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THE 
LONDON, EDINBURGH, ann DUBLIN 
PHILOSOPHICAL MAGAZINE 



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JOURNAL OF SCTENGE. 
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[SIXTH SERIES.]. SG; 
ERE 10k 
XXXVII. On Double Refraction in Matter moving through 
the Aither. By D. B. Bracr*. 
FENHE FitzGerald-Lorentz + “Contraction”? Hypothesis to 
explain the negative results of the Michelson-Morley t¢ 
experiment of interference between two rays, at right angles 
and parallel to the earth’s motion, has been tested by 
Rayleigh § in his experiments on the double refraction of 
liquids and of glass. He assumes the contraction to be 
(10-+)?, and also the excess of the index above unity to be 
proportional to the density. The first assumption is appa- 
rently in error by a half and should be 0°5x10-°. The 
second assumption does not seem to be entirely valid for 
glass, at least, when compared with the double refraction 
produced by a given strain. ‘The first correction reduces his 
margin down to 50 times for a liquid and 1°5 times for glass. 
The second will reduce the margin to considerably less than 
unity for glass, which would thus leave us only the obser- 
vations on liquids upon which to base our conclusion. 
While the method of Rayleigh cannot be regarded by any 
means asa conclusive test of the hypothesis, it is the only 
experimental one attempted and can be extended so as to give 
a safe margin for a solid like glass. 
This suggestion of the “contraction”? hypothesis by 
Lorentz, from considerations in regard to intermolecular 
forces analogous to the interaction, through the mediation 
* Communicated by the Author. 
+ Versuch einer theorie, Leiden, 1895; 
t Amer. Journ. of Sci. (8) xxxiv. p. 333 (1887). 
§ Phil. Mag. Dec. 1902. 
Phil. Mag. 8. 6. Vol. 7. No. 40. April 1904. Z, 
Pn Nye 
