210 



DOUBLE REFRACTION, ETC. 



have thus been derived from the single hypothesis that the disturb- 

 ance by which light is transmitted consists of solenoidal electrical 

 fluxes, and which apply to light of different colors and to the most 

 general case of perfectly transparent and sensibly homogeneous media 

 not subject to magnetic action,* are essentially those which are 

 generally received as embodying the results of experiment. In no 

 particular, so far as the writer is aware, do they conflict with the 

 results of experiment, or require the aid of auxiliary and forced 

 hypotheses to bring them into harmony there with. 1 



In this respect, the electromagnetic theory of light stands in marked 

 contrast with that theory in which the properties of an elastic solid 

 are attributed to the ether, a contrast which was very distinct in 

 Maxwell's derivation of Fresnel's laws from electrical principles, but 

 becomes more striking as we follow the subject farther into its details, 

 and take account of the want of absolute homogeneity in the medium, 

 so as to embrace the phenomena of the dispersion of colors and circular 

 and elliptical polarization. 



* The rotation of the plane of polarization which is produced by magnetic action has 

 been discussed by Maxwell (Treatise on Electricity and Magnetism, vol. ii, chap, xxi), 

 and by Rowland (Amer. Journ. Math., vol. iii, p. 107). 



