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Mr. V. E. Pound on the Secondary Rays 



in the secondary radiation. For if the gas occluded in the 

 carbon, as well as the carbon itself, produced secondary 

 radiation, then as the exhaustion proceeded gas would ooze 

 out of the carbon, and the secondary radiation would decrease, 

 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 experiments were 

 performed which will be described in the following section. 



6. Experiments showing the influence of occluded gas 

 on the Secondary Radiation. 



Fi*. 7. 



mercury 



to Pu 



to electrometer 



The essential parts of the apparatus (fig. 7) were two 

 parallel electrodes, B and C, in an air-tight vessel, separated 



