§4? SUMMARY OF HYDRAULICS. 



fame as if one leaped from a height of between two and three 

 feet. Mr. Garnerin, however, finds the mean velocity of de- 

 foent only eight feet, which agrees better with the experiments 

 of Borda, in which the refiftance appeared to be •§■ of the 

 weight of the column due to the velocity, and exceeded this 

 proportion as the furface increafed in magnitude. 

 Syphons. Chapter 15. Offiphons. 



For eftimating the difcharge of a fiphon, the head of water 

 mutt be reckoned equal to the difference between the levels of 

 the furface of the water, and of the lower orifice. The author 

 obferves, that the theory of waves has been treated in a new 

 and improved manner by Lagrange in his M£canique Analy- 

 tique. The problem is, however, not yet completely folved : 

 Lagrange's formula includes the depth of the water agitated 

 as a given quantity, but it does not inform us how to determine 

 this depth from theory. 

 Sucking pumps. Chapter 16. Of fucking pumps. 



The length of a lucking pump muft never be greater than 

 30 feet below the moveable valve : and there may be a lofs of 

 time in the afcent of the water, unlefs it be made even a few 

 feet ihorteY. The motions to be produced, and the refiftances 

 to be overcome, are confidered in detail; but the author re- 

 fers, for frill further information, to Langfdorf 's Treatife on 

 Machinery. 

 Nature of the The velocity of the ftroke fhould never be lefs than four 

 inches, nor greater than two or three feet in a fecond j the 

 ftroke fhould be as long as poflible, to prevent lofs of water by 

 the frequent alternations of the valves. The diameter of the 

 pipe fhould be about §• or ^ of that of the barrel. The lifting 

 pump is alfo here defcribed ; it only differs from the fucking 

 pump in having the lower valve moveable, and the upper one 

 fixed. A number of valves and piftons are defcribed in tto£ 

 chapter ; chiefly from models of Englifh manufactory. 

 Forcing pumps ; Chapter 17. Of forcing pumps. 



In defcribing the different kinds of folid pifton, the author 

 gyves the preference to that which has a conical leather project- 

 ing on each fide ; but remarks, that there is another form which 

 has the advantage in the fituation of the ring for receiving the 

 rod, which is prccifely in. the centre of the pifton, and is there- 

 made without fore fitter for communicating motion in each direction. He 

 leathering. ^^ lhat w here t j ie barrel is well polifhed, the pifton may be 

 uied without either wadding or leather. 



