1882,1 [The Principles of Magnetism. 75 
substance to be magnetic all its molecules must respond to 
external magnetic attraction, and shift the directions of their 
poles in accordance therewith. But it may be possible for 
the molecules to be so related to each other individually 
that a general conformity of direction is vigorously opposed 
by those local relations of harmony. As two or more mag- 
nets brought together upon the earth’s surface affeCt each 
other so strongly as to overcome the energy of terrestrial 
magnetism, and enter into local relations of astatic or gene- 
ral harmony, so it may be with molecules. They may be so 
combined as to form local groups, in which a certain astatic 
neutralisation takes place, and thus relieves them from the 
influence of other, similarly neutralised, groups. 
In such a case the molecules would probably resist the 
influence of a powerful exterior magnetism. It is a question 
of the balance of vigour between the local relations of the 
molecules and the vigour of the exterior magnet. In some 
cases the local relations may be overcome, and a general 
relation produced, either permanent or temporary. In other 
cases this general relation may be vigorously resisted, the 
local a( 5 tion of the molecules displaying the same resistance 
as the local aCtion of magnets does to terrestrial magnetic 
energy. In the latter case the phenomena of diamagnetism 
must appear. 
For if the molecules refuse to shift the directions of their 
axes in response to external magnetic energy, they must in 
some other manner respond to this energy. The positions 
of some of them must be such as to render them less resist- 
ing than others. In the case of certain crystals, for instance, 
the resistance is less effective in one crystalline axis than in 
the others, and the crystal sets axially in this direction. 
But if there be no such special axis the effeCt of resistance 
to magnetic leverage must tend to force the resisting mole- 
cules out of the line of magnetic force, until the smallest 
possible member remained in this line. The mass sets 
eqcatorially to the magnetic axis. 
There is here no repulsion. The effeCt is in direct 
response to magnetic traCtion. It is the result of a strain 
between external and internal forces. Where the molecules 
yield individually to the external energy, and shift their polar 
directions into conformity therewith, the mass must set 
axially. Where their mutual influences enable them to 
resist this individual aCtion, the same influence causes them 
to move bodily, and in such directions as to reduce the con- 
flict between external and internal energies to the smallest 
sum. The mass sets equatorially. If this be the case, then 
