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XXVIII. Note on ^Ether and Motion, 

 By Sir Oliver Lodge *. 



REFERRING to Dr. Houstoun's paper in the February 

 issue of the Phil. Mag., the supposition that the iEther 

 of Space can be in any sense attached to the body of the 

 Earth involves so many fundamental difficulties that it 

 cannot be considered an attractive hypothesis, and to my 

 mind it has been definitely negatived by a series of rather 

 elaborate experiments which I made at Liverpool in the years 

 1892-7. See Phil. Trans. 1893, vol. 184, p. 727, and 1897, 

 vol. 189, p. 149. 



Possibly these papers have escaped Dr. Houstoun's attention. 

 Taken in conjunction with the great experiment of Messrs. 

 Michelson and Morley, the combined result definitely drives 

 us to the view that the FitzGrerald-Lorentz contraction — so 

 probable on an electric theory of matter — is a reality. 



Dr. Houstoun seems inclined to think that to admit this 

 contraction is equivalent to admitting in full the negations 

 of the Principle of Relativity — not merely as a practically 

 convenient summary for dealing with phenomena which 

 otherwise would need detailed consideration, but as a law of 

 nature. I do not myself feel in the least compelled to admit 

 such a limitation, and hope that before very long some 

 method of detecting and measuring the drift of our solar 

 and stellar system through the stationary aether of space will 

 be forthcoming. At any rate the door ought not to be pre- 

 maturely shut on attempts in that direction, though the 

 problem is admittedly a curious and unexpectedly difficult 

 one : the compensations being so numerous and apparently 

 so complete. 



Incidentally I am glad to see, from his method of tackling 

 the matter, thatDr. Houstoun agrees with me in holding that 

 Fizeau's experiment does not establish any motion of the 

 aether of space inside a moving transparent medium: Fizeau's 

 result, anticipated by Fresnel, definitely proves that the main 

 body of iEther does not so move. All that moves with a 

 stream of illuminated water is the aetherial modification or 

 loading which is responsible for lessening the velocity of light 

 when travelling through a region occupied by matter. In 

 other words, the thing that travels is the extra K/z, which 

 belongs to the matter, over and above the value of the product 

 of these two fundamental aetherial constants in free space. 



Would that it were possible to determine the ratio or some 

 other function of these two constants, as well as their 

 product ! Then our knowledge of the iEther would indeed 

 begin to forge ahead. 



* Communicated by the Author. 



