Faraday. 217 



light gave interest to a short paper of a speculative character 

 which Faraday published* in 1846, under the title " Thoughts 

 on Kay- Vibrations." In this it is possible to trace the progress 

 of Faraday's thought towards something like an electro-magnetic 

 theory of light. 



Considering first the nature of ponderable matter, he suggests 

 that an ultimate atom may be nothing else than a field of 

 force electric, magnetic, and gravitational surrounding a point- 

 centre ; on this view, which is substantially that of Michell and 

 Boscovich, an atom would have no definite size, but ought 

 rather to be conceived of as completely penetrable, and extend- 

 ing throughout all space ; and the molecule of a chemical 

 compound would consist not of atoms side by side, but of 

 " spheres of power mutually penetrated, and the centres even 

 coinciding."t 



All space being thus permeated by lines of force, Faraday 

 suggested that light and radiant heat might be transverse 

 vibrations propagated along these lines of force. In this way 

 he proposed to " dismiss the aether," or rather to replace it by 

 lines of force between centres, the centres together with their 

 lines of force constituting the particles of material substances. 



If the existence of a luminiferous aether were to be admitted, 

 Faraday suggested that it might be the vehicle of magnetic 

 force ; " for," he wrote in 1851,{ "it is not at all unlikely that 

 if there be an aether, it should have other uses than simply 

 the conveyance of radiations." This sentence may be regarded 

 as the origin of the electro-magnetic theory of light. 



At the time when the " Thoughts on Eay -Vibrations " were 

 published, Faraday was evidently trying to comprehend every- 

 thing in terms of lines of force ; his confidence in which had 

 been recently justified by another discovery. A few weeks 

 after the first observation of the magnetic rotation of light, he 

 noticed that a bar of the heavy glass which had been used in 



* Phil. Mag. (3), xxviii (1846) : Exp. Res., iii, p. 447. 



t Cf. Bence Jones's Life of Faraday, ii, p. 178. 



J Exp. Res., $ 3075. Phil. Trans., 1846, p. 21 : Exp. Res., 2253. 



