Colours of Stars. 113 



E. A. Oli. 58m. 56s., D.N. 22° 55' (1860), which both Hind and 

 Pogson concur in representing as changing through blue, 

 yellow, and red ■ a third variable, R. A. 7h. 34m, 38s., D. N. 

 23° 46', is red and blue at different times ; a fourth, R. A. 7h. 

 40m. 54s., D. N. 24" 5', still more decidedly so. Should future 

 experience prove this phenomenon to be of frequent occur- 

 rence, we may be able to infer with some probability that a 

 change of colour in such cases may have its cause in variations 

 of brightness • but this will leave us as far as ever from an 

 unravelling of the mystery whence such changes can arise, so 

 long as the amount of light continues the same. Here we are 

 as much at fault as ever. 



The first step towards the solution of this latter problem, 

 if indeed it is not an irresolvable one, is obviously the more 

 distinct establishment of the fact whence it springs ; for 

 hitherto it may be said that such changes, except in the case of 

 variable stars, have been rather suspected than proved. The 

 evidence as to Sirius is strong ; but its light may also have 

 varied. Schmidt's idea that Arcturus has of late years been 

 losing its ruddiness does not seem confirmed by other observers. 

 The curious discrepancies between the colours of many double 

 stars as given by Smith and Sestini seem rather referable to 

 " personal chromatic equation," or in plain words, peculiarity 

 of vision on the part of the latter ; and a similar remark may 

 be made as to the colours given by some other observers. 

 There is, however, one pair now conveniently situated for 

 observation, to which attention has been recently directed, and 

 which ought to be carefully watched by those who are inte- 

 rested in these studies. This is the very beautiful double 

 star 95 Hercidis — No. 40 in our list (see Intellectual Observer, 

 Sept. 1862, p. 136) . During 1828, 1829, and 1 832, t (the astro- 

 nomical symbol for W. Struve, or Struve I.) always found the 

 p, or smaller of the two, reddish yellow, the /greenish yellow, 

 — remarking on the singularity of a difference so much greater 

 in colour than in brightness. Smyth made them cherry red 

 and greenish, 1833*8 ; Sestini, both gold yellow, 1844*5; 

 Smyth again reddish and pale green, 1851*3 ; his son, C. Piazzi 

 Smyth (Astronomer Royal for Scotland), both white, July 29, 

 or both yellow with tinge of bluish green, Aug. 4, 1856, at a 

 height of 8870 feet upon the peak of Teneriffe ; an estimate 

 confirmed by the eyes of some Spanish visitors : the admiral, 

 however, shortly afterwards found them cherry red and apple 

 green, just as they were nearly a century before. With this 

 description Dawes very nearly agreed, and four other obser- 

 vers, about the middle of 1857. Captain Higgens, in the 

 autumn of 1862, found the colours as given in the Bedford 

 Catalogue (apple green and cherry red) : 1863, April 23, he 



