DK. OLIVER LODGE ON ABERRATION PROBLEMS. 
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for, ill the time of one vibration, the earth, which is the quickest available vehicle, has 
only moved a distance of xoWo of a wave-length ; which is equivalent to a middle 
C fork sounding and creeping along at the rate of 15 inches an hour. No practical 
question as to imperfection in spherical form of wave from moving source is therefore 
likely to arise. See however § 19, for discussion of a question not of i/mpc but of 
intensity. 
There happen to be one or two interesting things connected with the reflexion of 
light from a moving source when there is some connexion established between the 
reflected ray and the subsequent position of the source, e.g., as when a ray is reflected 
back upon itself, with the object of causing interference ; these are specially dealt with 
in §§ 59, 60. 
Case of Soui'ce and Receiver moving together through Stationary Medium; or, 
correlative case of Medium drifting past fixed Source amd Receiver. 
15. Consider a telescope fixed relatively to source, and medium drifting freely past 
both. The object-glass must be set skew to the wave front, but normal to the 
advancing ray or radius vector. 
In fig. 4, SM is the axis of the telescope, and it points straight at the source. 
There is no resultant aberration, the object is seen in its true position. 
It is also seen of its right colour, for the waves are carried to the receiver at their 
accustomed frequency: there is no Doppler effect. A steady wind alone is powerless 
to influence either direction or pitch. 
But what about interference phenomena, depending on the time of a given journey ? 
Manifestly a motion of the medium will be able to affect this, and may accordingly 
bring about the displacement of fringes representing hurry or lag of phase. 
Consider a telescope fixed relatively to the source and placed so as to receive light 
along the radius vector r. 
If the medium is stationary, the light journey is accomplished in the time 
but if moving, the time of the journey is 
rp/ _ 
V cos e V cos 6 ’ 
and so there is a hurrying up of phase 
T 
= cos e + a cos 6 , 
or 
T _T' ^ aT cos e. 
