DR. OLIVER LODGE OR ABERRATION PROBLEMS. 
789 
and therefore neutralized ail refraction, except what was entirely caused by motion, 
when he proved that this latter was nil. 
Babinet, Hoek, and Mascart, all tried a modified form of the same experiment 
in an interferential manner, and likewise got a negative result. 
58. If we wish to follow out the ether motion through a prism into greater detail we can say :— 
Let the prism advance with velocity v to meet the waves, and let the ether in it be canled forward with 
velocity lev, then the virtual velocity of the light towards the prism is V + v, and inside the prism is 
hence, on ordinary notions of refraction the new index will be 
, _ (V + v) y . 
^ (V + -y) - le^iv ’ 
or 
^ = I - knoc, 
h 
where 
X — w/(V -f- I/) = tZX/X, 
or 
d/.L = hj-fia,, 
which, on Fresnel’s hypothesis, equals (/ti^ — 1) a. 
This seems to give a sort of theory of dispersion for the case :— 
or 
or 
- I 
/t — I 
_ dX 
“ T’ 
= AX2, 
/<- + 1 
c- + x: 
c2 - X'-J 
Interference Effects ivith Rays at Different Angles to Ether Drift, Effects of Normal 
Reflexion. Further Discussion of the Theory of Mr. Michelson’s Exjoeriment. 
59. The experiment of Michelson, already referred to in § 25, has to do with the 
effect of a plane mirror sending a ray straight back upon itself. Consider the aspect 
of the mirror necessary to do this ; first, for the case of a moving source in a stationary 
medium (fig. 15). 
Let Sj be initial position of the source, throwing olf a wave-front to M, and itself 
moving to S, so that 
SjS = ; and S^M = i\ — VT^. 
Let SM now be reflected at M so as to travel to Sg, and reach it the same time as 
source, then 
SSg = uTg; and 
