE. [Good Words, April 1, 1967. Let the reader, then, who desires to follow the train of our reasoning, take a piece of cardboard or stiff paper, about a foot or eighteen inches square; any colour is somewhat better than white, and it must be impervious to the light. In the middle of this, carefully cut a clean and even straight slit, parallel to one of the sides, not more than the twentieth of an inch wide, and about an inch and a half long. Fix this opaque paper, with wafers or otherwise, against a clean pane of glass in the window of a room, so that the thin slit shall be awoud alio vue vi godt tuis. ப bably he may see a variety of beautiful coloured bands flitting about, but what he seeks is the ribbon, which proceeds from the light of the slit, and this he may distinguish from all the others, by requesting an assistant to cover over the slit itself with a finger, from time to time. 4. No When the experimenter has at last caught the sight of this beautiful coloured ribbon, or spectrum, as we shall now call it, he will find that, as he humours the glass (always holding its edge vertical) the spectrum itself will greatly vary in length and in its distance to the left of the slit; he must then so place the glass as to obtain the shortest spectrum he can, and then he must gradually open it out a little. If he has succeeded, and unless the glass be D Diagram of the Compound Spectrum of the Temporarily Bright Star, T Corona Borealis. vertically upright, and at a height from the floor equal to the height of the observer's eye.. very uneven and full of veins, en he will now see something not , very dissimilar to the subjoined engraving ADD The colour near to c is red, towards D it becomes orange, de and then a little yellow, and Do.then green, and about F the colour is blue. But what he is especially to look for (and what, i in fact, is the object of the whole experiment), is the pre sence of one, or two, or three, or four, black vertical lines, like the lines C, D, and F, in the diagram. The writer himself, after a careless experiment like the one described, at this moment, on a dull day, sees two lines, namely, D and F. As we have already said, the sight of these dark lines is the object of the search, They are not to be seen without patience: few philosophers are even now aware that they can be seen at all with so rude an apparatus; and when they were for the first time observed by our great countryman Dr. Wollaston, in 1802, they immer Thirteen years after this, Fraunhofer, at Munich, by diminishing the breadth of the slit, by reflecting the direct sun-light through it from a looking-glass outside, by then using a prism of pure glass, and, lastly, by looking at the slit through the prism, not with the naked eye, but with a small telescope, abserved and accurately measured the position of many hundreds of these lines. Without a telescope, if the reader possesses a tolerably good prism, he may readily see more lines than he can count. These lines have henceforth been called Fraunhofer's Lines. In fact of priority, they are Wollas Now let him take a glass lustre off a chandelier. It will be best for him to select two or three, without veins, if such can fortunately be found, and much the better if the shape of the glass pendant happens to be, in section, an equilateral triangle; but in modern fashion these glass pendants for the most part have two of their faces perpendicular to each other. Through this rectangular edge vision is impossible, and the reader must avoid it. Now let him stand with his right, eye exactly opposite totalised the discoverer. the slit, and if he can, through the slit, see a bright white cloud, that will be in his favour: his distance from the slit may be eight, or ten, or twelve feet, or even more. The lustre is to be held with one of its acute edges (not the rectangular edge, if it has one) vertically upright, and therefore parallel to the slit and close to his right eye, and with this eye he is to look through the left hand face of the glass. The direction also in which he must look must be towards the left, and, as it were, to some place on the left not quite so far from the slit as he is himself distant from it. He will then see the thin line of light from the slit spread out into a ribbonton's; but, unfortunately, our countryman did not coloured with a variety of successive colours. The red colour will be nearest to the slit, on the right; and the blue will be furthest, on the left. To see this ribbon of coloured lights will require patience and some humouring of the glass lustre; but to the writer, who, nevertheless, bears in mind Columbus's egg, the whole actual manipulation at this moment has occupied less time than the description. The reader may consider himself fortunate if his is own success requires twenty minutes to achieve. Pro at once see the importance of his discovery, and he dropped the subject. Newton also, who a century before Wollaston first observed and studied the spectrum, lost the fame of this discovery from the simple fact of not placing the prism close to his eye. Strange to say, these dark lines contain the key to the enigma of the material constitution of a star. and of our sun; and that is the reason why we have been thus particular in describing the easiest 2017 and most simple way of seeing a few of the most conspicuous among them, námely, c, D, and F. The reader will probably have little or no difficulty in understanding that the coloured ribbon of light, called the spectrum, is nothing more than the thin line of light in the slit, spread out. He may conceive this line to resemble a bundle of innumerable coloured faggots, and that the glass or prism, through which they have passed, has arranged them all in an orderly manner. But then comes the question, What