It consists of a cylindrical copper rod about 30cms long x 25mm dia with its one end surrounded by a steam jacket for heating it from a boiler and the other end is kept cool by a system of water flowing through a spiral tube soldered to that end. Through two sockets two thermometers are inserted in the rod for finding the temperature at two points. Two more thermometers are inserted in the other end is kept cool by a stream of water flowing thorough a spiral tube soldered to that end for finding the difference of temperature between the inflowing and outflowing water. Fitted in teakwood case packed with felt with removable front, with thermometers.