4 ELEMENTS OF ELECTRICITY AND MAGNETISM. 



the key K, thus producing any desired series of signals at the 

 distant station.* 



The chemical effect of the electric current. When a solution 

 of a chemical compound forms a portion of an electric circuit, the 

 compound is, in general, decomposed by the current. This 

 chemical effect of the electric current is exemplified in the prac- 

 tical operation of electroplating. The essential features of an 

 electroplating outfit are shown in Fig. 5. VV 

 is a vessel containing, for example, a solution of 

 copper sulphate. The metal object O to be 

 plated is attached to one terminal of a battery 

 B, a copper plate C is attached to the other 

 terminal of the battery, and the current causes 

 copper to be deposited upon the object 0. 



r* Ig% o. 



The heating effect of the electric current. A 

 wire, or any substance which forms a portion of an electric circuit, 

 has heat generated in it by the current. This heating effect of 

 the electric current is exemplified in the ordinary electric lamp, the 

 carbon filament of which forms a portion of an electric circuit, 

 and is heated to incandescence by the current. 



Hydraulic analogue of the electric current. The flow of an 

 electric current through a circuit of wire is to some extent anal- 

 ogous to the flow of water through a circuit of pipe. The pump 

 which propels the current of water is analogous to the generator 

 which propels the electric current, and the circuit of pipe which 

 goes out from the pump and , returns to it is analogous to the 

 circuit of wire. Energy must be supplied to the pump to produce 

 the flow of water through the pipe, and this energy reappears as 

 the heat which is developed by the friction of the water in the pipe 

 or as the mechanical energy which is developed by a water 

 motor through which the water current is forced. Similarly, 

 energy must be supplied to an electric generator, and this energy 

 reappears in the electric circuit as heat or as the mechanical energy 



* The Morse Telegraph is described quite fully in Appendix D. 



