HYDRAULICS. 



fig 



even if its buckets are but small, and 

 the smaller they are the less power will 

 be required to give motion to the wheel. 

 It likewise requires none of that nicety 

 in its construction which is usually ne- 

 cessary in millwork, but will act if made 

 in the roughest manner. It may like- 

 wise be applied in many cases with ad- 

 vantage to the tail stream of a water- 

 mill, when water is scarce, so as to 

 work by the water after it has passed 

 the mill-wheel, in order to raise and re- 

 turn a portion of it, instead of letting it 

 all run to waste. 



Nearly allied to the Persian Wheel, 

 but much more elegant in its contriv- 

 ance, is The CochUon, or Scretv of 

 Archimedes, a machine invented and 

 used by this philosopher, for raising wa- 

 ter and draining land in Egypt, about 

 200 years before the Christian sera. The 

 Cochlion consists of a succession of 

 buckets or recesses to be filled with the 

 water to be raised ; but instead of their 

 "being separate and detache'd, as in the 

 last-described machine, they are formed 

 by the lower parts of the hollow thread 

 of a screw, and their motion and succes- 

 sion are brought about by turning that 



screw. This will be better understood 

 by referring to Jig. 5, which is a repre- 

 sentation of this machine, and in which 

 v u w x shows a flexible tube or pipe, 

 wound in a screw-like form round a 

 solid cylinder y y, the two extreme ends 

 of which are equipped with pivots, so 

 that the cylinder, with its encircling 

 screw-formed tube, may be made to 

 revolve on its axis by the force of run- 

 ning water, or any other power applied 

 to its upper or lower end. Lastly, this 

 machine must be supported by its two 



Eivots, so as to make an angle with the 

 orizon, as shown in the figure. If now 

 the lower end v of the tube be supposed 

 to be covered with water, that water 

 will flow to its own level within the 

 tube, and will occupy the lowest bend v ; 

 and if now the cylinder y y be turned 

 round by its handle, in a direction from 

 left to right, the lower end of the 

 spiral tube will become elevated above 

 the surface of the water in the reser- 

 voir, and that water which had entered 

 into the tube will have no opportunity 

 of escaping, but, by the motion of the 

 screw-tube, will flow within it, until, at 

 the end of the first revolution, it will be 



