MODERN THEORIES AS TO ELECTRICITY 287 



tance. Consider a plus electrified sphere far away from other bodies. 

 The lines of force radiate from it in all directions, and, heing symmetri- 

 cal around the sphere, they pull it equally in all directions. Now 

 bring near it a minus electrified body, and the lines of force turn toward 

 it and become concentrated on the side of the sphere toward such a 

 body. Hence the lines pull more strongly in the direction of the 

 negative body, and the sphere tends to approach it. 



In the case of a conducting body the lines of force always pass out- 

 wards perpendicularly to the surface, and hence, if we know the distri- 

 bution of the lines over the surface, or the so-called surface density of 

 the electricity, we can always tell in which direction the body tends to 

 move. It is not necessary to know whether there are any attracting 

 bodies near the conductor, but only the distribution of the lines. These 

 lines then do away with all necessity for considering action at a dis- 

 tance, for we only have to imagine a kind of ether in which lines of 

 force with given properties can exist, and we have the explanation of 

 electric attraction. 



But the question now arises as to how the lines of electric force can 

 be produced in the ether, or, in other words, how bodies can be charged. 



In the first place we know that equal quantities of plus and minus 

 electricity are always produced. As an illustration, suppose it is re- 

 quired to charge two balls with electricity. Pass a conducting wire 

 between them with a galvanic battery in its circuit. The galvanic 

 battery generates the lines of force ; these crowd together around it and 

 push each other sideways until their ends are pushed down the wire 

 and many of them are pushed out upon the balls. 



When the tension backwards along the lines of force just balances 

 the forward push of the electromotive force of the battery, equilibrium 

 is established. If the wire is a good conductor, there may be electrical 

 oscillations before the lines come to rest in a given position, and this I 

 shall consider below. 



The motion of the ends of the lines of force over and in the wire 

 constitutes what is called an electric current in the wire which is 

 accompanied by magnetic action around it and also by waves of electro- 

 magnetic disturbance which pass outward into space. 



If, after equilibrium is established, we remove the wire, we have 

 simply two charged spheres connected by lines of electrostatic force 

 and thereby attracted to each other. If we replace the battery by a 

 dynamo or by an electric machine the effect is the same. 



But there is another way by which bodies are often charged and 



