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Mechanics.

cannot be so equal, uniform, and steady as that of aWater-Mill, whose Power is always of the same Tenor,while the Jet of Water is so.

8. If the Area of the Sail and the Velocity of theWind be supposed constant, the Force of the Wind inthe Diredt Position will be to that in the Oblique one

as G C to G E’, as we have before shewn ; and it hasbeen also shewn that that Part of the Force which turnsthe Sail is represented by E F, when G E is the whole

Force: But GE : EF (: : GC: CE):: GE>:

(jr L

— to the Force which turns the Sail, when the whole

Force is represented by GE 1 , as is here the proper Ex-pression of it.

9. This Expression — q ’ q ~ begins from Nothing,

when the Angle of Incidence begins to be oblique, andincreases with the Obliquity of the said Angle to a cer-tain Number of Degrees; because that Part of theForce which is parallel to the Axis becomes lesser inproportion to that which is perpendicular to it; but af-ter it has pass’d this Limit, it again decreases, and be-comes nothing, when the Angle of Incidence vanishes ;as is easy to understand by considering that the Quanti-ty of Wind on the Sail does in this Cafe continually de-crease.

10. There is therefore one certain Position of theSail, in which the Force of the Wind is greatest of allupon it, or a Maximum ; and to find it, put Radius

GC — st, EC — x, and we have GE* — aa — *•*, and

r i » -r-. CEXGE aax—xxx ...

consequently the Force -——— —-, which

(j C «

must be a Maximum: Therefore its Fluxion aax—3 x xx - o ; whence a a — 3 * *, and so * —

which in Logarithms is 2°,°°Q°°0-°,477I2I =

2

9,761439, which is the Logarithm Sine of the Angle35 0 Iss—Angle CGE; and therefore the Angle ECG

is