94 MR. A. E. OXLEY ON THE INFLUENCE OF MOLECULAR 



heat with temperature would be to add to the normal variation, expressed by DEBYE'S 

 theory, the following positive term 



^j. <!., - : (17) 



where S- is the absolute temperature and J the mechanical equivalent of the calorie. 

 In a former paper the author has shown that a term of this nature is necessary 

 to represent the variation of the specific heat of substances in the neighbourhood of 

 the fusion point.* A corresponding term explains, on WEISS'S theory, the variation 

 of the specific heat of ferro-magnetic substances in the neighbourhood of the 

 transformation temperature, on the supposition of a ferro-magnetic molecular field 

 of the order 10 7 gauss. t [+The fact that NERNST and LINDEMANN have found 

 experimentally an abnormal increase of the specific heat of diamagnetic substances in 

 addition to the normal variation due to purely translational vibrations, as the fusion 

 point is approached, is additional evidence of the importance of the rotational 

 term (17). DEBYE'S quantum theory of specific heats is concerned with translational 

 vibrations of the molecules only, and, away from the fusion point, it agrees well with 

 experiment. Incidentally, in order that (17) may be a measurable fraction of the 

 specific heat, a' c and I must be large, for, from experimental data showing the 

 departure from DEBYE'S theory near the fusion point, the interval of temperature 

 over which the molecules have effective rotational vibrations amounts to several 

 degrees at least, so that the large value of (17) cannot be attributed solely to a large 



yr 



value of the gradient -^r. Unless a' c and I have values of the order we have already 



found for them, it would be impossible to account for the measurable departure of the 

 specific heat near the fusion point from DEBYE'S values. Only a fraction of the 



energy term . a' c . I 2 will be dissipated below the fusion point, the major portion 



disappears at the fusion point and corresponds to the latent heat (as described 

 above). 



The departure of the specific heat from the value calculated on DEBYE'S theory is 

 important in connection with the quantum theory, for if the latter be valid, the 

 above term, due to the rotation of the molecules, implies that the angular velocities 

 of the molecules go in definite units. We cannot have the quantum theory holding 

 for translational motion and not for rotational. The remarkable fact is that the 

 rotational term (17) is insignificant except near the fusion point. This means that 

 away from the fusion point the translational motion of the molecules is sufficient to 



* A. E. OXLIY, 'Proc. Camb. Phil. Soc.,' vol. XVII., p. 450, 1914. 

 t WEISS and BECK, ' Journ. de Phys.,' se>. IV., vol. 7, p. 249, 1908. 

 I [Added November 12, 1914.] 



'La Theorie du Rayonnement et lea Quanta,' Paris, 1912; particularly p. 272 and the memoirs of 

 NERNST and EINSTEIN. 



