1 8-3 HYDRAULICS. 



were both in the vessel, into which the water being 1 

 poured, it will rise in the -shorter leg of the ma- 

 chine, by its natural pressure upwards, to its own 

 level ; and when it shall have gained the bend of 

 the syphon, it will come away by the longer leg, 

 as already described. 



Upon the principle of the syphon, also, we may 

 easily account for intermitting or reciprocating 

 springs. Let A (Fig. 17.) be part of a hill, within 

 which there is a cavity B B, and from this cavity 

 a vein, or channel, running in the direction BCD. 

 The rain that falls upon the side of the hill will 

 sink, and strain through the small pores and cre- 

 vices in the hill, and fill the cavity B B with water. 

 When the water rises to the level of C, the vein 

 BCD will be full, and the water will run through 

 it as a syphon, and will empty the cavity B B. It 

 must then stop, and when the cavity is again filled, 

 it will begin to run again. 



ON PUMPS. 



The pump is at once the most common and the 

 most useful of all hydraulic engines. It was first 

 invented by Ctesibius, a mathematician of Alex- 

 andria, about 120 years B.C. 



Of this machine there are three kinds, viz. the 

 sucking, the lifting, and the forcing-pump. By 

 the two last, water may be raised to any height, 

 with an adequate apparatus and sufficient power ; 

 by the sucking-pump, it can only be raised 33 feet 

 from the surface of the water, as was observed 

 when treating on pneumatics, though, in practice, 

 this kind of pump is seldom applied to raising 

 water much above 28 feet ; because, from the va- 

 riations observed on the barometer, it is known 



