WHEEL AND AXLE, the second of the mechanical powers (q.v.), is a modification of the lever (q.v.). Its most primitive form is a cylindrical axle, on which a wheel con centric with the axle, is firmly fastened. When employed for raising heavy weights, the weight is attached to a rope which is wound round the axle, and the power is applied either to a rope wound round the grooved rim of the wheel, or to a handle fixed at right angles to the wheel's rim (in the latter case, the wheel may be dispensed with, unless it is useful as a conservator of moine:stum [see FLY-WHEEL], and an ordinary winch sub stituted). The wheel and axle is neither more nor less than a lever, whose extremities are not points as in the normal form, hut the circumferences of circles. Accordingly the power and weight are not attached to particular points in these circumferences, but to cords wound round them, and thus the imaginary simple lever (formed 1w joining the points where the cords become tangents to the circles), isifeserved unaltered in position and magnitude. The conditions of equilibrium are, that (the power) X the radius of
the wheel = W (the weight) X the radius of the axle, or, since the circumferences of circles are proportional to their radii, that P: W:: circumference of axle: circumference of wheel. When there is no wheel, but only a winch, the circumference described by the power in one revolution is substituted for the circumference of the wheel. The capstan and windlass are simple and common examples of this mechanical power, and combinations of toothed-wheels, or of wheels from one to another of which motion is communicated by an endless band, are compound illustrations or the same. See Witin LAss.
See ROTATORIA.