the much longer continuance of all the stages of its career, past and to come that it has been much longer in passing through the inchoate stage, and through its first stages as a formed sun, and that it will be very much longer in passing through all those stages which it has still to go through, than our own sun or other suns of the same class. Looking at such a sun as Sirius, for example, we may believe that at the beginning of its present stage of existence as a bluishwhite sun, our sun and Sirius may have both been bluish-white, but that our sun, being very much smaller, has passed onward into the stage when a star shines with yellowish-white lustre, and will perhaps pass onward to the later stages of which we have yet to speak, while Sirius and Vega are still shining as bluish-white stars. But we cannot assume that any small bluish-white star which gives (as many small stars do) the same sort of spectrum as Sirius, is in reality an enormously large sun, another Sirius in fact, shining with the same sort of light because, beginning its existence at about the same epoch, it has taken a much longer time than our sun to reach the same stage of sun life. It may be that a bluish-white star, with strong hydrogen lines in its spectrum, is no larger than our sun, or is even smaller than he is; but having come into existence as a sun much later, has not reached the same stage of development.

It is important that we should not here fall into an error of the same sort as that which vitiated the earlier reasonings of Sir William Herschel respecting the stellar distances. He regarded the brightness of a star as fairly indicating its distance, assuming all stars to be of the same general order; later we see a tendency on his part to fall into the opposite extreme, and regard brightness as rather indicating the real size of a star than proximity. Neither inference can in point of fact be relied upon; some faint stars are large ones very far off; others are really small stars not farther off, or even nearer, than their fellows.

So it is in the case before us. Some bluish-white suns with spectra indicative of stellar youth are no doubt enormously large orbs, compared with which our sun. is little more than as a dwarf compared with a giant; such suns are young be

cause they are large; the stages of their lives are all very much shorter than the corresponding stages of the lives of our sun. But others no doubt of these young suns are really young in years as well as in development; they are younger than our sun, not because they require longer time intervals for the various stages of their life, but because they began their stellar life later.

It should be noticed that the spectra of these bluish-white stars are not all exactly alike. They are distinguished from each other by the greater or less breadth and diffuseness of the lines of hydrogen, and also by various degrees of strength and visibility of the finer lines. It may possibly be that hereafter, in such distinctions as these, we may be able to recognize evidence as to the size of a star-that, for instance, a large star in passing through the first stage of stellar life may present characteristics always different in certain respects from those presented by smaller orbs in passing through the same stage. If so, we shall have a new means of dealing with the architecture of the heavens; for, knowing something of the real size of a star in this way, we may infer its distance from its apparent size, and thus place it correctly in position in space, instead of knowing only the direction in which it lies, at some distance unknown.

Pass now to the next order of suns, of which Aldebaran, Capella, and our own sun are examples. In the spectrum of Aldebaran," says Dr. Huggins, "the lines of hydrogen are reduced to about the proportion they possess in the solar spectrum; the other lines of the spectrum are no longer fine and difficult to see; we have in fuil the triple line of magnesium. I have seen the spectrum of Capella as photographed by Professor Henry Draper of New York, for comparison with the spectrum of the sun, as received after reflection from the surface of Jupiter. Matters were so arranged that the two spectra were of the same strength. Now when these photographs were placed side by side (the corresponding dark lines being brought into the same direction, so that the eye could run along a dark line of Capella into the corresponding dark line of the sun) I found it almost impossible to recognize the slightest difference between

the two spectra. Almost every line in the spectrum of Capella corresponded with a dark line in the spectrum of the sun; in each case the strength of the lines corresponded very closely. Only after a prolonged and close scrutiny could I satisfy myself that one or two lines of the solar spectrum seemed slightly stronger than the corresponding lines in the spectrum of Capella, and in these cases I found that these very lines are known to be slightly strengthened by absorptive action experienced as they pass through the atmosphere of Jupiter. In this case, apart from a slight disturbing influence due to this absorptive action, a comparison was made between our sun and Capella, precisely as from a world travelling round a sun equidistant from these two orbs. The practical identity of the two spectra is the best proof yet afforded of the oneness of constitution (with infinite variety of distribution) throughout our galaxy.

