VIII.] RECENT OPINION. 75 



that the sets of carbon fiutings in the green represent molecular 

 groupings of that substance other than that (or those) which gives us the 

 lino spectrum, as gratuitous. I showed that the flutings, which Messrs. 

 Liveing and Dewar ascribed to a hydrocarbon, were present in the 

 spectrum of tetrachloride of carbon which gave no trace of hydrogen, 

 This experiment at first gave them no reason to modify their con- 

 clusion, but later they repeated and endorsed it, and finally admitted 

 that "the spectrum of the flame of hydrocarbons is not necessarily 

 connected with the presence of hydrogen,"* and so far as I can under- 

 stand their paper they seem to accept the idea of different molecular 

 groupings, which they began by characterising as " gratuitous." 



The Complexity of the Line Spectrum. 



With regard to the view that the line spectrum integrates for us 

 the vibrations of several sets of molecules, as I have already stated 

 this was not accepted. The number of objections is legion, and it is 

 impossible to refer* to all of them here. But, at the same time, the 

 opinion of some of those workers who have approached the subject 

 from both points of view was, I think, coming round to my side, and I 

 shall briefly refer to one or two instances. 



Attention has recently been drawn to the variations in the appear- 

 ance of the magnesium lines in the celestial bodies by Dr. Scheiner, of 

 the Potsdam Observatory, who is not apparently acquainted with my 

 work of 1879 ; he, however, accepts the idea that the variations furnish 

 us with a precise indication of stellar temperature,! and he is now 

 employing it in the work of the observatory .J 



* Proc. Roy. Soc., vol. xxxiv, p. 423. 



t Astronomical Spectroscope, Frost's Translation, p. viii. 



Dr. Scheiner points out that in the spectra of nearly all stars of Class Ta 

 (Group IV) the line at 4481 " generally appears as a broad line in some spectra 

 as strong as the hydrogen lines but its intensity decreases just in proportion as 

 the number of lines in the stellar spectrum increases, so that it is hardly of the 

 average intensity in the solar spectrum, or other spectra of type Ha, and the 

 author is unable to detect it in the spectrum of a Orionis." My prior work, dating 

 from 1879, being probably unknown to Dr. Scheiner, Messrs. Liveing and Dewar 

 are credited with the discovery of the peculiar behaviour of this line in laboratory 

 experiments, and it is added that " the dependence of the line upon the temperature 

 thus readily suggests that the temperature of the absorbing vapours upon the stars 

 of Class Ilia (Group II) is something like that of the electric arc, while that of 

 the stars of Class Ha is higher, and that of stars of Class la is at least as high as 

 the temperature of the high-tension spark from a Leyden jar. This view receives 

 striking confirmation in the precisely opposite behaviour of the magnesium line at 

 A 4352-18. First becoming visible in the spectra of type la (Group IV), which 

 have numerous lines, it is strong in the spectra of type Ha (Groups III and V), 

 and increases jo as to be one of the strongest lines as we pass towards type Ilia 



