244 THE ORIGIN OF LIFE 



photography, believes the effect is due, not to the 

 influence of the red rays in undoing what the 

 blue and violet rays have done, but to a further 

 chemical action. 



This is the case of bromide of silver, the effect 

 of the more refrangible rays is to convert the un- 

 developable bromide into sub-bromide, which is de- 

 velopable : and the action of the less refrangible 

 rays is to convert this again into oxybromide, 

 which is once more undevelopable. 



In the case of phosphorescence, the effect would 

 appear to be somewhat similar, although the obstacles 

 in the way of ascertaining this point are, on the 

 whole, more difl&cult and complicated. 



According to Stokes the effect of the less refran- 

 gible rays is not due to heating and therefore is 

 not a case of thermoluminescence, because these 

 rays alter the colour of the phosphorescence, ren- 

 dering its light less refrangible, and he maintained 

 that merely heating a phosphorescent substance does 

 not alter its spectrum. 



It would therefore appear that, as in the case 

 of photography, the destructive effect of the red 

 and infra-red rays is likewise chemical. 



In studying the absorption of a fluorescent body 

 when fluorescing, it is a matter of importance that the 

 effect of the less refrangible rays should not be over- 

 looked, as if the source is a flame, these may exercise 

 a considerable influence in diminishing the brightness 

 of the fluorescent light and thus apparently increasing 

 the absorption of the transmitted light. 



