Consists of a brass ring carrying 25 elements (antimony and bismuth couples), with removable top and bottom, the whole forming a cylindrical box. An important application of the thermopile was as a constant source of electric current, long before reference voltages could be supplied by stable standard cells. At the same time as he was developing the thermopile as a differential thermometer for studying radiant heat, Leopoldo Nobili also made this version to supply a constant current for his differential galvanometer. Provenance: Lorraine collections.