282 Prof. Tyudall on the Nature vf the Force by which 



wax; a kind of rectangular box was thus formed, 1 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 B H 



plates of wood were pierced through at the ^ ° ^m 



centre, and in the aperture thus formed a ^_ _^ 



wooden pin was fixed, which could readily 

 be attached to 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 max- 

 imum 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 perpendi- 

 cular to it, is given in the following Table:— 



Compressed bismuth powder. 

 Repulsion. 



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 diamagnetiza- 

 tion, of the bismuth along the line of pressure ; and in the expe- 

 riment now to be described I availed myself of this fact to render 

 the efi'ect 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 from its centre of gravity 

 in the magnetic field, so that the two prisms were in the same 

 horizontal plane. Let the position of the box thus suspended 

 horizontally be that shown in fig. 2. For the sake of simplicity, 

 we will confine our attention to the action of one of the poles N, 

 which may be either flat or rounded, upon the prism ///adjacent 

 to it, as indeed all the phsenomena to be described can be pro- 

 duced before a single pole. The direction of the force emana- 



