Diameter: 4.5 and 3
Brass and iron
INDEX 1788 : F.III.130
Trochleae duae duplici trutina ac uncis ferreis munitae; una altera mayor est.
Two pulleys equipped with a double holder with iron hooks; one is bigger than the other.
This is a combination of a movable and a fixed pulley mounted on the universal stand (instrument 24). Because a movable pulley is used, a force whose intensity is P/2 must be exerted on the free end of a cord in order to maintain a body of weight P in suspension and equilibrium.
's Gravesande, Willem Jacob, Physices Elementa, Leiden, 1742, p. 60, Tab.IX, Fig. 3.