Relative Motion of the Earth and the JEther. 809 



diameter of an ether molecule must therefore be less than 

 •51 x 10 -8 cm. 



It follows, therefore, that since there are fifteen atoms in 

 an ether molecule, the average diameter of an atom in com- 

 bination is less than 5'1 X 10 -10 cm. Since this is less than 

 the accepted diameter of a molecule of hydrogen the result 

 suggests that the atoms contract when combining to form a 

 molecule. Further evidence that such a thing occurs will 

 be given in a subsequent paper. 

 Cambridge, Feb. 11, 1910. 



Z 



LXXXI. The, Relative Motion of the Earth and the ^.Etlier. 

 By Prof. Harold A.Wilson, D.Sc, E.K.S., McGill Uni- 

 versity, Montreal *. 



^P'HE following paper contains an attempt to reconcile 

 -L the phenomena of the astronomical aberration of light 

 and the negative results of the experiments made to detect 

 relative motion between the earth and the aether, without 

 supposing that bodies change in length when they are set in 

 motion relative to the sether. It is shown that this can be 

 done, and that the facts available are sufficient to determine 

 the relative motion at any point outside the earth. A theory 

 is then described which appears to offer an explanation of the 

 motion deduced. 



According to Sir George Stokes' well-known theory, 

 aberration can be explained by supposing that the motion 

 of the aether outside the earth is purely irrotational. It 

 appears to be generally supposed t that it is necessary in 

 Stokes' theory for the aether to be carried along by the earth 

 so that at the earth's surface there is no relative motion. 

 That this is not the case was pointed out by Stokes himself j. 

 He made this supposition merely because he regarded it as 

 unlikelv that the earth could move through the aether without 

 setting it in motion. The statement frequently made that 

 Stokes' theory fails because no irrotational motion of the 

 pether can be found which satisfies the condition that the 

 pether is at rest relative to the earth at the earth's surface is 

 therefore not really justifiable. As Stokes has shown, the 

 path of a ray of light is unaltered by any irrotational motion 

 of the aether, so of course aberration is unaffected by any 

 such motion. Irrotational motion of the aether can only 



* Communicated by the Author. 



t See, for example, H. A. Lorentz, ' Theory of Electrons,' p. 173. 

 J Mathematical and Physical Papers, vol. i. pp. L'39 & 15(3. Also 

 Phil. Mag-, vol. xxix. p. (i (July 1840). 



