and Stokes-Planck’s JEther.
161)
Such, then, would be the required refractivity of the •condensed aether, obeying aiiy law ^=/(/o). In particular, if it obeys Boyle's law, we have
.... (10 a)
which is of a surprisingly simple form, and reads: n2 —1 ^qual to four time'» the logarithm of condensation multiplied ly the squared ratio of the two velocities of propagation characterizing the cether.
Notwithstanding this temptingly simple form of the relation, I shall not try to “deduce” it from things more familiar. I prefer to regard it as an assumption, dictated by observation.
If the reader so desires, he can write n2 — l = 4w/c2, where w is the work, per unit mass of: matter, done by the gravitational field in condensing the aether. The small fraction w2 — 1 being known from the Eclipse results (for any r),the numerical value of this work is determined without any further assumptions. If we agree to the lowest estimate of log 5 at the Sun’s surface, as required by the aberration theory, we can also evaluate separately the ratio v/c, as already mentioned. This, however, is only a secondary matter.
7. Some details and further implications of the Stokes-Planck aether theory, supplemented by assumption (10), must be postponed to a later opportunity. Here it will be enough to add only a few more general remarks. It will be kept in mind that the proposed theory would account not only for the observed astronomical aberration and for the older terrestrial optical nil-effects, but manifestly also for the nil--effect of the Michelson-Morley experiment. The bending of rays round the more massive celestial bodies would be only a by-product of the theory. Again, in view of the exceedingly small condensation of the aether round single atoms or corpuscles there will be no difficulty in working out a satisfactory 'electromagnetic theory of ponderable media. The proposed theory would also have the advantage of not predicting th<* •obstinately absent gravitational shift of the spectrum lines. It might also react, in part at least, upon the 1905 relativity, depriving it of its indispensability in most cases, but by no means banishing it from the whole domain of physico-mathematical investigations. Finally, the just objections raised by the advocates of the physical principle of causality against the fixed and homogeneous aether of Fresnel-Lorentz would not apply to Stokes’s modified aether. For this
170
Sir Oliver Lodge on a Possible
latter would by no means be a mere framework of reference axes and, as such, illegitimately privileged. For in referring a class of phenomena to the aether here advocated we would ultimately refer them to assignable physical things, namely those most massive gigantic bodies which, so to speak, have the strongest grip upon that medium. It is, among other things, this latter remark that I hope to make particularly clear at an early opportunity.
London,
December 22, 1919.
XVI. Note on a Possible Structure for the Ether.
By Sir Oliver Lodge*.
DR. SILBERSTEIN’S communication gives me an opportunity for calling attention to a paper of mine on many points in connexion with the ether which must surely be of interest even to those who are contemplating the abandonment of that medium. In that paper an estimate is made of etherial density, and an attempt to measure experimentally its lower limit is described ; there are also comments of interest from Sir Joseph Larmor and Sir J. J. Thomson. The paper is in the Phil. Mag. ser. 6, vol. xiii. pp. 488—506, and is of date April 1907 ; though among other things it relates experiments conducted in and about 1893.
The transmission of transverse vibrations like light shows that the ether cannot be a mere structureless fluid; and if it is to be treated dynamically, which at first is surely a legitimate attempt, it must have properties akin to what we call, in matter, Rigidity and Inertia. Its inertia must be something fundamental, which underlies and accounts for the inertia we perceive in matter, possibly in a way having some analogy with a motion of a solid through a perfect fluid. For when an electric charge is moved, a magnetic field in the shape of an ether vortex-ring is generated (with an energy of circulation per unit volume equal to fi{eu sin Of/Hirr1), and this confers upon the charge its observed momentum if the medium has the requisite density (see Phil. Mag., April 1907, vol. xiii. p. 492). The rigidity may be explicable hydrodynamically by a vortex circulation—a turbulent motion having a circulatory velocity of the same order as that of the waves which the medium is able to transmit.
In Lord Kelvin's laminar vortex arrangement the velocity
* Communicated by the Author.