Comparisons of Mercury and Platinum Thermometers. 15 



vessel would allow a more free circulation of the slightly 

 warmed water coming from the top and sides, and thus the 

 difference could be accounted for ; but considering the 

 distance of the thermometer-coil from the top and sides, and 

 the compactness of the ice, this does not seem possible. 



The following (Table III.) is a preliminary determination 

 of R , made merely to test the working of the apparatus. In 

 this experiment ordinary ice and tap-water were used. The 

 thermal regulator was not yet adjusted and the temperature 

 of the coils was varying quite rapidly, yet the value of R is 

 almost identical with that obtained subsequently. 



Table III. 

 Platinum Thermometer in Ice. 



Time. 









Mar. 10, 





Coils 





1897. 









4.10 



CD. 



G, H 



= 255 





Coil 



cor. 



-■on 



4.20 



0, D, 



F... 



= 260 





Coil 



cor. 



+ ■017 



Bridge-Wire. 



4.23 C. D, F, H= 265 

 Coil cor. +-016 



B.W. Reading-l-3+61 

 Cal. cor. ... --025 

 Zero cor. ... — OH 



B.W. Eeading- 1608 

 Cal. cor. ... + 012 

 Zero cor. ... —-011 



Temperature 

 of Coils. 



Temp. 

 Cor. 



20-80 

 + •053 



20-90 

 Temp. 

 Cor. 



B.W. Beading -6643 

 Cal. cor. ... +"017 I Temp. 

 Zero cor. 



un xemp. . „,,,, 

 •011 Cor. + 062 



258467 



258-471 



258-471 



Mean 258+70 



Determination of B^. — Tbe resistance at 100° C, B, ls was 

 determined in an hypsometer in which the thermometer was 

 screened on all sides (by polished metal screens) from the 

 effects of radiation. The hypsometer was provided with a 

 small water manometer to indicate the excess of pressure 

 within. To determine the atmospheric pressure, the baro- 

 meter already described was used in connexion with the 

 standard B and D scale. The temperature of the barometric 

 column was taken by means of two Bender and Hobein 

 thermometers of normal glass, graduated to T ] ° C, whose 

 indications were reduced to the air-scale through a previous 

 comparison with the platinum thermometer and a Tonnelot 

 thermometer standardized at the Bureau International. The 

 entire barometric column was wrapped to a thickness of 

 several centimetres with asbestos paper and cotton to ensure 



