ETHER. 



Function of the tether in electromagnetic phenomena. Faraday conjectured 

 that the same medium which is concerned in the propagation of light might 

 also be the agent in electromagnetic phenomena. "For my own part," he says, 

 "considering the relation of a vacuum to the magnetic force, and the general 

 character of magnetic phenomena external to the magnet, I am much more 

 inclined to the notion that in the transmission of the force there is such an 

 action, external to the magnet, than that the effects are merely attraction and 

 repulsion at a distance. Such an action may be a function of the aether; 

 for it is not unlikely that, if there be an aether, it should have other uses 

 than simply the conveyance of radiation*." This conjecture has only been 

 strengthened by subsequent investigations. 



Electrical energy is of two kinds, electrostatic and electrokinetic. We 

 have reason to believe that the former depends on a property of the medium 

 in virtue of which an electric displacement elicits an electromotive force in the 

 opposite direction, the electromotive force for unit displacement being inversely 

 as the specific inductive capacity of the medium. 



The electrokinetic energy, on the other hand, is simply the energy of the 

 motion set up in the medium by electric currents and magnets, this motion not 

 being confined to the wires which carry the currents, or to the magnet, but 

 existing in every place where magnetic force can be found. 



Electromagnetic Theory of Light. The properties of the electromagnetic 

 medium are therefore as far as we have gone similar to those of the lumi- 

 niferous medium, but the best way to compare them is to determine the 

 velocity with which an electromagnetic disturbance would be propagated through 

 the medium. If this should be equal to the velocity of light, we would have 

 strong reason to believe that the two media, occupying as they do the same 

 space, are really identical. The data for making the calculation are furnished 

 by the experiments made in order to compare the electromagnetic with the 

 electrostatic system of units. The velocity of propagation of an electromagnetic 

 disturbance in air, as calculated from different sets of data, does not differ 

 more from the velocity of light in air, as determined by different observers, 

 than the several calculated values of these quantities differ among each other. 



If the velocity of propagation of an electromagnetic disturbance is equal 

 to that of light in other transparent media, then in non-magnetic media the 



* Experimental Researches, 3075. 



972 



