of Gases exposed to Rontgen Rays. 247 



position, while the zinc plate discharged more negative than 

 the copper. 



Other metals, like aluminium, lead, were tested, and in all 

 cases negative electricity was discharged with slightly more 

 facility than positive. 



The variable discharging power of the different metals 

 agrees in some respects with the results obtained by Minchin 

 C Electrician,' March 27, 1896), who found that under the 

 influence of the Rontgen rays insulated metal plates were all 

 charged up to a small potential. According to his results copper 

 was charged positively and zinc negatively, while sodium was 

 highly negative. He also found that the potential to which 

 some of the metals could be raised depended on the degree of 

 polish of the exposed surface. In the experiments on the 

 discharging power of the metals, the results were dependent 

 to some extent on the brightness of the surface, especially 

 in the case of tin and zinc. 



The amount of electrification discharged by a metal tube 

 one inch in diameter and a foot long is very large, amounting 

 in some cases to over one fourth of the whole charge on the 

 gas. It must be remembered, however, that the current of 

 air conveying the charged gas is travelling at a high velocity, 

 and is, in consequence, in a state of violent eddying motion, 

 so that probably a large proportion of the gas approaches 

 near the surface in its passage along the tube. 



The charge is taken from the gas not only when it passes 

 through metal tubes, but also wdien it passes through tubes 

 coated with an insulator. A metal tube was taken and 

 coated with a thin layer of paraffin, and it was found that the 

 charge on the cylinder was about the same as with the clean 

 metal. It was difficult to determine with certainty whether 

 insulators exhibited similar properties to rnetals in regard to 

 discharging power. The amounts of positive and of negative 

 electrification discharged were approximately the same, but 

 the differences were too small to make certain of. 



The conductivity of the charged gas was tested by placing 

 an insulated wire kept at a constant potential inside a metal 

 vessel through which the electrified gas was blown. It w r as 

 found that when the electrification was of the same sign as 

 the charged wire, the gas gave up its charge to the outside 

 vessel, and when of the opposite sign, to the charged wire. 

 The current through the gas was only temporary, and ceased 

 as soon as the current of electrified gas was stopped. 



