This instrument demonstrates the thermoelectric effect discovered in 1821 by Thomas Seebeck (1770–1831).
It is composed of a rectangular circuit of which three sides are made of copper, while the fourth is made of iron. On the side where these are joined there is a small lamp with a wick outside the rectangle. If the joint between the copper and iron is heated, an electric current is established in the circuit, which was indicated by the movement of a magnetic pointer (now missing) mounted on the pin placed in the centre of the rectangle.

Device on display.