MAST, a long round piece of timber, elevated perpendicularly upon the keel of a ship, upon which are attached the yards, the sails, and the rigging, in order to their receiving the wind necessary for naviga tion. A mast, according to its length, is either formed of one single piece, which is called a pole-mast, or composed of se veral pieces joined together, each of which retains the name of mast separate. ly. A top-mast is raised at the head or top of the lower mast, through a cap, and supported by the trestle-trees. It is coin posed of two strong bars of timber, sup• ported by two prominences, which are as shoulders on the opposite sides of the masts, a little under its upper end : athwart these bars are fixed the cross trees, upon which the frame of tile top is supported. Between the lower mast head and the foremost of the cross-trees, a square space remains vacant, the sides of which are bounded by the two trestle trees. Perpendicylarly above this is the foremost hole in the cap, wlnue after-hole is solidly fixed en the head of the lower. mast. The top-mast is erected by a tackle, whose effort is communicated from the head of the lower-mast to the foot of the top-mast, and the upper end of the latter is accordingly guided into, and conveyed up through the holes, be tween the trestle-trees and the cap, as be fore mentioned ; the machinery by which it is elevated, or, according to the sea phrase, swayed up, is fixed in the follow ing manner. The top-rope, passing
through a block which is hooked on one side of the cap, and afterwards through a hole, furnished with a sheave or putty on the lower end of the top-mast, is again brought upwards on the other side of the mast, where it is at length fastened t6 air eyebolt in the cap, which is always on the side opposite to the top-block. To the lower end of the top-rope is fixed the top-tackle, the effort of w hich, being tran mitted to the top-rope, and thence to the heel of the top-mast, necessarily lifts the latter upwards parallel to the lower mast. 'When the top-mast is raised to its pro per height, the lower end of it becomes firmly wedged in the square hole (above described) between the trestle-trees. A bar of wood or iron, called the fid, is then thrust through a hole in the heel of it, across the trestle-trees, by which the whole weight of the top-mast is support ed. See SHIP building.