784 
DR. OLIVER LODGE ON ABERRATION PROBLEMS. 
No Doppler effect, therefore, is produced by a stream of medium flowing past 
source and receiver if relatively fixed, i.e., if they be moving together through a 
stationary mediam. 
We may in short summarise thus :— 
Source approaching shortens Avaves, 
Receiver approaching alters virtual velocity. 
Medium flowing alters wave-length and velocity together, in an exactly 
compensatory manner. 
Steady Motion of Medium cannot cause any Doppler Effect. 
54. Before abandoning the present consideration of the Dopj^ler effect, let us dis¬ 
tinctly assure ourselves of the important fact that no steady motion of the medium 
can change the pitch even infinitesimally, unless source ajid receiver are moving 
relatively to each other. Let source recede with velocity v, then the wave-lengths 
approaching us at their ordinary velocity V are longer than usual. 
Let receiver approach with same velocity, then it SAveeps up per second a number 
of waves 
Y + v V 
n = 
So, without relative motion of source and receiver, there is no Doppler eftect,. 
however small. 
But the easiest way of assuring ourselves of the impotency of a steady wind or 
pitch, is to remember that such a wind cannot bring Avaves at a greater frequenc} 
than they are emitted from the source. Gusts Avill cause Availing, but a steady Avind 
has no eftect on pitch. 
This is true also on a corpuscular theory, though for a slightly diflerent reason. 
For, consider a machine-gun receding and firing at regular time intervals, it A\’ill bt 
seen that, while the distance betAveen the bullets is the same as if it were statioua]’}’ 
the speed with Avhich they travel is V — v ; and, if a target is chasing the gun al 
the same pace v, the number caught in a second will be 
, (V — v) + v- 
n = -^- = n. 
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