34 DR. FARADAY’S EXPERIMENTAL RESEARCHES IN ELECTRICITY. (SERIES XXII.) 
that there should be but one axis of crystalline force, either in the particle of Iceland 
spar, or in those of bismuth, does not seem to me to be any way consistent with the 
cleavage of the substances in three or more directions. 
2603. The optic axis in a piece of calcareous spar, is simply the line in which, if a 
polarized, or ordinary ray of light moves, it is the least affected. It may be a line which, 
as a resultant of the molecular forces, is that of the least intensity ; and, certainly, as 
regards ordinary and mechanical means of observing cohesion, a piece of calcareous 
spar is sensibly, and much harder on the faces and parts which are parallel to the 
optic axis, than on those perpendicular to it. An ordinary file or a piece of sand- 
stone shows this. So that the plane equatorial to the optic axis, as it represents 
directions in which the force causing crystallization is greater in degree than in the 
direction of the optic axis, may also be that in which the resultant of its magne- 
crystallic force is exerted. 
2604. I am bound to state, as in some degree in contrast with such considerations, 
that, with bismuth, antimony and arsenic, the cleavage is very facile perpendicular to 
the magnecrystallic axis (2475. 25 10. *2532.). But we must remember that the 
cleavage (and therefore the cohesive) force is not the only thing to be considered, 
for in calcareous spar it does not coincide with either the axial or the equatorial 
direction of the substance in the magnetic field : we must endeavour to look beyond 
this to the polar (or axial) condition of the particles of the masses, for the full un- 
derstanding and true relation of all these points. 
2605. I am bound, also, to admit that, if we consider calcareous spar as giving the 
simple system of force, we may, by the jaxtaposition of two crystals with their optic 
axes at right angles to each other, produce a compound mass, which will truly repre- 
sent the bismuth in the direction of the force ; i. e. it will, in the magnetic field, 
point with apparently one line of force only, and that in the axial direction, whilst it 
may be really moved by a system of forces lying in the equatorial plane. I will not 
at present pretend to say that this is not the state of things ; but I think, however, 
that the metals, bismuth, antimony and arsenic, present us with the simplest as they 
do the strongest cases of magnecrystallic force ; and whether that be so or not I am 
still of opinion that the phenomena discovered by Plucker and those of which I have 
given an account in these two papers, have one common origin and cause. 
2606. I went through all the experiments and reasonings with Plucker’s crystals 
(as the carbonate of lime, tourmaline and red ferro-prussiate of potassa), in reference 
to the question of original or induced power (2576.), as before, and came to the 
same conclusion as in the former case (2584.). 
2607- I could not find that crystals of red ferro-prussiate of potassa or tourmaline 
were affected by the earth’s magnetism (2581.), or that they had the power of affect- 
ing each other (2582.). Neither could I find that Plucker’s effect with calcareous 
spar, or red ferro-prussiate of potassa, was either an attractive or repulsive effect, 
but one connected with position only (2550. 2560.). All which circumstances tend to 
