Royal Institution. 323 



A consequence of magnecrystallic structure is that the same 

 body is more paramagnetic, or more diamagnetic in one direction 

 than in another ; and therefore it follows, that though such a crystal 

 may have no variation in set-force, produced by change of the 

 surrounding medium, it may have a variation produced in the 

 absolute force of attraction or repulsion ; even up to the point of 

 being attracted in one position and repelled in another, though no 

 change in form, or in the suiTounding medium, or in the force of 

 the magnet, or in the nature of the body itself, be made, but simply 

 a change in the direction of the structure. This was shown by a 

 crystal of the red ferroprussiate of potassa, which, being coated 

 carefully with wax, was suspended from the arm of a torsion balance 

 so that it dipped into a solution of protosulphate of iron occupying 

 the magnetic field*. When the magnecrystallic axis was parallel 

 to the lines of force the crystal was attracted by the magnetic pole, 

 when it was perpendicular to the lines of force the crystal was 

 repelled ; acting like a paramagnetic and a diamagnetic in turns. 

 No magnecrystal has yet been found having such a relation to 

 a vacuum, or to carbonic acid (its magnetic equivalent) ; calcareous 

 spar is nearly coincident with such a medium, and shows different 

 degrees of force in the two directions, but is always a little on the 

 diamagnetic side. Calcareous spar having a trace of iron has been 

 found very nearly up to the desired point, on the paramagnetic 

 side ; and as these preserve the full magnecrystallic relation of the 

 two directions, there is no reason to suppose that a crystal may not 

 be found which may not be paramagnetic in one direction, and dia- 

 magnetic in another, in respect of space as zero. 



There is every reason to believe that the general magnetic rela- 

 tions of a magnecrystal are the same with those of the same substance 

 in the amorphous state ; and that the circumstances which influence 

 one, influence the other to the same degree. In that case, the magnetic 

 aflPections of a body might be ascertained by the examination of the 

 magnecrystallic affections ; thus the effect of heat upon bismuth, 

 tourmaline, &c., might be examined by the set of the crystals ; and 

 with so much the greater advantage, that short globular forms 

 could be used, perfectly free from the magnetic influence of the 

 surrounding media required as temperature baths, and requiring no 

 displacement of these media with the motion of the crystal. So 

 crystals of bismuth, tourmaline, carbonate of iron, and other bodies 

 were suspended in baths of oil, water, &c., the temperature gradually 

 raised and lowered, and the torsion force of the set for each tem- 

 perature observed. With bismuth, a crystal having a force of 200 

 at 20° F. was reduced to a force of 70 at 300°, and the diminution 

 of force appeared to be nearly equal in all parts of the scale for an 

 equal number of degrees. A piece of amorphous bismuth, com- 

 pressed in one direction, gave nearly the same amount and degree of 

 change for the same alteration of temperature ; leading us to the 

 persuasion that the whole magnetic force of bismuth as a diamag- 

 netic body would suffer like change. A crystal of tourmaline, which 



* 2\ volumes of saturated solution, at 65' F., and 1 volume of water. 



