CHAPTEE XV 



ON THE FORMATION OF AGGREGATES OF LARGE 

 MOLECULES 



The effect of infra-red rays — Stokes' law reversed, or calor- 

 escence — The function of a nucleus in phosphorescent 

 bodies — The effect of surface tension on aggregation — In- 

 fluence of films — Chemical reaction in high vacua. 



Effect of Infra-red Rays, Etc. 



The effect of infra-red rays in general is to destroy 

 or discharge phosphorescence, see p. 234. This 

 phenomenon was discovered by Becquerel,^ and 

 investigated by Stokes. ^ By its means, as we have 

 seen, Becquerel and others have investigated the 

 solar spectrum in the infra-red. 



The cause of this phenomenon is not very 

 clearly understood, but it seems not improbable 

 that the explanation lies in the fact that, under 

 the influence of heat, phosphorescent bodies give 

 out their energy much more intensely, and there- 

 fore in a much shorter time, as in the case of 

 thermoluminescence, so that when a phosphorescent 

 screen is exposed to the infra-red part of the 

 Gemotes Bendus, 1882. ^ Jjoq^ gj^. 



