[ 433 j 



XLTII. Notes on Gas-Thermometry. By P. Ohappuis, Ph.D., 

 Savant Attache au Bureau International des Poids et 

 Mesures, Sevres, France*. 



I, "IN a recent research, the results o£ which have just 

 X appeared in the Philosophical Transactions o£ the 

 Royal Society, Dr. J. A. Harker and the author endeavoured 

 to compare the indications of the platinum resistance-ther- 

 mometer and the normal scale over the range —20° to 600° |. 

 Having been led to recognize that hydrogen could not be 

 employed as thermometric substance on account of its action 

 on the walls of the glass reservoirs at high temperatures, we 

 had recourse to a constant-volume nitrogen-thermometer 

 having an initial pressure slightly under 800 millim., and 

 assumed provisionally that the thermometric scale of this 

 instrument represents the normal scale of temperature. It is 

 of interest to ascertain whether this hypothesis is justified by 

 the facts, or in other words to determine the divergence of 

 the constant-volume gas-thermometer from the normal scale 

 at high temperatures. 



Corrections to the Nitrogen Thermometer. 



Measurements previously made with a constant-volume 

 nitrogen-thermometer \ having an initial pressure of one 



1 dP 



metre have shown that the cofficient p-^- varies to an appre- 

 ciable extent, so that under these conditions the divergence 

 between the nitrogen thermometer and the normal scale 

 attains 0*01 at its maximum near 40°. 



The expression for the dilatation of nitrogen at the tem- 

 perature f deduced from the observations made with this 

 thermometer is 



0-003 676 98 - 7"826 746 x l$~H + 4'780 076 x 10" 10 f 2 . 



* Communicated by the Physical Society : read June 22, 1900. 

 Translated from the Author's MS. by J. A. Harker. 



t The temperature scale adopted as the standard by the International 



Committee of Weights and Measures is defined as the Centigrade Scale 



of the Hydrogen Thermometer, having as fixed points the temperature 



of melting ice (0°), and that of the vapour of distilled water in ebullition 



(100°) under the normal atmospheric pressure; the hydrogen being taken 



under the manometric initial pressure of one metre of mercury, i. e. at 



1000 , , . 



fi( y =1-3158 of the atmospheric pressure. 



} Chappuis, Travanx et Mem. du Bureau International, vol. vi. 1888. 



