76 VAPOR NUCLEI AND IONS. 



In no form of the fog chamber have the initial yellows and browns of 

 the steam jet been approached. Coronas reach but to the equivalent of 

 the opaque zone. Below the large green-blue-purple corona, the com- 

 puted value of the water precipitated per cubic centimeter may now be 

 considered trustworthy. In Chapter I this was true below the middle 

 green-blue-purple corona. The drop of pressure (p - p 2 ) actually efficient 

 in producing low temperatures in the fog chamber must be computed 

 from the initial pressure of the isolated fog and vacuum chambers before 

 exhaustion, and their final pressure when in communication after exhaus- 

 tion, all data taken at the same temperature. 



As the intensity of radiation increases, coarser nuclei become much 

 more frequent, but beyond this the coronal method is not adapted to test 

 the lower limit in question. At the upper limit, however, most of the 

 observations show that the finer nuclei become more abundant when the 

 medium is more powerfully energized; or that new gradations of nuclei 

 of continually increasing smallness and continually increasing number 

 are produced by radiation increasing in strength indefinitely. These are 

 important questions, however, upon which I hope in the near future to 

 make some final tests. 



