THE ETHER AND MOVING MATTER 117 



indeterminate the units of transformation is here illustrated in the 

 theory of Larmor. 



In the most recent discussion by Lorentz, the necessity of a general 

 treatment is shown for not only the second but also the higher orders. 

 In a consideration of transparent media, his theory attempts to show 

 that translation would not alter interference, diffraction, or polar- 

 ization. He would thus, by means of the assumption of so-called 

 " Heaviside ellipsoids " as the shape of electrons, explain the negative 

 results of optical experiments, as well as the observations of Kauf- 

 mann on Becquerel rays. 



Attention should also be called to the recent theory of Abraham, 



4 / v\ 3 

 who gives as the ratio of the axes of the moving electron 1 - ( =.. j : 1, 



omitting fourth and higher orders. This would give a residual in 



l/v\ 2 

 double refraction of -f =z J = 2 X 10 ~ 9 for transparent media, which 



he acknowledges is difficult to reconcile with the experimental results 

 which show no double refraction to the first order beyond this. 



