19 1 2] Secondary Rays Excited by the Alpha Rays. 167 



Table XI. 



Fatigued carbon electrode 



Air in Apparatus 



Charge on polonium = 84 volts 



Time from initial reading 



The results given in these two tables are graphically illustrated by 

 the curves shewn in Fig. 6. The upper curve refers to the results in 

 Table X while the lower curve refers to Table XI. A comparison of these 

 curves with the curves shewn in Fig. 4 makes it plain that there was a 

 much greater recovery of the carbon fatigue when it was left in vacuo 

 a very short time and then surrounded by air than when it was left 

 for a long time before being surrounded with air. 



This pointed to the probability that the gas occluded in the carbon 

 was the cause of the large decrease with the time in the secondary radi- 

 ation. For if the gas occluded in the carbon, as well as the carbon it- 

 self, produced secondary radiation, then, as the exhaustion proceeded 

 gas would ooze out of the carbon and the secondary radiation would de- 

 crease until all the gas which could leave had disappeared entirely from 

 the surface of the carbon. Also, the longer the carbon was left in vacuo 

 the more occluded gas would come out and the more difficult it would 

 be for the same amount of gas to enter the carbon again. Hence this 

 would cause the fatigue to be more permanent when the carbon was left 

 in a vacuum a long time than when left a short time. This conclusion, 

 it will be seen, has been amply confirmed by the experiment described 

 above. 



In order to decide definitely whether the release of the gas occluded 

 in the carbon had to do with the decrease in the secondary rays which has 

 been called a fatigue, a special piece of apparatus was designed and ex- 

 periments were performed which will be described in the following section. 



VI. Experiments Shewing the Influence of occluded gas on the 



Secondary Radiation. 



The essential parts of the apparatus (Fig. 7) were two parallel elec- 

 trodes B and C, in an air tight vessel, separated a distance of about 6 mm. 



