Transactions of The Royal Society of Canada 
SECTION III 
SERIES III MARCH 1917 VoL. X 
Contact Resistance between Conductors in Relative Motion. 
By VIOLET HENRY, M.Sc. 
Presented by Pror. H. T. BARNEs, F.R.S.C. 
(Read May Meeting, 1916). 
Upon first consideration it might be expected that the resistance 
of a moving contact would be less than for a stationary one. Such 
a conclusion is, however, seen to be erroneous, when one considers 
the conditions at the surfaces of any two conductors making contact. 
It is now generally accepted that between the surfaces of two electrical 
conductors there exists a film through which it is difficult for an 
electrical current to flow. The nature of this surface film depends 
upon the composition of the conductor, the condition of the surface, 
and upon the length of time which has elapsed since the surfaces 
were cleaned. Motion between the conductors produces a condition 
which tends to oppose the establishment of a uniform electric flow 
across the contact, in as much as a continuous breaking down of new 
surface film results. 
DETAILS OF APPARATUS. 
The method of study used in the present investigation was some- 
what similar to that used by H. E. Reilley!, in which an account is 
given of the measurement of contact resistances for various pressures 
applied to stationary contacts. 
One of the conductors consisted of a flat disc, an alloy of silver 
and gold, which could be rotated. The other conductor consisted 
of a contact of the same alloy, connected with the moving coil of 
a Weston relay. The disc was 1-8 cms. in diameter, the relay needle 
4-4 cms. long. The end of the needle which pressed against the 
disc was shaped like an arrow head. See Fig. 1. 

1 See Fig. 1. Trans. of Royal Society, vol. 8, p. 125, 1914. 
Sec. III, Sig. 1 
