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from the Orifice of which it ifiueswit fi a great Velocity, to a very great

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inner Leg ; supposing the Mercury now stands at eln that, and at/in the other: And then the said Heightthe Water will be nearly 14 times the Height df,c e ' I think all this is very easy to understand fromthe common Principles of Hydrostatics, and if this beunderstood, the Nature of the Pump must, as beingthe very f ame Machine with a different Disposition of

"s Parts.

52. From this Theory of the mercurial Pump, ’tisa ’y to infer, that in constructing one, the Part ZF O Q_®"ght to be placed in the Middle of the Height fromthe Water H to be raised, to the Cistern AB whichReives and delivers it; or more nicely, tke level Sur-,a< ii a ^ c ^ the Mercury when the Pump is full, and1 l Zniug to work, oueht to be in the middle Point of^ Line P g ; the Reason is, because in the Descent andAscent of the Tube M S, the Differences between the■^■Litude cf the outer and inner Shells a d an r ar*>al, and in each Cafe a 14th Part of the Height of. e Water below or above it.

5Z- Suppose the whole Height from the Water toPiston be P|- = 60 Feet; then a P = ag — 30. eet , or 360 Inches; then also 14)360(26 nearly, thatcu Difference of the Altitudes in the mercurialshells will be about 26 Inches. The Place there-°re where they ouo-ht to be on a Level is at least 13. ncbes below M, or file Quicksilver must never be pouredln to a Height N a greater than about 15 or x6 Inches,

• ° r *7 at most. If the Height V g be greater than 60larg Tubes M S > & c - must be proportionahly en-

n, 54* To compute the Quantity of Quicksilver in thee ‘ls ; let A C B D be the Area of the Top of theTube X Y, and E H F G the Area of the Surfacethe inmost Mercury Shell surrounding it; then be-e A B == 6 Inches, we have A B 1 X 0,7854 =

X 0,7854 28,274 = the Area of the Circle A P B C*

Again,

PI. XX.Fig. 5-