This Leslie's cube is a tin-plate box with 13cm sides. Each of the four vertical faces is finished differently — blackened, roughened, varnished, and polished — so students can compare the thermal emissivity of surfaces at the same temperature. The top opening is fitted with a stopper. In use, the cube is filled with water kept at boiling point by a low Bunsen flame, and an infrared sensor is used to compare the radiant heat output from each face. A classical demonstration of Kirchhoff's law and surface emissivity in heat-radiation studies.