CONSTITUTION AND TEMPERATUIiE ON MAGNETIC SUSCEPTIBILITY. 
273 
different forces of crystallization in different directions (which forces determine the 
planes of cleavage) with the magnetic behaviour of the crystallized medium and lead 
us to suspect that the forces of cohesion are probably of magnetic nature. The fine 
points are so completely explained by the magnetic deportment that it is difficidt to 
dissociate the crystalline forces from a magnetic origin. If we assume that these 
forces are of an electrostatic nature, then it must be admitted that the electrostatic 
axis of the molecule must coincide with the magnetic axis if the action of a magnetic 
field is to be decisive, as Tyndall proved it to be, in isolating the planes of cleavage. 
But if the electrostatic and magnetic symmetries of the molecules are coincident the 
application of a field of either nature should induce a double refraction of the same 
kind in a given liquid. This, however, is not true experimentally, the electric induced 
double refraction in liquid carbon bisulphide being opposite in sign to the magnetic 
induced double refraction.'^ Moreover, in crystalline media, the greatest axes of the 
ellipsoids representing the magnetic and electric properties of the molecule do not in 
general coincide. We may therefore say that the evidence points to the conclusion 
that the forcive which holds the molecules together in a crystalline space lattice is 
magnetic in nature and not electrostatic, t 
Drude,| in his experiments on the relation between valency and dispersion, 
* Cotton and Mouton, ‘Comptes Rendus,’ vol. 155, p. 1232, December, 1912. 
t [A^o/e added April 26\ 1919 .—After the present communication had passed out of my hands, an 
important paper “On the Origin of Spectral Series” was published by Sir J. J. Thomson (‘Phil. Mag.,’ 
April, 1919). In this a new theory of atomic structure is suggested in which the atomic, nucleus and the 
revolving electrons play similar roles to those described on p. 274. Within the contour of the atom, 
according to Prof. Thomson, the electrostatic forcive due to the nucleus is of a periodic character and 
determines a series of spherical or approximately spherical surfaces where the electric force vanishes and 
over which the periodic motion of the boundary electrons is determined solely by the magnetic field of the 
atom. Ihis magnetic field is supposed to be radial. If this is the case, these intra-atomic fields must be 
of the order of magnitude 10® gauss (as a simple calculation shows, since v = to account for the 
\ 27r?/i / 
frequencies of the visible spectrum. Still larger intra-atomic fields will exist nearer to the nucleus, of the 
order 10® gauss. These will be sufficient to account for the frequencies of the K series. The infra-red 
series will be accounted for by fields of the order 10^ gauss. But this latter value is of the order of the 
intermolecular magnetic field which has been deduced independently in various ways in the present 
researches. Moreover, it is to this local field that we have ascribed the rigidity and other properties of 
crystalline media in general. The frequencies of the infra-red series will, on this view, correspond with 
the elastic vibrations of the rigid medium in' conformity with the quantum theory of specific heats of 
Einstein and Debye as already stated (see Part III., p. 94, and supra, p. 259). Reasons have already been 
given for assigning a magnetic nature to the intermolecular field in crystalline media (see Part III., 
pp. 101-3, and supra, pp. 270-276). This intermolecular magnetic field, which is of the order 10~ gauss, is 
suggestive in connexion with Prof. Thomson’s theory, referred to above. On p. 274 (footnote) it was 
suggested that the forces determining crystalline cohesion are magnetic in nature, the symmetry of the 
magnetic forces being determined, however, by the electrostatic action of the nucleus. Therefore, in 
this fundamental sense, the present theory and that of Sir J. J. Thomson are identical.] 
t ‘ Ann. der Phys.,’ vol. 14, p. 677 and p. 936, 1904. 
2 P 2 
