152 



SCIENCE. 



remarkable for the great breadth and distinctness of the 

 hydrogen lines. Indeed these stars are for convenience 

 often called " the hydrogen stars." All of them are 

 white or bluish-white. In Achernar the hydrogen lines 

 are not nearly so strongly marked as they are in some 

 others of the class. Indeed the star by no means nearly 

 approaches the type, and is probably to be considered as 

 holding a position between such stars as Sirius and 

 stars of the second class, like Procyon, though much 

 nearer to the former than to the latter. 



- Eridani — This beautiful little double-star is just 

 visible with the naked eye in fine weather. It is about 

 one degree from Achernar, north following. The two 

 components are of the same orange color, and of very 

 nearly equal magnitudes 7 and 7. When Sir John Her- 

 schel measured this star (anno 1835.0), he found the 

 angle of position with the meridian to be 122. 3 . Powell, 

 in 1863, found the angle to be 73.9 . Last week (say 

 anno 1879.75; the angle was 58. 8°. The distances for 

 the same dates are 3.65 ', 4.88", and 5.3". This interest- 

 ing double is, therefore, very probably a binary star of 

 comparatively short period. 



Eridani. — R. A. 2hrs. 53Tiin. 19.9 sees. Decl. 40 

 49' — 35' 17" S. In the Melbourne Catalogue, the magni- 

 tudes 5.2 and 6.2 are assigned to the components of this 

 fine double-star. There is most certainly serious error 

 here. The star is plainly, taken as a whole, a large 

 fourth, or a small third-magnitude star. Probably mag- 

 nitude 3.9 for the larger star, and 5.9 for the smaller 

 one, would not be far trom the trjth. The color of the 

 larger star is yellowish-white, with a faint green tinge ; 

 the smaller is a light shade of indigo blue. Sir John 

 Herschel's angle of position and distance, in the year 

 1835.75, were 81. 5 and 8.68 '. The angle at the epoch 

 1879.75 is 85 4 . I have not been able to get a thor- 

 oughly satisfactory distance, but it is now somewhat 

 over 10". Time and accumulated observations will, 

 of course, show either that the change in the angle and 

 the distance of the two stars of this double is owing to 

 the proper motion ot one, or both, of the components, 

 or that Eridani is a binary system. The latter alter- 

 native appears to me to be by far the more probable. 



232 Reticuli of the Melbourne Catalogue is a fine star 

 of a magnificent scarlet color. It is ot magnitjde 6%. 

 There is a distant companion white star of the eleventh 

 magnitude. The R. A. of 232 Reticuli, is 4hrs. 35mm. 

