DE. OLIVER LODGE ON ABERRATION PROBLEMS. 
753 
matter. If there is complete connexion, the ether near the earth is relatively 
stagnant, and negative results are natural. If there is complete independence, the 
ether is either absolutely stationary or has a velocity-potential, and the negative 
results are thereby explained. 
Ordinary astronomical aberration, and all other phenomena concerned with vision 
through strata high above the earth, so far as they have been accurately observed, 
are consistent with complete independence, but not with a viscous drag. 
On the other hand, the negative result of Mr. Michelson’s attempt to detect a 
second-order effect appears only to be consistent with relative stagnation. 
A doubtful positive result, supposed to be obtained by Fizeau (§ 26), on a change in 
the azimuth of the plane of polarization effected by transmission through oblique ' 
plates, would, if established, support relative motion between earth and ether. 
31. Is it possible for a sphere to move through a fluid without disturbing it 
rotationally and propagating rotary motion into space ? 
It is not possible for an ordinary solid moving through an ordinary fluid. Diffusion 
of motion, or viscosity, is bound to occur. 
It is possible for a vortex ring or assemblage of vortex rings, because at their 
surfa.ce there is no slip. It is possible also if the sphere be a solidified portion of the 
fluid, which condenses in front and evaporates behind (as already mentioned). 
Professor Stokes seems to say, that though not possible to retain a velocity- 
potential with any viscosity, yet with some kind of rigidity it may be possible, 
because deviations from irrotational motion go off into space with the speed of light. 
If so, the earth might possibly carry some ether with it, and }'et a ray be straight. 
I do not see any way in which it can abstain from rotationally disturbing the fluid 
if at the same time it has to carry some with it. Neither, I think, do Mr. Hicks or 
Mr. Larmor, to whom I wrote. 
Lord Kelvin, however (‘Papers,’ vol. iii., p. 436), has invented an “ether,” or 
kinematically rigid incompressible ideal substance, which satisfies electromagnetic 
equations and magnetic boundary conditions, whose equations of motion are like 
those of an elastic solid, and which yet permits locomotion of smooth solids filling 
vesicular hollows in it, and which in general “takes precisely the same motion for 
t any given motion of the boundary as does a frictionless incompressible liquid in the 
same space showing the same boundary.” 
The experiment now to be described proves, I think, that by the motion of ordinary 
masses of matter the ether is appreciably undisturbed, and raises a presumption in 
favour of the earth’s motion being equally impotent. 
The one thing in the way of the simple doctrine of an ether undisturbed by motion 
is Michelson’s experiment, viz., the absence of a second-order effect due to terrestrial 
movement through free ether. This experiment may have to be explained away; 
perhaps as suggested above (end of § 25). 
5 D 
MDCCCXCIIL —A, 