Again, however, we find ourselves confronted by a difficulty akin to that already experienced in dealing with the question of the relative dimensions of the bluish-white stars. Only that, whereas in their case we could only recognize the extreme probability that many stars of that order differ largely in size from Sirius and Vega, we have in the case of stars of the second order not only probable inference of this sort, but proof positive that two at least among the stars of the second order differ exceedingly in size from our own sun.

For although we do not know the actual distance of either Capella or Aldebaran (I disregard utterly all the measurements of Capella's distance which are given in our books of astronomy, or rather I regard these as proving conclusively that Capella lies utterly beyond the range of measurement*), we do

It is singular that any faith should be placed by professional astronomers in measurements so manifestly untrustworthy as those which have been given in the case of stars like Capella, Polaris, and Arcturus. When we remember that the star 61 Cygni, which comes next in distance-probably-to Alpha Centauri, was first set by the careful measurements of Bessel some three times as far away, and then brought by the equally careful and refined measurements of Peters to only twice the distance of Alpha Centauri -a correction of twenty millions of miles, or more than three

know certainly that our sun placed at the distance of either of these stars would shine with very much less light than either of them. We know that, set beside Alpha Centauri, he would shine with about a third part of the light of that star. Now, Capella shines with almost exactly half the light of Alpha Centauri, and Aldebaran with about three sevenths. Thus our sun set at the distance of Alpha Centauri would shine with about two thirds the lustre of Capella, and about seven ninths the lustre of Aldebaran. But each of these stars is at least five times farther away than Alpha Centauri, or otherwise the persistent efforts made to determine the distance of each must long ere this have been rewarded with more success than astronomers have hitherto attained in this direction. Thus each would look at least twenty-five times as bright as it actually does if removed from its present distance to that of Alpha Centauri. Therefore Capella may fairly be assumed to give about forty times (roughly) as much light as our Isun at the same distance, and Aldebaran at least thirty times as much. But in the case of two stars whose spectra are very similar to the spectrum of our sun, we may fairly assume that on (the average) each square mile of surface gives out about the same quantity of light as (on the average) each square mile of the surface of the sun. It would follow on this assumption, which is not a very bold one, that the surface of Capella is about forty times as large as the surface of the sun, and the surface of Aldebaran about thirty times as large-say, for convenience of

years' light journey-we see how utterly unreliable must be estimates like those (due to Peters) which set Arcturus about eight times, Polaris about fourteen times, and Capella about twenty-one times as far away as Alpha Centauri. The error in the determination of the annual displacement of 61 Cygni was fully one sixth the annual displacement of the nearest star in the heavens-Alpha Centauri-the only star in my opinion whose distance has been fairly, though roughly, measured. what use, then, to give us the annual displacements of the three stars named, when even that assigned to Arcturus is only the eighth of that nearest star's-that is, the whole displacement which Peters claimed to have observed in the case of that star is only three fourths of the discrepancy between his result and Bessel's in the case of another star?

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calculation, thirty-six instead of forty in the former case, and twenty-five instead of thirty in the latter. Then it would follow that the diameter of Capella is six times as great, that of Aldebaran five times as great, as the diameter of our sun. Hence the volume of Capella would be (216) times more than 200 times, and the volume of Aldebaran (125 times) more than 100 times our sun's. Of course the calculation is very rough, and a great deal is assumed. Albeit nearly all the assumptions have been such as rather to diminish than to increase our estimate of the size of these seemingly giant suns of our own sun's order. It is certain Capella and Aldebaran are at least five times farther away than the sun-they may be very much farther away even than that. There is no room for doubt about the photometric measurements by which the relative brightness of the sun, Capella, and Aldebaran, at the same distance, has been determined. It may perhaps be doubtful whether the intrinsic brightness of the surface of our sun is so nearly the same as that of the surfaces of Capella and Aldebaran as to leave the estimate we have formed appreciably unaffected by whatever correction may be due to this cause; but be it noticed that we have already made a correction, since we have reduced the estimate of Capella's surface from forty to thirty-six times, and that of Aldebaran's from thirty to twenty-five times, that of the sun's surface.

