468 Mr. S. S. Richardson on Magnetic Rotary 



The Correlation of Additive Properties in Magnetic 

 Rotation and Refraction. 



In seeking to obtain additive relations between the optical 

 properties of a substance, it is necessary to bear in mind that 

 the electrons associated with the atom of a given element 

 will possess different periods in different substances. The 

 polarization of the medium set up by the electric force of 

 the light- wave which, if averaged or smoothed-out would 

 be neutralized by the polar field of the medium as a whole, 

 owing to the discontinuous structure of matter, is locally 

 concentrated in the vicinity of the individual molecules. 

 The polarization near the molecules therefore exceeds the 

 polar field, and the excess constitutes a force acting on the 

 electron in opposition to the controlling force exerted by 

 the atom. The period of the electron is thus increased, and 

 must be distinguished from the period which the electron 

 would have if the atom were isolated. The degree of 

 augmentation, since it depends upon the degree of polari- 

 zation, will vary with the nature and density of the 

 substance. Any term of the dispersion formula which 

 represents the effect of the electrons of a given kind of 

 atom will possess different constants in respect of different 

 substances. This of course applies equally to magnetic 

 rotation. In order that the dispersion formulae for different 

 substances may all contain the same term for the electrons 

 of a given kind of atom, it is necessary to eliminate the 

 polarization effect and to obtain a summational expression 

 in terms of the isolation frequencies of the resonators. 

 Whilst the necessity for doing this has been generally 

 recognized in the case of refraction, it is noteworthy that, 

 with regard to the magnetic rotation, additive relations have 

 been sought for always from the values of this quantity as 

 directly measured. The influence of polarization on refrac- 

 tion has been fully investigated by H. A. Lorentz, and the 

 components of* molecular refraction are usually determined 

 from the well-known Lorenz-Lorentz formula. The results 

 are more consistent than those obtained from magnetic 

 rotation, and the latter quantity has therefore been regarded 

 as more highly constitutive than refraction. Whilst this 

 may be quite true, it is clear that polarization effects should 

 be eliminated in the magnetic case and the contribution of 

 each electron expressed in terms of the isolation frequency 

 of that electron. 



Lorentz * deduces an expression for the rotation which, 



* ' Theory of Electrons/ p. 163, eqn. (246). 



