Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/84

40 aries either from the attrition of contiguous bodies as they lide by one another, or from the coheion of continuous bodies that are to be eparated, or from the weights of bodies to be raied, the exces of the force remaining, after all thoe reitances are overcome, will produce acceleration of motion proportional thereto, as well in the parts of the machine as in the reiting body. But to treat of Mechanics is not my preent buines. I was only willing to how by thoe examples the great extent and certainty of the third Law of motion. For if we etimate the action of the agent from its force and velocity conjunctly; and likewie the reaction of the impediment conjunctly from the velocities of its everal parts, and from the forces of reitance ariing from the attrition, coheion, weight, and acceleration of thoe parts; the action and re-action in the ue of all orts of Machines will be found always equal to one another. And o far as the action is propagated by the intervening intruments, and at lat impreed upon the reiting body, the ultimate determination of the action will be always contrary to the determination of the re-action.