emitted by Zinc bombarded by Alpha Rays. 

 Table I. 



495 



Sensibility of Electrometer, S, =22 



3 mm. per volt. 



Capacity of Electrometer, C, =140 



e.s.u. 



D = deflexion in mm. scale-divisions 



per minute. 



The current, i, = C.D./300.S.60e.s.u." 



Voltage on 



Deflexion in 



Current X 10° 



Polonium. 



mm. per min. 



e.s.u. 



Volts. 



mm. 









-35 



-127 



4- 2 



— 22 



- 80 



4- 4 



4- "3 



4- 11 



+ 6 



11 



4- 40 



+ 10 



16 



4- 58 



4-16 



20 



4- 73 



4-22 



20 



4- 73 



4-28 



21-5 



4- 78 



-f-40 



21 



4- 76 



4-50 



23 



4- 84 



4-60 



23 



4- 84 



4-80 



23 



4- S4 



From the numbers in the Table and from the curve in 

 fig. 2 it will be seen that, although the terminal P was 

 always either at zero or at a positive potential relative to X, 

 the current was initially negative and remained so until a 

 potential of about 4 volts was reached, when it passed through, 

 zero and became positive, gradually increasing to a maximum 

 with an applied positive potential of about 40 volts. 



In this experiment it will be noted that the current 

 between P and X consisted of : (1) a very small positive 

 current in the residual gas due to ionization ; (2) a positive 

 current consisting of the stream of alpha particles emitted 

 by the polonium ; (3) a positive current consisting of a 

 stream of recoil atoms from the polonium; (4) a positive 

 current due to electrons passing from X to P arising from 

 the bombardment of X by the alpha particles ; and (5) a 

 negative current due to electrons passing from P to X which 

 accompanied the alpha particles and had their origin either 

 in the polonium or in the copper surfaces on which the 

 polonium was deposited. With zero or low positive voltages 

 the stream of electrons mentioned in (5) it will be seen 

 completely masked the other four constituents of the current. 

 As the positive applied voltages, however, were increased 

 this stream of electrons was more and more prevented 

 from leaving the electrode P, and finally when a potential 



