Recent Progress in Theoretical Physics. 259 



cularly-polarized ligbt, when the direction of its vibratory rotation 

 and the direction of the magnetic rotation of the medium are the 

 same, is different from the rate of propagation when these direc 

 tions are opposite. 



The only resemblance which we can trace between a medium 

 through which circularly-polarized light is propagated, and a me- 

 dium through which lines of magnetic force pass, is that in both there 

 is a motion of rotation about an axis. But here the resemblance 

 stops, for the rotation in the optical phenomenon is that of the 

 vector which represents the disturbance. This vector is always 

 perpendicular to the direction of the ray, and rotates about it a 

 known number of times in a second. In the magnetic phenome- 

 non, that which rotates has no properties by which its sides 

 can be distinguished, so that we cannot determine how many 

 times it rotates in a second. 



There is nothing, therefore, in the magnetic phenomenon which 

 corresponds to the wave-length and the wave-propagation in the 

 optical phenomenon. A micdium in which a constant magnetic 

 foi'ce is acting, is not, in consequence of that force, filled with 

 waves traveling in one direction, as when light is propagated 

 through it. 



The only resemblance between the optical and the magnetic 

 phenomenon is, that at each point of the medium somicthing exists 

 of the nature of an angular velocity about an axis in the direction 

 of the magnetic force. 



ON THE HYPOTHESIS OF MOLECULAR VORTICES. 



The consideration of the action of magnetism upon polarized 

 light leads, as we have seen, to the conclusion that in a medium 

 under the action of magnetic force something belonging to the same 

 mathematical class as an angular velocity, whose axis is in the 

 direction of the magnetic force, forms a part of the phenomenon. 



This angular velocity cannot be that of any portion of the me- 

 dium of sensible dimensions rotating as a whole. We must, 

 therefore, conceive the rotation to be that of very small portions 

 of the medium, each rotating on its own axis. This is the hypoth- 

 esis of molecular vortices. 



