BOOK VI. 



195 



shaft, which slopes and twists like a screw and gradually descends. The 

 lowest of these machines is set in a deep place, which is distant from the 

 surface of the ground 660 feet. 



The fourth species of pump belongs to the same genera, and is made 

 as follows. Two timbers are erected, and in openings in them, the ends of a 

 barrel revolve. Two or four strong men turn the barrel, that is to say, one 

 or two pull the cranks, and one or two push them, and in this way help the 

 others ; alternately another two or four men take their place. The barrel 

 of this machine, just Uke the horizontal axle of the other machines, has a 

 drum whose iron clamps catch the links of a drawing-chain. Thus water 

 is drawn through the pipes by the balls from a depth of forty-eight feet. 

 Human strength cannot draw water higher than this, because such very 

 heavy labour exhausts not only men, but even horses ; only water-power 

 can drive continuously a drum of this kind. Several pumps of this kind, as 

 of the last, are often built for the purpose of mining on a single vein, 

 but they are arranged differently for different positions and depths. 



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

 E — Drum in which iron clamps are fixed. 



