34 ROYAL SOCIETY OF CANADA 



To examine their resistance the rods were laid side by side about 

 1 cm. apart in two sets of four each, and their ends soldered together 

 in series. In tihis way four rods at a time were placed in the bath 

 and examined in succession. The resistance of each specimen was 

 deduced from the observed value of the potential difference at the ends 

 of a five cm. length of the alloy, and from the value of the current 

 passing through it according to the equation — 



and from this result the .specific resistance was calculated according to 

 the equation 



R A 



^= -17 



where A = the cross section 



L = the length of the specimen. 

 Apparatus: — The current traversing the alloys was supplied from 

 a storage battery, a rheostat being used to make small adjustments when 

 desired. To measure the current at any time, the difference of poten- 

 tial at the ends of a ohm standard resistance in circuit with the 



alloys was observed by means of a Siemens and Halske potentiometer 

 provided with a sensitive galvanometer. 



To determine the potential difference at the ends of a 5 cm. length 

 of the alloy, a pair of calipers fitted with ebonite arms bearing brass 

 V-shaped tips with platinum edges made a sliding contact at any two 

 points desired along the specimen and wires leading from the brass 

 tips served to make connection with the same potentiometer, the read- 

 ings for current and potential difference at the points of contact being 

 taken in succession. To determine the resistance of the 5 cm. length 

 of a specimen, the calipers were adjusted to a length of 10 1/^ cms. and 

 the difference of potential observed. The calipers were then shortened 

 to 5^ cms. and the potential difference again noted. The difference 

 of the two readings gave the potential difference at the ends of a 5 cm. 

 length of a specimen, and from this, the dimensions of the rod being 

 known, the specific resistance was deduced. 



No special difficulty was encountered in preparing baths at the 

 chosen temperatures. For the highest temperature a narrow copper ves- 

 sel was used long enough to contain the alloys laid upon proper insulat- 

 ing blocks. The paraffin was heated by gas and kept at a constant tem- 

 perature of 160° C. 



For the lowest temperature a quantity of liquid air was poured over 

 the alloys while resting in a narrow dish made of thin brass placed in 



