I9I2] 



Secondary Rays Excited by the Alpha Rays. 



185 



Table IV. — Air in Apparatus. 

 Carbon electrode at temp. -192** C. Charge on Carbon =-84 volts. 



The results given in these tables are plotted in Figures (i), (2), (3) 

 and (4). The curve drawn on the first half of each figure shews the way 

 the rate of charging of the polonium decreased or increased with the time 

 until it became approximately constant. The curve drawn on the re- 

 maining half of the figure shews the way the rate of charging of the pol- 

 onium decreased to a constant value as the magnetic field was gradually 

 increased from zero upwards. The curves drawn on the first half of 

 Fig. (3) and of Fig. (4) shew a remarkable difference from the corres- 

 ponding curves in Figures (i) and (2). The curves of Figures (i) and 

 (2) drop gradually with the time and come to a constant value while 

 the curves of Figures (3) and (4) first decrease and then increase to an 

 approximately constant value. The only difference in the conditions 

 under which the experiments were made was a difference in the temper- 

 ature of the carbon. When the carbon was at room temperature or at 

 a temperature of iio°C, the rate of charging of the polonium decreased 

 with the time before becoming constant while when the carbon was at 

 -78° C or at -192° C the rate of charging decreased slightly and then in- 

 creased. The cause of this difference is readily seen when it is remem- 



