44 
PROFESSOR TYNDALL ON THE DIAMAGNETIC FORCE, ETC. 
APPENDIX. 
Received December 21, 1854. 
Reflecting further on the subject of diamagnetic polarity, an experiment occurred 
to me which constitutes a kind of crucial test to which the conclusions arrived at in 
the foregoing memoir may be submitted. 
Two square prisms of bismuth, 0*43 of an inch long and 0*2 of an inch wide, M^ere 
laid across the ends of a thin plate of cedar wood, and fastened there by white wax. 
Another similar plate of wood was laid over the prisms, and also attached to them by 
wax ; a kind of rectangular box was thus formed, one inch long and 
of the same width as the length of the prisms, the ends of the box 
being formed by the prisms, while its sides were open. Both plates 
of wood were pierced through at the centre, and in the aperture thus 
formed a wooden pin was fixed, which could readily be attached tq a 
suspending fibre. Fig. 1 represents the arrangement both in plan 
and section. 
The prisms first chosen were produced by the compression of fine bismuth powder, 
without the admixture of gum or any other foreign ingredient, the compressed mass 
being perfectly compact and presenting a surface of metallic brilliancy. If such a 
mass be placed on the end of a torsion balance and a magnetic pole is brought to 
bear upon it, I have proved the repulsion to be maximum when the direction in which 
the mass has been compressed is in the continuation of the axis of the magnet. A 
comparative view of the repulsion in this direction, and in another perpendicular to it, 
is given in the following Table. 
Compressed bismuth powder. 
Repulsion. 
A 
Strength of magnet. 
line of pressure axial. 
line of pressure equatorial. 
5-8 
22 
13 
8-4 
46 
31 
10-0 
67 
46 
] 1-9 
98 
6/ 
We see here that the repulsion, when the line of pressure is axial, exceeds what 
occurs when the same line is equatorial by fully one-half the amount of the latter. 
Now this can only be due to the more intense magnetization, or rather diainagneti- 
zation, of the bismuth along the line of pressure ; and in the experiment now to be 
described I availed myself of this fact to render the effect more decided. 
The prisms of bismuth were so constructed that the line of pressure was parallel 
to the length of each. The rectangular box before referred to was suspended frprn 
