273-275] Ratio of Specific Heats 227 



and H/K is no longer a small quantity. Hence we cannot safely neglect 

 those particular subsidiary temperatures which measure energy of rotation 

 about an axis of symmetry. 



If we suppose H to be comparable with K in equation (524), the value of 

 H in the normal state is given by 



| 



2e 





so that H and K may be in any ratio. 



In general when a subsidiary temperature cannot be neglected, it is clear 

 that the value of 7 obtained after taking account of the influence of this 

 subsidiary temperature must be expected to vary with T. 



Neglecting the deviation from Boyle's Law, we may replace vj, by v, and 

 then obtain from equations (516) and (518), 



Since /(T), f 2 (T) ... and f,' (T), f,'(T} are positive and increase with T, 

 the value of 7 given by this equation will be smaller than the corresponding 

 value given by the formula 



and will decrease with the temperature. 



275. We have now found two causes which ought to combine in 

 producing a decrease in the value of 7 as the temperature increases. Also 

 we can see that the amount of variation in the value of 7 ought to be 

 greatest for gases in which the value of 7 is furthest removed from the 



values of the form 



2 



L+ 7^T3' 

 given by simple theory. 



These conclusions are fully borne out by experiment. It is impossible to 

 quote the whole experimental evidence. The two following results due to 

 Leduc * may be taken as illustrations : 



Gas 7 at 0C. y at 100 C. 



Air 1-4040 1-4031 



Carbon Dioxide 1'3190 1-2827. 



* Leduc, Comptes Rendus, cxxvii. p. 661. 



152 



