1911-12.] The Molecular Theory of Magnetism in Solids. 231 
Mr ? 2 
Hence, in the plane y = 0, T' 2 becomes y T' 2 — 2— -g-(G — D)a/3(a 2 — fi 2 ). Fig. 5 
represents this curve and the curve (19) on the same scale, the latter being 
in dashes, the former in full lines. The dotted curve refers to § 15. 
If G > D, (19) and (20) show that the internal force opposes the 
magnetisation when that is parallel to a principal (quaternary) axis in 
the cubic arrangement ( e.g . a = 1, /3 = 0, y = 0). On the other hand, the 
internal force is positive when the magnetisation is along a binary axis 
(e.g. a — /3 = 1/J2, y — 0), or a ternary axis (e.g. a — = y = 1/^/3). 
