OF CRYSTALS BY THE POLES OF A MAGNET. 359 



a magnet ; and that this repulsion, in ordinary cases when the 

 mass of the tourmaline is magnetic, at a sufficient distance from 

 the pole itself, and when the largest dimensions of the crystal 

 are in the axial direction, overcomes the produced magnetic 

 attraction of the axis. 



Here it naturally occurs to us to inquire, whether the above 

 phaenomena may not perhaps stand in close relation with the 

 well-known fact, that the tourmaline, when heated and cooled, 

 exhibits electric polarity. That must however be decidedly an- 

 swered in the negative. 



15. It might certainly have been possible, that by touching 

 the tourmaline w^hilst suspending it, electric currents had been 

 excited in its substance. But after the tourmaline had remained 

 undisturbed under the glass case of the torsion-balance for 

 twenty-four hours, and the electro-magnet was then set in ac- 

 tion, it exhibited exactly the same phaenomena ; and no difference 

 could be perceived in it even when it was rendered electrical at 

 its extremities by being heated whilst between the poles of the 

 magnets. 



16. When the tourmaline was suspended in water, it also as- 

 sumed a decided position, from which it was not disturbed when 

 the water was heated to near the boiling-point. With the moist- 

 ening of the surfaces of the crystal which occurs in this experi- 

 ment, no electric tension can occur ; if this tension, however, 

 is the consequence of internal electric fluctuations, it might per- 

 haps be expected that the latter were promoted by the continual 

 conduction of the free electricity appearing on the surface. 



17. The most decided proof of the inaccuracy of the assump- 

 tion of electric currents ivithin the crystal which have not been 

 primarily excited by the magnet being the cause of the phaeno- 

 mena in question, exists in the fact, that these currents, whatever 

 direction may be ascribed to them, w^ould produce a polar repul- 

 sion of the axial direction. But experiment contradicts this 

 most decidedly. 



18. Since the repulsion of the axial direction by the poles of 

 the magnet is therefore not of pyro-electric origin, we should 

 expect that it would not be. confined to tourmaline, in which I 

 had first accidentally met with it, and to a few other crystals. 

 After a preliminary experiment upon a small piece of rock-cry- 

 stal had shown it to exist in this also, I commenced examining 

 various crystals, and first those which are uniaxial. In doing 



