188 M. E. Edlimd 07i the Nature ofEleciricitij. 



chief cause of the phenomena studied by Wiedemann. But 

 regard must also be had to the current-force expressed by for- 

 mula (16), in virtue of which force the current tends to cause 

 the sether molecules at rest to move in a direction opposite to 

 its own. Now, if these molecules are intimately united with 

 material particles, these latter must be carried along in the same 

 direction. It is possible, therefore, to obtain for the particles in 

 a liquid traversed by a galvanic current a motion in the one 

 direction as well as in the other, since the direction depends 

 upon which force presents the greatest intensity. We think that 

 the phenomena of this category studied by Quincke "^^ may be 

 explained in this way, without having recourse to the action of 

 the free electricity which is found at the surface of the liquid. 



The circumstance that particles from the negative pole of a 

 voltaic arc are carried to the positive pole, although in consider- 

 ably less quantity than that of the particles which are detached 

 by the current and impelled in the opposite direction, it must 

 also be possible to attribute to the inductive force of the current, 

 understood according to the theory here given. 



7. Rotation of the ylane of iiolarization of light under the 

 action of the current. — In order to explain this phenomenon, it 

 has generally been supposed that the material molecules of the 

 transparent body in which the rotation is effected undergo a 

 direct action from the galvanic current, and that this action 

 produces the rotation of the plane of polarization. C. Neumann, 

 on the contrary, considers that the rotation results from the 

 action exerted upon the ssther molecules by Ampere^s molecular 

 currents, which are due to the action of the galvanic current. 

 He endeavours to demonstrate that the phenomena in question 

 can be explained by the hypothesis that those molecular currents 

 act upon the ?ether molecules as if these were electric. The 

 preceding statement upon the nature of electricity shows that, 

 of the two opinions, Neumann^s approaches nearest to the truth. 

 The eether of the transparent body round which the galvanic 

 current passes cannot, under the action of the current, be in the 

 normal state. The aether molecules have changed their posi- 

 tions of equilibrium ; and molecular currents of aether are esta- 

 blished, or, if they previously existed, have received a determined 

 direction under the influence of the galvanic current. Neumann^s 

 opinion relative to the direct action of the molecular currents 

 upon the molecules of aether is no longer an hypothesis requiring 

 confirmation, but a truth, if it be true that the phenomena of 

 electricity take place in the aether. Certainly, however, in this 

 explanation we must also have regard to the change in the 

 positions of equilibrium of the aether particles. 

 ^ Pogg. Ann. vol. cxiii. p. 513. 



