206 



EXPERIMENTAL GENERAL SCIENCE 



carbon rod. The zinc cup takes the place of the zinc strip 

 in the Voltaic cell, and the carbon rod takes the place of the 

 copper. 



171. Direction of the Current. The two strips of metal in 

 the Voltaic cell are called the electrodes, or poles, and the liquid 

 in which they are placed, is the electrolyte. The zinc is called 

 the negative pole, and the copper is the positive pole. The 

 electric current is supposed always to flow from the positive 

 to the negative pole in the current through the wire and from 



FIG. 74. The gravity cell. (Tower, 

 Smith and Turton.) 



FIG. 75. The Leclanche cell, 

 "dry" type. (Tower, Smith and 

 Turton.) 



the zinc pole to the copper pole through the electrolyte to 

 the starting point. So long as the two poles are connected, 

 the current continues to flow and the circuit is said to be closed. 

 If an electric bell be connected 'into the circuit it will ring, 

 or an electric light may be made to glow. When the circuit 

 is broken at any point, the current ceases. 



172. Induced Currents. Electricity produced by chemical 

 means is too expensive for the thousand purposes to which 

 electricity is now put. The current used for moving street 



