﻿72 Effect of Radium on the Electric Discharge in Vacuo. 



It was not found possible to obtain as large currents 

 through these radium tubes as through oxide tubes under 

 similar conditions as regards voltage, degree of exhaustion. 



and temperature of cathode ; but, having regard to the very- 

 small quantity of radium employed in comparison with the 

 quantities of oxide, this is not surprising. 



Experiments were next made without any heating of the 

 cathode, but using alternating currents of higher voltages 

 than were available in continuous current. 



Employing the tube with one central electrode and two 

 symmetrically placed loop electrodes, one of the latter being- 

 treated with radium and the other being plain, the following- 

 results were obtained, the voltages being measured by means 

 of a Duddell thermo-galvanometer. 



It was found that, using the untreated electrode, it required 

 from 800 to 900 volts to get a visible discharge to pass ; 

 whereas, using the radium treated electrode, a visible discharge 

 could be got to pass with from 700 to 800 volts. The exact 

 voltages required in each case to cause a visible discharge 

 were somewhat variable ; but it was always found that a 

 visible discharge could be got to pass, using the radium treated 



