OF HYDRAULIC ENGINES. 



129 



Buttering any air to come between it and the pipe or 

 pump barrel. 



We shall explain the construction both of this and 

 the forcing-pump by pictures of glass models, in which 

 both the action of the pistons and motion of the valves 

 are seen. 



Hold the model D C B L 

 upright in the vessel of water 

 K, the water being deep 

 enough to rise at least as 

 high as from A to L. The 

 valve a on the moveable 

 bucket G, and the valve b on 

 the fixed box H, (which box 

 quite fills the bore of the 

 pipe or barrel at H) will 

 each lie close, by its own 

 weight, upon the hole in the 

 bucket and box, until the en- 

 gine begins to work. The 

 valves are made of brass, 

 and lined underneath with 

 leather for closing the holes 

 the more exactly : and the 

 bucket G is raised and de- 

 pressed alternately by the 

 handle E and rod D d, the 

 bucket being supposed at B 

 before the working begins. 



Take hold of the handle E, and thereby draw up the 

 bucket from B to C, which will make room for the air 

 in the pump all the way below the bucket to dilate it- 

 self, by which its spring is weakened, and then its force 

 is not equivalent to the weight or pressure of the out- 

 ward air upon the water in the vessel K: and therefore, 

 at the first stroke, the outward air will press up the 

 water through the notched foot A, into the lower pipe, 

 9. 



LECT. 

 V. 



