Chap, 3. PHILOSOPHICAL DISCOVERIES. 147

CHAP. III,

Of the mechanical powers.

1. r i A H E knowledge of mechanics is one of those things| that contribute most to distinguish civilized nationsfrom barbarians : the works of art derive their chief beauty andvalue from it ; and without it we can make very little pro-gress in the knowledge of the works of nature. It is by thisscience that the utmost improvement is made of every powerand force in nature, and the motions of the elements, water,air, and fire, are made subservient to the purposes of life,when industry, with materials for the necessary instruments,are not wanting. However weak the force of man appears tobe, when unassisted by this art, yet with its aid, there is hardlyany thing above his reach. It is a science that admits ofthe. strictest evidence; and certainly it is worth while toestablish it on its just principles, and to cultivate it with thegreatest diligence.

It is distinguished by Sir Isaac Newton into praBical andrational mechanics; the former treats of the mechanical powers,viz. the lever , the axis and wheel , the pulley , the wedge, andthe screw , to which the inclined plane is to be added ; and oftheir various combinations together. Rational mechanics com-prehends the whole theory of motion ; and shews, when the .powers or forces are given, how to determine the motions thatare produced by them ; and, conversely, when the phæno-mena of the motions are given, how to trace the powers orforces from which they arise. Thus it appears that the wholeof natural philosophy, besides the describing the phenomena

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