Page:A Letter on the Subject of the Cause (1797).djvu/69

 its return thither, when the piſton of the pump returns to make a dip. This valve is placed in a hanging or vertical poſition, ſimilar to an eſcutcheon over a key hole; and ſuch nicety is requiſite, that was it placed in any other poſition, ſo as to preſs on the part againſt which it ſhuts, with only a moderate degree of force, it would very materially hinder and deſtroy the power of the Engine. Suppoſe it to preſs only one pound on every inch ſquare, comprehended on its ſurface, the Engine would be thereby deprived of, at leaſt, one twelfth part of her whole power; and ſo on, to any greater preſſure up to twelve pounds on the inch; by which it would be entirely counteracted. This, my Lord, is alſo an incontrovertible fact, that no perſon can ſee this valve in any Engine, without entirely diſorganizing it; as it is fixed down in a ciſtern filled with water, in many inſtances, ſeven or eight feet deep; and cannot, therefore, be diſcovered without this difficulty.

I humbly hope your Lordſhip will pardon ſo long and minute a detail on theſe parts; which were repreſented ſo extremely eaſy to hit upon, that an Engineer who ſhould miſs his way muſt be a blockhead, and unacquainted with his buſineſs. I was ſorry to obſerve many in the Court laugh very loudly at theſe expreſſions; for