is the significance of the dark interruptions? Do the colours which would otherwise properly belong to these dark spaces, not enist in the nature of things? Or do they not exist in solar light? Or do they in reality exist in light emanating from the sun, but subsequently have been absorbed "somehow and somewhere? These are natural, inevitable questions occurring in relation to Fraunhofer's lines; but for upwards of fifty years these lines remained a perplexing mystery. The Sphinx had spoken, but Edipus was not. Who could have conceived that the true solution lay in the existence of heated terrestrial substances dispersed in the sun and throughout the universe? The next step in advance was taken by Professor Wheatstone, about three years after Brewster's discovery of the absorption of certain lights by certain coloured vapours. By a process of considerable difficulty he contrived to render the vapours of certain of the metals incandescent; and then viewing the light emitted by these vapours through a slit and prism, as before, he found that the spectra did not consist of a continuous coloured ribbon of light, but simply of a few detached bright coloured lines. The incandescent vapours of no two metals gave precisely the same lines. In fact, so extremely definite was the spectrum of each metallic vapour, that Professor Wheatstone did not hesitate to say that by this method the presence of extremely minute portions of the metals could be detected with greater certainty than by any other known process. The reader may easily try the experiment on a small scale for himself, by burning a little magnesium wire (now, thanks to the wide diffusion of scientific knowledge, so easily procured,) behind the slit, when he will at once recognise a peculiar. spectrum of certain bright greenish lines. Or if he drop a little salt into the flame of a lamp or candle, will immediately see a bright yellow line in the precise position of the line marked D in the diagram. And further, if while he is viewing a good spectrum of the light from the candle, an assistant opens and shuts with some violence an old dusty book close to the light, he will probably see, for the moment, a vast number of bright-coloured lines suddenly start into existence throughout the spectrum. These lines arise from the vapourization and incandescence of a vast number of minute substances collected in the dust. But these lines in the spectra of metallic vapours— and the same remark applies equally to incandescent gases, such as hydrogen, &c.,-are all bright lines, whereas those in the solar spectrum are dark. What, then, is the relation between the two? In 1832 that is just thirty years after their discovery by Wollaston-Dr. Brewster, by a very simple experiment (which we advise our readers to repeat, however roughly), demonstrated that these dark lines are produced by the absorption of those particular coloured lights which, in the spectrum, they displace. Let the reader take a candle or a lamp, and in front of it let him place the narrow alitas before, and let him as before obtain the spectrum of the light; he will then see the same sort of beautiful coloured ribbon with which by this time he must be familiar; but he will see no dark lines, it will be continuous and uninterrupted. But now let him procure a small uncut glass tumbler, in it let him place some small copper coin, and upon it let him, with all necessary caution, pour as much aquafortis (or nitric acid) as will just tever the coin, and immediately place a paper cover And now came a variety of guesses; one might on the top, in order to confine the orange-coloured almost call them divinations of the truth. The vapours of nitrous gas which will presently fill the annals of Science tell us that such divinations of glase. This glass is to be quickly placed between truth beforehand not rarely precede the discovery the light and the slit, and the spectrum is now to of great, comprehensive, pregnant truths. They be observed. It is no longer the bright uninter- preceded the discovery of the Law of Gravitation; pted spectrum which he had seen from the lamp they preceded the discovery of oxygen; they prebefore, but the coloured ribbon is crossed with a ceded the discovery of electro-magnetism; and even multitude of lines, greatly resembling, but not now they seem to loom before the discovery of the identical, with the lines discovered by Fraunhofer. yet unknown cause of gravitation itself. Newton The experiment, if well performed, is extremely divined the combustible nature of the diamond a beautiful, and one not likely to be forgotten. Here century before Allen and Pepys succeeded in showthere is a demonstrated fact, that media do existing it was nothing but pure crystalized carbon. capable of absorbing light, and of producing a phenomenon closely resembling the dark lines in the solar spectrum. But what is it we may ask what is it which, as it were, causes coming and substantial discoveries so often to throw their shadows before But then comes the question, What is it that them? Is it some single word, or some chance exabsorbs certain portions of the solar light? Is it pression, which, as a winged seed falling from one something in the atmosphere of the sun, or some-master-mind, is wafted, like a rumour, amongst thing in the atmosphere of the earth? Thus the mystery became increased! Em other minds, until, at length, it finds a proper and kindred home, and then germinates' and 'fructifies into the ripeness of some general truth? Or is it that the minds of men, after some unknown process, and in accordance with some magnificent prearrangement of the Great Eternal Mind, become, from time to time, by the interaction of circumstances, polarised, and when the tension becomes extreme, break forth at length into the