of Pure Metals fyc. at the Boiling-point of Oxygen, 329 



(2) At about 20° C. when immersed in a paraffin or alcohol 



bath at normal temperatures. 



(3) At about 0° 0. when in a paraffin-oil or alcohol bath 



cooled by melting ice. 



(4) At — 80° C. when immersed in a bath of ether and solid 

 carbonic acid. 



(5) At — 100° O. when immersed in a test-tube full of liquid 



ethylene boiling freely under atmospheric pressure. 



(6) At — 182° C. when immersed in a test-tube full of liquid 



oxygen boiling freely under atmospheric pressure. 



(7) At —197° 0. when immersed in a closed tube containing 



liquid oxygen boiling under a reduced pressure of about 

 25 or 30 mm. of mercury. 



§ 3. In the case of the measurements in liquid oxygen and 

 ethylene, the liquid gases were contained in double test-tubes 

 holding about 200 cub. centim., which were kept filled up 

 as fast as the liquid boiled away, in order that the resistance- 

 coil might always be fully covered. Each measurement of 

 resistance was repeated several times. We thus obtained a 

 mean observed resistance, which is the mean resistance as 

 measured on the bridge. This had then to be corrected by 

 deducting the resistance of the leads up to and including that 

 of the mercury cups in which the resistance-coil terminals were 

 dipped. This correction was found to be equal to "025 B.A.U. 

 at 20° C. The corrected resistance is the resistance of the 

 coil after this deduction. A further correction was then 

 applied for the temperature of the Bridge coils, which were 

 used at a temperature of about 19°*5 C, or 4° C. above the 

 temperature at which they were correct ; and also a reduction 

 to true ohms, effected by the use of the factor -9866 recom- 

 mended by the Board of Trade Electrical Committee (1 B.A. 

 unit=*9866 true ohm). 



If B is the corrected resistance in B.A. units of any coil of 

 wire, the length of which is I centimetres and the mean dia- 

 meter d mils (1 mil = *001 inch), and if p is the resistance of 

 one cubic centimetre of the metal between opposed faces, in 

 absolute electromagnetic units, then it was found that p and R 

 were related by the equation 



/> = 5000yR; 



in which the numerical constant embodies all the above cor- 

 rections. In this reduction no correction has been applied for 

 the change in volume which the wire undergoes when raised or 

 lowered in temperature. Hence the values of p thus obtained 

 for various temperatures are not the true equi-volume specific 

 resistances, or resistances across opposed faces of one true 

 centimetre of the metal whatever its temperature ; but the 



