FORMATION OF AGGREGATES 269 



produce nuclei in the substances through which 

 they pass, and vice versd. Thus the cathode rays, 

 the radiation from radio-active substances, Becquerel 

 rays, Eontgen rays and ultra-violet rays all pro- 

 duce nuclei by their passage through gases and 

 give rise in suitable circumstances to phosphores- 

 cence. 



Now cathode rays have precisely the same 

 effect as infra-red rays.^ They increase the bright- 

 ness, and thereby diminish the duration of the 

 phosphorescence. 



The infra-red rays alter the molecular structure 

 of a body as in the case of chlorophyll, and it is 

 to their power of effecting this change that their 

 destructive influence on phosphorescence should be 

 attributed. The effect of these rays like that of 

 negative ions is to facilitate the growth, as it were, 

 of the molecular groups and thus cause them 

 to be subsequently broken up. 



The question is how this is accomplished, and 

 whether it is a necessary consequence of the 

 phenomena which have previously been considered. 



By far the most conclusive and also remarkable 

 results I have obtained in the endeavour to 

 establish this point have been with radio-active 

 bodies. Before entering into the subject, however, 

 it would be of interest to consider the effect of 

 surface-tension in producing aggregation, 



1 Philosophical Magazine, March, 1901. 