force and light of discovery? Be all this as it may, it is certain, that Professor Stokes, in England; Balfour Stewart, in Scotland; M. Foucault, in France; aud M. Angström, in Sweden, all assigned a probable cause for portions, at least, of the obscure but interesting phenomena before us, and had any one of them followed up his reasoning but one step onwards, he would have anticipated the grand discovery of Kirchhoff which, in 1859, grasped the whole question, and soon laid open to the human mind very much of the material constitution of the sun, the stars, nebule, and comets. What Kirchhoff did was virtually this. He demonstrated experimentally that if the vapour of a metal, or a gas, when incandescent, emits light of a certain quality, that same metallic vapour or gas, when less heated, absorbs precisely the same quality of light. The vapour of sodium, for instance, when sufficiently heated, emits a bright yellow light, all of which is coincident with the dark line D of the solar spectrum; but if this light be made to pass through vapour of sodium less heated than the emitting vapour, it will be absorbed entirely, and no light at all will be visible. Aud so with other metals and various gases. Here, then, was not only a clear explanation of the origin of Wollaston's or Fraunhofer's lines, but an insight is thereby given into the material constitution of the sun : and the same remark applies equally to the stars. The sun, or the star, must be considered as consisting, first, of some nucleus with its solid or liquid surface intensely heated, so that the light emitted from it, like the light from every other intensely heated solid or liquid with which we are acquainted, affords a continuous uninterrupted spectrum. In front of the incandescent surface must be various heated gases and metallic vapours, and each of these stops precisely those qualities of light which, if more intensely heated, it would emit.* There was but one step more to be taken, in order to prove incontestably that such metals as iron, sodium, magnesium, &c., and such gases as hydrogen, &c., do actually exist in the sun and in the stars. Kirchhoff took this step. Through the lower half of the slit, so often spoken of, he admitted solar light, and obtained its spectrum; through the upper half he admitted the light emanating from various incandescent metallic vapours, from iron, for instance. Thus the two It is important here to observe that the less intensely heated vapours themselves emit some rays of the same quality or refrangibility as those which they have wholly absorbed; but these are so feeble as to appear dark when contrasted with the adjacent lights in the spectrum. spectra lay superposed before him, and admitted the most exact comparison. The iron spectrum consisted of thirty or more definite and widely separated bright lines, and these were absolutely coincident with as many dark lines in the solar spectrum. This coincidence of so many lines, and of all of them, could not arise from chance, but demonstrated the existence of heated iron vapour absorb. ing certain qualities of light emanating from the incandescent body of the sun. And in the same manner Kirchhoff obtained the spectrum of incandescent hydrogen superposed upon the solar spectrum. The hydrogen spectrum cousisted mainly of the bright lines c and F of the diagram on page 252, in absolute coincidence with two of the lines dis covered by Wollaston, and marked by Fraunhofer with the same letters o and F. Hydrogen, therefore, exists in the atmosphere of the sun, and it stops or absorbs the red light c and the bluish green light F, which emanate from its incandescent nucleus. The reader is now in a condition to intelligently understand the evidence upon which we conclude that the remarkable outburst of light in the star, which has been described in the former part of this article, probable arose from, or was accompanied by, a conflagration of hydrogen gas. On the night of the morning when the intelligence reached Fro fessor Miller and Mr. Huggins, relative to the sud den appearance of the star, they at once viewed its spectrum with the same admirable apparatus which had already conducted them to so many important discoveries connected with the physical constitution of the heavenly bodies. But what a sight was there revealed to the well-practised initiated eye of a philosopher! There lay before them the evidence which suggested the atmosphere of a star, a stu, a world, on fire. And the evidence was this: the instrument revealed two spectra, the one superposed upon the other: one of them was the usual species of spectrum generally afforded by the stars, viz., a spectrum interrupted, as we have seen the sol spectrum is, by numerous dark lines, and indicati for the star, an incandescent solid or liquid nucleus surrounded by an atmosphere containing the vapour of sodium, and it may be iron, or magnesium, of various other elements which are found upon this our earth. But besides this spectrum there wa another, and that other full of a remarkable signif cance. It consisted of four bright lines, and from their relative position two of them appeared to aris from INCANDESCENT HYDROGEN. This, within their knowledge and experience, was a solecism in the heavens. Of the dark lines c and F in the spectra of stars, evidence enough existed; the significance o these lines was hydrogen indeed, but of hydrogen not heated to extreme incandescence. 