This instrument, which demonstrates the composition of forces and the principle of the parallelogram of forces, is nearly identical to the one illustrated by Willem Jacob 's Gravesande in Physices elementa mathematica, experimentis confirmata (3rd ed., Leiden, 1742).
A round wooden base supports a column topped by a disk. Four vertical sheaves run in a groove around the rim and can thus be positioned at different angles to one another. The ends of two pairs of cords (knotted together in the center) pass over the sheaves and hold four small pans with weights.
By changing the angles between the sheaves and the weights, one can visualize—thanks to the angles formed by the cords on the disk—the sum of the forces and the equilibrium conditions. Provenance: Lorraine collections.