BOOK VI. 



171 



to draw water alone, I will explain how heavy bodies, such as axles, iron 

 chains, pipes, and heavy timbers, should be lowered into deep vertical shafts.- 

 A windlass is erected whose barrel has on each end four straight levers ; it 

 is fixed into upright beams and around it is wound a rope, one end of which 

 is fastened to the barrel and the other to those heavy bodies which are slowly 

 lowered down by workmen ; and if these halt at any part of the shaft they 

 are drawn up a little way. When these bodies are very heavy, then behind 

 this windlass another is erected just like it, that their combined strength 

 may be equal to the load, and that it may be lowered slowly. Sometimes for 

 the same reason, a pulley is fastened with cords to the roof-beam, and the rope 

 descends and ascends over it. 



-Straight levers. C — Upright beams. 

 F — Timbers to be lowered. 



E— Pulley. 



Water is either hoisted or pumped out of shafts. It is hoisted up after 

 being poured into buckets or water-bags ; the water-bags are generally 

 brought up by a machine whose water-wheels have double paddles, while the 

 buckets are brought up by the five machines already described, although in 

 certain localities the fourth machine also hauls up water-bags of moderate 

 size. Water is drawn up also by chains of dippers, or by suction pumps, or 



