﻿excited by the Alalia Rays from Polonium. 



827 



together. Now the decrease in the ionization current through 

 the air space with the time would be the same in all three 

 experiments, because this decrease is dependent on the air 

 pressure and, as the pump was kept going regularly, the 

 air pressure, in all three cases, would be the same at equal 

 intervals of time after the pump was started. Hence, since 

 the upper curve shows a much greater drop than the two 



Fie. 4. 



too 



115 



50 75 



Time in Minutes 

 lower curves, there must have been a much greater decrease 

 in the secondary radiation in the first experiment than in the 

 two later experiments. Therefore there must have been a 

 much more copious emission of secondary rays at the beginning 

 of the first experiment than at the beginning of the other two 

 experiments. This is indicated by the height of the initial 

 point of the upper curve above the initial points of the other 

 two curves. 



The above experiments, therefore, show that when fresh 

 carbon is used as an electrode and subjected to bombardment 

 by u rays and the air withdrawn from around the carbon, 

 there is a great decrease in the secondary rays as time goes 

 on, until finally the secondary rays emitted reach a constant 

 value. Then, if the carbon is kept in vacuo for some time 

 (one week) it will not regain its primary power of emitting 

 secondary rays by being surrounded again by air while still 

 under bombardment by a rays even for periods of time 

 extending up to 22 hours. 



