Vibrations of Light with Electrical Currents. 301 



tial equations would remain the original and only valid ones on 

 which the physical explanation would have to depend. The 

 theoretically important conclusion would thence follow which 

 has been already indicated, that electrical forces require time to 

 travel, and that these forces only apparently act at a distance 

 (as would follow from equations (A) if they were regarded as the 

 fundamental equations), and that every action of electricity and 

 of electrical currents does in fact only depend on the electrical 

 condition of the immediately surrounding elements, in the manner 

 indicated by the differential equations (B). This is well known 

 to be an idea indicated by Ampere, and which several physi- 

 cists, more particularly Faraday, have defended. 



The present general opinion regards light as consisting of 

 backward and forward motions of particles of sether. If this 

 were the case, the electrical current would be a progressive mo- 

 tion of the aether in the direction of the (positive or negative) 

 electrical currents. But it is impossible that the same equations 

 which theory deduces for very small displacements from equili- 

 brium should hold good for all kinds of displacements whatever ; 

 and it just follows from the whole of this investigation that the 

 same equations hold for both cases. Light cannot, therefore, 

 consist of vibrations of the kind hitherto assumed; and this last 

 consequence of the theory of aether makes it untenable. 



There is, on the other hand, another conception of the nature 

 of light- vibrations, to which I have already adverted*, and which 

 perhaps now becomes more probable. For if we suppose light 

 to consist of rotating vibrations in the interior of bodies, about 

 axes which, according to the theory of electricity, we regard as 

 directions of vibration, the electrical current is no translatory mo- 

 tion, but a rotation continued in one direction, and the axis of 

 rotation becomes then the direction of the current. This rota- 

 tion will only be continuous in good conductors, and the motion 

 travel there in the direction of the axis, whereas it becomes 

 periodical in bad conductors, and is propagated by what in 

 electricity we call induction, in a direction at right angles to the 

 axis of rotation. In this idea there is scarcely any reason for 

 adhering to the hypothesis of an aether; for it may well be as- 

 sumed that in the so-called vacuum there is sufficient matter to 

 form an adequate substratum for the motion. 



This hypothesis as to the nature of light and of electrical cur- 

 rents will probably, as science progresses, cither assume a new 

 form, or be totally rejected. But the result of the present in- 

 vestigation, that the vibrations of light are electrical currents, 

 has been obtained without the assumption of a physical hypo- 

 thesis, and will therefore be independent of one. 



* Pogg. Ann. vol. cxviii. p. 113; Phil. Mag. S. 4. vol. xxvi. p. 82. 



