SPINNING ELECTRONS 
217 
xvi. 2] 
electricity spins about its axis with high velocity. The author * * * § 
has pointed out the capacity of this model for explaining optical 
activity and optical isomerism, and has made estimates of the 
constants of the ring electron, assuming that the angular momen 
tum is determined by the usual quantum condition. The local 
magnetic field quite near the ring assumes a very high value, 
being of the order io 8 gausses at a distance equal to the diameter 
of the ring. 
In a paper read before the American Association for the. 
Advancement of Science in December, 1920, A. H. Compton f 
concluded that the electron itself, spinning like a tiny gyroscope, 
is probably the ultimate magnetic particle. Reference was made 
to the ring electron and also to Nicholson’s idea of an electron 
with a strong concentration of electric charge near the centre, 
and a quantized spin was suggested for the electron which may 
perhaps be regarded as a sphere. 
Apart from a disinclination to attribute any structure to 
the electron, perhaps the chief objection to these early models 
was due to the fact that the size of the electron seemed too large 
to be in harmony with prevailing theories. The size was deter 
mined by assuming the peripheral velocity to be not greater than 
the velocity of light. 
2. The Spinning Electron and the Bohr Atom 
Two Dutch physicists, Uhlenbeck and Goudsmit,| in interest 
ing letters published at the end of 1925 and the beginning of 
1926, ignored the difficulties arising from velocities in excess of 
the velocity of fight, and boldly applied the hypothesis of the 
spinning electron to the motion of an electron round a nucleus. 
They considered the effect which would be produced by the 
quantized spin of the electron on the manifold of the stationary 
states. 
According to Eddington § the theory of relativity raises no 
objection to the periphery of the spinning electron moving faster 
than fight. “ It is only when energy or signals are alleged to go 
faster than fight the relativity theory is moved to intervene.” 
The mass and energy of an electron are considered as residing 
in the electro-magnetic field, outside its boundary. “ In describ 
ing the electron as spinning ... we make our thought skip faster 
than fight round its boundary and by so doing succeed in seeing 
* H. S. Allen, Phil. Mag., vol. 40, p. 426, 1920 ; vol. 41, p. 113, 1921. 
f A. H. Compton, Journ. Frank. Inst., p. 145, August, 1921. 
X Uhlenbeck and Goudsmit, Naturw., vol. 13, p. 953, 1925, and Nature, 
vol. 117, p. 264, 1926; Zeits. f. Physik, vol. 35, p. 618, 1926. 
§ Eddington, Nature, vol. 117, p. 652, 1926.