1044 Proceedings of Royal Society of Edinburgh. [sess. 
be accounted for are represented in figs. 2 and 3. Weiss’s state- 
ment is, “ If one lays off along radii proceeding from a point the 
magnetisation which the matter acquires in a field of constant 
strength, directed along the radius considered, one obtains a 
surface having cubic symmetry. For the value of the field which 
we have used it resembles a cube with hollow faces and rounded 
edges. This surface has four circular sections parallel to the face 
of the octahedron. The value of the magnetisation varies much 
with the magnitude of the field. The aspect of this magnetic 
surface should then be very variable ; what is of more importance 
to note than its form in such or such a particular case, is the very 
complete concordance of its symmetry with that of the cubic system.” 
The properties of the magnetisation quartic show that, when the 
magnetisation is along a given radius vector, the external force 
must have a component, perpendicular to the radius vector, which 
will be representable by the subnormal on the same scale as that 
on which the subnormal represents the transverse component of 
internal force. Therefore the external force will, on that scale, be 
representable by a line drawn from the extremity of the subnormal 
to some point on the line of the radius vector. But it is quite 
