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114 iron and copper soldered together. The points at which the two metals are fixed together are called junctions. The apparatus is put into connection with a galvanometer, and you will observe the coils of the galvanometer contain only comparatively few coils of wire. Such a galvanometer is said to be of low or small resistance, and it is well adapted for

such an experiment as we are now about to make. Now if I heat one set of the iron and copper junctions by simply pressing them together at a a (Fig. 56) while the other set is kept cool, a current of electricity is generated which passes round the coils of the galvanometer and causes a deflection of the needle. A very small difference in the temperatures of the two sets of junctions is quite sufficient to produce a current. This arrangement is made more sensitive by having a large number of thermo-electric