THE KINETIC THEORY OF MATTER 



425 



ford, that the mean value of the charge carried by these electrons was 

 the same as the charge carried by the hydrogen atom in electrolysis; 

 and about the same time Sir J. J. Thomson found a way of making a 

 rough determination of the absolute value of this mean charge. This 

 method was improved in 1902 by H. A. "Wilson, now of McGill Uni- 

 versity, and actually formed the starting point some five years later 

 of the work out of which grew, by a series of natural steps, the experi- 

 ments which are herewith presented and which have made it possible 

 to capture and make accurate measurements upon one single isolated 



F 



i^\\\\\\m\v\\\\i 



Gl(L5s\Yool 



^To Pressure Taak. 



Earth. 



Fig. 1. 



electron or any desired number of such electrons up to one hundred 

 and fifty. 



Imagine two circular plates M and N (Fig. 1) 22 centimeters 

 (about 10 inches) in diameter and 16 millimeters (f inch) apart which 

 can be electrically charged, one positively and the other negatively, by 

 making them the terminals of a ten-thousand-volt storage battery B. 

 Suppose also that with the aid of a switch 8 the plates can be instantly 

 discharged when desired so as to possess no electrical properties at all. 

 Now when the plates are suddenly charged the air between them is 

 found to remain perfectly quiet and free from convection currents of 

 any kind — a result which shows that practically all of the air molecules 

 between the plates are electrically neutral. But if now a beam of X- 



