38 ROYAL SOCIETY OF CANADA 



So far the experiments made indicate that the negative charge 

 acquired )by the cylinder results from a process in which an excess 

 of positively charged corpuscles is expelled from its surface. This 

 process is probably identical with the a radiation observed by Euther- 

 ford^ and others in the highly radioactive substances radium, thorium 

 and uranium, and experiments are now being made by the writers to 

 determine its relation to the effect observed by Guthrie- and deve- 

 loped by Elster and Geitel,^ J. J. Thomson/ Eichardson,^ Strutt*' and 

 others, that a metal, platinum for example, when heated to a dull red 

 will discharge a negatively charged body placed near it, but not one 

 positively charged. 



Experiments — Metal Effect. In these experiments cylinders of 

 aluminium, zinc, lead, tin and copper were used, the outer ones being 



h::s.^ 



a,,a ""^ /o.' 





F^i^± 



120 cms. in length and 24 cms. in diameter, and the inner 110 cms. 

 in length and 19 cms. in diameter. The measurements were made 

 with a quadrant electrometer whose sensitiveness was such as to give 

 a deflection of 1,000 mms. on a scale situated at one metre from the 

 needle for a potential of one volt. 



The apparatus and its connections ar,e shown in Fig. I., where A 

 and B represent the cylinders of the metal examined. The wire which 

 led from the inner cylinder to the electrometer was of brass and was 

 surrounded by a tube of the same metal to screen off induction effects. 

 This tube, as well as the outer cylinder B and the metallic screen over 

 the electrometer, was kept joined to earth during an experiment. The 

 inner cylinder and the free quadrants were earthed by means of the 

 brass rod D, which carried a platinum tip and made contact with a 

 small platinum plate attached to the connecting wire as shown in the 

 figure. The tube was provided with a small opening so arranged that 

 the withdrawal of the rod D did not affect the capacity of the system. 

 Plugs and supports of paraffin wax provided insulation for the apparatus. 



* Phil Mag., Feb., 1903, p. 177. 



' Phil. Mag. [4], 46, p. 257, 1873. 

 » Wied. Ann., 38, p. 27, 1889. 



* Phil. Mag., XLIV., 1897, p. 203. 



» Proc. Camb., Phil. Soc, XI., p. 286. 



* Phîl. Mag., Vol. IV., Sixth Series, 1902, p. 98. 