Now, if Capella really has a diameter six times greater than the sun's, every stage in the cooling of Capella—that is, every stage of this star's life-would probably last about six times as long as the corresponding stage in the lifetime of our sun. For the volume being on this assumption 216 times as great, it would be in that degree that the quantity of heat in Capella, at any the same stage of its existence, would exceed the quantity of heat in the sun, whether we consider actual or potential heat arising from the contraction due to gravity. The heat would pass away from a surface only 36 times greater that is, not 216 times as fast (which would make the supply last just as long, but at one sixth that rate); therefore the supply would last about six times as long. In the

case of Aldebaran the supply for each stage of star-cooling would last about five times as long. These numbers are, of course, very far from exactness; but they suffice to show that the lifetime of one star of a given class or order may exceed very much in duration that of another star of the same kind.

We come next to the stars or suns of the third order, whose light, instead of being bluish-white like that of Sirius or Vega, or yellowish white like that of Capella or of our sun, is of an orangeyellow tint. The best representative of this class of sun is Arcturus, whose spectrum is somewhat like that of our own sun, but presents characteristic peculiarities, which the late Father Secchi regarded as corresponding to what we might expect in a sun like ours at a time when a great number of spots were present on its surface. If we adopt this opinion, we should regard Arcturus as a permanently spotted sun. Dr. Huggins merely remarks of Arcturus that it is a star of another order, which includes the solar type, but the star seems to be removed farther than the sun is in the order of change from the typical form as we meet it in Vega and Sirius. Here the typical lines are no longer present as a strong group. The line which has been regarded as belonging to both calcium and hydrogen is stronger, relatively, than in the solar spectrum. The spectrum of this star is crowded with fine lines, and in the visible part resembles the solar spectrum, but in the ultraviolet part, which hitherto alone photography has recorded, the lines are more intense than in the solar spectrum, and are differently grouped.

The inference from the observed peculiarities of the spectrum of the star Arcturus is that this is a sun further advanced in sun-life than our own.

Now, here again the question as to size is answered in a way suggesting that there is no present correlation between the size of a star and its age or state of development. So far as size is concerned, Arcturus, if it had begun its existence as a sun at the same time as our own sun, should have been much less advanced than he is. For Arcturus is half as bright again as Capella, yet lies at least as far away as that distance which we have assigned as the least

possible distance for Capella.

fore all that we have said about Capella and Aldebaran applies with increased force to Arcturus. His surface is probably at least sixty or seventy times as large as the sun's, even if we assume that the intrinsic brightness of the surface of this older star is equal to that of our sun's surface; but it is probably less, in which case to account for the great amount of light emitted by Arcturus we must assume the surface to be greater in proportion as its intrinsic brilliancy is less. Even with a surface only sixtyfour times as great as the sun's, Arcturus would have a diameter exceeding his eight times, and a volume exceeding his nearly five hundred times. Arcturus would therefore be a sun marvellously surpassing our own in volume, and presumably in mass also. We may infer, reasonably enough, that the family of worlds over which this mighty orb bears sway surpasses in like degree in dignity and importance that ruled over by our

own sun.

