360 Dr. T. Ewan and Mr. Haldane Gee on 



place obtained by interpolation from the deflections of the 

 galvanometer. 



The resistance coils were of German silver, and were 

 correct at I9°C. The temperature was taken by a ther- 

 mometer (graduated in tenths of a degree) placed inside 

 the box, but owing to the construction of the latter the 

 thermometer could not be in actual contact with the coils, 

 which introduces a considerable uncertainty into the correc- 

 tion for the temperature of the coils. Most of the 

 irregularities in the measurements of temperature by 

 platinum thermometer are probably due to this. The 

 correction was applied by the formula 



Ri9 = R,[i -0-0004433 (19- ^)] 



An error of 1° in taking the temperature of the coils may 

 make an error of 0'2° in the temperature measured by 

 platinum thermometer. 



The platinum coil was connected with the resistance 

 •coils by thick leads, consisting of bundles of copper wires. 

 Three or four Leclanche cells were used, and a commutator 

 was included in the circuit. 



After several unsuccessful attempts the apparatus shown 

 in Fig. 2 for boiling water under diminished pressure was 

 found to give satisfactory results. 



It consists of a copper vessel A, such as is used for 

 determining the boiling point of thermometers. The 

 upper end is closed by an india-rubber stopper, through 

 which two glass tubes pass. One of them terminates shortly 

 below the stopper, and through it the stem of the platinum 

 thermometer passes, the joint being closed air-tight by a 

 piece of india-rubber tubing slipped over both tubes. The 

 other is long enough to admit the mercurial thermometer, 

 and is closed at the lower end, and filled with water covered 

 by a layer of paraffin, or better, with mercury. 



