bij Electricity. 423 



It will perhaps be permitted me to cite a single additional 

 experiment, which exhibits all the necessary evidence withont the 

 reversion of the voltaic current. 



Experiment No. 4.—B, fig. 4, is a curved bar of bismuth, 

 with each end of which a bar of antimony, A, is brought 

 into close contact. In front of the two junctions arc chambers, 

 hollowed out in cork and filled with mercury as before. A cur- 

 rent was sent from the cell B in the direction indicated by the 

 arrow; at M it passed from antimony to bismuth, and at M 

 from bismuth to antimony. Now if Peltier's observation be 

 correct, we ought to have the mercury at M warmed, and that 

 at M' cooled by the passage of the current. After three minutes' 

 circulation the voltaic circuit was broken, and the test-pan- dipped 

 into M' ; the consequent deflection was 



38°, 

 and the sense of the deflection proved that at M' heat had been 

 absorbed. 



The needles were brought quickly to rest at zero, and the 

 test-pair was dipped into M ; the consequent deflection was 



60°; 

 the sense of the deflection proved that at M heat had been 

 generated. 



The system of bars represented in fig. 4, being imbedded 

 in wood, the junction at M cooled slowly, and would have 

 taken a quarter of an hour at least to assume the temperature of 

 the atmosphere. The voltaic current was reversed, and three 

 minutes' action not only absorbed all the heat at M, but gene- 

 rated cold sufficient to drive the needle through an arc of 20° 

 on the negative side of zero. 



These experiments. Gentlemen, corroborate a result which to 

 my mind is sufliciently well established without them. Never- 

 theless 1 would say, that the conclusions of Mr. Adie are such 

 as a restricted examination of the subject will most probably 

 lead to. I have no doubt as to the correctness of his results 

 described in the September Number of the Magazine; but I 

 have just as little doubt, that had Mr. Adie varied the strength 

 of his current sufficiently, he would have spared himself the 

 statement, that " in his experiments he had never met a fact 

 which in the least encourages the view that electricity reduces 

 temperatures." 



I remain, Gentlemen, 

 Queenwood College, Your obedient Servant, 



November 18.52. John Tyndall. 



