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DEVELOPMENT OF THE QUANTUM 
THEORY 
CHAPTER XIII 
PLANCK’S CONSTANT AND THE ELECTRON 
That there are discrete mechanical and electrical systems, char 
acterized by quantum conditions and marked out from the infinite 
continuity of “ classically ” possible states, appears certain. But 
where does the deeper cause lie, which brings about this discon 
tinuity in nature ? Will a knowledge of the nature of electricity 
and of the constitution of the electromagnetic field serve to read the 
riddle ? 
Fritz Reiche, The Quantum Theory, 1922 
1. The Quantum and the Electron 
I N the last chapter of his book, The ABC of Atoms, Bertrand 
Russell refers to some of the problems connected with the 
new physics and relativity. When we wish to consider what is 
happening in some very small region, we must not take merely 
a small region of space, but a small region of space-time. “ This 
leads us to consider, not merely the energy at an instant, but the 
effect of energy operating for a very short time ; and this, as 
we saw, is of the nature of action. ... It is a fact which 
must be significant that action thus turns out to be funda 
mental both in relativity theory and in the theory of quanta. 
But as yet it is impossible to say what is the interpretation 
to be put upon this fact; we shall probably have to wait for 
some new and more fundamental way of stating the quantum 
theory.” 
In atomic physics we find a number of questions which have 
hitherto seemed unanswerable. “ We do not know why there are 
two kinds of electricity, or why opposite kinds attract each other 
while similar kinds repel each other. This dualism is one of 
the things which is intellectually unsatisfying about the present 
171