This experimental apparatus was described in the eighteenth century by Jean-Antoine Nollet in Leçons de physique expérimentale. It served to demonstrate the effects of combining a horizontal movement and a vertical movement.

A wooden base holds a vertical panel whose upper part carries two horizontal rails formed by a pair of metal wires. A small brass trolley can be pulled horizontally along the rails by means of a cord holding a weight and passing over a pulley. A second cord, fastened to one end of the rails, passes over a pulley attached to the trolley. This second cord carries a weight as well.

When the trolley is pulled along the rails, the displacement of the pulley connected to it causes the weight to rise along the diagonal. This demonstrates that the result of the combination of two orthogonal movements is a diagonal path.

A curious application of this device was used in contemporary opera houses. An actor or object placed in a similar contraption, hidden to the public, was raised over the stage, creating the illusion of flight.