Demonstration of Peltier and Thomson Effects

THE following method of demonstrating the Peltier and Thomson effects may be of interest. In Fig. 1 the current passes through an Sb-Bi-Sb bar, the points of contact being amalgamated to reduce the resistance. Two coils of No. 36 covered copper wire are wound on the bismuth one near each junction, and by means of the leads A and B are placed in the gaps of a metre bridge, and a balance produced. On passing a current of 1 ampere through the bars, one junction is heated and the other cooled, which is indicated by a galvanometer deflection of about 40 mm. due to the change in resistance of the copper coils. The direction indicates a heating where the current flows from Sb to Bi, and vice versa.