Deposit of Radium in an Electric Field. 



485 



suspension. The needle was charged to a potential of 120 

 volts, and with this potential the sensitiveness was 180 mra per 

 volt on a scale about 1 meter distant. 



The Rontgen-ray bulb, which was enclosed in a lead-covered 

 box and which was employed whenever it was desired to 

 increase the ionization current in the test-vessel, is not shown 



Fig. 1. 



E 



gzzzzmzzza vzzzzzzzzzzzzq ZZZZZZZZZZZ2. 



V/w?r;/j;»j<>//;j>/;???»>s?rrrn 



r 



VWWWWVWWSA— 



b 



in the diagram ; the rays were admitted through an aperture 

 in the lead directly beneath the aluminium bottom of the 

 vessel. 



For potentials up to 1200 volts a battery of small accumula- 

 tors was employed. For the larger potentials a Wimshurst 

 machine was used which was driven by an electric motor ; it 

 was found that the voltage obtained by this means was surpris- 

 ingly steady, although the slight variations were sufficient to 

 prevent any accurate measurements of the ionization current 

 through the gas. The voltage was regulated by means of an 



Am. Jour. Sci. -Fourth Series, Vol. XXXIII, No. 197. -May, 1912. 

 32 



