Lessons in elementary physics / by Balfour Stewart.

  • Balfour Stewart
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: Lessons in elementary physics / by Balfour Stewart. Source: Wellcome Collection.

    429/502 page 409
    of metiils such that the positive current shall go across the heated junction from the metal nearest the top to that nearest the bottom of the list. The following is such a list :— T.vble No. 42.—Thermo-Electric Series. Bismuth. Silver. Nickel. Zinc. Lead. Iron. Tin. .Antimony. Copper. Tellurium. Platinum. We see that the metals bismuth and antimony are near the opposite extremities of the list, and as they can be easily pro- cured, they are often used in thermo-electric combinations. Fig. 128. A law holds with respect to this series similar to that which held for the series of .^rt. 386. Thus in the circuit of Fig. 128, if the wires at the two extremities be copper wires leading to the galvanometer, or instrument for measuring the intensity of the current (see Art. 291), and if we have at A a copper and tin junction, while at B we have <a tin and antimony junction, and at c an antimony and copper junction, and if we heat through 1° C. the copper and tin, and also, at the same time, the tin and antimony junction, we shall get a current of the same intensity as if we heat at once the copper and .antimony junction through the .same temperature range. Only we see from the figure that the latter current will pass along the circuit in an opposite direction to the former, so that the practical elTect of healing .all Ihe three junctions together to the .same extent will be to gener.ale currents which cancel one another. 394. Cumming’s Effect.—Within eertain limits the strength of the current produced by a thermo-electric
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