Mechanics.

103

The third, general Law is founded onReason and Experience: We know from

the

somewhere In the said Line ce. For the same Reason itwill at the End of the said Time be carried to a Distancefrom be equal to bd, and therefore it must also at thesame Moment be found somewhere in the Line de-, butit cannot be in the Line ce and de at the same Time ;unless in that Point e, where they intersect each other,as the Proposition asserts.

2. We may now conceive the Body B moving by thesingle Impulse of some Power in the Direction be, suchas will carry it thro’ the Space be in a given 'I'ime:then this may be resolved into any other two Forcesacting in the Directions be or de, and b d or ce, whichLines will also represent the Efficacy of the laid Forcesin the fame Time.

3. This Doctrine of the Composition and Resolutionof Forces will be found of very frequent Use ; and willbe farther illustrated in an Application to the Doctrineof Oblique Percussion, as follows. Let the Body A im-pinge on B at rest in the Direction A C, which be-cause it does not go through the Center of the Body B,the Stroke will not be Direct, but Oblique ; and let theForce of the Stroke be represented by the said LineAC.

4. This Force A C may be resolved into the twoForces A I, and I C ; the former of which being pa-rallel to the horizontal Line G F, cannot affect theBody B at all; for the Motion in that Line would onlypass by the Superficies of B, and touch the uppermostPoint without any Stroke or Force to remove it.

5. But that Part of the Stroke represented by I C,passes thro’ the Center of B, and therefore expressesthe whole Force with which the Body A strikes it inthe Direction A C. Therefore the Force of an obliqueStroke is to the Force of a direct Stroke, as I C to A C,paffng through the Center of the Body B,

H 4

Plates V.Fig. 12,

6. Now