SCIENCE. 



153 



in which this theory will not hold good. The small com- 

 panion of a Scorpii'xs undoubtedly really greenish. I saw 

 it on the 23rd of March, 1878, emerge from behind the 

 moon after an occultation while its bright companion was 

 still hidden, its color then was a pale pea-green. There 

 could have been no contrast here, except with the moon's 

 light ; admitting this exception, however, it seems to me 

 highly probable that while, in such wide double stars as it 

 Argus and y Cruets the orange or yellow star is really what 

 it seems, the star that appears green or blue is, as a rule, 

 really white. If this view is the correct one, it follows 

 that those observers who spend a great deal of time in 

 observing the tints of the companions to large stars, are, 

 to a great extent, wasting their time. 



y Argus. — This fine second-magnitude multiple-star 

 has a very curious spectrum. It belongs to a very small 

 class of stars, the only other one that 1 have heard of is 

 in the Northern constellation Cassiopeia. In the spect- 

 rum of >' Argus there are certainly three very bright lines, 

 one rather faint, and, I believe, many finer ones. I am 

 almost certain, too, that there are several fine dark lines 

 in the spectrum. The brightest line is, not improbably, 

 the F hydrogen line ; and the somewhat fainter one, the 

 C hydrogen line. Of the other two very distinct bright 

 lines, one is certainly not very far from the position of 

 the D sodium line ; but I cannot place the other. The 

 presence of bright lines in the spectrum renders it far 

 more difficult than usual to estimate the positions, but 

 the other line seems to be about one-third of the distance 

 trom D towards the iron line E. Not improbably then, 

 outside the photosphere of y Argus, there are ever-pres- 

 ent enormous masses of hydrogen and sodium, as well 

 as other substances in the gaseous condition, which have 

 been ejected from the more central parts of this sun ; 

 and, the temperature of these incandescent gases being 

 much higher than that of the solar photosphere below, 

 their spectrum is super-imposed on the ordinary spectrum 

 of the star proper. 



e A'gus. — This yellow star belongs to Secchi's second 

 class. In these stars the lines are very fine, and not 

 easily seen unless the weather is very favorable. To this 

 class our sun belongs. In the spectrum of e Argus the 

 F line can be seen pretty easily, but the D sodium line 

 seems to be the most distinct of this spectrum. 



ji Argus. — Magnitude, one and a-half. Color, white. 

 A first-class star. The hydrogen lines are pretty broad 

 and distinct. 



The blue Planetary Nebula near the Southern Cross. — 

 This object, No. 3365 in Sir John Herschel's Catalogue, 

 is in R. A. 11 his. 44m., and decl. 56 31' S. The color 

 of this strange object is a bright unmistakable blue. This 

 nebula, like other planetary nebulae that have been ex- 

 amined in the Northern Hemisphere, gives a spectrum of 

 one bright line. Possibly, in a larger instrument, more 

 lines -might be seen. It is, of couise, impossible with my 

 apparatus to determine the position of this line, as there 

 are no landmarks, so to speak, to guide one to a decision. 

 It is most probable, however, that it is one of the ^hy- 

 drogen or of the nitrogen lines, and that this planetary 

 nebula is a spherical mass of one or both these gases in 

 an incandescent state. 



