^4 T/ztf Principles of MagnetisVn . [February, 
mass upon mass, in the production of permanent or of tem- 
porary magnetism, is the result of the aCtion of molecule 
upon molecule, they in the one case assuming a permanent, 
in the other a temporary, magnetic arrangement. It is not 
improbable that the differences in magnetic energy of dif- 
ferent substances arise from two causes only — the original 
weakness or strength of the magnetism of the atoms, and 
the degree of contiguity into which they are brought in their 
compounds. They necessarily aCt upon each other like 
separate magnets. If these be close together they control 
each other’s solar direction. Placed at a certain distance 
apart they fail to control each other’s direction. The same 
rule doubtless holds with atoms and molecules. Thep may. 
in their incessant motions, frequently come together so close 
as to mutually control each other, but they must be normally 
in this intimate relation to yield a permanent mutual control. 
Thus in one case the atoms of molecules may be so far 
separated as to feel no permanent mutual influence. In a 
second case they may permanently aCt upon each other, and 
the molecule become magnetic. But again the magnetic 
molecules of a mass may be so far separated as not to affeCt 
each other. In another case they may be close enough 
together to aCt upon each other magnetically. But even in 
this case local aCtion between them seems to hinder general 
aCtion, and to produce magnetic neutralisation in the mass 
as a whole. Only when forced into harmony through the 
energy of a strong exterior magnetism is this local aCtion 
overcome, and temporary or permanent magnetic relations 
produced between the molecules. as a whole. Astatic rela- 
tions arise between surface and axis, the equatorial diameter 
decreases through their mutual attraction, and the polar 
diameter increases through the pressure exerted. 
The relation thus produced between the molecules of a 
permanent magnet is one that is easily disturbed. Heat, by 
separating the molecules, overcomes it, local aCtion is re- 
sumed, and magnetic neutrality results. Tne influence of 
exterior magnets also disturbs, and often reverses it. Thus 
general magnetic relations between molecules is not a nor- 
mal condition of masses, since it never arises of itself, but 
always through external influence. 
It may be that the diverse magnetic behaviour of different 
substances is a consequence of the above relations of their 
molecules. All substances whose molecules are susceptible 
of assuming harmonious magnetic relations may be mag- 
netic ; all whose molecules resist being brought into harmo- 
nious magnetic relations may be diamagnetic. For a 
