[m'lbnnan] 



ON ELECTRIC CHARGES 



93 



Bponds to a pressure of .15 mm. and in the second to a pressure of .08 

 mm. The rate of movement, as was to be expected, is greater for the 

 lower pressure than it was for the higher one. The fact that positive 

 charges were acquired under these circumstances lends further support 

 to the conclusion drawn from the earlier experiments that equal quan- 

 tities of opposite kinds of electricity were emitted with the rays from 

 uranium nitrate when freely exposed. 



TABLE IV. 



V. Potassium Salts: Electkical Charging Action. 



In making the observations with potassium salts pieces of apparatus 

 similar in form and dimensions to the two shown in Figs. Til and IV 

 were used in turn. In the first experiment a layer of potassium chloride, 

 about 4 mms. thick, was spread on the tray BB in Fig. Ill, and then 

 the space surrounding the tray was as highly evacuated as possible. 



Some preliminary observations had shown that extreme care had to 

 be taken to see that no electrification was imparted by friction to the 

 insulating support HH, during the operation of setting up the apparatus. 

 Even touching it slightly with the finger or allowing its surface to be 

 scraped with any object, was found to leave an electrification behind 



