On Thermo-eledro-magnetism. 129 



ice placed on the solderings at every two intervals. The deviation 

 of the magnetic needle was in this case 31|°, in the same circum- 

 stances in which the simple circuit of equal length, in the third 

 experiment, produced a deviation of only 13° or 15°. But it must 

 be recollected that the circuit of the second experiment, which 

 had only half the length of circumference, and half the number of 

 elements, afforded nearly the same effect. Hence we perceive, 

 what will be confirmed by ulterior experiments, that the deviations 

 of the needle, produced by the thermo-electric circuit, augment 

 with the number of elements when the length of the circuit re- 

 mains the same, but that they become feebler in proportion as the 

 length is increased. It is seen, moreover, that these two effects 

 counterbalance each other, as will be made more evident in the 

 sequel. Hence the effect of a circuit does not change when the 

 length of its circumference augments in the same proportion as the 

 number of its elements; or in other terms, that elements of equal 

 length, form circuits which produce equal deviations, whatever 

 may be the number of these elements. These results were con- 

 firmed, by comparing the effects of circuits of one, two, three, 

 four, six, thirteen, and twenty elements. In order to form com- 

 plex circuits capable of producing a very great effect on the 

 magnetic needle, very short elements must be employed. One 

 inconvenience, it is true, will thence arise; the equilibrium of tem- 

 perature will be rapidly restored in the circuit, unless with regard 

 to the alternate solderings, one be put in communication with a 

 continual source of heat, and the other, with a continual source of 

 cold. The thermo-electric action may be rendered sensible by 

 means of the electro-magnetic multiplier, but the effect is not so- 

 good as by the preceding simple arrangement. Hence it is in- 

 ferred that the thermo-electric circuit contains electrical forces, in 

 much greater quantity than any hydro-electric circuit of equal 

 size; while, on the other hand, the intensity of the forces in the 

 latter circuit is much more powerful than in the other. In the 

 first electro-magnetic experiments it was well seen that the de- 

 viation of the compass-needle, produced by the electrical current, 

 was regulated by the quantity of the electrical forces, and not by 

 their intensity faction electro-metrique.) The considerable de- 

 viation, therefore, which the thermo-electric current produces, is 

 an indication of the great quantity of force which it contains. 

 They tried the effect of the complex circuit on the needle of the 

 multiplier, and found that it increased considerably with the num- 

 ber of the elements of the circuit, even in cases where this mul- 

 tiplication of the elements added nothing to the effect on the 

 simple compass needle. It appears, therefore, that the intensity 

 of the forces increases, in the circuit, with the number of its 

 elements, precisely as happens in the pile of Volta. The circuit 

 had no sensible effect, however, on the needle, when the commu- 

 Voi. XVI. K 



