Thermopile is a device used to measure high temperature of furnaces. It works on the principle that if a large number of thermocouples are connected in series, the thermoemf gets multiplied. Its construction is shown below:
It consists of several thermocouples of antimony and bismuth connected in series. The junctions at one side are coated with lampblack, which can absorb incident heat radiation and becomes hot junction, whereas the junctions at other side are covered with cotton cloth to avoid incidence of heat radiation and becomes cold. As a result, thermoemf gets multiplied i.e., more thermoemf is produced.