 15.15 sec, and the declination 62° 20' 0.63" S. The spec- 

 trum of this star is very remarkable. It belongs to 

 Secchi's fourth class. The typical star of this division 

 is small — invisible, in fact, to the naked eye; it is varia- 

 ble both in light and color; it is a very distinct red, ruby, 

 crimson, or scarlet ; and its spectrum consists of bauds 

 of light, sometimes containing faint bright lines wittydark 

 spaces between the bright bands. 232 Reticuli, though 

 so small, gives a fine spectrum when the spectroscope is 

 used with the reflector, because the light is not spread out 

 over the whole length of the spectrum, but is concentrated 

 in certain parts of it. Thus the red part of the spectrum 

 is very bright, buf the place of the orange is occupied by 

 a very thick black " bar." The yellow, again, is pretty 

 bright, and so is part of the green, but towards the vio- 

 let end of the spectrum the light is very faint, and the 

 colors are quite cut out for large spaces by intervals of 

 almost complete darkness. I tailed to notice here what 

 is said to be characteristic of this class of stars — a grad- 

 ual diminishing blackness of the bars in the direction of 

 the violet end of the spectrum ; nor could 1 distinguish 

 any bright lines in any part of the spectrum. The study 

 and observation of stars of this class is none the less in- 

 teresting to us, because in the present state of our knowl- 

 edge their spectra are unintelligible, for it is generally felt 

 by those who have been in the habit of observing them, 

 that there is a grea' secret of nature waiting to be discov- 

 ered in connection with them. Their being for the most 

 part so very variable both in light and color, the strongly- 



pronounced red color of all of them, and their strange and 

 beautiful spectra, all point to the conclusion, that the man 

 who succeeds in " reading the riddle" of the nature and 

 constitution of the red variable stars, will have made a 

 very important contribution to our knowledge of the pro- 

 cess by which suns and systems are evolved out of the 

 primordial nebula, or whatever the substance may be, 

 from which such systems are formed, and to which, per- 

 chance, when their mission is fulfilled, they again return. 

 In the meantime these red stars seem to set anything, 

 even like rational conjecture, at defiance. 



a Argus {Canopus.) — This great star, the only rival of 

 Sirius, is a hydrogen, or first-class star. In its spectrum, 

 the F and C hydrogen lines, and that near G, are broad 

 and distinct, though less so than in the spectrum of Sirius. 

 There area great many very fine lines in the spectrum of 

 Canopus, but these are not generally visible. It is only 

 when the atmosphere is very steady and clear that they 

 can be plainly seen. A fine line, however, or rather a 

 small group of lines, in all probability that called b, and 

 due to the presence of magnesium in the photosphere of 

 the star, can generally be made out in moderately fine 

 weather. 



~ Argus. — This is a wide telescopic double-star, form- 

 ing, with a very distant companion of about the fifth 

 magnitude, another double, easily visible as such with the 

 naked eye. The color of the large third-magnitude star 

 is a strongly-marked orange ; the other two are indigo- 

 blue. It is a well-known fact, that a large yellow or 

 orange-colored star has frequently a distant companion of 

 a blue or green color. It is generally supposed that this 

 is a sort of prima facie evidence that the two stars are 

 in some way physically connected. It seems to me that 

 the existence of these complementary colors in appar- 

 ently neighboring stars in no way indicates per se that 

 they are physically connected. I am inclined to think 

 that, given a large bright orange star, with a smaller star 

 naturally very white and nearly in the line of sight, this 

 latter must appear greenish or bluish. The light of the 

 bright orange star fatigues the eye as far as its power of 

 receiving the impressions which we call red, orange, and 

 yellow is concerned. Now, when the eye is directed to 

 the smaller star, the less refrangible portion of the light 

 coming from this fainter object is unable to act with its 

 normal effect, while the green, the blue, and the violet 

 rays, by which the eye has not been fatigued at all, pro- 

 duce their ordinary impression. 



It is commonly said that this explanation may be true 

 enough in a few cases ; but that, if the bright star is hid- 

 den behind a thick bar placed across the field of the teles- 

 cope, and the smaller star still appears blue or green, it 

 is a proof that the light of the smaller star is really blue 

 or green, and that its color cannot be the effect of mere 

 contrast. This is, I feel sure, fallacious. I have often 

 tried the experiment and at first it was very disappointing, 

 for one would naturally expect that a star, which appeared 

 colored in the presence of a very blight companion, would 

 show its color still more distinctly when that companion 

 was hidden from view. But this never happened, the 

 more completely the light of the larger star was removed, 

 the less was color in the companion observable. I feel 

 persuaded that, if the light of the larger star could be 

 entirely cut oft", which, by-the-by, is impossible, the blue 

 color would entirely disappear. It is worth noting, too, 

 that the longer one looks at a blue star, its companion 

 being hidden, the more completely does the blue color 

 disappear ; that is, 1 take it, as the eye recovers its 

 normal condition, after being exposed to a severe strain 

 from the light of the large star, so does its sensitiveness 

 to the feeble red, orange, and yellow rays of the small 

 star return, and it sees the small star to be white or nearly 

 so. On the other hand, I have often noticed that the 

 longer one looks at a double star of this kind, both stars 

 being in the field, the more pronounced does the blue be- 

 come. There is only one instance, that I am aware of, 



