26 



NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



ceases to be effective. Finally the necessity of producing sudden 

 cooling simultaneously with extreme dilatation is a complication ; for 

 in view of the relative slowness of diffusion, it will eventually be im- 

 possible to keep the instantaneously dilated water vapor saturated 

 without arresting the growth of the fog particles. Above 8p = 40 cm. 

 the effect of sudden exhaustion might actually dry the air, seeing that 

 the density of vapor is instantly reduced more than one-half. It is 

 thus conceivable that even slight differences of supersaturation at the 

 outset may show themselves effectively at these high exhaustions. In 

 table 1 6, however, the nucleation N (reduced to normal pressure) 

 increases almost linearly with the pressure difference even at the high- 

 est exhaustions. The evaporation of the smaller fog particles is 

 probably an essential part of the whole phenomenon. 



FIGS. 20-25. Change of apertures (s) of coronas and number of efficient nuclei (n) 

 varying with different pressure differences (5 p) for the cases of superior 

 and inferior coronas. Dust-free air. 



Table 6, referred to in fig. 20, will be fouud as table 15, p. 24. 

 Table 7, referred to in fig. 22, will be found as table 16, p. 24. 

 Table 8, referred to in fig. 24, will be found as table 17, p. 25. - 



