176 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXX.) 
diamagnetic force of a crystal in a given position at different temperatures. 1 have little 
doubt, however, that, according to the general action of heat, the power of the crystal 
to suffer a certain amount of induction in a given direction through it, is lessened in 
every direction as the temperature rises, and that the effects I have measured are 
simply the differences between the whole changes in each of two directions. Expe- 
riment only can decide, whether a sphere of tourmaline, or carbonate of lime, would 
remain affected by the magnet at temperatures which would cause the magnecrystallic 
character of these bodies to disappear ; but it seems almost certain that the diamagnetic 
force of a granular piece of bismuth must be equal to the sum of the forces of the 
variously arranged crystalline parts of which it is composed, and would disappear 
when their magnecrystallic character was taken from them by heat ; and it is also 
certain that the magnecrystallic character of such crystals as can hold together, is 
retained at very high temperatures. 
3420 . If the absolute magnetic and the magnecrystallic character of bodies should 
be found to coincide, then the examination of rnagnecrystals by heat would acquire 
increased interest. In many cases we can examine the magnecrystallic disposition 
of force better than the whole sum of force, and an examination of a part of the rate 
of diminution might give us a considerable insight as to the nature of the whole. 
Further, if the magnecrystallic and tlie magnetic indications agree, so that the one 
set may be accepted as representing the other, then we have tfie advantage in magne- 
crystals, of dismissing the influence (changeable as it is by temperature) of the 
surrounding medium altogether ( 3376 .). It is remarkable, that as no unmixed body 
has as yet altered in the character of its magnetism by heat, i, e. has not passed by 
heat from the paramagnetic to the diamagnetic class (assuming space, or its magnetic 
equivalent carbonic acid gas, to be at zero), or vice versa, so no simple magnecrystal 
has shown any inversion of this kind; nor have any of the three chief axes of 
power changed their character or relation to each other. This has to be borne in 
mind when considering the possible case of a magnecrystal at zero, before referred 
to ( 3393 .). 
It does not appear, from the direction of the lines in the diagram, that much increase 
in the diamagnetic power of the bismuth is to be expected from the application of 
any low temperature within our reach. Being the chief diamagnetic substance, and 
a metal, one would have wished it to have given a curve rather like that of carbonate 
of iron or even tourmaline. 
§ 40 . Effect of heat upon the absolute magnetic force of bodies. 
3421 . The time is coming on when we shall require to know the effect of heat on 
the total magnetic force (under induction) of such bodies as, being paramagnetic or 
diamagnetic, are near to zero, i. e. as near as bismuth or oxygen ; so that, amongst 
other points, we may examine the relation of the whole change of power to the change 
of the differential condition which occurs in rnagnecrystals. A difficulty, not met 
