ELECTEICITY CONVERTED INTO HEAT. 393 



by a rotating magnet or by solution of zinc in the galvanic 

 battery. Such a current, in circulating through a thick or 

 thin wire, exhibits the same deportment as a fluid flowing 

 through a wide or narrow tube. As a given quantity of fluid 

 requires more time or greater pressure to pass through a nar- 

 row tube than through a large, so a thin wire offers a greater 

 resistance than a thick one to the passage of a current of elec- 

 tricity. The current is thus retarded and diminished, one 

 portion only passing through the conductor, the other being 

 converted into heat. According to the amount of heat thus 

 produced by the conversion of the electricity, a conducting 

 wire of platinum can be fused, one of gold fused and con- 

 verted into vapour, and a considerable quantity of water 

 brought into violent ebullition by passing the current through 

 a thin platinum wire wound round a glass tube in a spiral 

 form. 



If the electrical current circulates through a wire wound 

 spirally round a bar of iron, the latter is converted into a 

 powerful magnet capable of attracting and carrying several 

 hundred weights of iron. The electrical is conrerted into the 

 magnetic force, by which a machine may be set in motion. 

 The power of attraction communicated to the iron bar is in 

 exact proportion to the amount of electricity circulating in 

 the surrounding wire, and this current is again dependent on 

 the property of the conductor. That portion of electricity 

 which in the conductor is converted into heat, produces no 

 power of attraction in the iron bar. It follows, from the 

 foregoing, that the quantity of electricity which circulates, of 

 that which produces heat, and the amount of magnetic power 

 convertible into working power, stand in the same relation to 

 each other, as the working power produced in a machine by 

 the pressure of falling water to the heat generated by friction 

 and concussion in the same machine. The same amount of 

 electricity which, when converted into heat by the resistance 

 of the conductor, raises by one degree the temperature of one 

 17* 



