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THE TELEPHONE.

OTHER MEANS FOR GENERATINGELECTRICITY.

THERMO-ELECTRICITY.

If two strips of different metals, such as silverand iron, be soldered together at one end, andthe other ends be connected with a galvanometer,on heating the soldered junction of the metals itwill be found that a current of electricity trav-erses the circuit from the iron to the silver. Ifother metals be used, having the same size, andthe same degree of heat be applied, the currentof electricity thus generated will give a greater ora less deflection, which will be constant for themetals employed. The two metals generallyemployed are bismuth and antimony, in barsabout an inch long and an eighth of an inchsquare. These are soldered together in series soas to present for faces the ends of the bars, andthese often number as many as fifty pairs. Sucha series is called a thermo-pile. This method of