GALVANIC ELECTRICITY. 103 



ously lighted throughout the whole establishment by 

 electricity developed by the friction of the machinery. 



247. CONDUCTION OF ELECTRICITY. Like 



Explain the . . 



conduction of heat or caloric, electricity may be conducted 



electricity. ^ Qm Qne body tQ another< ThuSj if ft piece 



of metal be electrically excited, or, in other words, 

 charged with a quantity of either the positive or nega- 

 tive fluid, another piece of metal will immediately be- 

 come so on connecting it with the first by a metallic 

 wire. The connection being formed, it will attract or 

 repel filaments of silk or other material, precisely as the 

 first one does. The fluid is supposed to flow from one 

 piece of metal to the other, through the wire, and we 

 therefore speak of a current of electricity. But it is 

 not certain that any thing actually passes, any more 

 than in the case of light and heat before considered; 



248. GALVANIC ELECTRICITY. It is also 



What is gal- 

 vanic electri- found that electricity is developed when 



Clty ? two metals are placed in contact with each 



other, and with an acid at the same time, < 

 as is represented in the figure. This is 

 called galvanic electricity, from the name 

 of an early experimenter in the science. 

 The acid acts on the zinc, arid the cur- 

 rent flows continuously in the direction 

 indicated by the arrows. This apparatus is the sim- 

 plest form of the galvanic battery. 

 ,, . . 249. ELECTRODES. For convenience in 



What is an 



electrode ? certain experiments, it is customary to at- 

 tach platinum wires, to the exterior portions of the me- 

 tallic slips. These are called electrodes. The wire con- 



