32 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXII.) 
one I am supposing-, and therefore I venture to put forth the idea*. The hope of a 
polarized bundle of magnetic forces is enough of itself to make one work earnestly 
with such an object, though only in imagination, before us ; and I may well say that 
no man, if he take industry, impartiality and caution with him in his investigations 
of science, ever works experimentally in vain. 
2592 . I have already referred, in the former paper ( 2469 .), to Plucker’s beautiful 
discovery and results in reference to the repulsion of the optic axis^f- of certain crystals 
by the magnet, and have distinguished them from my own obtained with bismuth, 
antimony and arsenic, which are not cases of either repulsion or attraction ; believing 
then, with Plucker, that the force there manifested is an optic axis force, exerted in 
the equatorial direction ; and therefore existing in a direction at right angles to that 
which produces the magnecrystallic phenomena. 
2593 . But the relations of both to crystalline structure, and therefore to the force 
which confers that condition, are most evident. Other considerations as to position, 
set, and turning, also show that the two forces, so to say, have a very different rela- 
tion to each other to that which exists between them and the magnetic or diamag- 
netic force. As, therefore, this strong likeness on the one hand, and distinct sepa- 
ration on the other is clearly indicated, I will endeavour to compare the two sets of 
effects, with the view of ascertaining whether the force exerted in producing them is 
not identical. 
2594 . I had the advantage of verifying Plucker’s results under his own personal 
tuition in respect of tourmaline, stanrolite, red ferro-prussiate of potassa, and Iceland 
spar. Sinee then, and in reference to the present inquiry, I have carefully examined 
calcareous spar, as being that one of the bodies which was at the same time free 
from magnetic action, and so simple in its crystalline relations as to possess but one 
optie axis. 
2595 . When a small rhomboid, about 0’3 of an inch in its greatest dimension, is 
suspended, with its optic axis horizontal, between the pointed poles ( 2458 .) of the 
electro-magnet, approximated as closely as they can be, to allow free motion, the 
rhotnboid sets in the equatorial direction, and the optic axis coincides with the mag- 
netic axis ; but, if the poles be separated to the distance of half, or three-quarters of 
an inch, the rhomboid turned through 90 ®, and set with the optic axis in the equato- 
rial direction, and the greatest length axial. In the first instance the diamagnetic 
force overcame the optic axis force; in the second the optic axis force was the 
stronger of the two. 
2596 . To remove the diamagnetic effect I used flat poles ( 2463 .), and then the little 
rhomboid always set in, or vibrated about, that position in which its optic axis was 
equatorial. 
* See note (2639.) at the end. 
t On the Repulsion of the Optic Axes of Crystals hy the Poles of a Magnet, Poggendoeff’s Annalen, vol. 
Ixxii., October 1847, or Taylor's Scientific Memoirs, vol. v. p. 353. 
