276 THE ORIGIN OF LIFE 



then, is that during the period of fluorescence 

 separate molecules are formed which are gradually 

 or quickly broken up, according as the body is 

 phosphorescent or fluorescent. 



There is reason to think that these molecules 

 are very much larger than ordinary molecules, and 

 may be made to difi"use through narrow metal 

 tubing in the case of phosphorescent gases ; that 

 in the case of phosphorescent liquids they may be 

 fixed by the addition of glycerine or gelatin ; at 

 any rate, that by increasing the viscosity and 

 diminishing the frequency of collisions between 

 the molecules, their life-period and the duration 

 of the phosphorescence are greatly increased ; 

 whilst the optical experiments on solids and 

 liquids show distinctly that the existence of 

 altered periods is the cause of the change of 

 refrangibility. 



Phosphorescent gases also present a semi- 

 opacity, but as no measurements have ever been 

 made on this point, nor, indeed, is it easy to make 

 them, and as the possibility of optical illusion 

 in such matters is great, in judging contrasts 

 the matter may be said to be an open 

 question at present. But although the quantity 

 of matter in a vacuum tube is very small, 

 such opacity is nevertheless possible if the 

 number of luminous molecules is proportionally 

 very great. 



If the gas can radiate there is no reason why 

 it should not also, at the same time, absorb ; 



