IMPORTANT DEFINITIONS. 5 



tion of equilibrium is but momentary, the current lasts only 

 for an instant ; it is in that case a discharge. But if the cause 

 persists, the current becomes, continuous, and may be com- 

 pared to a stream supplied by a spring : this is the electric 

 current properly so called. 



As the effect of a current is to re-establish the equilibrium 

 which has been disturbed at some point of a conducting sys- 

 tem, it naturally follows that the two free extremities of the 

 conducting system must be united in order that the current 

 may show itself; the system then forms a true circuit, which 

 more or less resembles the circle, but which is always formed 

 in the same way; that is to say, the current having a certain 

 direction at the point where the disengagement of electricity 

 or destruction of the electrical equilibrium occurs, it will 

 have the contrary direction in the opposite part of the 

 circuit. 



That which produces the destruction of equilibrium just 

 spoken of is named the electro-motive force. The extreme 

 partisans of the electro-chemical theory do indeed reject 

 this expression, because it is associated with Volta's theoiy, 

 which they will not accept; but whatever theory may be 

 adopted, this expression is entirely suitable; for since an 

 electric current is a phenomenon of motion, and every 

 motion is the effect of a force, it is quite certain that in every 

 circuit traversed by a current there is a force put in action, 

 and this force may therefore be termed the electro-motive 

 force. 



The tension of a current, which is now often confounded 

 with the potential, is the property of the electric fluid, which 

 in a manner gives the impulse to the electrical movement, 

 and which outwardly manifests itself by a tendency to act 

 on the adjoining objects, and to produce the effects peculiar 

 to static electricity. It is the quantity of electricity kept 

 free at the poles of a battery when these are not connected, 

 and which escapes recomposition during the time that the 

 disengagement of electricity continues. 



