146 THE ROYAL SOCIETY OF CANADA 
In a more recent paper by Mr. H. E. Reilley! is given an account 
of experiments for the determination of the relation between contact 
resistance of similar metals and alloys and the pressure applied to the 
electrical junction. 
The author also considered the effect on the pressure-resistance 
ratio of conductors due to careful cleaning of the surfaces forming 
electrical contact. It was clearly shown that the resistance at the 
junction of two substances in contact depends upon the pressure to 
which the contacts are subjected. 
The paper contains curves for nickel, constantan, german silver, 
platinum-silver, fery-wire, gold, copper, manganin, gold-plated wire 
and platinum. In all these cases, the electrical conductivity increases 
in proportion to the pressure. 
By means of a mechanical device he measured the absolute 
pressure, that is the pressure necessary to reduce the electrical resist- 
ance from infinity to zero. Furthermore, he was able to measure the 
effect of immersing the contacts in kerosene oil. In every case the 
pressure on the contacts when in oil was less than the pressure in air 
for any given contact resistance value. The following table gives 
the values for the various substances investigated. 






Substance. Pressure Pressure in oil Residual 
in air. (Approx. value). Resistance. 
Ferv-Wireé:.... acte 200 mgms 160-170 mgms. 1-5 ohms 
German-Silver............ 2200 180 S 2214 
Platinum-Silver........... 100 40 s SAR 
Constantanys.-42 ise 160 4 100 . sve 
Manvanimune tete aie oe 40 “ 30-40 4 AE 
Copper Tete re Oe 600 50 = 0-1 
Silver: st talers.c sy Te ia ar CU Rove 34 . bey 
INCRE soe Ur Sane oe TERRE 50 . 1-0: “ 
PHARES eases SDL 25 £ ONE 
Golde es RNA 100" “ 25 ¢ JM 
Gold-Plated Manganin..... 49° 1f 20 bs Ce. PR 
Alain ner sit 180 grams 100 grams. SU 

In the latter part of the paper are given the results of investiga- 
tions upon the effect of carefully cleaning the contacts, and as was 
expected, cleaning brought about a large decrease in the absolute 
pressure, the change being from 200 mgs. to 50 mgs. approximately. 
—_—_—_— om 
1 Trans. of Royal Society. Vol. 8, p. 125, 1914. 
