■470 Dr. Gr. Owen and Mr. H. Pealing on Condensation 



Experiments on the Growth of the Nuclei in the Light 

 and their Decay in the Dark. 



Table III. shows how the density of the cloud depends 

 upon the duration of the illumination. 



Table III. 



Duration of illumination. 



Result of the Expansion. 

 Pressure- fall =18"5 cms. 







About \ second. 



1 second. 



2 seconds. 



Good shower (=Wilson effect). 



Dense shower. 



Cloud. 



Cloud (same as above). 



Thus the nuclei grow under the influence of the light and 

 attain a maximum size in less than one second. 



Table IV. shows that the nuclei disappear very quickly 

 after their formation. The bulb was illuminated in each 

 case for the same period and then kept in the dark for 

 various intervals before expansion. 



Table IV. 



Period for which the Nuclei 



weve kept in the dark 



before expansion. 



Eesult of the Expansion. 

 (Pressure-full = IS'5 cms.) 



3 minutes. 



1 minute. 



.30 seconds. 



10 seconds. 







Good shower. } ~ 



[ fcame as 



Good shower, j Wilsou effects - 



Very dense shower. 



Cloud. 



Cloud. 



Thus nearly all the nuclei live for ten seconds, but all 

 have disappeared in one minute. This may be due to the 

 nuclei diffusing to the walls of the vessel, or to their actual 

 break up. If the latter is the correct explanation, evidently 

 the substance forming the nuclei is very unstable. 



