ATOMICITY IN ELECTRICITY 
29 
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cumstances in which they are exerted, definite for each body, we learn 
to estimate the relative degree of force which resides in such bodies : and 
when upon that knowledge comes the fact, that the electricity, which we 
appear to be capable of loosening from its habitation for a while, and 
conveying from place to place, whilst it retains its chemical force, can be 
measured out, and being so measured is found to be as definite in its action 
as any of those portions which, remaining associated with, the particles of 
matter, give them their chemical relation ; we seem to have found the 
link which connects the proportion of that we have evolved to the pro 
portion of that belonging to the particles in their natural state. 
869. The harmony which this theory of the definite evolution and 
the equivalent definite action of electricity introduces into the associated 
theories of definite proportions and electro-chemical affinity, is very great. 
According to it, the equivalent weights of bodies are simply those quan 
tities of them which contain equal quantities of electricity or have naturally 
equal electric powers ; it being the electricity which determines the 
equivalent number, because it determines the combining force. Or, if we 
adopt the atomic theory or phraseology, then the atoms of bodies which 
are equivalents to each other in their ordinary chemical action, have equal 
quantities of electricity naturally associated with them. But I must con 
fess I am jealous of the term atom ; for although it is very easy to talk 
of atoms, it is very difficult to form a clear idea of their nature, especially 
when compound bodies are under consideration. 
Thus Faraday’s laws of electrolysis point clearly to an atomic 
view of the constitution of electricity. This fact was emphasized 
by Helmholtz in a celebrated lecture, commemorating Faraday’s 
work, delivered in 1881. In 1874 Johnstone Stoney gave a 
clear statement of the atomic theory of electricity, and in 1891 
he suggested the term “ electron ” to designate the “ natural 
unit of electricity,” which is that quantity of electricity which 
must pass through a solution to liberate at one of the electrodes 
one atom of hydrogen or one atom of any equivalent substance. 
He even estimated the amount of the charge as 3 x io —11 absolute 
electrostatic units of quantity. This is a somewhat smaller 
value than that now accepted, 
e = 4-774 x 10 10 E.S.U.* 
Johnstone Stoney wrote : “A charge of this amount is 
associated in the chemical atom with each bond. There may 
accordingly be several such charges in one chemical atom, and 
there appear to be at least two in each atom. These charges, 
which it will be convenient to call ‘ electrons,’ cannot be 
removed from the atom, but they become disguised when atoms 
chemically unite. If an electron be lodged at the point P of 
the molecule which undergoes the motion described in the last 
chapter, the revolution of this charge will cause an electromagnetic 
undulation in the surrounding ether.” f 
* See Millikan, The Electron (University of Chicago Press, 1924). 
f Johnstone Stoney, Sci. Trans. Roy. Dublin Soc., vol. 4, p. 563, 1891.