DR. OLIVER LODGE ON ABERRATION PROBLEMS. 
751 
presence of dense matter (water-filled telescopes) or otherwise {cf. ‘ Nature,’ vol. 4G, 
p. 498). 
However matter affects or loads the ether inside it, it cannot on this theory he said 
to hold it still, or carry it with it. ^ The general ether stream must remain unaffected, 
not only near, but inside matter, if rays are to retain precisely the same course as if 
it were relatively stationary. 
But it must be understood that the ethereal motion here contemplated is the general 
drift of the entire medium, or its correlative the uniform motion of all the matter con¬ 
cerned. There is nothing to be said against aberration effect being producible or modi¬ 
fiable by motion oiparts of the medium, as, for instance, by sliding one portion of the 
ether past another portion, as by the artificial motion of slabs and other partitioned-off’ 
regions. These matters are to some extent mixed up with the law of refraction, wliich 
we consider later, but the general ideas concerning them have been already given. 
Artificial motion of matter may readily alter both the time of journey and the path of 
a ray {cf §§ 7 and 52). 
Effect of placing Ordinary Matter in the j>cith of a ray in a Drifting Medium. 
Fresnel’s Law a special case of a universcd Potential-function. 
28. Inside a transparent body light travels at a speed V/p,; and the ether, which 
outside drifts at velocity v making an angle 6 with the ray, inside may be drifting 
with velocity v and angle 6'. 
Hence the equation to a ray inside such matter is 
T' = 
1 
ds 
(V/p) cose' -H v' cos 6' 
. sm 6 V , 
in in., wnere ^a . 
sin 0 \ fL 
This may be written 
T' = 
cos e' ds 
vif. (1 - 
cos 6' ds 
the second term alone involves the first power of the motion, and assuming that 
pV cos 6' = df /ds, and treating a.'^ as a quantity too small for its possible variations 
to need attention, the expression becomes 
rji/ _ rri COS 6 4*8 0 A 
~ ^ 1 - ~ VMl - cc'f ’ 
T being the time of travel through the same space when empty. Now, if the time of 
journey and course of ray, however they be affected by the dense body, are not to be 
more affected by reason of ethereal drift through it than if it w^ere so mucli empty 
