PKEFACE 



IN 1902 I was asked by the President of the 

 Institution of Electrical Engineers to give to that 

 body a discourse on recent progress towards know- 

 ledge of the nature of Electricity, especially con- 

 cerning its discontinuous or atomic structure. This 

 discourse, greatly extended, appeared in Vol. 32 of 

 the Journal of the Institution, and constitutes the 

 nucleus of the present book. 



Many additions have now been made, and some 

 of the difficulties recently promulgated concerning 

 the possibility of an electric theory of matter are 

 touched upon. They are of date too recent to have 

 been mentioned even in my "Komanes Lecture" 

 before the University of Oxford, published under 

 the title Modern Views of Matter by the Clarendon 

 Press. 



The most important addition is a more detailed 

 account of the proof of the purely electrical nature 

 of the mass or inertia of an electron : an investi- 

 gation generally associated on the experimental 

 side with the name of Kaufmann, but of course 

 based on the work of many predecessors and con- 

 temporaries. A proof that the atom of matter is 

 essentially composed of such electrons, and that 

 its mass too is of purely electromagnetic nature, 

 is lacking : the electromagnetic theory of Matter, 



