﻿excited by the Alpha Rays from Polonium. 815 



carried the second electrode, A. A circular surface, ab, o£ 

 this electrode A, about 15 mm. in diameter, was coated with 

 a deposit of polonium. The distance between the polonium 

 deposit and the surface of the electrode B was 6 mm. The 

 polonium and the surface of the electrode B were coaxial. 

 The brass cylinder, which was made air-tight with wax, was 

 connected to the McLeod gauge and the Gaede air-pump by 

 a tube D. The polonium-coated electrode, A, was connected 

 to a battery, and the brass electrode, B, to a sensitive quadrant 

 electrometer. The brass cylinder surrounding the two elec- 

 trodes was connected to earth. 



3. Repetition of Logemans Experiment. 



The experiment which Logeman* made was first repeated, 

 and the results obtained were similar to those obtained by 

 him with identical electrical fields. The experiment was 

 conducted in the following manner. By means of the Gaede 

 pump the air was pumped out from the apparatus to as low 

 a vacuum as possible. The pressure of the air was measured 

 by means of the McLeod gauge, and when the pressure 

 became so low that the McLeod gauge could not measure it, 

 which was less than 1/1000 of a millimetre of mercury, the 

 polonium was connected to earth, and the rate of charging 

 of the brass electrode opposite was measured by means of 

 the electrometer. Then the polonium was charged to a 

 series of different potentials by means of a storage-battery, 

 and the corresponding rates of charging of the brass electrode 

 were ascertained. Throughout the experiment the Gaede 

 pump was kept going continuously in order to withdraw any 

 gas which might come from the walls of the apparatus. 



The results which were obtained are given in Table I. 



Table I. 

 Pressure less than *001 mm. Distance between electrodes 6 mm. 



Voltage on polonium. 



Rate of charging. 



volts 



-49 



'44 „ 



-16 



2-1 „ 



451 



7 



81 



19 



89-5 



40 



88-5 



76 



86 



179 



82 



258 



80 



502 



75*5 



* Logeman, Froc. Hoy. Soc. vol. lxxviii. Sept. 6, 1907. 



