326 POPULAR SCIENCE MONTHLY 



ether on the one hand and the relations of electricity to matter on the 

 other. It is in this last and more complicated phase of our suhject 

 that the most brilliant advances have recently been made. 



To state the case between electricity and ether, we must begin with 

 Faraday and some of the mental images he formed of the connection 

 between them, which have proved at once the most simple and useful 

 aids to thought to be found in the whole history of physics. Faraday 

 realized as well, perhaps, as we do to-day that electricity could no more 

 be made outright than could matter. The utmost which could be 

 done was to separate positive and negative electricity. If, therefore, 

 any one exhibited a positive charge, there was somewhere in the universe 

 an equal negative charge, to which it was drawn by invisible means 

 across the intervening space. 



Faraday maintained the forces of attraction were due to some kind 

 of strain in the ether lying between. To picture the more vividly to 

 himself and to others, the character of the stresses in this medium 

 transmitting the force which one charge exerts upon another, he sup- 

 posed contractile filaments called lines of force to traverse the ether 

 between the charges. To make the case more definite he gave direction 

 to these lines, assuming that they originated on the positive charge 

 and terminated on an equal negative charge near-by, or far away, ac- 

 cording to circumstances. 



The motions of electric charges when free to move, and the dis- 

 tribution of stresses in the ether round-about, show that all happens as 

 if each line of force were pulling like a stretched elastic thread to 

 shorten itself and draw the charges together, and at the same time 

 unlike any elastic thread we know, it was repelling or pushing sidewise 

 at the other force lines near it. 



If a charge of positive electricity be given to a metal sphere, and the 

 negative charge from which it has been separated be dissipated to 

 remote bodies or be carried so far away that its position is no longer 

 of any immediate importance, lines of force will start from the spherical 

 surface of the conductor in all outward directions, and will be precisely 

 radial. As many lines will leave from any one half of the sphere as 

 from another. This equal radial arrangement of the lines of force is 

 produced by the sidewise shoving of each line of force upon its neigh- 

 bors until the stresses in the ether at the bounding surface of the metal 

 are equal on all sides. 



If now the metal sphere with its charge be put in steady motion, it 

 will carry its lines of force along with it, and if the motion be not too 

 swift, all the lines of force will continue radial. But with this motion 

 of the lines of electric force through the ether, a wholly new and addi- 

 tional ethereal force appears — a magnetic force which did not exist 

 when the charge was at rest. This magnetic force is always at right 

 angles both to the lines of electric force and to the direction of their 



