256 NOTICES OF THE MEETINGS [Feb. 11, 
The beautiful researches of Pliicker in this domain of science are 
well known. Pliicker’s first experiment was made with a plate of 
tourmaline. Suspended in the magnetic field with the axis of the 
crystal vertical, it set its length from pole to pole, like an ordinary 
magnetic body. Suspended with the axis of the horizontal, on 
exciting the magnet, Pliicker found to his astonishment that the 
largest dimension set equatorial. Let us see whether we cannot 
obtain this deportment otherwise. Suspending the piece of shale 
already made use of, so that its lamine were horizontal, on exciting 
the magnet the longest horizontal dimension of the plate set axial: 
moving the point of suspension 90° so that the laminz were vertical, 
on exciting the magnet the length of the plate set equatorial. In 
the magnetic field the deportment of the crystal was perfectly 
undistinguishable from that of the shale. But it may be retorted 
that tourmaline possesses no such laminz as those possessed by the 
shale : true— nor is it necessary that it should do so. A number 
of plates, bars, and disks, formed artificially from magnetic dust, 
exhibited a deportment precisely similar to the tournaline, — sus- 
pended from one point they set their lengths axial, suspended from 
another point the lengths set equatorial. Let us now turn to 
what may be called the complementary actions exhibited by dia- 
magnetic bodies. A homogeneous diamagnetic bar sets its length 
equatorial. But bars were exhibited composed of transverse dia- 
magnetic lamine which set their lengths axial. This experiment is 
complementary to that of the shale, &c.; the magnetic lamine set 
axial, the diamagnetic equatorial; and by attention to this the 
magnetic body is made to behave like a homogeneous diamagnetic 
body, and the diamagnetic body like a homogeneous magnetic 
body. Diamagnetic bars and disks were also examined, and a 
deportment precisely complementary to that of the magnetic bars 
and disks was exhibited. A magnetic disk set its thickness from 
pole to pole and consequently its horizontal diameter equatorial ; a 
diamagnetic disk set its thickness equatorial and its horizontal 
diameter from pole to pole. Two bodies of the same exterior form 
and of the same colour, were suspended simultaneously in the fields 
of two electro-magnets, and both the latter were excited by the 
same current; the eye could detect no difference of deportment. 
Both bodies possessed the shape of calcareous spar, and both set 
the crystallographic axis equatorial. One body however was com- 
posed of wax, while the other was a true crystal. In the same 
way a crystal of carbonate of iron exhibited a deportment precisely 
the same as that of a model formed of magnetic dust. The 
explanation of these phenomena may be given in a few words. 
In the construction of the models, the magnetic or diamagnetic 
dust was formed into a kind of dough and pressed between two 
glass plates ; the same process was applied to the wax; and it is 
a universal law, that in diamagnetic bodies the line along which the 
density of the mass has been increased by compression, sets equatorial, 
