Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/68
24 Book I.
and of the direct ratio of pH to pN, the weights will have the effect towards moving the wheel and will therefore ſuſtain each other; as any one may find by experiment.
But the weight p preſſing upon thoſe two oblique planes, may be conſidered as a wedge between the two internal ſurfaces of a body ſplit by it; and hence the forces of the Wedge and the Mallet may be determined; for becauſe the force with which the weight p preſſes the plane pQ is to the force with which the ſame, whether by its own gravity, or by the blow of a mallet, is impelled in the direction of the line pH towards both the planes, as pN to pH; and to the force with which it preſſes the other plane pG, as pN to NH. And thus the force of the ſcrew may be deduced from a like reſolution of forces; it being no other than a wedge impelled with the force of a lever. Therefore the uſe of this Corollary ſpreads far and wide, and by that diffuſive extent the truth thereof is farther confirmed. For on what has been ſaid depends the whole doctrine of Mechanics variouſly demonſtrated by different authors. For from hence are eaſily deduced the forces of machines, which are compounded of wheels, pullies, levers, cords, and weights, aſcending directly or obliquely, and other Mechanical Powers; as alſo the force of the tendons to move the Bones of Animals.