THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



\ c/ 



FEBRUAR Y 1920. 



XV. The recent Eclipse Results and Stokes-Planck's JEther. 

 By L. Silberstein, Ph.D., Lecturer in Mathem. Physics 

 at the University of Rome*. 



1. TT is well known that, in 1845, Stokes proposed a 

 JL theory of aberration (Phil. Mag. xxvii. p. 9), which 

 was based on the assumption that the luminiferous aether 

 surrounding our planet is dragged along in its annual motion 

 so that the velocity of the aether relative to the Earth is nil 

 at its surface, and, increasing continuously, becomes equal 

 and opposite to the Earth's velocity at very large distances 

 from the Earth or, to put it short, at infinity. The purpose 

 of this hypothesis, as opposed to that of Fresnel's stagnant 

 aether, was to give a rigorous independence of all purely 

 terrestrial optical experiments from the Earth's annual 

 motion (combined with that of the solar system). In order 

 to account for the semi-terrestrial phenomenon known as 

 astronomical aberration, Stokes had to assume that the 

 motion of the aether, between the Earth and the stars in 

 question, is purely irrotational. But, by a well-known 

 theorem of hydrodynamics, this assumption was not com- 

 patible with the incompressibility of Stokes's aether and, at the 

 same time, with the absence of slipping over the Earth's 

 surface. 



2. In order to overcome this essential difficulty Max 

 Planck has suggested that the incompressibility could be 



* Communicated by Sir Oliver Lodg-e. 

 Phil. Mag. S. 6. Vol. 39. No. 230. Feb. 1920. M 



