466 : REPORT— 1904. 
5. An Effect of Electrical Vibrations in an Optically Active Medium. 
By Professor W. Vora. 
Optically active isotropic bodies, which I propose to call psewdo-isotropic 
bodies, differ in their physical symmetry from the ordinary or real isotropic bodies 
by opposite directions of rotation being not equivalent. In the case of regular 
crystals, which in many respects show themselves to be physically isotropic, this 
difference is expressed in the crystalline form; in the case of isotropic bodies the 
phenomenon proving the pseudo-isotropic nature is that the right-handed and 
left-handed circularly polarised waves are propagated with different velocities. 
Compared with the real isotropic, the pseudo-isotropic bodies exhibit a peculiar 
property as regards the action of vector fields upon them. In real isotropic media 
a field of either polar or axial character always establishes a parallel field of the 
same character; for example, an electric force establishes a parallel electric 
moment, a magnetic force a parallel magnetic moment. In pseudo-isotropic 
media, on the other hand, an avial field can establish a polar field, and vice versa. 
These symmetric relations have been put to account, though without a definite 
knowledge of that general and fundamental law, in the trials made to deduce 
theoretically the laws of optical activity, whereby the components of a polar vector 
always were combined additively in the usual differential equations with the 
parallel components of an azial vector; for example, with the parallel components 
of the curl or of the rotation of this polar vector. 
Such procedure has, however, hitherto furnished no results other than the mere 
laws of the singular optical phenomena for the deduction of which it was conceived. 
But it is still highly probable that the pseudo-isotropic bodies differ physically 
from the real isotropic bodies also in other ways than their optical properties. 
I wish to speak to-day of an electro-magnetic action in the proper sense of this 
term, which is indicated by the equations of the electro-magnetic theory of optical 
activity, and with the experimental realisation of which I have busied myself within 
the past few months. 
The optical equations for the pseudo-isotropic media which I have proposed, and 
which Professor Drude also subsequently established, with the help of a special 
conception of the motion of electrons, are as follows : 
If € be the electric force, 
 , ,, magnetic force, 
v ,, 5, electric polarisation, 
yy) » magnetic polarisation, 
then, according to Maxwell and Hertz, 
RK=c rot H, £= —e rot G, 
and I put 
K=E+3x, L = 64395 
L+ar+ bi +eH=eG, 
where 2, U,,...is a system of polar vectors and a, b, c, e are constants individual 
to these vectors. 
The last formula expresses by the combination of ) and € that, in the pseudo-~ 
isotropic media, the electric vibrations excite parallel magnetic vibrations. 
For deducing by theory an observable electro-magnetic effect the following 
problem may be considered :— 
Let infinite space be filled with a system of standing plane electric waves, the 
wave surface being parallel to the Y / plane and the electric force parallel to the 
f axis. In one of the loops of these standing waves let a sphere be cut from some 
pseudo-isotropic medium. The diameter being small in comparison with the length 
of the waves, the sphere is always in a homogeneous field whose strength varies 
periodically. 
