19'2 HYDRAULICS. 



namely, part of that which had come out of the 

 suction-pipe h; and the next descent of the piston 

 must drive more water into the rising-pipe k, and 

 along with it, most, if not all, of the air which 

 remained below the piston, and must rarefy still 

 more the air remaining above the piston ; and more 

 water will come in through the pipe h, and get into 

 the barrel. It is evident, that a few repetitions 

 will at last fill the barrel on both sides of the piston 

 with water. When this is accomplished, there is 

 no difficulty in perceiving how, at every rise of the 

 piston, the water of the cistern will come in by the 

 valve n, and the water in the upper part of the 

 barrel will be driven through the valve o ; and in 

 every descent of the piston, the water of the cis- 

 tern will come into the barrel by the valve p, and 

 the water below the piston will be driven through 

 the valve m; and thus there will be a continual 

 influx into the barrel through the valves n and p, 

 and a continual discharge along the rising-pipe /, 

 through the valves m and o. 



This machine is certainly equivalent to two 

 forcing-pumps, although it has but one barrel and 

 one piston ; but it has no sort of superiority. It is 

 not even more economical, in most cases ; because, 

 probably, the expense of the additional workman- 

 ship will equal that of the barrel and piston which 

 is saved. There is, indeed, a saving in the rest of 

 the machinery ; because one lever produces both 

 motions. It, therefore, cannot be called inferior to 

 two pumps ; and there is undoubtedly some inge- 

 nuity in the contrivance. 



Fig. 6. is anotherpump for furnishing a continued 

 stream, invented by Mr. Noble. A B, the working- 

 barrel, contains two pistons, C and B, which are 

 moved up and down alternately by the rods fixed 





