20 x 3 (diameter)
Iron and brass
INDEX 1788 : F.III.131
Polyspaston, in quo sex orbiculi aequales inter duas regulas ferreas sibi parallelas sunt dispositi.
Block, in which six identical small wheels are arranged between two parallel iron bars.
This block consists of two iron bars, 20 cm in length, ending with a ring, each bar holding a set of three pulleys, 3 cm in diameter. A rope passes round the pulleys in such a way that the two sets are separated by six equal sections of rope. The end of the seventh section is free, and the experimenter pulls on this to lift an object hanging from the moveable bar. In order to maintain the balance of the set of pulleys, the force applied to the free end of the rope must be equal in strength to one sixth of the weight of the object suspended.
From Colégio dos Nobres, catalogue n.º 122.'s Gravesande, Willem Jacob, Physices Elementa, Leiden, 1742, Vol. I, § 264, Tab. IX, Fig. 4.