516 Mr. W. Huggins and Dr. W. A. Miller on the 



unbroken spectrum containing rays of light of every refrangibility 

 within the portion of the spectrum which is visible. As this 

 condition of the light is connected with the state of solidity or 

 liquidity, and not with the chemical nature of the body, it is 

 highly probable that the light when first emitted from the pho- 

 tosphere, or light-giving surface of the sun and of the stars, 

 would be in all cases identical. 



The source of the difference of colour, therefore, is to be sought 

 in the difference of the constituents of the investing atmospheres*. 

 The atmosphere of each star must vary in nature as the consti- 

 tuents of the star vary ; and observation has shown that the stars 

 do differ from the sun and from each other in respect of the ele- 

 ments of which they consist. The light of each star therefore 

 will be diminished by the loss of those rays which correspond in 

 refrangibility to the bright lines which the constituents of each 

 atmosphere would, in the incandescent state, be capable of emit- 

 ting. In proportion as these dark lines preponderate in parti- 

 cular parts of the spectrum, so will the colours in which they 

 occur be weaker ; and consequently the colours of other refrangi- 

 bilities will predominate. 



Of this the spectrum of « Orionis affords a good example. 

 The green and blue parts of the spectrum are comparatively dark, 

 from the numerous and close groups of dark lines. In the 

 orange they are less strong. Hence it might be anticipated that 

 the light of the star would be characterized by "an orange 

 tinge," as noted by Smyth. j3 Pegasi is described by Smyth as 

 "deep yellow ;" and the appearance exhibited by its spectrum, 

 which closely resembles that of a Orionis, though much fainter, 

 supports the same view. 



Aldebaran is recorded by Smyth as of a "pale rose tint." In 

 the spectrum of this star, with the exception of the hydrogen 

 line C, there are but few strong lines in the red, whilst the orange 

 portion is considerably subdued by dark lines, which are less 

 numerous in the green and blue. Sirius, on the contrary, is 

 "brilliant white" (Smyth); and the continuous brightness of 

 the spectrum, with the exception of five strong lines, is, as com- 

 pared with Aldebaran and a Orionis, unaffected by the dark lines 

 which cross it. The spectrum is indeed crowded with numerous 

 fine lines ; but the intensity of these lines is extremely feeble as 



* The presence in the atmospheres of Aldebaran and a. Orionis of metals, 

 such as iron, which require an exceedingly high temperature to convert 

 them into vapour, renders untenable the supposition, which might other- 

 wise have been entertained, that the orange and red tints of the light of 

 these stars might be due to an inferior degree of incandescence of the pho- 

 tosphere as compared with the temperature of the stars the light of which 

 is white. 



