Theoretical Evaluation ofy. 649 



oxygen, hydrogen, nitrogen, and carbon monoxide, all 

 diatomic*. 



As an instance of an irregular gas we may take carbon 

 dioxide. Leduc's values | of 7 are 



0°. 100°. 



y = 1-3190 1-2827. 



The value of 7 for this gas has also been determined by 

 CapstickJ. As a result of six experiments, all at a tempera- 

 ture of about 15°, he finds the value y = 1*308, The variation 

 with temperature is therefore very marked. These results 

 are all arrived at by measurements on the velocity of sound. 

 As regards the value of 7 obtained by direct methods we may 

 quote Capstick§ : "The accepted value of 7 for carbon 

 dioxide obtained by Kundt's method is about 1*3. Regnault's 

 value for C p between 15° and 100° is *2025. Joly's value 

 for C y between 12° and 100° is *1653, and the ratio of these 

 is 1*22. Both C P and C c are difficult to measure accurately, 

 but 7 per cent, seems to be too much to attribute to experi- 

 mental error. It would seem that we have here to do with 

 forms of vibration that only take their share of the energy 

 when given more time than is afforded by sound vibrations/' 



As other instances of irregular gases may be mentioned 

 the gases N 2 0, iNH 3 , C 2 H 4 , and possibly 2 H 6 and C 3 H 8 2 . 



In many gases the variation of 7 with temperature is com- 

 plicated by chemical dissociation. It is probably for this 

 reason that methyl ether and methylal show an increase of 7 

 with temperature. 



§ 11. It appears that, to reconcile our theory with experi- 

 ment^ it is necessary to suppose that the numerical values of 

 the quantities concerned are such as to make /'(E) very small 

 for a subsidiary degree of freedom, at any rate at normal 

 temperatures. Hence, from equation (23), e(l — 0) must be 

 large compared with (a — fj^E, and the value of /'(E) be- 

 comes I N/E(§a + J)/e(l — 0). If we neglect the "pulses" sent 

 out at collisions, the radiation is of amount Fe(l— 6) or 

 Ei(±a-f£). There is no difficulty in supposing £ to be so 

 small as to be negligible, but the case is different as regards a. 



OCT/ tJ 



* Tables giving lists of values of y will be found in Meyers ■ Kinetic 

 Theory of Gases,"' p. L25, and also in a paper by J. W. Capstick, ' Science 

 Progress,' iii. p. 10. 



t Lednc, I. c. ante. 



\ J. W. Capstick, Phil. Trans, clxxxvi. p. 581. 



§ J. W. CapsticK, ' Science Progress/ iii, p. 19. 



