250 THE ORIGIN OF LIFE 



the body, as we have seen, appears to be changed. 

 "When the fluorescent body is not under the in- 

 fluence of the external source which can excite 

 luminosity in it, the radiation which it can emit in 

 such circumstances is not absorbed. 



The conception of a fictitious temperature or 

 temperature of luminescence has been suggested by 

 E. Wiedermann. But Guillaume (loc. cit.), in dis- 

 cussing the change of absorption, has pointed out 

 that such an extension of the notion of temperature 

 only leads to the heaping up of difl&culties instead 

 of arriving at something definite, so much so that it 

 would seem far simpler to evade the notion of 

 temperature altogether in the discussion, as it thus 

 appears to be far too general to be limited by con- 

 ceptions which ought to have a precise and definite 

 signification. 



A. Cotton has entered into a criticism of many 

 important points, in connection with the application 

 of Balfour Stewart and KirchofF's law with special 

 reference to the change of absorption in fluorescent 

 bodies when fluorescing, and concludes that the rule 

 connecting absorption and emission for the same 

 body applies in a great number of cases, particularly 

 of luminescent bodies, which are not governed by 

 the law properly so called. 



How the aspect of the question taken in this 

 chapter bears upon physical metabolism in its most 

 general form receives further confirmation in the 

 sequel. 



