112 Colours of Stars. 



solar light, yet it would be difficult to conceive any light slow 

 enough to admit of the possibility of the explanation. And 

 besides this,, it is inconsistent with experience ; since many of 

 the colours of binary pairs, revolving rapidly, and favourably 

 situated for such an observation, continue unchanged. It is 

 possible, indeed, as the admiral has shown, that a newly-created 

 or recently-extinguished star might show a succession of 

 colours, from the different times in which the different undula- 

 tions would probably reach us ; all merging at last into white, 

 or disappearing in darkness. Or if a star were conceived only 

 to exist for a very short time, we might have all the hues of 

 the spectrum in succession, without any white combination, 

 though possibly with intervals of invisibility corresponding 

 with the non-luminous bands already referred to, which tra- 

 verse in great numbers the breadth of the spectrum. But in 

 the case of a star shining from time immemorial, its colour, so 

 far as it depends upon any such cause, would be nearly white. 

 The same eminent astronomer has pointed out that on this 

 supposition of unequal velocity in the several colours — which it 

 will be remembered is merely a hypothesis, though a very pro- 

 bable one — a change of brightness alone in a star might occa- 

 sion a change of colour, for " the strong blue of a bright epoch 

 arriving with the faint red of a dull period, will make blue 

 appear to us as the predominating colour — will cause indeed the 

 star's light to appear decidedly blue at one time, and, mutatis 

 mutandis, red at another, although all the while the star's 

 colour may not really have altered at all ; but may have been 

 really, and would have appeared to observers close by, as white 

 as ever, varying only in quantity and not in quality." The 

 celebrated " variable " Algol was examined by Arago in order 

 to test this idea, but without success ; the admiral, however, 

 remarks that other stars might be picked out where the natural 

 circumstances are more promising, and that more accurate 

 modes of comparison than that adopted by Arago might be 

 employed.* Mr. Hind is of opinion that he has detected such 

 alterations, and that several variable stars are blue in increas- 

 ing, become yellow after their maximum, and are red in their 

 decrease ; and I am indebted to the kindness of Mr. Knott, to 

 whom our readers are thus often laid under much obligation, 

 for the following instances : 1848, Sept. 3, a star, R. A. 5h. 

 34-8m., D. N. 21° 6' (1800), was entered by Hind as "very 

 red ;" it was closely watched for variable light without change 

 till 1850, Nov. 14, when it was found " decidedly bluish, the 

 red tinge having vanished entirely." A second is a " variable," 



* Students who are desirous of examining this subject more in detail, and as 

 developed by the hand of a master, may receive full satisfaction in the sEdes 

 Hartwelliance and Speculum llartiueUianum. 



