356 PLUCKER OX THE REPULSION OF THE OPTIC AXES 



when suspended very near one of the polar apices, it was at- 

 tracted by it. 



5. The same plate of tourmaline was now suspended in such 

 a manner, that the direction of its breadth coincided with that 

 of the silk thread, and thus tfie optic axis could oscillate freely 

 in a horizontal plane. The apices of the poles were not too near 

 each other, and were at last entirely removed. As a magnetic 

 body, the plate should have assumed such a position, that its 

 longitudinal and axial direction coincided with the line of the 

 apices of the poles. However, it assumed that position which 

 a diamagnetic body of the same form would have done, i. e. with 

 its axial and longitudinal direction perpendicular to the line of 

 the apices of the poles. 



6. The same plate of tourmaline was lastly again suspended 

 so that it, consequently its optic axis, could oscillate horizon- 

 tally. Again, as on its second suspension, it assumed the same 

 position as a diamagnetic body of the same form would have 

 done ; the direction of its breadth being in the line of the apices 

 of the poles, and its longitudinal and axial dXreciion perpendicular 

 to it. 



7. By opening and closing the circuit, in each of the three 

 positions of suspension, the tourmaline could be turned round 

 and retained in exactly the opposite position. 



8. If we admit that an equal repulsive force is exerted by 

 each of the two poles of the electro-magnet upon the axial direc- 

 tion of the plate of tourmaline, and that this repulsion is stronger 

 than the attraction of the same poles exerted upon the same axis 

 in consequence of the magnetic distribution in the ferruginous 

 mass of tourmaline, we obtain a comprehensive point of view, 

 under which the phaenomena above described may be conceived. 



As in the position assumed by the plate of tourmaline in ex- 

 periments 5 and 6, the magnetic attraction must first be over- 

 come by the new force producing the repulsion, it might be an- 

 ticipated that the phaenomena in question would be modified 

 when the magnetic rectilinear force was so increased that the 

 form of the crystal was such that the dimensions of its axial direc- 

 tion were very considerably greater than its other dimensions, and 

 the two apices of the poles were approximated as much as possible. 

 Thei'efore, after having again convinced myself of the accuracy 

 of my former experiments, and having found them confirmed by 

 means of a second plate of tourmaline of the same dimensions. 



