646 Proceedings of the Royal Society of Edinburgh. [Sess. 
tion it has to be observed that, while in these investigations the magnetic 
unit of the cubic arrangement has been regarded as a single magnet of 
constant moment, the results of the investigations are not altered in their 
general nature if the unit be complex with a variable moment so long as 
the moment does not change sign. In the latter case effects analogous to 
the one discussed below would occur. 
In the most open arrangement, alignment of the magnets parallel to 
a ternary axis is unstable so far as the internal forces are concerned. 
Therefore such alignment could only take place if the external applied 
field exceeded the internal field. If the internal field is greatly in excess 
of the external, the arrangement would be strictly almost unmagnetisable 
along the ternary axes, although it would apparently be magnetisable in 
these directions, because of their inclination to the quaternary axes, to 
one-third of the extent to which it is magnetisable along a quaternary 
axis. 
If the lines of stable magnetisation were at right angles to a line of 
unstable magnetisation, the substance would seem to be almost unmagnetis- 
able in the latter direction if the internal field were relatively strong 
enough. An investigation, similar to the above, of the properties of a 
hexagonal arrangement would almost certainly give an explanation of the 
magnetic properties observed by Streng and Weiss in pyrrhotine, which 
is almost unmagnetisable along its axis. 
There can, I think, be little doubt that in the question of magnetic 
arrangement lies the explanation of the non-magnetic quality of 
certain alloys containing one or more normally magnetic constituents, 
and of the magnetic quality of others containing normally non-magnetic 
constituents. 
[Table 
