188 HYDRAULICS. 



reaches nearly to the bottom of" the vessel. When 

 the water is forced along the rising pipe S, it gets 

 into this vessel, and rises above the lower part of 

 the pipe T. The air which is above the water in 

 the vessel, being "now confined, and being con- 

 densed into a smaller space by the admission of 

 more water at each action of the piston, presses by 

 its elasticity upon the surface of the water, which 

 cannot return by the valve S, and forces it up the 

 pipe T, in a continued stream. This air-vessel 

 must be so large, that the change of bulk of the 

 compressed airs during the inaction of the piston, 

 may be inconsiderable ; otherwise the stream will 

 not continue until the next stroke. 



To describe, or even to enumerate, the immense 

 variety of combinations of these three simple 

 pumps, would fill a volume. We shall select a 

 few which are most deserving of notice. 



The common sucking-pump may, by a small 

 addition, be converted into a lifting-pump, fitted 

 for propelling the water to any distance, and with 

 any velocity. Fig. 4. is a sucking-pump, whose 

 working-barrel A B has a lateral pipe C, connected 

 with it close to the top. This terminates in a 

 main, or rising-pipe, furnished, or not, with a 

 valve. The top of the working-barrel A B is shut 

 by a strong plate, having a hollow neck terminating 

 in a small flanch. The piston-rod passes through 

 this neck, and is nicely turned and polished. A 

 number of rings of leather are put over the rod, 

 and strongly compressed round it by another 

 flanch and several screwed bolts. By this con- 

 trivance, the rod is closely grasped by the leathers, 

 but may be easily drawn up and down, while all 

 passage of air or water is effectually prevented. 

 The piston is perforated, and furnished with a 



