236 
Proceedings of the Royal Society of Edinburgh. [Sess. 
at 30° and 60°. The transverse component is thus representable by a 
symmetrical twelve-looped curve in the plane y = 0. The sign of any one 
loop of this component, and the maximal or minimal nature of the parallel 
component in, say, the direction a = 0, are only determinable by numerical 
evaluation of the coefficients. 
17. In the case of the cubic system, in a face plane of the cubic lattice, 
i.e. with y = 0, we have by (6) and (19) with a — cos 0 
yL 2 — 0 , T 0 = 0 . 
And, by (19) and (20), 
" D)(sin s 20 -||) , 
yT' 2 = Ma 2 (G-D)sin ^ 
Also, by (24) and (25), 
yL' 4 = - ■ ^[231A 8 - 315C' 3 + 30R' 3 ](W 26 - A) , 
y T 4 = - • IflSIA', - 315'C'j + 30R' 3 ] sin 4 6 . 
The latter pair have the same geometrical form as the preceding pair. 
Calculation of the numerical values of G and D ( Proc . R.S.E., 1905, 
1907) shows that G is greater than D. Evaluation of A' 3 , C' 3 , and 
D' 3 has not yet been carried out, but the multiplier a 2 /p 2 in the latter pair 
probably makes y I/ 4 and y l v 4 small relatively to 7 L' 2 and y T' 2 apart from 
the smallness of A' 3 , etc. 
In an octahedral plane (plane normal to a ternary axis of the cubic 
system), the variable part of the parallel component of the internal field 
is proportional to a 2 /3 2 y 2 . For, under the condition a + ( 8 + y = 0 which 
then subsists, we have 2(ct 4 + /3 4 + y 4 ) = 4(a 2 /3 2 + /3 2 y 2 + y 2 a 2 ) = 1 and 
2(a 6 + /3 6 + y 6 )= 1 — 3a 2 /3 2 y 2 . Referring now to rectangular axes in the 
plane a + /3 + y = 0, and measuring 0, counter-clockwise from a binary axis 
in that plane, we find that the variable part of the component I/ 4 of the 
internal field parallel to the direction of magnetisation is proportional to 
sin 2 #(3 - 4 sin 2 #) 2 . 
Similarly, L' 2 is constant and I/ 0 is zero. 
In Weiss’s experimental investigation of magnetite no observations were 
made in an octahedral plane, but such observations have been carried out 
by his pupil V. Quittner (Ann. d. Physik, 30, 1909). In the paper above 
referred to (Proc. R.S.E., 1905), the molecular theory was applied to the 
