3/4 PLUCKER ON THE REPULSION OF THE OPTIC AXES 



my opinion, sufficient to establish the general law laid down in 

 the first paragraph, and the existence of a new force which had 

 not hitherto been indicated by any phaenomenon. The relation 

 of the new results obtained by their means to the two discoveries 

 of Faraday, which form epochs in science, is too intimate to 

 allow of my passing it over unnoticed. 



It appears to me that philosophers do not yet attribute to one 

 of these discoveries, viz. that all bodies without exception are 

 either magnetic or diamagnetic, that importance which it really 

 possesses. Faraday has not only observed and described indi- 

 vidual phaenomena, like others before him, who could only have 

 been acquainted with half of them, when they designated them 

 as transversal magnetism, but he has announced a general law, 

 to which I without hesitation subscribe ; and he has pointed 

 out an entirely new action of the magnet in diamagnetism, 

 whereby the nature of magnetic attraction, which is already 

 essentially so enigmatical, is rendered still more so. I have made 

 many but unsuccessful experiments to discover a diamagnetic 

 polarity, or a test for matter in a state of diamagnetic excitation. 

 The simplest hypothesis at present appears to me, especially if 

 Ave wish to retain the established ideas regarding magnetic distri- 

 bution, to be that in which diamagnetism is regarded as a general 

 repulsive force of matter. 



As regards Faraday's other discovery, I agree with the com- 

 mon view, that in the observed rotation of the plane of polariza- 

 tion there is no direct action of the magnet upon the hght; but 

 that this is primarily produced by a magnetic or diamagnetic 

 action upon the ultimate particles of the mass, of which we have 

 permanent instances in many bodies occurring in nature, but 

 among crystals in rock-ci'ystal alone, and this only in the direc- 

 tion of the axis. 



48. My experiments have shown that a peculiar action is 

 exerted by the poles of a magnet upon every uni- or binaxial 

 crystal, for which we find an explanation when we suppose the 

 resulting action to be a repulsion of the axial directions, which 

 is independent of the magnetic and diamagnetic property of the 

 matter. This repulsion is evidently connected with the form of 

 the ultimate particles of the crystal, and appears to come into 

 play where the magnetism is not in a condition to produce a 

 transient molecular change, the result of which is the rotation of 

 the plane of polarization discovered by Faraday. 



