BOOK VI.

195

shaft, which slopes and twists like a screw and gradually descends. Thelowest of these machines is set in a deep place, which is distant from thesurface of the ground 660 feet.

The fourth species of pump belongs to the same genera, and is madeas follows. Two timbers are erected, and in openings in them, the ends of abarrel revolve. Two or four strong men turn the barrel, that is to say, oneor two pull the cranks, and one or two push them, and in this way help theothers ; alternately another two or four men take their place. The barrelof this machine, just like the horizontal axle of the other machines, has adrum whose iron clamps catch the links of a drawing-chain. Thus wateris drawn through the pipes by the balls from a depth of forty-eight feet.Human strength cannot draw water higher than this, because such veryheavy labour exhausts not only men, but even horses ; only water-powercan drive continuously a drum of this kind. Several pumps of this kind, asof the last, are often built for the purpose of mining on a single vein,but they are arranged differently for different positions and depths.

B —Levers. C —Toothed drum. D —Drum made of rundles.

E —Drum in which iron clamps are fixed.

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