180 Dr. Tyndall on Diamagnetism and Magneerystallic Act,ion, ^ 



perpendicular thereto in the ratio of 15 : 11 nearly. The general 

 fact of superior repulsion in the direction of tlie cleavages has 

 been already demonstrated by Mr. Faraday. 



What is it, then, which causes this superior manifestation bf^ 

 force in a cei-tain direction ? To this question experiment returns ' 

 the following reply: — "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 proxi- 

 mity, other circumstances being equal, will be that of strongest , 

 attraction in magnetic bodies and of strongest repulsion in dia- 

 magnetic bodies.'' 



The torsion-balance enables us to test this theory. A quan- 

 tity of bismuth was ground to dust in an agate mortar, gum- 

 w^ater was added, and the mass was kneaded to a stiff paste. 

 This was placed between two glasses and pressed together ; from 

 the mass when dried two cubes were taken, the line of compres- ' 

 sion 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 line of compression 

 turned strongly into the equatorial position, exactly as the plane 

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

 w^ere placed one upon each end of the torsion-balance ; first with 

 the line of compression parallel to the cores, and secondly with t 

 the said line perpendicular to the cores. The following are the 

 repulsions exhibited in both cases respectively. 



Table XL — Cubes of powdered bismuth, edges 7 millims. 

 of compression parallel to axes of cores. 



Line 



From this table we see that the law of increase for the artificial 

 cube is the same as that for diamagnetic substances generally. 



Table XIL— The same 



cubes. Line of compression perpendi- 

 cular to cores. 



