154 



SCIENCE. 



This history might be something like this : Let us 

 suppose that, countless ages ago, y Cruets was a white 

 star, like Sirius. It was then far more intensely heated 

 than it is now. All the elements of which it is composed 

 were there uncombined. Hydrogen, the gas of the smal- 

 lest density, ordinarily extended furthest from the centre 

 of the globe, and this hydrogen, its outer envelope, was 

 nearly always near the confines of the normally cold re- 

 gions of space. Thus it would have a somewhat lower 

 temperature than the rest of the sphere, and hence well- 

 marked hydrogen lines would appear in its spectrum at 

 this period. Comparatively small quantities of other 

 elements, however, would frequently be erupted from the 

 interior portions of the sphere, and would reach what 

 may be called the surface. The presence of these would 

 cause the appearance of numerous fine lines in the spect- 

 rum. As eternity went on, if I may use the expression, the 

 star radiated a large portion of its heat into space, the 

 elements began to combine chemically to a certain extent, 

 large volumes of hydrogen ceased to exist as such, 

 through combining with oxygen and forming water-vapor, 

 ol which the outer star envelope would now consist. In 

 place of the hydrogen lines of the white star therefore, 

 we now find the aqueous vapor spectrum — "the atmos- 

 pheric lines " as they are called. The result of the com- 

 bination of the oxygen and the hydrogen would, of course, 

 be a great decrease in the volume of the outer envelope. 

 This would probably bring the lines of sodium, magne- 

 sium, iron, and calcium into greater prominence, and we 

 should have the spectrum which y Cruets now presents. 

 Between the two conditions described there would be an 

 intermediate one. Through such a stage our Sun may 

 possibly be passing now. It may be, in short, that our 

 Sun was once a Sirius, is now a Procyon, and will by- 

 and-by be a y Crueis. This is a mere hypothesis, of 

 course, though it appears to account pretty fairly for some 

 of the phenomena of the stars. In fact, I give it merely 

 as a suggestion, feeling that it is as little entitled to carry 

 weight with it as an hypothesis, founded on observed 

 phenomena and not at variance with known facts, can be. 



y Centauri. — R. A. I2hrs. 34mm. 2i.46secs. Decl. 

 58 14' 43.24". — This is a very fine close pair of stars, 

 each component being of the fourth magnitude, and 

 purely white. In his " Results of Observations at the 

 Cape of Good Hope," Sir John Herschel gives the po- 

 sition-angle as 354.3 , the epoch being 1835.89, while the 

 distance is stated to be To this estimate of distance 



Herschel attaches no value. For the year 1878.93 the 

 angle of position is 6.6°, or 186. 6°, and the distance 2.2", 



\i Crueis. — This fine white star has a distinct deep 

 blood-red companion, the position angle being 260^° 

 and the distance (i879)-2o8\ It seems to me that the 

 small star varies in size from about the eleventh to nearly 

 the eighth magnitude. It would be well if the small star 

 could be watched, so that its period and the amount of 

 its variation in brightness might be accurately ascertained. 



a Centauri. — R. A. I4hrs. 3o:uin. 47.o7secs. Decl. 

 6o° 17' 53-93'- Magnitudes, 1-2. The following table 

 will give the position-angles, and the distances of the 

 components ot this star, for selected epochs during the 

 torty-five years which have elapsed since 1834, when it 

 was first accurately measured by the greatest of all 

 astronomers, Sir J. Herschel: 



OlSSERVBK. 



Date. 



Sir J. Herschel 1834.7 



Sir I. Herschel 1834.8 



Sir J. Her»chel 1835.7 



Sir J. Herschel 1837.3 



Sir J. Herschel 1837.4 



Pcwell (from Webb) . 1864 



Computed from mean places in F. M. G. C. 1870.0 



My recent measures '878.7 



My recent measures J 1879.75 



Position. 



218 30' 

 219° 30' 



/20° 42' 



5° 7' 

 17 19' 

 156° 19' 

 183 8' 



Distance. 



