﻿produced by Action of Light on Iodine Vapoi 



415 



The table gives the results obtained when the plug was 

 freshly set up. 



A. 



Wilson apparatus containing moist 

 dust-free air. 



B. 



Wilson apparatus containing moist 



dust-free air freshly saturated 



with iodine vapour. 



Press. Fall. 



Result 

 (Ordinary Wilson Effect ) 



Press. Fall. 



Result. 



15'4 em. 

 15-8 „ 

 173 „ 

 18-7 „ 

 197 „ 

 203 „ 



Nothing. 

 Few drops. 

 Thin shower. 

 Good shower. 

 Slightly tinted shower. 

 Coloured cloud. 



91 cm. 

 16-6 „ 

 17-8 „ 

 18-3 „ 



Nothing. 

 Thin shower. 

 Good shower. 



Coloured cloud. 



C. 



Same as B. one day later. 



Same as C, but iodine-laden air 



admitted, through freshly set 



up glass wool plug. 



Press. Fall. 



Result. 



Press. Fall. 



Result. 



15*7 cm. 

 167 „ 



17-7 „ 

 18-8 „ 



Few drops. 

 Few drops. 

 Fair shower. 

 Heavy shower. 



157 cm. 

 17-7 „ 



18-8 „ 



Few drops. 

 Good shower. 

 Dense coloured cloud. 



A comparison of C and D of the table shows that the glass- 

 wool is instrumental in producing a very large number of 

 nuclei, but it soon ceased to be effective, as after one day the 

 effect produced for an expansion of 18' 7 cm. was a very 

 heavy shower. Its power was temporarily restored when air 

 was drawn through the glass-wool after it had bubbled 

 through water. The power of the glass-wool to produce 

 nuclei was brought back and intensified in the following 

 manner. Wheu the glass-wool had ceased to produce nuclei 

 and was strongly discoloured with iodine throughout its 

 length, a small quantity of tap-water was sucked through it. 

 The amount of water used was just sufficient to saturate half 

 the wool. When air was drawn through, the wool became 

 wet throughout its entire length and the air which got 

 through contained an enormous number of nuclei. An 

 expansion of 18' 7 cm. produced a dense fog, but after one 



