328 Double Refraction in Matter moving through the Aither. 
between the two components which could exist in this kind 
of glass. 
If we estimate the contraction from the change in density 
by means of the excess of the index above unity, as was done 
in the case of water and as assumed by Rayleigh, the above 
fraction would become 
Oley 
On 
approximately. This is 50 times smaller than 0-5 x (1074), 
the change to be expected on the “ contraction ” hypothesis, 
and is 80 times less than the sensibility obtained with water. 
If, on the other hand, we take Wertheim’s * results for 
glass, we have approximately for Faraday’s flint, 5 x 10" as 
Young’s Modulus and 2-4x 107 dynes on a millimetre cube 
to give a relative retardation of one A. From above we have 
65 x 10° 
445 
as the relative retardation for 1 mm. 
Thus, the force to produce the least observable effect is 
2°4 x 10’ x 1°46 x 10-'=3°4 dynes per 1 mm. 
Young’s Modulus for 1 mm. square becomes 5x 10° and 
the contraction becomes 
a4 
a> LO? | 
which is seven times smaller than that expected on the ‘ con- 
traction ” hypothesis. If we correct by + for Poisson’s ratio, 
as we should if the interference problem were done on a 
glass support, the calculated contraction becomes 
03x (10-4)? <4 KL 
or six times larger than our margin for glass. 
Hence, if the test is a valid one, the “ contraction *’ hypo- 
thesis cannot explain the negative results of the interference 
experiments; and, with the same reasoning, we also conclude 
elther that the ether moves with the embedded matter, or 
that the effect of the relative motion on the intermolecular 
forces and the possible consequent relative change in dimen- 
sions are very small. 
x45x 10-2 or 107%, 
=1°46x107-'X% 
= OROrxTLO ae: 
Physical Laboratory, 
University of Nebraska, Lincoln. 
* Ann. de Chim. et de Phys, (3) t. xl. p. 202. 
