CONSTITUTION AND TEMPERATURE ON MAGNETIC SUSCEPTIBILITY. 
137 
We may regard the crystalline state as isotropic to a first approximation, since the 
crystals formed in the experiments have all kinds of orientations. The introduction 
of the term y(P) will then represent the effect due to the modification of the internal 
motions of an atom or molecule, by the process of crystallization, and will no longer 
characterize the different properties which the substance really possesses along its 
crystalline axes. 
We shall follow the electron theory of M. L angevin* and refer the electron system 
of any molecule to axes fixed in direction relative to the aether, but whose origin 
always coincides with the centre of gravity of the whole system of electrons. Let 
x, y, z be the co-ordinates of a particular electron. Then 
Ex = 'Ey — Ez — 0, and since the medium is assumed to be 
isotropic, 
Exy = Eyz = Ezx = 0. 
Let a, b, c be the co-ordinates of the centre of gravity of a 
molecule. Then, since the medium is isotropic, 
Ea = Eb = Ec = 0 
and 
Eab = Ebc = Eca = 0. 
The co-ordinates of an electron, with respect to the centre of the molecule in which 
it is situated, will be denoted by 
(£, n, C) = (x-a, y-b, z-c ). 
The above equations give 
E£ = Erj = EZ = Efr = EtjZ = E& = 0. 
The areal velocity of an electron, with reference to the centre of gravity of the 
molecule, will have a component along 0 z given by 
®z — h(£n—y£)> .(!) 
and, assuming that we can interpret the magnetic effect of the electrons spinning in 
their orbits by the magnetic moment M 2 where 
M 2 = Ee.QJ .(2) 
we may write from (l) and (2) 
M, -„f I.(3) 
J-i 
* ‘ Ann. de Chim. et de Phys.,’ VIII., vol. 5, p. 70, 1905. For clearness I have borrowed the treatment 
up to equations (4) directly from M. Langevin’s paper. 
t Sir Joseph Larmor (‘Phil. Trans.,’ 1897, A, p. 230), has shown that this relation implies the 
existence of a constraint to prevent the accumulation of displacement during the action of a steady 
magnetic field on a system of spinning electrons. See also Leathem, ‘Roy. Soc. Proc.,’ vol. 89a 
p. 31, 1913. 
VOL. CCXTV.—A, 
T 
