64 ROYAL SOCIETY OF CANADA 



positive terminal, TMs goes to show that part at least of the deposit 

 particles carry a positive charge and reach the electrode under the in- 

 fluence of the field. 



The manner in which these particles gain their positive charge, 

 however, is not clear. 



From experiments by Logeman i and others it is known that a plate 

 of copper on which polonium is deposited emits a copious stream of delta 

 particles. These it is also known are beta particles of low velocity which 

 are very probably ejected either from the copper or from the polonium 

 or its transmutation product under the bombardment of the alpha par- 

 ticles. It is possible, too, that they may be produced by and accompany 

 the alpha particles in the course of their expulsion from the parent 

 atoms. Such a plate of copper as that mentioned above is known to 

 acquire a positive charge Avhen placed in a very high vacuum, which 

 shows that an excess of negative electricity leaves it as a result of the 

 action of the various radiations. It is possible then that some of the de- 

 posit particles from actinium or other active emanations may gain a 

 pcsitive charge under the action of the alpha radiations present in much 

 the same way as the copper plate in the polonium experiments. This 

 would then account for the positive charge on the particles and conse- 

 quently for their removal under the field to the negative terminal. 



On the other hand some experiments recently made by H. W. 

 Schmidt 2 have brought out a parallelism between the amount of active 

 deposit obtained in air under different electric fields and the intensity 

 of the ordinary conduction current through the air under the same fields. 

 This would seem to show that the charges are acqiiired by the deposit 

 particles as a result of collision with the gaseous ions present in the same 

 vessel. 



Many of the results obtained in the present investigation go to sup- 

 port this view and one in particular is of special interest. 



In this experiment the electrodes were 2 mm. apart, the salt was 

 placed 1.3 mm. below the electrodes in the exposing vessel, and the ex- 

 posures were made under different voltages in air at a pressure of 9 mm. 

 The exposures were made first with the two electrodes at the same po- 

 tential, and then with them at different potentials ranging in extent up 

 to 1,150 volts. 



The results of the various activity measurements are given in Table 

 IX and curves drawn from these numbers are shown in Fig. XV. 



From these results it will be seen that when the potentials of the 

 two plates were the same the activities of both were alike, but that for 

 all potential differences the activity of the negative terminal was greater 



1 Logeman, Proc. Roy. Soc. A 78, p. 212, 1907. 

 2 Phys. Zeit. 9, pp. 184-187, March, 1908. 



