DR OLIVER LODGE ON ABERRATION PROBLEMS. 
785 
Effect o f Moving Medium on Doppler Effect. 
55. Bnt finally examine if wind ha,s any eftect on pitch when source and receiver 
are not moving at the same pace, i.e., when a Doppler effect certainly exists. Let 
source recede with speed u, receiver advance with speed v, and let the medium flow 
from source towards receiver at speed w (or in any direction at speed sec d ; the 
argument is the same):— 
Then speed of wave is 
V + m. 
Length of each is 
, Y + vj + 1/ V + ?n + n 
A = -r:;- A =- 
\ a. 
The number caught per second is 
/ 
n 
+ to 4 - V 
V 
+ 'W + 7' 
V + 7r + ■!(, 
or 
(ill u — V 
n \ + 70 + r 
The medium velocity does, therefore, enter into the expression for the ordinary 
Doppler effect, though in a very subordinate manner, by affecting the velocity of light. 
It cannot cause the effect, but it can modify it when otherwise produced. 
The simplest plan of detecting this effect of a moving medium, would be by some 
direct observation of the velocity of light itself; either simultaneously from stars in 
two opposite directions, or in a given direction at six months’interval. No terrestrial 
object must be used as source, because it would be moving at practically the same 
rate as receiver. Hence, for a six-months’ experiment, the Jupiter’s satellites method 
of determining the velocity of light would seem the best plan ; and, if observations 
could be exact enough, one could thus get 
V — {w v) 
V + ( 7 /; + v) ’ 
and so determine iv the unknown speed of the ether past the solar system. 
A simultaneous aberrational method, such as comparing the aberration of two 
stars 180° apart, will not work well; for if they be at 90° to the apex of earth’s 
motion there will be no discrepancy, while if one be toward that apex and the otlier 
away from it there will be no aberration. 
MDCCCXCTII.—A. 5 H 
