

oN 
‘ae ea 
LXIX. On the ascertained Absence of Effects of Motion through 
the Aither, in relation to the Constitution of Matter, and on 
the Fitz Gerald-Lorent: Hypothesis. By Prof. J. Larmor, 
Sec.R.S.* 
ia a recent paper by Prof. D. B. Brace (Phil. Mag. April 
1904, p. 318) the author removes by very refined experl- 
menting all trace of doubt from Lord Rayleigh’s conclusion 
that motion of transparent solids through the “ether does not 
induce any double refraction, even to the second order of the 
ratio of the velocity of the translation to that of radiation ; 
but he infers from this the non-existence of the second-order 
deformation of the solid due to its translation, suggested by 
FitzGerald and by H. A. Lorentz to account for Michelson’s 
earlier demonstrated absence of effect on optical interferences 
over long paths in free ether. As he remarks, it had 
previously been suggested by Lord Rayleigh that such an 
inference might possibly follow from this result. The object 
of this note is to explain that the inference in question is the 
opposite to that which I still hold to be the natural result of 
the theory of the motion of molecular aggregates through 
ether, as hitherto developed +. 
The argument of Prof. Brace proceeds on the basis that 
the whole effect of the convection through the ether is to 
introduce new ferces between the molecules, causing the 
shrinkage aforesaid along the direction of convection ; and it 
can be readily g oranted that if this were all, double refraction 
must result. But both the line of argument suggested as 
probable by Lorentz f, and the molecular analysis offered by 
me some years later §, proceed by comparing a system shrunk 
in the FitzGerald-Lorentz manner and convected through 
the ether, with the same system unshrunk and at rest, and 
finding a “complete correspondence between them as regards 
the states and activities of the individual molecules. As the 
argument is somewhat complex and has been misunderstood, 
a brief re-statement of the result may prove useful. 
We are to compare the field of physical activity of a 
system of molecules at rest, with the field of the identically 
same configuration of molecules in uniform translatory motion 
through ether. If small quantities of the order of the square 
of the ratio of the velocity of convection to that of radiation 
(v/c) are neglected, the Maxwellian physical equations for the 
* Communicated by the Physical Society: read May 27, 1904. 
+ ‘ Ather and Matter,’ Camb. Univ. Press, 1900, chapter Xi, 
t § Versuch emer Theorie,’ 1895, §§ 91-2 ' translated in part in ‘ Ather 
ea Matter,’ p. 186. § Loe. cit. 
