[MCLENNAN- ON THE DELTA RAYS EMITTED BY ZINC 

 found] 



Table I. 



223 



Sensibility of Electrometer, S, = 220 mm. per volt. 

 Capacity of Electrometer, C, = 140 e.s.u. 

 D = deflection in mm. scale divisions per minute. 

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



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 nega- 

 tive 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 ionisation; (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 posi- 

 tive 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 



