i3°

Mechanics.

projeBile Force., and that of Gravity. Bythe first, the Body passes over equal Spaces ,AB, B C, C D, &c. in equal Times ; andby the second, it descends through SpacesA G, A H, A I, &c. which are as theSquares of the Times ; and therefore bythese two Forces compounded, the Bodywill describe, not a Right Line , but a CurveA Qj and of that Sort which we call a Pa-rabola ; and this will be the Cafe in allDirections but that in the Perpendicular,when the Path of the Projectile will be (toPlate V. Appearance) a Right Line. The greaterFig- 7 * the Angle of Elevation K A M of the Can-non is, the greater will be the Height D Bto which the projected Body will rife. Also,the greater will be the Distance or Amplitudeof the Projection, till the said Angle becomesequal to 45 Degrees K A O; upon whichElevation the Random A C will be thegreatest possible, and equal to twice theAltitude A G of the perpendicular Pro-jection. On any Elevation A M or A M,equally above or below 45 Degrees, as on40 and 50, 30 and 60, 20 and 70 Degrees,the Random A C will be the fame; whichCafe an Engineer frequently finds of verygreat Use.

If the Object be situated above the Ho-rizon, then, in order to strike it with theleast Impetus , let a Piece of Looking-glass

be