the They mod ynamic Scale of Temperature. 355 



Employing Regnault's data as quoted by Lord Kelvin 

 {he. clt.\i. 181), we obtain the following numbers for the 

 value of t. 



Hydrogen 273*13 



Air 273-21 



If we prefer to work with the numbers quoted by M. 

 Chappuis in his paper '' L^echelle thermometrique normale et 

 les echelles pratiques " we shall have 



Hydrogen 273*04 



Nitrooen 273-13 



{loc. c'lt. pp. 3 & 8). 



There is another way of reaching an estimate of t^ without 

 making use of the Joule-Thomson numerical results. I have 

 shown in my paper already quoted that for such gases as air 

 and hydrogen we may write 



1 V ^^^" 

 pv = \it — ; 2, 



(Phil. Mag. ii. p. 133). Let the suffix applied to p and t 

 refer to the freezing-point, and let the suffix 1 refer to the 

 boiling-point. Then keeping the volume constant and equal 

 to V we have 



B.an 



(n4 



p,v'^ = 'RtoV — % 



^.an 



Xext keeping the yolume constant and equal to v^ we 

 obtain 



p,^v-=my-ij--^^„ 



py'=i^ty-t 





(.2 + 1)^/- 

 By subtraction we o-et 



e^ 



Hence 



py-py^^-'^Uv-v). 



p,v^-py^ _h 



PQ^-'-piiV-^ t^ 

 t -(t -/V Ipiv^'-Piv' ^' -,1 



2 A2 



