Mechanics.

Stroke shall be but one fourth Part so great, of 25000,look in the Table for the Number nearest to this, andyou will perceive it to lie between 14 and 15 Degrees,and therefore about 14 Degrees and a Half is the Anglerequired.

29. In the last Place : It was said, That the Force of

the IVind on the Sail is proportional to the Squares of theSines of the Angle of Incidence. This may be illustratedby Numbers, thus : If the Sail be turned to the fameWind, first under an Angle of 45 Degrees, and thenunder an Angle of 30 Degrees; the Sine of the firstAngle is (by the Table) 707x0, and of the latter

50000, the Squares of which are 4999904100 and2500000000, which Squares areas 50 to 25 or'as 2to 1 ; and therefore the Power of the Wind is twice asgreat upon an Angle of 45 Degrees, as upon an Angleof 30.

30. Because the Square of the Sine of 45 Degrees is5000000000, twice that Square will be 10000000000,which is equal to the Square of Radius IOOOCO ; it isevident the Sum of the Squares of the Sines of any twoAngles above 45 Degrees will be greater than theSquare of Radius ; and therefore the Force of theWind upon two oblique Sails, in that Cafe, will begreater than upon one Sail set direct before the Wind.

31. After the fame manner, the Table of Sines maybe applied to Calculation in any other Cafe of the likeNature, where t'.e Proportion of Radius and Sine of anAngle is required to be expressed or stated in Numbers.And since each Degree is divided into 60 equal Parts orMinutes , therefore the Sine of any Number of Degreesand Minutes also may be easily found by the fore-going Table, by those who understand the Rule ofProportion.

32. I shall only further observe here, that as I L isthe Sine, and L M the Co-fme , of the Arch I E : so ifon the extreme Point E of the Radius C E we raise aPerpendicular which shall cut the Line C I, continued,in F, then is the said Perpendicular E F called theTangent of the Angle ICE, and the Line F C theSecant of the fame Angle. In like manner the Per-pendicular D G is-the Tangent of the Angle D C I, and

0.2 GC

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