THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOUBNAL OF SCIENCE. 



[FIFTH SERIES.] 



AUGUST 1881. 



X. On the Electromagnetic Theory of Light. By Lord 

 Rayleigh, F.R.S., Professor of Experimental Physics in 

 the University of Cambridge*. 



rilHE claims of the theory propounded by Maxwell, accord - 

 J- ing to which light consists of a disturbance in a medium 

 susceptible of dielectric polarization, are so considerable that it 

 is desirable to extend its application as far as possible to 

 various optical phenomena. The question of the velocity of 

 propagation in vacuum and in singly or doubly refracting 

 transparent dielectrics was considered by Maxwell himself; 

 and the agreement with experiment, though far from perfect, 

 is sufficiently encouraging. More recently it has been shown 

 by Helmholtzf, Lorentzf, Fitzgerald §, and J. J. Thomson ||, 

 that the same theory leads to Fresnel's expressions for the 

 intensity of light reflected and refracted at the surface of sepa- 

 ration of transparent media, and that the auxiliary hypotheses 

 necessary in this part of the subject agree with those required 

 to explain the laws of double refraction. In this respect the 

 electromagnetic theory has a marked advantage over the older 

 view, w^hich assimilated luminous vibrations to the ordinary 

 transverse vibrations of elastic solids. According to the latter, 

 Fresnel's laws of double refraction, fully confirmed by modern 



* Communicated by the Author. 



t Crelle, Bd. lxxii., 1870. t Schlomilch, xxii., 1877. 



§ Phil. Trans. 1880. || Phil. Mag. April 1880. 



Phil. Mag. S. 5. Vol. 12. No. 73. Aug. 1881. G 



