AIR ENERGIZED BY RADIUM. 



37 



after the radium tube was introduced, is not easily interpreted, but the 

 action of radium is obviously weaker. In most cases there is marked 

 periodicity, and part 4 of the table proves that the nucleation is over 

 9 times greater for the superior than for the inferior coronas. After 

 an exposure of 18 hours, the uucleation of the superior coronas is 

 fully 20 times greater. 



In table 19 the nucleations of the superior and the inferior coronas 

 are particularly striking atS/> = 25.8, and the ratio is actually n 

 (fig. 30). Thereafter periodicity vanishes with falling nucleations and 

 the return w-curve is along an average path. If periods were due to 

 the gradual growth of nuclei, supposing that the time between two 

 successive exhaustions is needed to bring the nuclei within the scope 

 of the given pressure difference, there would be no reason for the rela- 

 tively unbroken return. Oscillation appears to be wiped out by high 

 pressure differences as well as in a march of decreasing values. 



TABLE 20. Radium at different distances from line of sight. 



exhaustions usually 2 minutes. 



Interval between 



* Periods?. t After 40 minutes' exposure. 



34. Fog limits raised by weaker ionization. The view taken in this 

 paper that the size of the nucleus increases with the intensity of the 

 ionization may be tested by removing the radium from the apparatus 

 and allowing it to act from increasing distances (figs. 33, 34). This is 

 the case in table 20, where observations to determine the fog limit are 



