38 DRS. J. A. BARKER AND P. CHAPPUIS ON A 



Page. 



XXX. Preliminary determinations with gas thermometer with glass reservoir .... 74 



a. Capacity of the reservoir 74 



b. Coefficient of expansion of " verre-dur " 74 



f. Pressure coefficient of the reservoir 76 



(/. Determination of volume of " dead space " 75 



e. Determination of the " index error " V .... 77 



/. Corrections of scale and vernier 78 



XXXI. Calculation of the temperatures on the gas scale 78 



XXXII. Corrections relating to the " dead space " 79 



XXXIII. Method of preparing the nitrogen 80 



XXXIV. Determination of the initial pressure 80 



XXXV. Determination of the coefficient of expansion of nitrogen 82 



XXXVI. and XXXVII. Comparisons between the platinum thermometers and the nitrogen 



thermometer up to 200 85 



XXXVIII. Comparisons between the platinum thermometers and the nitrogen thermometer 



between 250 and 460 87 



XXXIX. New gas thermometer with porcelain reservoir 89 



a. Capacity of the reservoir 90 



b. Coefficient of expansion of porcelain . . 90 



c. Pressure coefficient of the reservoir 92 



d. Determination of the volume of the " dead space " 92 



XL. First determinations with the porcelain gas thermometer 93 



XLI. Explanation of the tables of results 97 



XLII. Determination of the boiling-point of sulphur 97 



XLIII. Reduction of results to the normal scale *.. 101 



XLIV. Conclusion . . - . 104 



Appendix I. Explanation of tables 112 



Numerical results of comparisons 114 



Tables for reduction of observations with platinum thermometers . 131 



Appendix II. Recalculation of the boiling-point of sulphur experiments .... 132 



I. INTRODUCTION. 



IN a paper entitled " The Practical Measurement of Temperature," read before the 

 Royal Society in 1886, Professor CALLENDAR drew attention to the method of 

 measuring temperature based on the determination of the electrical resistance of a 

 platinum wire. He showed that the method was capable of a very general application, 

 and that the platinum resistance thermometer was an instrument giving consistent 

 and accurate results over a very wide temperature range. 



CALLENDAR pointed out that if RO denote the resistance of the spiral of a particular 

 platinum thermometer at 0, and R, its resistance at 100, we may establish for the 

 particular wire a temperature scale, which we may call the scale of platinum 

 temperatures, such that if R be the resistance at any temperature T on the air-scale, 



this temperature on the platinum scale will be =r- ^7 X 100. For this quantity, 



K, Kg 



