342 plCcker on the theory of diamagnetism. 



admixture of magnetic substances and the empirical law that the 

 diamagnetic excitation decreased more slowly with the distance 

 from the exciting pole than the magnetic. The manner of re- 

 viewing the subject stated in a former paragraph seemed to de- 

 rive additional confirmation from this new analogy. 



6. New experiments caused this analogy completely to disap- 

 pear. Whatever may be the intensity of the magnetism of the 

 electro-magnet, the prism of tourmaline always turns at the same 

 distance from the one position into the other. Quite otherwise, 

 however, was the deportment of the coal; here the moment when 

 the change of position takes place depends upon the inductive 

 force of the electro-magnet. Here, therefore, the law of distances 

 subordinates itself to another still more general law : as empiri- 

 cal law it remains true, but obtains another signification. The 

 distance as such comes into consideration only so far as the in- 

 tensity of the inductive action is dependent upon it. Thus I was 

 led to the assumption of the view that magnetism and diamag- 

 netism are forces of the same nature, and that the resistance 

 alone which presents itself to their excitation is different for the 

 various magnetic and diamagnetic bodies. 



7. According to this the peculiar action of an electro-magnet 

 upon crystals stands isolated. Could this action, could the re- 

 pulsion of the prism of tourmaline, to keep the same example in 

 view, be only apparent ? Such a prism, after it has taken up 

 the axial position, is really not the less attracted. For when 

 one of the two magnetic poles is removed, the prism approaches 

 the other pole without changing its direction. Hence we find, 

 particularly where the prism is caused to approach very near to 

 the pole, that an attraction of the mass and a repulsion of a di- 

 rection take place simultaneously. 



8. The idea which first presents itself, is to assume that the 

 magnetic induction suffered by the prism of tourmaline between 

 the poles is different in different directions. Assuming it to be a 

 minimum in the direction of the axis, we can easily give a gene- 

 ral explanation of the different positions assumed by a prism of 

 tourmaline between the poles of a magnet. 



9. But this hypothesis is contradicted by experiment. From 

 this hypothesis it would follow that a cube cut from such a 

 crystal would not be attracted with equal force when the three 



