VOLTAIC GENERATORS. & 



that their internal resistance shall be equal to that of the ex- 

 ternal circuit ; and if the circuit is composed of two parts, 

 one serving simply for electric transmission, the other for the 

 production of a calorific or electro-magnetic work, it is neces- 

 sary that the resistance of the inactive circuit, including that oj 

 the battery, shall be equal to the resistance of the electro-magnetii 

 organ.oiio that of the conductor developing the calorific effect 



Mode of Propagation of Electricity. Before study- 

 ing the magneto-electric generators, which have solved the 

 problem of electric lighting, it seems to us important to give 

 some details as to the conditions of charge and discharge in 

 a circuit, and as to the mode of propagation of a current. 



It is often asked in what conditions are the insulated wires 

 of a circuit in connection with the battery when that circuit 

 is not closed, and one would be apt to suppose that in order 

 to produce a movement of the charge it would only be neces- 

 sary to put a conductor in communication with one or other 

 of the electric poles. But matters do not happen quite in 

 this way. 



To charge conductors it is necessary that the positive and 

 negative charges shall be able to flow in the same propor- 

 tion. Thus, a very long conductor applied to the positive 

 pole of a battery can be charged only when the negative 

 charge can be transmitted to a conductor of the same length 

 attached to the negative pole, or when that charge is able to 

 flow away into the earth. Then the charge is successively 

 transmitted to the end of the positive wire, and when it has 

 there reached the same tension as near to the battery, the 

 current which resulted from that transmission ceases, and the 

 whole of the conductor is charged to the potential of the 

 battery. When this positive wire is placed in communication 

 with the ground a new electric movement is produced, be- 

 ginning at the end of the wire, and a discharge current is 

 obtained which now is continuous and constitutes the cur- 

 rent properly so called. 



3 2 



