130 
of theory we can expect to derive some insight into the molecular 
mechanism of the magneto-rotatory power; I hope I shall be able 
to revert to this subject in a subsequent paper. In the following 
pages I intend to consider a particularity of the phenomenon which 
I thought would be of interest to examine more closely than has 
hitherto been done. 
§ 1. It will be proper to commence with the consideration of 
a simple kinematical proposition. Suppose a right-handed circularly 
polarized wave, of amplitude oq, propagated with velocity c x in the 
direction of 2 : 
(la) 
(lb) 
and a left-handed circularly polarized wave, of amplitude a 2: tra¬ 
velling with velocity c 2 in the same direction: 
(2a) 
(2b) 
The superposition of the two waves gives an elliptic vibration 
(3a) 
(3b) 
g-—a cos n (t — a) 
r\ — b cos n(t — ß) ; 
here: 
(4a) 
IVA/ . 
a cos n a = cq cos-1- a 2 cos — 
Ci c 2 
nz . nz 
(4b) 
YIZ 1%Z 
a sin na = a x sin- \~ a 9 sin — 
(4c) 
7ÏZ 71Z 
b cos n ß = a x sin- a 2 sin 
c t c 2 
. nz 
(44) 
7 • a i 
b sin n ß = — a ± cos- [- a 2 cos — . 
Ci c 2 
nz . nz 
It follows that if we put 
( 5 ) 
