DR. OLIVER LODGE ON ABERRATION PROBLEMS. 
743 
V ( CO.S e H— cos 6 
instead of 
or the equivalent air thickness, instead of being (/x 1 ) 2 :, is 
fJiZ 
cos e -I— cos 0 
0 - 
V cos e — a cos 0 
2; = 1 ^ - 1 2;, 
I 
0 ! 
or, to the first order of minutiae, (/r — \ )z — az cos 6 ; 6 being the angle between ray 
and ether drift inside the medium. 
So the extra equivalent air layer due to the motion is approximately ± olz cos 9, 
a quantity independent of jx. 
Hence, no plan for detecting this first-order effect of motion is in any way assisted 
by the use of dense stationary substances; theii’ extra ether, being stationary, does 
not affect the lag caused by motion, except indeed in the second order of small quan¬ 
tities, as shown above. 
Direct experiments made by Hoek,* and by Mascart, on the effect of introducing 
tubes of water into the path of half beams of light, are in entire accord with this 
negative conclusion. 
Thus, then, we find that no general motion of the entire medium can be detected 
by changes in direction, or in frequency, or in phase ; for on none of them has it any 
appreciable {i.e., first-order) effect even when assisted by dense matter. 
The remaining possible effect that may be looked for is a change of energy, 
Effect of Motion on Intensity of Radiation in Different Directions. 
t 
18. At first sight it looks as if there ought to be an unequal distribution of energy 
round a source past which the medium is streaming. For when the waves are drifting 
along, their energy moves too, and it can thus be distributed unsymmetiically round 
the source. 
The energy emitted per second, or the power of the radiation, is 
P = fTTp^Vq', 
where q is the energy per unit volume at distance p from the wave centre; supposing 
that radiating power is unaffected by the motion. So at a place r, 6 , reckoning from 
source as origin, and line of drift as initial line (as in fig. 4), since r = p (cos e -j- a co.s 9), 
* ‘ Ai’cliives Neerlandaise.s ’ (1869), \'oL 4, p. 443, or ‘ Nature,’ vol. 26, p. 500, 
