792 
DR. OLIVER LODGE ON ABERRATION PROBLEMS. 
dnces any disturbance. At first I thought the lens and glass slabs used by him 
might possibly be the cause of his failure to get any result, because the ray across 
the motion travels through the glass obliquely, while along the motion it travels 
normally. But a little consideration shows that both along and across the motion the 
eftect of the glass would be to increase the lag in a simply proportional manner to 
the ]n-evious lag. And calculation gives as the time of the journey, when a total 
thickness 2 of glass is interposed, using Fresnel’s theory that the speed of the ether 
inside the glass is \I}j? of what it is outside. 
T — — 
' 1 “ ^ 
r — 5 
Y cos e + V cos 0 
+ 
V . V . 
— cos 6 + ^ cos a 
and T 3 = corresponding expression with v negative. 
So 
+ T3 = 
2 (?’ — z) cos e , „ 2yLi:' cos e 
Y (1 - «2) " 
2T cos e 2fMZ cos e / 1 
Y 1 - 
1 - 
+ 
1 - 
1 
w 
diere 
1 
.•> 
— a* 
T — ~ 1 ) " 
Y ’ 
wherefore the effect of introducing glass is to increase the lag, but not quite so much 
as by the equivalent of the extra distance thus virtually added, the second term in 
the above expression being negative ; but the diminution is independent of direction, 
except when fourth powers of aberration magnitude are attended to. Neglecting 
these, the effect of the glass is merely to cause, in addition to the lag naturally to be 
expected, an extra term, independent of direction, of this value : 
Mictiei.son’s Interference Experiment in a Different Medinrn. 
62. Indeed, the simplest plan would be to consider the effect of immersing the whole 
arrangement in a different medium. It is merely to change the light velocity Y to 
V/)u., and its mechanical velocity v to the ethereal velocity inside it. Con¬ 
sequently a becomes a/p. 
The aberration angle e changes to e'. such that 
O O' 
• ' _ ^ • /) 
sin € = “ sin u. 
