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The value, io 7 gauss, of the local molecular field found above, 

 is of the same order as that in ferro-magnetic substances 

 (Weiss & Beck, Jonm. de Phys. IV, vol. vii, p. 249, 1908). 

 Locally, the diamagnetic molecule is ferro-magnetic, and the 

 repulsion observed in a magnetic field, on diamagnetic matter 

 in bulk, is purely an induction effect produced in a system of 

 molecules each of which has a zero magnetic moment. 



Energy of the Molecular Field. — If H c be the intensity of 

 the local molecular field in a diamagnetic crystalline medium, 

 / the aggregate local intensity of magnetisation for all the 

 molecules in unit volume, the energy associated with one gram 

 of the medium, over and above that associated with one gram 



of the liquid, will be — . H c . I, p being the density of the 



crystalline medium. 1 If we assume that H c is proportional 



to /, and write H c = A e . /, the energy term becomes — . A c . P, 



I 2 P 



which is analogous to the energy term — . N . P . obtained by 



Weiss for ferro-magnetic media. N, which corresponds to A c , 

 is the coefficient of the ferro-magnetic molecular field. The 

 local molecular fields in the two cases are comparable, and so 

 are the values of the local intensity of magnetisation ; hence 

 the energies, associated with one gram of the crystalline media 

 in virtue of the crystalline grouping of the molecules, are of 

 the same order. This energy is approximately io 9 ergs. During 

 fusion this molecular potential energy is dissipated, and there- 

 for the latent heat of fusion should be of the order io 9 /4' 2 x IC>7 

 or 25 gram calories. The following are values 2 of the latent 

 heat for some of the substances experimented on in Part 1 : 



Benzene, 30 Chlorobenzene, 30 Aniline, 21 



Xylene, 39 Bromobenzene, 30 Acetophenone, 23 



Pyridine, 22 Nitrobenzene, 22 Naphthalene, 35 



It should be noted that these are comparable with the 

 values for the elements : 



Bismuth, 13 Cadmium, 14 Silver, 22 



Zinc, 28 Gallium, 19 Iron (magnetic 



change-point), 59 



Of course, until we know the disposition of the molecules in the 

 space lattice, their distances apart, and the law of force which 



1 For details of the argument leading up to the derivation of this term, see 

 Part 3, p. 90. 



2 Rccueil des Constantes Physiques, Paris, 1913, p. 323. 



