422 SCIENCE PROGRESS. 



seem already almost in a position to do in the case of some 

 gases. The dichroism of some crystals makes it possible 

 that some at least of their double refraction may be due to 

 a difference of frequency of the vibrations that control dis- 

 persion in different directions. 



The question thus arises whether we cannot, in accor- 

 dance with their principles, explain the differing rates of 

 propagation of right- and left-handed circularly polarised 

 light that Faraday observed to exist in matter in a magnetic 

 field. This Faraday effect might be due to one or other of 

 two causes. Either the magnetic field might cause a greater 

 interconnection between the matter and the ether for one 

 of the circularly polarised vibrations than for the other, 

 or it might cause the molecules that are vibrating round in 

 one direction to have their frequency increased while the 

 frequency of those vibrating round in the other direction 

 was decreased. Either of these causes would explain the 

 Faraday effect. The first of these is the kind of effect we 

 might expect to be produced by that action of magnetic 

 force on matter by which it is supposed to orientate the 

 molecules. This is the generally accepted cause of para- 

 magnetism and the Faraday effects in paramagnetic bodies 

 are sufficiently different from those in diamagnetic bodies 

 for it to be probable that their cause is somewhat different. 

 From this point of view it would seem natural to conclude 

 that in diamagnetic bodies magnetic force had the power 

 of altering the rates of vibration of the molecules and 

 causing the right-handed circularly polarised component 

 rotating round the lines of magnetic force to be executed 

 at a different frequency from that of the left-handed com- 

 ponent. It is well to consider these right- and left-handed 

 circular vibrations as components of a more general vibra- 

 tion because it is improbable that the actual vibration in 

 any one molecule is an accurately circular motion. It may 

 also be worth while pointing out that the result of com- 

 pounding two equal circular vibrations in the same plane, but 

 of slightly different frequencies is to produce a linear vibra- 

 tion whose line of vibration rotates in the plane of the two 

 circular vibrations. Hence we migrht describe the effect 



