HYDRAULICS. 



159 



friction of the water against the surfiices upon which it flows, and to the fric- 

 tion of the wlieel wliich receives the force of the current i'orce is also lost 

 bj changing the direction of the water in order to convej^ it to the machinery ; 

 iu the sudden change of velocity which the water undergoes when it tirst 

 strikes the wheels ; and more than all, from the feet that a considerable amount 

 of force is left unemployed in the water which escapes with a greater or less 

 velocity from every variety of wheel. It may be considered as practically 

 impossible to construct any form of water-engine which will utihze the whole 

 force of a current of water. 



357 Water, although one of the most abimdant substances in nature, and 

 a universal necessity of life, is not always found in the location iu which it is 

 desirable to use it. Mechanical arrangements, therclbre, adapted to raise 

 water from a lower to a higher level, have been among the earliest inventions 

 of every country. 



What were ^^S. The application of the lever, in the 

 rangeraentsf'; ^rm of the old-fashioned well-sweep (still 

 raising water ? ^^gyj -j^ many pai'ts of this country, and 

 throughout Eastern Asia), of the pulley and rope, and 

 the wheel and axle in the form of the windlass, were un- 

 doubtedly the earliest mechanical contrivances for raising 

 water. 



The screw of Archimedes, invented by the philosopher 

 whose name it bears, is a contrivance for raising water, of 

 great antiquity. 



This machine, represented in Fig. 

 150, consists of a tube wound in a 

 spiral form about a solid cylinder, A 

 B, which is made to revolve by turn- 

 ing tlie handle H. This cylinder is 

 placed at a certain inclination, with 

 its lower extremity resting in the 

 water. As the cylinder is made to 

 ^^\ revolve, the end of the tube dijis into 

 the water, and a certain portion er- 

 ters the orifice a. By continuing 

 the revolution of the cylinder, the 

 water flows down a series of inclined 

 planes, or to the under side of the 

 tube, and if the inclination of the 

 jube be not too great, the water will finally flow out at the upper orifice into 

 A proper receptacle. 



The foUowing diagram, Fig. 151, representing the curved tube in two 

 opposite positions, will illustrate the action of the Archimedes screw. Suppose 

 a marble dropped into the tube at a, fig. 1, : if it was kept stationary iu the 



Descnbe the 



Archimedes 



screw. 



Fig. 150. 



