for the Advancement of Science. 269 



nevertheless from pole to pole with an energy far surpassing that with 

 which ihe optic axis of carbonate of lime sets perpendicular to the line 

 joining the poles- But why is it that one direction in the crystal takes 

 up a particular position ? The torsion balance gives a prompt answer 

 to this question. A sphere of calcareous spar was placed upon each 

 of the spoon-shaped hollows of the beam, the direction of the optic 

 axis through each sphere being carefully marked. The spheres were 

 first placed so that the optic axes were parallel to the axes of the soft- 

 \ iron cones, — and secondly, perpen(5icular to the same. The repulsion 



in the former case was to the repulsion in the latter in the ratio of 53 

 to 48. If a bismuth crystal be suspended between two poles, the plane 

 of nnost eminent cleavage will always set perpendicular to the line join- 

 ing the poles, that is, equatorial* A cube formed from this crystal was 

 placed on each end of the little beam ; first, so that the planes of prin- 

 cipal cleavage were parallel to the axes of the cones; and secondly, 

 perpendicular to them. The repulsion in the former case was to the 

 repulsion in the latter, in the ratio of 53 to 38. The diamagnetic mass 

 'n both these cases is repelled with a greater force in one direction 

 than in any other direction. When the crystal is suspended between 

 two poles, the line which marks the direction of maximum repulsion re- 

 V cedes as far as possible from the poles, and hence sets equatorial. 



A result the exact antithesis of the above was observed with mag- 

 netic crystals. A cube of sulphate of iron was attracted in one direc- 

 tion by a force of 43, and in another direction by a force of 36*3. A 

 sphere of carbonate of iron was attracted in the direction of the optic 

 axis by a force of 43, and in a direction perpendicular thereto by a 

 force of 30-5. When these crystals are suspended between two poles, 

 these lines of chief attraction approach the poles, and finally set axial. 

 Thus we see that the peculiar phenomena exhibited by crystals in the 

 ^Tiagnetic field are to be referred to a modification of magnetism or dia- 

 ^T^agnetism brought about by the peculiar structure of the crystal. Let 

 ^^ endeavor to penetrate this mystery of structure. Our next inquiry 

 IS— what direction is that which is chosen by the respective forces for 

 the manifestation of their greatest energy } To this question the au- 

 f thor imagines that a full and Intelligible reply is returned by experi- 



"^eni. If the arrangement of the component particles of any body, be 

 such as to present different degrees of proximity in different directions, 

 then the line of closest proximity (other circumstances being equal) 

 ^vill be that of strongest attraction in magnetic bodies, and of strongest 

 repulsion in diamagnetic bodies. The torsion balance furnishes us with 

 the means of submitting this conclusion to a direct test. A quantity of 

 bismuth was ground to dust in an agate mortar, gum-water was added, 

 and the mass was kneaded into a stiff paste. This was placed between 

 two glasses and pressed together. From the mass when dried two 

 cubes were taken, the line of compression being perpendicular to two 

 of the faces of each cube and parallel to the other four. Suspended 

 by a silk fibre in the magnetic field, upon closing the circuit the Itne of 

 compression turned strongly into the equatorial position, exactly as the 

 plane of most eminent cleavage in the case of the crystal. The cubes 

 jyere placed one upon each end of the torsion balance, first with the 

 ^^ne of compression parallel to the axis of the cones, and secondly per- 



