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Hydraulics.

length is so far increased, as to re-act withgreat Force on the Surface Y Z of the sub-

jaceirt

of the middle one , of an Inch, and of the inner on e >tVu of an Inch, and the Bottom of the Tube Z O i0come within an Inch of the Bottom N S of the outetTube. . .

46. These Dimensions afford sufficient Strength uthe Tubes or Barrels are made of Copper, or cast Iron*and of such a Diameter, that the Distance between eachmay be f the Tenth of an Inch ; and this should henicely effected by having the Tubes truly turned in aLathe. A transverse Section of a Part of the Circuit 1 'science of those Tubes, their Thicknesses, and Spac eSbetween, you fee represented in the Fig. 2. wh c{CA B is the outer, C D the middle, and E F the inn efTube. The Spaces between are so narrow, hecau^otherwise too great a Quantity of Quicksilver would b enecessary, and yet of no Use; because Fluids press odtyaccording to the Altitude, and not the Quantity.

47. If now every Part be fitted for Work, and M er "cury poured in to the Height of 24 Inches, as stre^ssby a N S d-, and the Barrel and Pipe sill’d with Wass 1 "*so that the whole Pump be full, and in Equilibria .the Atmosphere; if the outer Tube M S be moV edown through the Space of 14 Inches, at the Cod 1 'mencement of the Motion, the Equilibrium in the Puss?is destroyed by the greater Space which would enf^upon the Descent of the Inner Tube X Q_, andcannot be suffered, because of the Pressure of the •A 1 ’,on the Water at H, and on the Mercury in the ou t& ;Shell at «, d. And because these Pressures of theoutwardly at H and a are equal, but there is not ^equal Pressure inwardly on the Valve I, and the tfss e ..Shell of Mercury c ; the Valve being press’d withthe Water in the Pipe above it, and which is prop 0 ^tional to the Altitude C g ; and the Surface of the Mf*.cury of the inner Shell at b, c, being press’d only "st,!the Altitude of Water C b, ’tis plain the Water V 1

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