64 CONDENSATION OF VAPOR AS INDUCED BY NUCLEI AND IONS. 



Using the method of successive equal exhaustions for standardization 

 and a single spot of light as the source of diffractions, the coronas of 

 cloudy condensation were overhauled in the above chapter with special 

 reference to the use of an efficient plug-cock fog chamber. The ratio 

 of the section of the exhaust to the section of the fog chamber was about 

 one to six. The useful equations are summarized. The chief difficulty 

 encountered is the extreme sensitiveness of the coronas produced to 

 any lack of homogeneity in the nucleation of the air. 



Given types of coronas, like the green pattern, for instance, seem to 

 recur for the ratios of 4, 3, 2, i in the diameters of the fog particles. 

 The results as a whole show fairly good agreement with the earlier 

 results below the middle green-blue-purple corona, but above this the 

 divergence of values has not been much improved. In the definite 

 region specified, corrections need be made for subsidence only. The 

 fiducial value of the nucleations of normal coronas has been accepted as 

 heretofore. 



It does not seem probable that fog particles as small as o.oooi cm. 

 are ever measurably encountered in the fog chamber. This is larger 

 than Wilson's estimate made in terms of the wave-length of light; but 

 detailed comparisons are unsatisfactory, because of the difficulty of 

 identifying his colors as to their place in the observed cycles of colors. 



