772 
MR. J. LARMOR OX A DYNAMICAL THEORY OF 
But a difficulty now presents itself as to why the molecule say of hydrochloric 
acid is always H -f Cl —, and not sometimes H — Cl +. This difficulty would 
however seem to equally beset any dynamical theory whatever of chemical com¬ 
bination which makes the difference between a positive and a negative atomic change 
representable wholly by a difference of algebraic sign.] 
The Connexion between xEther mid Moving Matter. 
71. A mode of representation of the kind developed in this paper must be expected 
to be in accord with what is known on the subject of the connexion between aether 
and matter, both from the phenomena of the astronomical aberration of light, and 
from recent experimental researches'^ on the motion of the aether relative to the 
Earth, and relative to transparent moving bodies. 
Let us consider a wave of light propagated through the free aether with its own 
specific velocity, and let it be simultaneously carried onward by a motion in bulk of 
the aether which is its seat. That motion will produce two effects on a wave ; the 
component along the wave-normal of the velocity of the aether will be added on to 
the specific velocity of the wave ; while the wave-front will be turned round owing 
to the rotational motion of the medium. The second of these effects will result in 
the ray being turned out of its natural path ; in order that the motion of the 
medium may not affect the natural path of the ray, it must therefore be of 
irrotational character. This will be the case as regards all motions of the free aether 
so long as we consider it to be hydrodynamically a frictionless fluid ; and the 
phenomenon of astronomical aberration is, after Sir George Stokes, explained, 
so far as it may depend on motion of the external aetiier. 
72 . The motion of the Earth through space may however be imagined as the 
transference of a vortex-aggregate through the quiescent aether surrounding it and 
permeating it; the velocity of translation of the aether will then be null, and 
consequently in the comparatively free aether of the atmosphere the velocity of the 
light will be unaffected, to the first order of aipproximation. But what should 
happen in transparent material media it is apparently not easy to infer. On the 
present A"iew of Optics, the density of the aether is constant throughout space, the 
mere presence of mobile electrified Amrtices in it not affecting the density though the 
effectiA-e elasticity is thereby altered. The nature of the further slight alteration 
of this elasticity produced by a motion of the matter as a Avhole, there appears to be 
no easy means of directly determining [see § 124] ; but the experiments may be 
taken as Aerifying Fresnel’s hypothesis that its effect is to add on to the velocity 
of ])ropagation of the ligfit the fraction 1 — of the A^elocity of the matter through 
Avhich it is moving, Avhere g represents the index of refraction. 
* .A. A. Michelsox and E. W. Moelea', ‘American .Tonrnal of Science,’ 1881 and 1886, also ‘Phil, 
Mag.,’ Dec., 1887; 0. J. Lodge, ‘Phil. Trans.,’ A, 189.3. 
