517 
The times expressed in seconds, which the light requires to pass 
over each of the parts we call RODE nnen bern ep GER 
If the quartz is at rest, of course ¢,— 1", ete. If, however, the 
quartz moves with the velocity w, the time required to traverse the 
quartz column (length /) in the direction from 1 to 2 
= = iy reat. erker oD) 
c 1 c w 
A NED er 
in which the difference between the velocity of the light in quartz, 
and of that of the column itself must be taken into account. While 
the light is passing through the quartz, the quartz moves on, hence 
i, is changed by an amount: 
lw 1 
= = (2) 
C w C 
ema? 
We get for the ray in the opposed direction: 
l 
“= (3) 
c w 
u Wg 
and for the other quantity : 
lw 1 (4) 
planken 
in Ap 
u u 
For the first ray the entire difference of time becomes, therefore: 
l lw 1 
En : w ¢ w : c 
' Is TR 
and for the other 
