256 THE ORIGIN OF LIFE 



purely molecular type, such as are contemplated in 

 the kinetic theory of gases, whilst the almost uni- 

 versal acceptance now of this law is the strongest 

 argument for the chemical theory of radiation for 

 which we plead. Whilst there may be a small 

 fraction of the emissive power due to newly roused- 

 up latent modes of oscillation, the correct meaning 

 of the law is that at any given temperature a 

 body absorbs the rays which it actually emits at 

 that particular temperature, but that the relative 

 values of its emissive and absorptive powers may 

 change with the temperature. This, indeed, is the 

 correct interpretation of the law, in its most 

 general form, in which it can at once embrace all 

 forms of luminosity. Thus once more the absorp- 

 tion in all cases remains constant when the tem- 

 perature rises, so long as dissociation or association 

 or any other molecular change does not set in, 

 but when this happens the absorption increases 

 rapidly, the rate of increase being proportional to 

 that of the molecules of the particular period. 



It is, therefore, or ought to be, possible from what 

 has been said to separate or rather to distinguish 

 between the energy due to one cause and that due to 

 the other ; in the case of a gas-burner, for instance, 

 we may suppose the radiation to be due partly to the 

 one cause and partly to the other ; the luminosity 

 resulting in the one case from previously existing 

 free periods which have merely been roused up 

 and in the other to entirely new free periods result- 

 ing from new molecular and atomic connections. 



