I9I2] 



Secondary Rays Excited by the Alpha Rays. 



187 



increases in the secondary radiation when the carbon was at the lower 

 temperatures are readily accounted for by the increase in the secondary 

 radiation from the gaseous air layer at the surface of the carbon which 

 increases in density as the temperature is lowered. 



In order to find out whether this same effect would occur when the 

 carbon was in other gases than air, experiments were also tried with 

 oxygen and hydrogen. A fresh piece of carbon was used for each gas. 

 The air which was occluded in the fresh piece of carbon on account of its 

 being in an atmosphere of air was got rid of by putting the carbon in the 

 apparatus and exhausting and leaving it for a long time. The apparatus 

 was then filled with the gas which was to be experimented upon and left 

 for some time in order that the carbon might take up the new gas as 

 much as possible. After this the carbon was cooled or heated to the de- 

 sired temperature, the gas was pumped from the apparatus and a series 

 of readings was taken, in the manner indicated above, of the rate of 

 charging of the polonium both with and without the magnetic field. 

 The same characteristic results were obtained with these gases at the 

 different temperatures as with the air. The readings taken with the 

 carbon at temperatures 1 15° C, 23° 0,-78° C and -192° C in an atmosphere 

 of oxygen are given in Tables VI, VII, VIII and IX below and the read- 

 ings taken with the carbon at temperatures 24° C and -192° C in an at- 

 mosphere of hydrogen are given in Tables X and XI. 



Table VI. — Oxygen in Apparatus, 

 Carbon electrode at temp. 115° C. Charge on carbon =-84 volts 



