3.5 (diameter)
Brass and iron
INDEX 1788 : E.III.129
Trochleae septem suis capsulis ex orichalco, et unco ferreo munitae.
Seven pulleys equipped with brass holders and with an iron hook.
The tackle comprises five movable pulleys and one fixed pulley. The multiplication factor of the tackle is 2n, where n represents the number of movable pulleys in the system. Thus, if we want to maintain a body of weight P suspended in equilibrium from this tackle, a force of P/32 has to be exerted at the free end of the cord. Originally, the set had seven movable pulleys. The wooden arm serves as an accessory to the universal stand (instrument 24).
The fixed pulley used in this set has the inscription A.IV. 128, the same as the recorded in the Index, which means that it was stored in cabinet A. It is not understood why it was stored so far from other identical machines. This is a complettely removable pulley, with a holder which turns freely around the axle by which it is fixed to the support. In this way it can be positioned, after fixing, as required.
On the holder of one of the moveable pulleys the name of the maker, C. PIETRA, has been inscribed.
From Colégio dos Nobres, catalogue n.º 121.'s Gravesande, Willem Jacob, Physices Elementa, Leiden, 1742, Vol. I, p. 301, Tab. X, Fig. 6.