THE CONQUEST OF NATURE 



which the name electron (or corpuscle) has been given, 

 each of which is about one thousand times smaller than 

 a hydrogen atom, and each of which carries uni- 

 formly a unit charge of negative electricity. 



Electrons are combined, in what may be called 

 planetary systems, in the substance of the atom; in- 

 deed, it is not certain that the atom consists of any- 

 thing else but such combinations of electrons, held to- 

 gether by the inscrutable force of positive electricity. 

 Some, at least, of the electrons within the atom are 

 violently active perhaps whirling in planetary orbits, 

 and from time to time one or more electrons may escape 

 from the atomic system. In thus escaping an electron 

 takes away its charge of negative electricity, and the 

 previously neutral atom becomes positively electrified. 

 Meanwhile the free electron may hurtle about with its 

 charge of negative electricity, or may combine with 

 some neutral atom and thus give to that neutral atom a 

 negative charge. Under certain conditions myriads of 

 these electrons, escaped thus from their atomic systems, 

 may exist in the free state. For example, the so-called 

 beta (/?) rays of radium and its allies consist of such 

 electrons, which are being hurtled off into space with 

 approximately the speed of light. The cathode rays, 

 of which we have heard so much in recent years, also 

 consist of free electrons. 



But, for that matter, all currents of electricity what- 

 ever, according to this newest theory, consist simply of 

 aggregations of free electrons. According to theory, if 

 the electrons are in uniform motion they produce the 

 phenomena of constant currents of electricity; if they 



