468 Colours of Stars. 



Miller, in identifying them by patient and laborious measure- 

 ment. As Admiral Smyth has said, in his recent interest- 

 ing treatise on Sidereal Chromatics, " it is only on the finest 

 nights that the lines in the stellar spectra are steady enough 

 for measurement. Indeed, the difficulties of observation are 

 now so complex, that the complete scrutiny of the spectrum of 

 a single star may probably be the work of some years." 



Fortunately, however, for those interested in these delight- 

 ful studies, a subordinate, but very useful branch of the same 

 inquiry is open to the possessors of even moderate optical 

 means, who may do essential service by collecting data, to be 

 used as materials in its future prosecution. We are not now 

 referring to the phenomena of variable light, though these 

 well merit a close scrutiny, but to those of changes of colour. 

 This curious subject has been repeatedly brought before our 

 readers, and we may refer them especially to a paper at page 

 436 of Yol. v., as enumerating some of the cautions necessary 

 in the study of it.* But the additional interest which, as we 

 have said, it has received from recent discoveries, induces us 

 to revert to it; especially as the beautiful pair 95 Herculis 

 described in that paper is now coming into a convenient posi- 

 tion again. Since that time, some further remarks on these 

 stars have appeared in the Sidereal Chromatics of Admiral 

 Smyth, from the late deeply-regretted Captain Higgens, of 

 Bedford. Thirty-eight observations between May 21 and 

 August 8, 1 864, led him to the inference that the colours were 

 less vivid than in the previous September, and that A (the 

 green star) showed more loss of colour than B (the red), 

 " though neither to the extent of justifying their being 

 classed as anything but normal, though somewhat faintish.-" 

 Professor Piazzi Smyth, however, from an extended com- 

 parison of the observations of W. Struve, Admiral 

 Smyth, Sestini, Fletcher, Wrottesley, and himself, including 

 a series of years from 1828*71 to 1862*72, has come 

 to the more decided conclusion that A passes through 

 the successive tints of yellow, greyish, yellowish with blue 

 tinge, greenish, light green, light apple green, " astonishing 

 yellow green," and yellow again, in a period of probably twelve 

 years, while B in the same time passes from yellow, through 

 greyish, yellowish with reddish tinge, reddish, cherry red, 

 " egregious red," to yellow again. Should this deduction be 

 confirmed by testimony so extensive and accumulated as to 



*" Further consideration and experience have led to the conclusion that the 

 superiority of silvered specula in such inquiries was there somewhat overrated. 

 Since brilliant objects seen through the imperfectly transparent film acquire a 

 blue tint, the reflected rays from which this has been abstracted cannot be per- 

 fectly white, but must be very slightly tinged with the complementary orange. 

 The great advantage, however, of the absence of any outstanding fringe remains. 



