24 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



TABLE 15. Cyclic variation of pressure difference. Cylindrical condensation chamber. 

 vjV=o.o6. Plug valve (i-inch bore). Goniometer 85 cm. from fog chamber. 



* Initial excess. 



TABLE 16. Effect of pressure difference. Cylindrical condensation chamber. In- 

 stantaneous valve. Eye at goniometer, 85 cm. from fog chamber. A r reduced to 

 normal atmospheric pressure. 



* Valve injured. 



In table 16 the occurrence of marked periodicity gives rise to two 

 distinct ^-curves, both of which soon approach an asymptote (figs. 22, 

 23). In the last group of observations the alternations are not regu- 

 lar (leakage of valve), but the extremes are indicated. Differing from 

 this, the results of table 17 in the outgoing series of apertures (8p, 

 increasing) are remarkably free from periodicity and show a tendency 

 to pass through a maximum. In the return series much fresh air was 

 drawn through the filter into the fog chamber and thence into the 



