Correction of the Gas- Thermometer. 65 



It appears that these discrepancies are due in the main to 

 errors of Regnault's pressure-coefficients, which subsequent 

 observations have shown to be much less accurate than his 

 expansion-coefficients, though Regnault himself considered 

 them more accurate. If we employ OhappmV values of 

 the pressure-coefficients, which are certainly nearer the truth 

 than Regnanlt 7 s ? we obtain the following results. 



Table IV. — Absolute Zero from Chappuis 1 

 Pressure-Coefficients. 



Gas employed Nitrogen. Hydrogen. CO. 



Pressure-Coefficient (^ =:100 cms.), a 

 Fundamental Zero of Gas, T = l/« .. 



Absolute Zero deduced, 



0036747 



•0036625 



•0037251 



272°-ll 



273°-03 



268°-45 



-f0°-98 



+o°-n 



+ 5° -55 



273° -09 



273°-14 



274°-00 



These evidently agree very closely with the results deduced 

 for the same gases from Regnault's expansion-coefficients. 

 The cooling- effect for nitrogen was found by Joule and 

 Thomson to be larger than for air in the proportion of 103 

 to 88. I have allowed for this in Table IV. and also in 

 Table VI. as it gives a better agreement with experiment 

 on the assumption n = 2. But Joule and Thomson did not 

 regard their experiments on nitrogen with much confidence, 

 and the true value of n is probably more nearly 1*5 for 

 diatomic gases (see below, section 20). The value found for 

 C0 2 , namely 274*0, differs from that calculated by the direct 

 method of: formula (22), which is certainly correct. The 

 explanation of this apparent discrepancy is given below in 

 section 15. 



The values of the scale-correction for the same gases, 

 calculated by formulae (41) and (43) with the values of the 

 constants given in Table II., deduced from the observations 

 on the cooling-effect alone on the assumption n = 2, are given 

 in the following table. The table covers a wide range of 

 temperature, and is intended to illustrate the general effect 

 of the correction, but it must be remembered that the 

 observations on which it rests were confined to the range 

 0° to 100° C. 



Phil. Mac/. S. 6. Vol. 5. No. 2o. Jan. 1903. F 



