30 
THE QUANTUM [ m . 2 
It is to be noticed that the term " electron ” is here used 
for the elementary quantity of electricity, whether that quantity 
be positive or negative in sign. 
Convincing evidence in favour of the existence of such 
“ electric atoms ” has been accumulating within the past quarter 
of a century, largely as the outcome of the experiments of Sir 
Joseph Thomson and his fellow workers at the Cavendish 
Laboratory at Cambridge. The charge carried by the negative 
electron, or “ corpuscle ” to use Thomson’s term, is now 
known with considerable accuracy, and its mass has been found 
to be about tsW of the mass of the positive electron or 
“ proton,” the name given by Sir Ernest Rutherford to the 
nucleus of the hydrogen atom. 
It is unnecessary to recount here the experimental methods 
that have been employed in determining the electron charge. 
For these reference may be made to Sir Joseph Thomson’s Con 
duction of Electricity through Gases or to Professor Millikan’s 
interesting book on The Electron. Nor is it needful to describe 
the development of the electron theory of matter, according to 
which material bodies are built up of atoms, each of which is 
an electrical system composed, according to Rutherford’s theory, 
of a minute but massive nucleus (itself built up of electrons and 
protons) surrounded by the necessary number of negative elec 
trons to give a neutral system. These subjects have been 
discussed by many writers, sometimes in a popular fashion, 
sometimes in a severely technical way. Mention may be made 
of Professor Andrade’s book, The Structure of the Atom. 
2. Faraday Tubes of Electric Force 
The processes occurring in the electric field can be expressed 
by means of the conception, introduced by Faraday, of tubes 
of electric force, or rather of electrostatic induction. He showed 
that static electric induction took place in curved lines, a result 
which he regarded as incompatible with action at a distance, 
but in favour of his view of the action of contiguous particles 
of the dielectric (1166).* Although he usually regarded the lines 
of force as chains of polarized particles, he seems to have realized 
that these lines of inductive action may stretch across a perfect 
vacuum (1616). This is the view adopted by Sir Joseph 
Thomson f who regarded the Faraday tubes as having their 
seat in the aether, the polarization of the particles which accom 
panies their passage through a dielectric being a secondary 
phenomenon. 
* Faraday, Experimental Researches in Electricity. 
t Recent Researches in Electricity and Magnetism, Chap. I, 1893.