Dr. Tyndall on Diamagnetism and Magnecrystallic Action. 177 



tact. The magnet was then excited and the sphere attracted. 

 The index was then turned in a direction opposed to the attrac- 

 tion until the ball gave way ; the torsion necessary to effect this 

 expresses the attraction. The crystal was first placed so that its 

 axis was parallel to the magnet^ and afterwards so that it was 

 perpendicular to the same. The following tables exhibit the 

 results in both cases respectively : — 



Table VII. — Carbonate of Iron, 

 axis of Magnet. 



Axis of Crystal parallel to 

 ?z = 25*5. 



Table VIIL 



•Carbonate of Iron. Axis of Crystal perpendicular 

 to axis of Magnet. /i = 20*7. 



We learn from these experiments that the law according to 

 which the attraction of carbonate of iron increases^ is exactly 

 the same as that according to which the repulsion of the calca- 

 reous spar increases, and that the respective forces manifest 

 themselves in both cases with the greatest energy in the direc- 

 tion of the optic axis. 



Let us observe for an instant the perfect antithesis which 

 exists between carbonate of lime and carbonate of iron. The 

 former is a diamagnetic crystal ; suspended before the single 

 pole of a magnet the entire mass is repelled, but the mass in one 

 direction is repelled with peculiar force, and this direction, when 

 the crystal is suspended in the magnetic field, recedes as far as 

 possible from the poles, and finally sets equatorial. The crystal 

 of carbonate of iron is, on the contrary, strongly magnetic ; sus- 

 pended before a single pole the entire mass is attracted, but 

 in one direction the mass is attracted with peculiar energy, and 

 this direction, when the crystal is suspended in the magnetic 

 field, will approach the poles and finally set axial. 

 . Sulphate of iron in the magnetic field displays a directive 

 action considerably inferior to that of carbonate of iron. Some 



