1 80 llesearclies 07i Light, Heat, Electricity, ^'C. 



neous current of ^° {stationary) was the ?-esuIt. Thus it is seen, 

 that with the same heat developed in each case, by the mecha- 

 nical arrangement, is given an immediate current, which heat 

 will not give a current at all by the thermo-electric process, and 

 it is therefore evident that thermo- and mechanical electricity 

 are not derived from the same source. 



These experiments appear very decisive. The fact of the 

 current invariably pursniiig the course of Ihathi electro-motion, 

 or contact of dissimilar metals, in all cases where metals illus- 

 trative of this phaenomenon are employed, speaks in favour of 

 the dissimilarity of the source of these two modifications. 



It is also to be remarked here, that if mechanical electricity 

 were the result of the heat applied to the extremity of the 

 metal, the friction of flat surfaces, "which is knoivn to produce 

 much ?nore heat than simply cutting or turning with a sharp 

 edge, would produce the greatest deflection of the needle ; 

 but by this means it is found that none, or scarcely any cur- 

 rent is developed, even with a disc of bismuth. (See 22, 23.) 



Exp. 46. Is mechanical or thermo-electricity conductible 

 by water? A rod of bismuth was arranged for thermo-elec- 

 tricity in this experiment, and the voltaic decomposition ap- 

 paratus was employed; it was discovered that the thermo- 

 electric current is utterly inconduciible by "water or acidulated 

 water ; the heat was carried on to fusion, but the galvanometer 

 did not deflect in any appreciable manner. It is also incon- 

 duciible by a strong solution of sulphate of copper, 



Exp. 47. The thermo-electric current from bismuth passed 

 through a large piece of bismuth, deflecting the galvanometer 

 gradually up to 15°, by the steady heat of a spirit-lamp. 



Exp. 48. Mechanical electricity is not conducted at all by 

 solution of sulphate of copper. 



Exp. 49. And is also inconductible by acidulated "water, in 

 the ordinary decomposition apparatus. 



Exp. 50. But is readily transmitted by an intervening piece 

 of bismuth of equal temperature. 



Remarks. 



The direction of the current from every individual metal, 

 and from one metal relatively with another, is at all times in- 

 variable, both in mechanical and thermo-electricity. 



The quantity of force circulating through the galvanometer, 

 and proceeding from any given metal or specific pair of me- 

 tals, is constantly about the same in amount, proportional to 

 the intensity of the developing process, in both modifications. 

 Each metal evinces cm amount of force comparatively jnopor- 

 ticmal with that of every other metal employed, both in the 

 mechanical and in the thermo-electricity. 



