178 



BELL SYSTEM TECHNICAL JOURNAL 



The curves /, // and /// illustrate the fact that Ohm's law is found 

 to hold for all contacts up to about 0.1 volt and that above these 

 values the contact resistance decreases with increase of voltage. 



Fig. 



14 — The single contact device is mounted in a heavy container on a spring 

 suspension to minimize acoustic and mechanical disturbance. 



The fractional decrease in resistance with voltage above 0.1 volt is 

 independent of the contact resistance and whether or not the measure- 

 ments are made in air or vacuum. 



In curves /', //' and ///' we have changed the voltage scale of the 

 curves /, // and III to a temperature scale in accordance with the 

 relation, 



T = 7^0 + 40 71 



