62 Prof. H. L. Callendar on the Thermodynamical 



The constant C is employed in calculating the scale- 

 corrections in Table VI. below. The values are given for 

 p {) =16 cms. = l'0133xl0 6 c.g.s. 



8. Method of Calculating the Correction. 



An incomplete table of corrections, for the air-thermometer 

 only, was calculated by Rowland (Proc. Amer. Acad. 

 vol. vii. 1880, p. 114) with the object of correcting the 

 air-thermometer which he employed in the reduction of 

 his observations on the mechanical equivalent of heat. The 

 method of calculation was not given, but he employed only 

 Joule and Thomson's later results (1862) as represented by 

 Rankine's equation. His work was probably the first 

 application of the thermodynamical correction to the actual 

 results of experiment. 



A similarly incomplete table of corrections for the air- 

 thermometer was given in my own paper " On the Practical 

 Measurement of Temperature" (Phil. Trans. A. 1887, p. 162) 

 for reducing the indications of the platinum-thermometer 

 to the absolute scale. The method of calculation adopted 

 was as follows. 



For purposes of gas-thermometry the characteristic equa- 

 tion of the gas employed may be written in the following 

 form : 



6=pv/R + g, (32) 



in which g is a small quantity of the dimensions of tem- 

 perature, which represents the deviations of the gas from 

 the ideal state. In using a gas-thermometer we assume an 

 equation of the type T=pvfR , J in which T is the temperature 

 on the scale of the gas-thermometer, and R/ is a constant, 

 differing slightly from R, and depending to some extent on 

 the method of thermometry employed. The values of R and 

 R' are determined in each case from the observations at the 

 fixed points 0° and 100° C, which give the following- 

 relations : 



B' = (Ptt-iW) AW, R=R\l+{ gi -g )/100), (33) 



in which p , v 0i g are the values of p, v, g at 0° C. and 

 Pit v u 9.1 are * ne Yaraes a ^ 1-00 C. In deducing these 

 relations small quantities of the second order involving 

 squares and products of q are neglected. 



To find the value of the absolute zero we have the equation 



o =lWB+?o=To+yo- (?i-?o)0o/1OO. . (31) 