a Cruets.— This superb pair of stats, by far the finest 

 in the sky, consists of two stars, bluish white in tint, and 

 very nearly equal in size, each being of the second mag- 

 nitude. There is a distant six-magnitude companion, of 

 a sea-green color, as well as three smaller comites of 

 magnitudes, 12^, 14, and 13 respectively, These latter 

 are well seen in the 8>£-inch reflector, but a small teles- 

 cope of course does not show them. I have made a very 

 great number of measures of the angle of position of this 

 star, and having weighted the observations wtth reference 

 to the state of the atmosphere, etc., at the time when the 

 measures were taken, I find the angle of position for the 

 year 1878.7 to be 118.5 . This by a very singular coin- 

 cidence, is exactly the same angle as that obtained by 



Powell in the year 1863. Herschel gives the angle for 

 1835.33 as 120.6°. I may say that, if I had rejected two 

 of my observations, which were made in rather bad 

 weather, and which exceeded the average of the rest by 

 1)4° and respectively, the angle obtained, taken in 

 connection with Powell's and Sir John Herschel's, would 

 have indicated, I believe, a very slow but really regular 

 angular motion, in a retrograde direction, since Herschel's 

 time, and would, with the measures of distance given be- 

 low, have convinced me, at all events, that a Crueis is a 

 binary star of very long period. The temptation in such 

 cases to " cook one's accounts " a little to omit taking into 

 account facts or numbers which do not square with one's 

 own views or wishes, is very strong, but the man who 

 cannot resist it had better give up science altogether and 

 take to something else in which it is not of vital import- 

 ance that he should tell the truth, the whole truth, and 

 nothing but the truth, with regard to his observations. The 

 distance between the two stars at the epoch, 1836.36, was 

 5.65"; in 1863, Powell made it 4.98 " ; and at the end of last 

 month, 1879.75, the distance, a mean of several measures, 

 was 4.79". a Crueis is a hydrogen star, but its spectrum is 

 very difficult to observe, except in the finest weather. 

 Even then the only lines that I can make out are the hydro- 

 gen lines, and they are by no means very easy to see. 



y Crueis. — It has been customary for astronomers to 

 catalogue this star — the " Head of the Cross " — as a 

 double star ; but the proper motion of the large orange- 

 colored star is rapidly carrying it away from its five-and- 

 half-magnitude blue companion. The spectrum of y 

 Crueis is perhaps the finest of all stellar spectra. The 

 groups of lines are so numerous and so well marked that 

 this spectrum may be observed under almost any atmos- 

 pheric conditions, if the star can be seen at all. y Crueis 

 is a typical star of Secchi's third class, which are all 

 orange color verging towards red. In their spectra there 

 are numerous, easily-seen, close groups of lines; but the 

 hydrogen lines are either very indistinct or altogether ab- 

 sent, a Ononis and a Herculis are good specimens of 

 the two principal subdivisions of this class. In the 

 spectrum of y Crueis there are at least eight bi oad groups 

 of lines, and some of these occupy the parts of the spect- 

 rum at which sodium, iron, magnesium, and calcium 

 lines are found in the solar spectrum. But, because they 

 are groups, it is much more difficult to say whether they 

 contain the lines belonging to those elements or not, than 

 it is in the case of a first or second-class spectrum. Still, 

 I anticipate that careful measurements will confirm my 

 opinion that iron and magnesium lines, especially the 

 latter, are present in the specirum of this star ; the sodi- 

 um line is probably there too, There is, also, a fine line 

 just at the part where the green merges into the blue of 

 the spectrum. This is possibly the F hydrogen line. 



There is one very significant feature in this spectrum, 

 so at least it seems to me. It is well known that when 

 the Sun is near the horizon, especially in damp weather, 

 his spectrum contains certain groups of lines which are 

 due to the aqueous vapor in our own atmosphere, and 

 that, as he reaches a greater altitude, these lines become 

 faint or disappear. Now, two at least of the groups in 

 the spectrum of y Cruets appear to occupy the same po- 

 sition as two of the principal groups of atmospheric lines. 

 Now this being verified, important conclusions might 

 follow. Secchi, on grounds of this sort, infers the exist- 

 ence of aqueous vapors in the neighborhood of sun- 

 spots. The Spectroscope knows nothing, so to speak, 

 about distance, except indeed where motion of approach 

 or recession is concerned. If these aqueous vapor-lines 

 are produced in spots on the sun, may they not be pro- 

 duced in much the same way in y Crueis, the principal 

 difference being that on the distant star the cause is more 

 general and the effect greater than it is on our own Sun. 

 If I am not mistaken, the existence of these spectrum 

 lines should enable us to read a certain portion of the 

 "life history " of a star. 



