148 Rutherford: Modern 



charge of electricity through gases was found to be sim- 

 ply explained by supposing that the electricity was car- 

 ried by positively and negatively charged particles or 

 ions which moved in opposite directions in an electric 

 field. 



The discontinuous structure of these electric charges 

 was shown by making each ion the center of a visible 

 globule of water. The actual number of these ions in 

 the gas could be counted, and the charge on the ion or 

 the natural unit of electrical quantity was measured. At 

 the same time, J. J. Thomson and Drude independently 

 attacked the difficult problem of the mode of transmis- 

 sion of an electric current through a metallic wire. It 

 was supposed that the metallic conductor contained a 

 large number of free electrons carrying a negative 

 charge which could pass freely between the atoms of 

 matter. These mobile electrons were prevented from 

 escaping from the wire by the attractive force of a cor- 

 responding quantity of positive electricity, which was 

 carried by the atoms of matter. The carriers of the 

 positive charge were either immobile or moved ex- 

 tremely slowly compared with the electrons. Under the 

 influence of an electric field the electrons were set in 

 motion, and were the true carriers of the electric current. 

 This conception was found to offer a satisfactory expla- 

 nation of some of the most recondite phenomena shown 



