Kknnkdv — Large Ions and Condensation-Nuclei from Flames. 73 



by producing a sufficiently great expansion and consequent cooling and 

 supersaturation. If this cloud be evaporated, by the heating due to sudden 

 compression, it disappears very rapidly, but a very small expansion again 

 produces a dense cloud. It is evident, therefore, that the drops of the 

 first cloud did not entirely evaporate, but remained in a stable state in the 

 form of very minute invisible drops, as suggested by Langevin's theory. 

 These invisible drops serve as nuclei of condensation for a very small 

 expansion, apparently similar to the nuclei produced by flames and occurring 

 in the atmosphere. 



Again, deBroglie' has shown that when pieces of moist pumice are heated, 

 nuclei are driven off from the surface, and when these nuclei are charged by 

 ionizing the air containing them, the mobility of the ions so formed is the 

 same as that of the ions from flames. He points out, too, that the formation 

 of the nuclei is due, not to the production of large quantities of water- vapour, 

 but to the driving off of the last surface layer of moisture. 



Before, however, being able to identify the nuclei obtained in these two 

 ways with those produced by flames, it would be necessary to see if the 

 manner of disappearance of the nuclei is the same as for those from flames. 



Su 



ry. 



1. The rate of decay of ionization in the case of large ions from flames is 

 according to the law 



dt = - ^2"' 

 where q is the charge of one sign per c.c. 



2. The rate of decay of nuclei, measured by Aitken's apparatus, is accord- 

 ing to the law 



(In 



and is the same whether the nuclei are charged or uncharged. 



3. The large ions do not carry the simple electronic charge but some 

 multiple of it. The charge varies under diflerent conditions. 



4. The equations in (1) and (2) do not hold when the time gets very great, 



' de Broglie : ' ' Aurf de Chimie et de Physique, " vol. 16, 1909. 



R.I. A. PROC, VOL, XXXIII, SECT. A. [Hj 