In passing, let it be noticed that all these considerations as to the great size of many, if not most, of the stars of the first order (the bluish-white suns), of some at any rate of the stars of the second order (the yellowish-white suns), and of one at least of the stars of the third order the (orange-yellow suns) are enormously, one may say overwhelmingly, strengthened, if we accept Dr. Siemens' view of the exhaustion of each sun's rays as they do their work in space. For in that case all the stars must emit very much more light than we have been assuming that they do. In fact, if that theory were true, the mere visibility of a star at the distance of Sirius would imply that the sun so seen across depths of space exceeding at least a million times the entire span of the earth's orbit, was an orb compared with which our sun is less than the tiniest meteor compared with the mighty mass of our earth. For our own sun, if he does anything like the work assigned him by Dr. Siemens, must exhaust all his light-giving as well as heat-giving energies long before he can extend the news of his existence as a sun even to the distance of the nearest star. Yet there in the star depths are ten thousand suns which do much more

But apart from all such questions as these, there is to me something most impressive in the thought of what, as thus interpreted by spectrum analysis, the heavens reveal to us. Of old it was known that one star differs from another in glory-meaning perhaps in brightness only. In color, too, it had been seen that the stars are unlike. But who would have ventured to surmise that in real size the suns that people space are so unlike? Who could have supposed that any instruments men could devise would enable us to judge which are the younger, which the older stars? Yet even the most cautious among our astronomical physicists, Dr. Huggins, the ablest of our spectroscopists, accepts this as the only reasonable solution of the observed differences in star spectra. 'We cannot resist," he says, "the feeling that in Arcturus (and the other stars of that class) we have to do with a star which has departed farther from the condition in which Vega now is than our sun has yet done. The question presents itself, Have we before us stars of permanently different orders, or have we to do with some of the life-changes through which all stars pass? Does the sun's position, somewhere before Arcturus in the order of change, indicate also his relative age? On these points we know nothing certainly." may give some play to the scientific use of the imagination," he added, addressing his audience at the Royal Institution, "I would ask you to imagine an inhabitant from some remote part of the universe, seeing for the first time an old man with white hair and wrinkled brow, to ask, ' Was he born thus?' the answer would be, No; in this child, this youth, this man of mature age, you see some of the life-changes through which the old man has passed.' So, giving play to the scientific imagination, there may have been a time when a photograph of the solar spectrum would have presented the typical lines only which are still in Vega. At a subsequent period these

If I

would have been narrower and more defined, and other lines would have made their appearance. And if we allow this scientific imagination to project these Royal Institution Friday evenings into the far future, the lecturer, clad it may be in the skin of a white bear, may have to describe how the spectrum of the then feeble sun has already passed into the class of spectra distinguishing those stars which shine with red light,'

It is evident that our great astronomical physicist recognizes no perpetual energy in suns, even in the mightiest. He sees them passing downward along the scale of stellar being, gradually parting with more and more of their storedup energies, not recruiting themselves with their own energies stored up after doing their full work! And in this, with all respect to an eminent practical physicist, he shows himself more philosophical as well as more practical. He recognizes that the same law which affects the small and the short-lived, the large and the long-lived must also submit to. Practically eternal though to our conceptions the duration of each stage of a sun's life may be, each such stage is neverthe

less finite, even though a sun exceed our own a million times in volume or in mass. The heavens present to us a scene of tremendous-nay, of inconceivable energy. Suns upon suns, to millions, to tens of millions, to ghundreds, even to thousands of millions, occupy space around us. In every stage of stellar life they are at work, illumining, heating, and guiding the systems which circle around them. Beyond the limits of the most powerful telescope lie thousands of millions more, repeating the same story of seemingly infinite energy, seemingly endless duration. Yet each one of those orbs, and therefore the sum of all, or the universe as we know it, tends to an end an end which may be, however, but the beginning of new forms of existence, while the gaseous nebulæ, now mere masses of vapor, may then have entered on sun-life, to carry on the same story, to teach the same lesson, that though each order of created things tends onward to an end, yet to such orders we can trace no visible limit-" End is there none to the universe of God; lo, also, there is no beginning."-Cornhill Magazine.