Theories of Electricity 149 



by the passage of an electric current through a con- 

 ductor. 



From the above brief sketch we can see how extraor- 

 dinarily fertile the electronic conception has proved for 

 the explanation of diversified physical phenomena. We 

 believe that the electron is a definite physical entity 

 which has an independent existence. It is present in all 

 matter but can be readily released by a variety of agen- 

 cies and its properties studied apart from matter. 



At the same time, it must be remembered that the pres- 

 ence of an electron can only be detected when it is in 

 rapid motion, and strange to say, the greater its speed 

 the easier it is to determine its properties. 



We are now in a position to consider the fundamental 

 question, "What is an electron?" " Is it a fragment of 

 an atom of matter carrying a negative charge, or is it 

 a disembodied electric charge?" "What relation does 

 the electron bear to the atom, which before the advent 

 of the electron posed as the fundamental unit of matter?" 



These fundamental problems have to some extent been 

 answered and with remarkable consequences, as we shall 

 see, in clarifying our conception of electricity and matter. 



In order to answer these questions, it is necessary first 

 of all to consider what are the effects to be expected 

 when a small charged sphere is set in motion. This 

 problem was first attacked by J. J. Thomson in 1887, 

 and has later been developed by Heaviside, Searle, 



