40 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXVI.) 
a proper relation to the positive and negative optic axis of such bodies*. In these 
cases a crystalline body sets powerfully, or takes up a particular position when placed 
in a field of magnetic force (2464.2479. 2550.), without reference to its paramagnetic 
or diamagnetic character (2562.), and also without assuming any state which it can 
on its removal bring away with it (2504.). 
2837. If the idea of conduction be applied to these magnecrystallic bodies, it would 
seem to satisfy all that requires explanation in their special results. A magnecry- 
stallic substance would then be one which in the crystallized state could conduct 
onwards, or permit the exertion of the magnetic force with more facility in one direc- 
tion than another ; and that direction would be the magnecrystallic axis. Hence, 
when in the magnetic field, the magnecrystallic axis would be urged into a position 
coincident with the magnetic axis, by a force correspondent to that difference, just 
as if two different bodies were taken, when the one with the greater conducting 
power displaces that which is weaker. 
2838. The effect of position would thus be accounted for (2586.) ; and also the 
greater aptness for m.agnetic conduction in one direction than in another (2588. 2591.) : 
and, what appeared to me as an anomaly in the supposition, that a line of force could 
have reference indifferently to any part of a plane (2600.) disappears. That heat 
should take away this conducting power (2570.) seemed perfectly consistent with 
what we know of the effect of heat on the magnetic condition of iron, oxygen, &c., 
and also upon the conducting power for electricity in such cases as platina, sulphuret 
of silver, &c. Finally, the assumption did not appear inconsistent with the state 
which the body seems to assume for the time during which it is under the magnetic 
force (2609. &c.). 
2839. But if such a view were correct, it would appear to follow that a diamag- 
netic body like bismuth ought to be less diamagnetic when its magnecrystallic axis 
is parallel (as nearly as may be) to the magnetic axis, than when it is perpendicular 
to it. In the two positions it should be equivalent to two substances having dif- 
ferent conducting powers for magnetism, and therefore, if submitted to the differen- 
tial balance, ought to present differential phenomena, corresponding in kind to those 
of oxygen and nitrogen (2774.), or phosphorus and bismuth, or any other two differ- 
ing bodies. Though I have given certain results on a former occasion which seemed 
to bear on this point (2551. 2552. 2553.), they are not satisfactory in the present 
state of our knowledge, because the difference, if any, would be small (2552.), and 
quickly hidden by the employment of a single pointed pole. Other experiments, 
formerly described (2554-2561.), would not show a small difference in diamagnetic 
force (though quite fitted for their intended purpose), because they were made with 
flat-faced poles, and a field nearly equal in magnetic power. 
2840. The differential torsion balance (2773.) enabled me to return to this matter 
with better hopes of success. A consistent group of bismuth crystals was selected 
* Philosophical Magazine, 1849, vol. xxxiv. p. 450. 
