I9I2] 



Secondary Rays Excited by the Alpha Rays. 



183 



measure of the magnitude of the secondary ray current from the carbon 

 excited by the « ray bombardment. 



In the following tables the results obtained with air filled carbon, 

 first at a temperature of 110° C, second at room temperature, third at a 

 temperature given by a mixture of solid carbonic acid gas and ether, 

 namely, -78° C, and lastly at liquid air temperature, -192° C are given. 

 After each experiment air was allowed to remain in the apparatus at 

 atmospheric pressure until the next experiment. Before beginning the 

 set of experiments a piece of carbon, the surface of which was freshly 

 cut and which had never before been exposed to « rays was placed in 

 the apparatus. For comparison all the readings were reduced to the 

 same date by the use of the standard equation, 



T-T ~^^ 



the half decay period of the polonium being taken as 140 days.* 



Table I. — Air in Apparatus. 

 Carbon electrode at temperature iio°C. Charge on carbon = -83 volts. 



Pressure of air 

 in vessel. 



Time from initial 

 reading taken 7 min. 

 after starting pump. 



Current through 

 magnet. 



Current to 

 Polonium. 



•See Physical and Chemical Constants by Kaye and Laby, page 107. 



