6

Hydraulics.

tuation above the highest Part of the Towit(LXX.)

Hence

pi XVI (BXX.) i. Let ACDB Le a Reservoir with apjg. g ' Duct or Conduit-Pipe F K L, and at L turn’d off from- " the Perpendicular to give the Water by a Stop-Cock

into a Cistern for the Use of a Family. It is plain theWater will issue out from L with the fame Force as itwould be made to rife to the Height LO, were theTube or Pipe continued upright to Oj for on oneSide the common Base K, the Pressure (when the Cockis shut) is proportional to the Altitude E K, but on theother it is only LK; the Difference therefore, El —LO, is the Force of Pressure by which the Water isprotruded from the Cock at L. In the fame Mannerit is shewn, that the Force by which it is made to spoutfrom the Cocks at M and N is proportional to the Al-titudes H E and G E, or M O and N O, of the Fluidin the Reservoir above them.

2. The Running of Rivers is upon the fame Principleas the Descent of Bodies on inclined Planes; for Wa-ter no more than a Solid can move on an horizontalPlane, the Re-action of such a Plane being equal andcontrary to Gravity entirely destroys it, and leaves theBody at rest; here we speak of a Plane of small Ex-tent, and such as coincides with the curved Surface ofthe Earth. But if we consider a large Extent or longCourse of Water, then we shall find that such Watercan never be at Rest, but when the Bottom of the Chan-nel coincides every where with the curved Surface ofthe Earth.

Fig. 9. 3- Let AD F be the curved Surface of the Earth, C

its Centre, C D, C E two right Lines drawn fromthence, and E G a Tangent to the Earth in the PointD. Then ’tis plain if BD were a Channel of Wa-ter, the Water could not run, or move, because theyare every where at an equal Distance from the CentreC, and therefore equally affected by Gravity. But ifthere beany Place above the Surface of the Earth as E,where Water can be found, ’tis evident that Water