Spectra of some of the Fixed Stars. 519 



which the colour of the star was blue, was remarkable for the 

 faintness of the orange and yellow portions, compared with the 

 rest of the spectrum. The diminished brightness of these parts 

 appears to be produced by several groups of closely set fine lines, 

 while towards the more refrangible limit of the spectrum a few 

 strong lines separated by considerable intervals are seen. 



The observation of this star, on account of the faintness of 

 its spectrum, is so difficult and fatiguing to the eye, that we 

 have not been able to examine it more accurately or in greater 

 detail. 



We have by the same method of observation examined the 

 spectra of the components of ex. Herculis. The spectrum of A is 

 remarkable for the great strength of the groups of lines in the 

 green, blue, and violet ; fainter bands are visible in the yellow 

 and orange, also two strong bands in the red. This arrange- 

 ment of the bands of absorption agrees with the orange colour 

 which strongly predominates in the light of this star. 



B is bluish green in colour. The more refrangible portions of 

 its spectrum are very bright in consequence of the absence of any 

 strong bands. The yellow and the orange parts are crossed by 

 several groups of lines. — August 31, 1864.] 



The suggestive fact that stars of these more highly refrangible 

 colours are always observed in close contiguity with much brighter 

 stars, generally of an orange or red tint, would afford counte- 

 nance to the supposition that these exceptional colours are due 

 to some special physical conditions essentially connected with 

 the stellar systems of which they seem to form a part. 



Arago* remarks, " Among the sixty or eighty thousand iso- 

 lated stars, the positions of which are to be found in the cata- 

 logues of astronomers, there are none, I think, inscribed with 

 any other indications in regard to colour, than white, red, and 

 yellow. The physical conditions which determine the emission of 

 blue and green light appear, then, to exist only in multiple stars." 



These stars are without exception feeble in the intensity of 

 their light. The explanation is not admissible, that the faint 

 blue or violet light is due to a less intense incandescence of the 

 radiating surface, since it is precisely these more refrangible 

 rays which would be the first to fail as the temperature dimi- 

 nished, and upon this supposition the star should be dull red. 

 It is of course to be supposed that in the process of gradual 

 cooling some bodies which are less volatile than others would 

 cease to exist in the atmosphere at an earlier period than others, 

 or that they might enter into new combinations more readily 

 than others, and so modify the tint of the light emitted. 



The existence around these blue stars of an extended atmo- 



* Popular Astronomy, translated by Smith and Grant, vol. i. p. 295. 



2M2 



