178' WEBER ON THE CONNEXION OF DIAMAGNETISM 



were coincident, until the discovery of the phsenomena of inter- 

 ference led to the more accurate investigation of those points in 

 which the theories contradicted each other. Now, although 

 the two theories resulting from the assumptions of magnetic 

 fluids and of molecular currents have heretofore exhibited a 

 surprising coincidence in their results, it might, nevertheless, be 

 expected that here, as in optics, the discovery of a new class of 

 phaenomena would lead to a closer discussion of the points 

 wherein both theories differ. Both theories, indeed, coincide — 

 1st, in all phaenomena which relate to permanent magnets', 2ndly, 

 in the circumstance that each permits of a division of variable 

 magnets into two classes, namely, into such as owe their mag- 

 netism to the mere arrangement of already existing rotatory 

 molecules (molecular magnets or molecular currents), and into 

 such as owe their magnetism to the excitation of the motion of 

 imponderable fluids in motionless molecules (the separation of 

 magnetic fluids in the molecules, or the excitation of electric 

 currents in definite circular paths around the molecules) ; 3rdly, 

 both theories agree in their results with regard to the first class 

 of variable magnets. The theories, however, contradict each 

 other in the results which have reference to the second class of 

 variable magnets, for their conclusions regarding the positions of 

 the poles are opposed to each other. In accordance with the 

 one, the positions of the poles, in the second class of variable 

 magnets, must be the same as those in the first class ; in 

 accordance with the other, the positions of the poles in the 

 second class must be the reverse of those in the first. So long, 

 therefore, as variable magnets in which the positions of the 

 poles (for similarly directed magnetizing forces) were identical 

 were the only ones known, both theories might be applied ; but 

 as soon as variable magnets (diamagnets) were discovered, in 

 which the positions of the poles (for similarly directed magnet- 

 izing forces) were opposed to each other, no further choice 

 remained between both theories, for the second alone can render 

 an account of the generation of two classes of magnets with 

 poles oppositely situated, the directions of the magnetizing 

 forces being the same. 



The diamagnetic phaenomena discovered by Faraday serve, 

 therefore, to decide the alternative between both theories, just 



