CH. xv.] CONSTITUTION OF ATOM 



mental phenomena of electric currents, of magnetism, 

 and of the production of light. But in order to explain 

 chemical action, the details of radiation such as 

 groups of spectrum lines and the like, the differences 

 observable between conductors, and the properties of 

 magnetic bodies, it is necessary to treat of matter also ; 

 and to consider whether its inertia too, and therefore 

 its whole nature and properties, can be reduced 

 and simplified and explained as electromagnetic 

 phenomena. 



For observe that though an electron has been 

 shown to possess purely electrical inertia, the same 

 proof has not yet been extended to an atom : the 

 constitution of an atom is so far unknown, and is the 

 subject of hypothesis only. Moreover the only 

 electron observed, so far, has been the negative 

 electron ; the positive has hitherto escaped observa- 

 tion in any isolated form, since it has never been met 

 with apart from a mass comparable with an atom in 

 bulk and weight. It may be that it can have no 

 separate existence apart from the atom of matter, 

 but in that case it will hardly be proper to speak of 

 it as an electron at all ; it may be that an indi- 

 visible positive charge itself constitutes the bulk of 

 an atom of matter ; in any case its nature must be 

 investigated, and many have been the attempts 

 made in that direction, among the best known in 

 recent times being the experiments of Prof. Wien 

 and others on " Canal rays." According to Larmor 

 positive electricity must be the mirror image of 

 negative, and experimental results must be inter- 

 preted to suit that theoretical conclusion. The 

 relations of positive electricity constitute in fact the 

 main outstanding problem of Physics at the present 

 time, and until they can be probed, further progress 