16.12" 

 7.85" 

 i°-7.V 



4-S5" 



With this table as a basis, it will be found that the 

 major axis of the apparent orbit lies nearly in the direc- 

 tion 26)4 Q to 2o6)4°, and that the greatest elongation 

 north is about il", while the greatest elongation south is 

 27". Mr. Powell makes the period between 76 and 77 

 years. If the places of the two stars given by Lacaille 

 (1750) were correct, however, the period would be just 

 about 85 years, for the angle of position computed from 

 his places of the stars is 21 8° 44', which a reference to 

 the above table will show, was very nearly Sir John Her- 

 schell's micrometrically-determined position 84.79 years 

 afterward. As, however, the distance obtained by Sir 

 John Herschel disagrees very materially with that de- 

 duced from Lacaille's places of the stars, but little weight 

 is attached to the observation of 1750. 



This magnificent double star is the finest object of the 

 kind in the heavens. Besides being a binary star of very 

 short period, every one knows that a Centauri is our next 

 neighbor among the stars, and that it was the first to give 

 up the secret of its parallax under direct Transit Circle 

 observations. The color of this star is straw-yellow, or 

 sometimes golden-yellow, according to the slate of the 

 atmosphere. When there is haze, of course the smaller 

 star is somewhat more affected by it than the larger. 

 This tends to give it a slight brownish tint when the sky 

 is not clear, a Centauri is a star ot the second class. Its 

 spectrum is very like that of the sun. Even the principal 

 dark lines are fine, and they apparently occupy the same 

 relative positions as do the well-known lettered lines in 

 the solar spectrum. 



The resemblance between the two spectra is so striking 

 that any one seeing the two spectra for the first time could 

 hardly fail to notice the similarity. More dispersive 

 power, however, and the means of accurately determining 

 the position of the lines of a Centauri might show that 

 they are not the same as the solar lines. Such a result 

 would surprise me much. The D sodium line, the E 

 iron line, the b magnesium line, and the F hydrogen line 

 of the Sun have, almost certainly, their counterparts in 

 the spectrum of a Centauri. There can be little doubt 

 that the physical constitution of this great star is, in most 

 respects, the same as that of the Sun. It is probable, 

 however, that a Centauri is less developed than the Sun ; 

 for, as Mr. Proctor has pointed out, its light is brighter 

 than its mass would lead us to expect it to be, judging 

 from the light of our Sun, as compared with his mass. 

 While the mass of the star is to the mass of the Sun as 

 2 : 1, the light of the star is to the light of the Sun as 3:1. 

 Now, if it is true, as physicists have good grounds for 

 believing, that the Sun is, and has been, very slowly but 

 surely losing his heat, just as our earth has most certainly 

 lost an enormous amount of hers, there must have been 

 a time when the Sun and his system were less developed, 

 but far hotter and brighter than they are now — when they 

 formed, probably, as I said when speaking of y Crueis, a 

 white star — that is to say, there was, quite possibly, a time 

 when the light from our Sun bore the same relation to his 

 mass as the light from a Centauri bears to its mass. We 

 may also believe that matters are less advanced in the 

 planets (if there are any) of this neighboring system than 

 they are with us. 



a Trianguli. — The spectrum of this star is not very 

 striking, but it is rather curious, as showing, apparently 

 that tl}e star is in a condition intermediate between that 

 of a Centauri and that of 7 Crueis. The lines of the 

 second class, and also the groups, are very faint, but 

 they are there. It will be seen that this fact has some 

 bearing on the suggestion I made respecting the gradual 

 development of stars while speaking of y Crueis. Here 

 it looks as if we had, so to speak, caught a star in the 

 act of changing from the second to the third class. What 

 I have seen of the spectra of the stars, so far, leads me 

 to think it probable that if every star, down to the sixth 

 magnitude, could be examined even with my instrument, 

 and mapped roughly, it would be found that the spectra 



