Sunday, February 5, 2012

5. If exceedingly large weights are to be raised, they must not be trusted to a mere axle; but the axle being retained by the gudgeons, a large drum should be fixed on it, which some call a drum-wheel (tympanum): the Greeks name it ἀμφίρευσις, or περίτροχος.

6. In these machines the blocks are constructed differently from those already described. Having, at top and bottom, two ranks of pulleys, the rope passes through a hole in the lower block, so that each end of the rope is equal in length when extended. It is there bound and made fast to the lower block, and both parts of the ropes so retained, that neither of them may swerve either to the right or the left. The ends of the rope are then returned to the outside of the upper block, and carried over its lower pulleys; whence they descend to the lower block, and passing round its pulleys on the inner side, are carried up right and left over the tops of the higher pulleys of the upper block;

7. whence descending on the outer sides, they are secured to the axle on the right and left of the drum-wheel, about which another rope is now wound, and carried to the capstan. On the turning of the capstan, the drum-wheel and axle, and consequently the ropes fastened to it, are set in action, and raise the weights gently and without danger. But if a larger drum-wheel be affixed, either in the middle or on one of the sides, of such dimensions that men may walk therein, a more effectual power is obtained than the capstan will afford.

8. There is another species of machine, ingenious in respect of its contrivance, and of ready application in practice; but it should not be used except by experienced persons. A pole or log of timber is raised, and kept in its situation by means of four guy ropes in opposite directions. Under the place where the guy ropes at top are made fast to the pole, two cheeks are fixed, above which the block is tied with ropes. Under the block, a piece of timber about two feet long, six inches wide, and four inches thick, is placed. The blocks have three ranks of pulleys latitudinally, so that it is necessary to conduct three leading ropes from the upper part of the machine; these are brought down to the lower block, passing from the outer sides of the lower pulleys to the inner sides of the lower pulleys of the upper block.

9. Descending once more to the inferior block, they pass round the second rank of pulleys from the inner to the outer side, and are then returned to the second rank of pulleys in the higher block, over which they pass and return to the lowest, whence they are again carried upwards, and passing round the uppermost pulley, return to the lower part of the machine. A third block is fixed near the bottom of the pole, whose Greek name is ἐπάγων, but with us it is called Artemo. This block, which is made fast to the pole at a small distance from the ground, has three pulleys through which the ropes are passed, for the men to work them. Thus, three sets of men, working without the intervention of a capstan, quickly raise the weight to its required height.

10. This species of machine is called Polyspaston, because the facility and dispatch in working it, is obtained by means of many pulleys. One convenience in using a single pole is, that the situation of the weight in relation to the pole, whether before it or to the right or left of it, is of no consequence. All the machines above described, are not only adapted to the purposes mentioned, but are also useful in loading and unloading ships, some upright, others horizontal, with a rotatory motion. On the ground, however, without the aid of the poles, ships are drawn on shore by the mere application of blocks and ropes.


Marcus Vitruvius Pollio:
de Architectura, Book X

Translated by Bill Thayer

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