'Here, how ever, the lines c and r were brighter than the con tiguous parts of the spectrum, and thus they spoke unmistakably for themselves. But so far the co incidence of two of the bright lines with c and Fo Fraunhofer was rather suspected than proved, an consequently these cautious experimentalists put into requisition the exquisite apparatus and arrangements with which they were provided. They produced the spectrum itself of incandescent hydrogen, and they placed it exactly over the spectrum of the star; the coincidence of two of the bright lines of the star with the two bright lines of incandescent hydrogen was absolute. The other two bright lines of the star are not ascertained as yet to indicate the existence of any element known to the inhabitants this earth. Thus the sudden outburst of light in this star, or tall events the light of the star, was in great part last owing to hydrogen. As the light of the star aned, so the splendour of these bright lines waned, and so also the other continuous spectrum declined in brightness, and we are in a manner forced upon the conviction that the outburst of light was accompanied with the blaze of hydrogen in combustion, which gradually spent itself, and is now nearly extinguished. But is it possible to make even any plausible guess as to the cause of the outburst of light and heat in this wonderful star? Thoughtful men have ready made some guesses, and we shall now ature upon another; it is given simply as a guess nd as a mere speculation only, though we hope at wholly an uninstructive one. On referring to the Royal Observatory, Greenich, it was soon discovered that this star, now alled T Corona Borealis, is not a new star, but was very probably observed by Sir W. Herschel, and by K. Wollaston; and certainly it is, in the catalogue M. Argelander, and is there marked as a star of between the ninth and tenth magnitude; just the feeble brilliance to which it has now sunk. If this ar be like other suns, there will be worlds circling round it, and these worlds may like our earth have Satellites. Now it is the settled opinion of some ntious philosophers that in the lapse of ages, that after the lapse of many millions of years we do say millions of millions of years-the sun will e lost the greater part of its heat and light, and earth and its satellite will at length approach it arer and nearer, and ultimately will rush into the at darkened luminary; then utter indeed will be ruin, and vast the outburst of light from the thereof. There is nothing chimerical, nothing losophical in the belief or the expectation of this ultimate phenomenon. But the time is not Now it may have been that the outburst of light in Corona may have arisen from the falling into it, t of a world like our own, and subsequently of its tellite. Such an hypothesis is somewhat consistent ith the greater, and with the lesser outburst which succeeded the former. If the world in colon was provided with a great ocean like our , then there is the source of the hydrogen; and as it cooled somewhat, it recombined with the en, we can account for that peculiar blue tinge kich Mr. Baxendell observed, and which blue tinge may be seen in perfection when the wind blows over and provides a supply of oxygen for an illumination by gas. Such a state of things would also go far to explain the great variability in the colour of the star. The collision of an oceanless satellite would consistently account for the second and smaller outburst. But we are confessedly in the regions of speculation, and there let us leave the subject, or at all events this truly hypothetical part of it. In the course of this article we have been speaking of many things, in the contemplation of which it is difficult to silence the imagination, and sometimes equally so to suppress a rising emotion. What are we to say, for instance, of the evidence which such researches have brought to light, of that scattering of material substances in patches as it were throughout the universe, just as, in like patches, we find metallic substances scattered in various parts of our own earth? Some stars, we have seen, afford evidences of the existence of iron and lime, and others do not; most of those hitherto examined contain magnesium, and almost all of them sodium. Of gold, and of silver, so far, they contain not a trace; shall we here then repeat the remark which centuries ago Tacitus made regarding the ancient Germans:-", aurum et argentum, dii irati an propitii negaverint, dubito." And lastly, there is another thought regarding this Stella Mirabilis, which we have already briefly touched on, and with it we shall conclude. It has reference to the inconceivable distance of a body of whose material constitution we nevertheless make, and reasonably make, such confident assertions, and regarding a possible catastrophe in which we have ventured, though not without reserve, tc speculate. The thought is this: the conflagration in this atmosphere of a star was first observed on the 12th of May, 1866; but when did it actually occur? If this star is as near to this our world as is the nearest yet known of the stars, which proximity nevertheless we have no reason to suppose, then the increased outburst of the combustion of hydrogen must have taken place at least three years before it was visible at Tuam and interpreted at Tulse Hill. But if, as is far more probable, this star is among those more distant orbs which shine with a light so pale as to be visible only in our more powerful telescopes, then the conflagration, of which the first tidings have reached us only to-day, must have actually waxed and waned for its little week, not now, nor yesterday, but it may be even hundreds of years ago. The imagination shrinks within itself at the thought, how the bright light from that evanescent ephemeral outburst, winged its way, leaping century through century, from world to world, and telling successively the tale of its glory to (it may be) creatures nobler and more intelligent than ourselves, at length, reaches the little speck of our mortal abode, in its course onward we know not whither. But let us remember it is not the prism, |