12 NUCLEATION OF THE UNCONTAMINATED ATMOSPHERE. 



TABLE 8. Miscellaneous experiments, chiefly with screens. Long fog chamber, vol. 

 13,000 cm. 3 . Sp usually 17-18 cm. Coil with 4 cells. Observations at middle of 

 chamber," 29 cm. from end. 



* All lead screens earthed. 



t Campanulate on B side. 



Since the front and rear faces of the fog chamber can only contrib- 

 ute a distribution of nuclei corresponding to round coronas with the 

 given line of sight, while the lead cuts off most of the efficient radia- 

 tion from the top and bottom, round coronas should appear if the 

 nuclei come out of the walls. This was, in fact, the case in the first 

 and second experiments, where clear, round, strong coronas were ob- 

 served ; the third observation, however, leaves the question in doubt. 



