CHAPTER XIV 



MOTIONS OF ELECTRONS 



THE phenomenon of the electrification of two dis- 

 similar substances was explained in Chapter VIII as 

 due to a redistribution of the electrons. The electrical 

 charges thus produced might therefore be expressed as 

 a definite number of electrons, that is, measured by 

 counting the number of similar particles of electricity 

 which were added or subtracted. Of course, the actual 

 operation of counting would be impossible, because of 

 the size and the large number. 1 During the 120 years 

 preceding the demonstration of the existence of the 

 electron, knowledge of electrical phenomena and of 

 methods for their measurement had developed rapidly. 

 To make such measurements units were adopted which 

 are not as logical as would be the electron for unit quan- 

 tity. When the electron was recognized its electricity 

 was measured and expressed in terms of a previously 

 chosen unit. The units adopted are simpler than the 

 more logical unit because they are defined in terms of 

 magnitudes which are directly measurable and are also 

 of convenient amount. 



1 In fact, if during the electrification the number transferred is 

 such that as we separate the two bodies we find a force of 1 dyne 

 when they are 1 cm. apart, we know to-day that about 2.1X10 9 

 electrons have been transferred. 



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