174 . K0YAL:S0CIETY of CANADA 



The potentiometer current was supplied by Columbia dry cells, 

 either one or two as required. The current from this source is very con- 

 stant, as the balance for the standard cell showed. 



Four significant hgures were obtained from the potentiometer read- 

 ings, and the fifth from interpolation on the galvonometer. 



In Fig. 1 the diagram of connections is shown. 



Method of Experiment. 



In all eases the wires were stretched below the elastic limit for a dav 

 or two in order to remove any possible kmks, and were then rested for 

 at least an equal period. 



The current used was as small as possible to give the necessary drop 

 on the potentiometer; the heating effect was small, as a thermometer 

 constantly touching the wire, showed. This thermometer indicated the 

 changes of temperature of the wire, and corrections were afterward made 

 for them. Weights were placed in the scale pan and the wire was allowed 

 to extend. No readings were taken until everything in connection with 

 current and temperature was constant. 



The temperature of the room, where the wire was suspended, was 

 v<ery constant as the thermometer readings show. 



If B is the standard resistance, E^ the drop across it ; R^ the resist- 

 ance of the test wire between potential terminals, and E^^ the drop 

 across it : — 



Then. Current = 



or 



IfP , is the reading of the potentiometer for the drop across the 

 wire, and Ps the reading for the drop across the standard then : — 



Ë~P^ 



or 





in th's way the resistance of the wire, after the various extensions, was 

 measured. 



The values shown for specific resistance, in the tables given here, are 

 calculated on the assumption that the volume of the wire remains con- 



