QUANTITY OF ELECTRICITY PROPORTIONAL TO NUMBER OF PAIRS. 



97 



370. It would therefore seein that, when wires of the same metal are used as electro- 

 motors, the quantity of electricity evolved depends on the quantity of caloric that can he 

 communicated in a given time. Time, therefore, under these circumstances, must enter 

 as an element of thermo-electric action. In the case of a single metal, the maximum 

 effect would be produced when the hot element is a mass, and the cold one a point. 



371. And, lastly, " That the quantities of electricity evolved in a pile of pairs are 

 directly proportional to the number of the elements." 



372. In the first trials which I made to determine the effect of increasing the num- 

 ber of pairs in a pile, the results obtained were contradictory ; by operating, however, 

 in the following way, the proposition was at last satisfactorily determined : 



1st. The resistance to conduction was made nearly constant by uniting all the pairs 

 intended to be worked with at once. The current, therefore, whether generated by 

 one, two, three, four, or more pairs, had always to run through the same length of wire, 

 and experienced in all cases a uniform resistance. 



2dly. By making each individual element of considerable length, the liability of trans- 

 mission from the hot to the cold extremity was diminished. 



373. Having, therefore, taken six pairs of copper and iron wires, one sixteenth of an 

 inch thick, and each element 38 inches long, I formed them, by soldering their alter- 

 nate ends, into a continuous battery. Then I successively immersed in boiling water 

 one, two, three, &c., of the extremities, their length allowing freedom of motion, and 

 the other extremities not differing perceptibly from the temperature of the room. 



374. The following table exhibits one of this series of experiments : 



TABLE IV. 



Hence there cannot be any doubt that the quantities of electricity evolved by com- 

 pound batteries, at the same temperature, are directly proportional to the number of the 

 pairs. 



375. With some general remarks, arising from the foregoing subjects, I shall conclude 

 this chapter. 



376. It is of importance to remember that thermo-electric currents traverse metallic 

 masses only on account of differences of temperature existing at different points. 



377. When a current of electricity, flowing from the poles of a battery, is made to 

 traverse a metallic sheet, the whole of it does not pass in a straight line from one pole 

 to the other, but diffuses itself through the metal, diverging from one point and conver- 

 ging to the other. The greater part of the current is found, however, to take the shortest 

 route. 



378. Combining, therefore, the foregoing observations, we perceive that there are 

 certain forms of construction which will give to thermo-electric arrangements peculiar 

 advantages. For example, the surfaces united by soldering must not be too massive. Let 



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