( 673 ) 
definite value r, the same for the two kinds of rays. If then, Vj’ 
und Vs are the velocities of propagation, taken relatively to the 
moving ponderable matter, we shall have 
de 1 ) ‘ 
OOS = = ee IE . Py ° e e e 
Gn (11) 
For the velocity of one of the circularly polarized rays, Larmor 
finds (p. 214) 
‘ c v 
LA s 
where 
2 ne 
= K+ EP ECU Te Te 
À being the wave-length. a AE this value in (12), putting 
at the same time 
VN GAN blond zt Oe) 
we might obtain an equation, by means of which V;' could be 
elerinined in function of 7. We may however simplify by observ- 
ing that se has a very small value and that in (13) 4 occurs only 
in a term, containing this factor ¢. For this reason, it is allowed 
to substitute for 4 the value corresponding toe == 0. Thus, by (12), 
(13) and (14) 
i= (a 2). ERNA we erate Gt 
Let us now put 
C 
=p — Uy 
Ky? 
i. e., on account of (13), if we neglect the square of «s, 
c TEs 
U == ja = 1 a eos 5 . . . . . . 
then (12) takes the form 
; Ut 
Vi ZEE U, ke 2 Vv e ° ® . e e . (17) 
In order to obtain the velocity of the other circularly polarized 
ray, we have only to change the sign of &, so that we may write 
U2 
V;' = U >», OEE ele 2 aay 
where 
c Eg 
Y= zl! Sl Wah wee, eed okra Van CAP EN AAS 
It is to be remarked, that in this equation, as well as in (16), 
À has the value (15). 
Now, if we neglect terms containing v?, as we shall always do, 
