519 
Through the relativity transformation: 
mar bet , tai NO (4) 
c 
and 
' Li U b ' 
nest deb gtt 
c 
we may pass to a system, in which the rod moves with a velocity : 
be 
ee atten) re eer Eft (BD) 
a 
From (2) and (3) we derive 
a, cos |» (« — =) - | and a, cos E (« — = + n' p | . (6) 
c c 
Tad) eenn a Te ee as dak CD) 
The phase difference between (1) and (2), ie. the change of phase 
brought about by the presence of the rod, is given by (3) in angular 
measure, and this same difference of phase still exists between the 
expressions (6). 
Expressed in wave-lengths or periods, it is: 
A <t 
bele): NN) 
2Za\e v 
Here, however, we must express n/ and v’ in the n and v corre- 
sponding to it. When we neglect the terms of the second order, 
