Mechanics. i i 3

Body descends from the fame Height thro’several contiguous Planes, ever so differentin Number or Situation, it will always ac-quire the fame Velocity in the lowestPoint. (7.) The Times or Velocities ofBodies descending through Planes similarlysituated, qr alike inclined to the Horizon, asDB, EC, will be as the Square Roots of Fig. 2.their Lengths DB, EG (XXVII).

From

equal to the uniform Motion of a free Descent, the Mo-tion will be every where uniform, because the Resis-tance of the Medium is equal to Gravity. But if a Bo-dy (as a Ball from a Cannon) be projected with a Ve-locity greater than that, the Motion will be jx tarded,inasmuch as the Resistance is now greater than Gravity,and so will diminish the uniform Motion, arising fromthe Equilibrium just mentioned.

12. Hence light Bodies (as an Arrow) thrown di-rectly upwards, spend less Time in rising than falling,because the Motion upwards is altogether retarded,whereas that of the Descent is in some Part uniform-Also the greater the Velocity with which a Body (as aBullet) enters a dense Medium (as Water) the lessthe Effect at a given Distance therein ; and with thegreater Force they are reflected or thrown out again,when projected obliquely, as we fee in a Stone thusthrown into the Water, &c.

(XXVII) Let BD be an inclined Plane, A a Bodydescending thereon ; from the Centre C draw CE per- Plat? VIpendicular to the Plane, and CG perpendicular to the Fig. i.Horizon or Base CD, and meeting the Plane in F.

Now since the Body gravitates in the Direction CF, letCF represent the Weight of the Body or absolute Forceof Gravity ; this may be reloiv’d into two Forces, act-ing in the Direction CE and EF, of which the first ;sperpendicular to the Plane, and is that by which it

Vol. I. I presses