MECHANICS. The science of motion, or that branch of mixed mathematics which treats of the effects of powers or moving forces, and applies them to machines and engines. Newton divides this science into practical and rational; the former of which relates to the mechanical powers, namely, the lever, balance, wheel and axis, pulley, wedge, screw, inclined plane, &c. (see MECHANICAL POWERS I) and the latter, that is, rational mechanics, relates to the theory Of motion, showing when the forces and powers are given, how to determine the motion that will result from them ; and conversely, when the circumstances of the motion are given, how to trace the forces or powers from which they arise. As to the practical part of mechanics, this was doubtless one of the first branches of knowledge which necessity would lead men to acquire, it being impossible to pursue any of the mechanic arts successfully, without the aid of mechanical powers in raising weights or exerting forces. That all the mechanical powers were well known to the ancients, Is certain, from the number and perfection of the machines which they had in use. The theo retical part of mechanics appears, however, not to have engaged their attention before the, time of Archimedes, who particularly applied himself to this subject ; and, in his book on Equiponderants, has given us the theory of the lever, the inclined plane, the pulley, and the screw. From his time to the sixteenth cen tury, the theory of the mechanical science re-1 reamed, with little or no addition or change.
Stevinus, a Flemish mathematician, revived the subject by treating on the laws of equilibrium of a body placed on an inclined plane, dm.; and Galileo afterwards, in his treatise on statics, extended his researches on the theory of the inclined plane, the screw, and all the mechanical powers, but more particularly on the theory of accelerated motion. Torricelli, a pupil of Galileo, added several propositions concerning projectiles ; Huygens treated of the motion of bodies along given curves ; and, in 1661, Huygens, Wallis, and Sir Chrism. pher Wren, all discovered the true laws of per cussion, without any previous communication with each other. Henceforth the study of me chanics, like every other branch of the mathe matical science, was illnstrated and enlarged by different writers of great name; as by Newton, in his Principia ; Leibnitz, in his Resistentia Solidonun ; Desohales, in his Treatise on Motion ; Parent, in his Elments of Mechanics and Physics; Oug,htred, in his Mechanical Institutions ; Keil, in his Intro duction to True Philosophy ; De la Hire, in his Mechanique ; Ditton, in his Laws of Mo tion ; Gravesande, in his Physics ; Euler, in his Tractatus de Motu; Muscbenbrock, in his Physics ; Bossu, in his Mechaniques ; La grang in his Mechanique Analytique ; At, wood, in his Treatise on Motion ; Gregory, in his Mechanics, Theory, and Practice, &e.