310 M. Becquerel on the Electric effects of Contact 



In Table No. II. the joint which was at zero in No. I. is 

 brought to 50°, and in No. III. to 100. But in Table II, the 

 electro-dynamic force 11, produced by the temperatures ICO 

 and 50, is equal to the difference of the forces 22 and 11, ob- 

 tained in Table I. by the temperatures 100° and 50° of the 

 same joint. Besides the force 20 is equal to the difference of 

 the forces which have been given in Table I. by the tempera- 

 tures 150° and 50°, and so on. The force 9, Table III. is equal 

 also to the difference of the forces produced by the tempera- 

 tures 150 and 1 00 of Table I. 



Hence we obtain this general rule, that in a circuit formed 

 of two metallic wires soldered end to end, when we raise each 

 of the joints to different temperatures, the resulting electro- 

 dynamic intensity is equal to the difference of the forces pro- 

 duced successively by each of the temperatures in the same 

 joint, the other being at zero, and not to the intensity of the 

 force produced by the difference of temperature alone. 



But since the electric state of each joint depends on its tem- 

 perature, and not on the temperature of the neighbouring 

 joints, we may form a table similar to that in p. 309, without 

 employing four metallic wires. I take, indeed, four copper 

 wires and four iron wires, about 5 decimetres long, and \ of a 

 millimetre in diameter, and solder them end to end, in such a 

 manner as to have alternately a copper and an iron wire, and 

 the whole communicates with the wire of the apparatus already 

 mentioned. I then raise successively to the same temperature, 

 one joint, two joints, &c. taking these alternately, in order to 

 have currents in the same direction. We shall then obtain an 

 electro-dynamic force, simple, double, triple, &c. and it will 

 then be easy to construct a table the same as that of p. 309- 



II. On the Laws of the eleclric effects of Contact, when the 

 temperature of each metal is equally varied. — In the present state 

 of the science, it is impossible to determine the absolute quan- 

 tity of electricity which disengages itself in the contact of two 

 metals, or at least to compare together those which result from 

 the contact of the same metal with several others. For this 

 purpose, it would be necessary that we should be able to join 

 the two metals by a body which is a good conductor of elec- 

 tricity, and which should not exercise electromotive actions 



