A PRACTICAL ELECTRICAL METHOD OF MEASURING THE 
DISTANCES BEWTEEN PARALLEL CONDUCTING 
PLANES, WITH APPLICATION TO THE 
QUESTION OF THE EXISTENCE OF 
ELECTRON ATMOSPHERES. 
BY F. C. BROWN. 
In the Philosophical Magazine for August, 1912, Professor R. W. 
Wood raises the interesting question concerning the existence of con- 
ducting atmospheres surrounding metallic surfaces. The necessity for 
this hypothesis arose from a number of experiments, in which electrical 
conduction took place between metallic surfaces, when they were sepa- 
rated between 20 and 30 wave lengths of sodium light. The result 
appeals to the imagination but it is not easy to reconcile it with the well 
known experiments by Earhart, 1 Hobbs, 2 Kinsley, 3 Almy, 4 Williams, 5 
and others who found using interferometer methods that there was good 
insulation when the conductors were much closer than the distances 
observed by Wood. Perhaps the argument may be urged against the 
interferometer methods that no allowance was made for a possible de- 
formation of the metallic surfaces under the electrical stresses, nor have 
such methods as used been infallible in detecting the absolute point of 
contact between the surfaces. 
And Wood’s experiments considered alone do not seem consistent with 
the electron atmosphere hypothesis, for such an atmosphere should extend 
out the same distance from the surface regardless of the insulating ma- 
terial between those surfaces, particularly so when the material is in 
discontinuous sheets. His results should not have shown a greater vari- 
ation than the variation of his optical flat from that of a true plane. 
I have tested out an electrical method for measuring small distances 
in order to gain information toward explaining the above discrepancies. 
I have found the method useful and the application interesting. The 
iphil. Mag. (6) 1, p. 147, 1901. 
2 Phil. Mag-. (6) 10, p. 617, 1905. 
3 Phil. Mag. (6) 9, p. 692, 1905. 
4 Phil. Mag. (6) 16, p. 156, 1908. 
5 Phys. Rev. 31, p. 212, 1910. 
