186 APPENDIX TO MEMOIR OF PELTIER. 



To tlirow better liglit on the nature of these phenomena, Peltier varied the 

 experiments. He formed a quintuple helix of 240 coils ; in other words, on a 

 helix of 240 coils he superposed a second in all res])ccts similar, but insulated 

 from the first, then a third, a fourth, and finally a fifth. This quintuple helix 

 was so constructed that the homologous ends might be united and then form 

 but one helix of 240 coils, having five times more of substance ; they might 

 also be united in a battery, that is to say the end of the first might be joined 

 to the beginning of the second, the end of the second to the beginning of the 

 third, &c. ; forming thus a helix of 1,200 coils, being a helix five times longer, 

 but having five times less substance than each spire. 



When a magnetized bar is placed in this apparatus to produce a cuiTcnt of 

 induction, results exactly inverse are obtained according as one or the other 

 of these last arrangements is employed. Suppose that we unite the helices by 

 their homologous ends, and that we have taken a rheometer of a single coil, 

 the deviation will increase as the number of helices united by their homologous 

 ends ; that is to say, as the quantity of substance modified. Thus, assuming 

 that with one helix we have 5° of deviation, with two we shall have 10°, with 

 three 15°, and proportionally with five 25°. If we replace the galvanometer 

 of one coil l)y a multiplier of 2,000 coils, we shall have 35° of deviation with 

 a single helix. But we obtain no more by employing two, three, four, or five 

 helices, still supposed to be united by their homologous ends. 



Suppose now that in place of uniting the five helices by their homologous 

 ends, we unite them in a battery, and that we make use of the rheometer of 

 one coil ; we shall have 5° of deviation with a single helix, and we shall obtain 

 no more with two, three, four, or five helices united in battery. On the other 

 hand, suppose that we employ the rheometer of 2,000 coils, the deviation of the 

 needle will go on increasing in proportion as we augment the number of helices, 

 and it will attain its maximum or 90° after the fourth. 



Thus we see there is complete opposition between the results, the reason of 

 which is simple : with a rheometer of a single coil, the resistance of the con- 

 ductor may be considered as null. When the helices are united by their homo- 

 lofifous ends, the quantity of substance altered is augmented, and consequently 

 the quantity of electricity produced. Now, as the conductor ofiers no resist- 

 ance, this constantly increasing quantity of electricity passes without difficulty 

 and gradually augments the angular deviation of the needle. On the contrary, 

 when we take a rheometer of 2,000 coils, the resistance of the conductor is 

 fi^reat. the quantity of electricity produced is in vain augmented ; no more of it 

 passes, it returns backward and is neutralized by the electromoter itself. The 

 sole means of making more pass, is to unite the helices in battery ; then, in 

 eft'ect, we augment the difficulties to the retrogradation of the two electricities, 

 and force them consequently to recombine in advancing. Peltier formed still 

 another multiple helix, of which the wires were of difierent and proportioned 

 magnitudes. The result was still that the quantity was given by the mass, and 

 the intensity by the reduplication of the spires. He repeated the same experi- 

 ments with thermo-electric and with hydro-electric pairs. These gave analo- 

 gous results; the quantity depended on the quantity of matter altered in each 

 element, and the intensity on tlie number of interposed pairs undergoing the 

 same alterations. We shall content ourselves with speaking of the results 

 yielded by the hydro-electric pairs. 



In one exiicriment, five scjuare centimetres of a voltaic pair, immersed in 

 acidulated water, gave two proportional degrees : 



10 square centimetres gave 40° 



15 square centimetres gave 60° 



20 square centimetres gave 80° 



In this experiment the conductor was short and very large, consequently the 

 resistance might be considered as null ; on repeating the same experiments with 



