Second: Flooring is formed by joists or strong beams of timber reaching from wall to wall, where they rest upon other beams, called wall plates, which are built into the walls themselves. The floor boards are nailed over the upper edges of the joists, and the lower edges receive the laths and plaster, which form the ceilings of the rooms beneath. Large buildings are sometimes fitted with double framed floors, with two sets of joists, and building joists resting on girders; and in superior houses, the _wall plates_ are often supported by “corbels,” or, portions of the timber projecting from the inside of the wall, which prevents the necessity of opening the wall to admit the ends of the joists. Third: Roofing consists of the roof covering, which is laid upon rafters or slender beams, which are supported by stronger horizontal beams called _purlins_; and these, again, rest on upright _trusses_, or strong frames of timber, placed on the walls at regular distances from each other. Upon the strength and firmness of these trusses, and the skill of the carpenter’s work, depends the entire safety of the roof. Large roofs are supported by cross beams, called _collars_, or _tie beams_; and they are further strengthened by an upright pillar in the centre, called a _King post_, from which slanting beams, called “struts,” support the rafters. We have now only spoken of common roofs, but there are many roofs of open timber-work in churches and other public buildings, which are wonderful specimens of the skill of the Carpenter and the Joiner. One of these, perhaps the grandest as well as the most ancient, is that of Westminster Hall; but there is one also in the Great Hall, at Hampton Court Palace; and others may be seen in Churches and Halls in various parts of England. The Joiner, as his name implies, frames and joins together the wooden finishings and decorations of buildings, such as floors, staircases, skirtings, door and window frames, sashes, or, the sliding parts of windows that contain the glass, shutters, doors, chimney-pieces, &c. This work requires much greater nicety and finish than that of the Carpenter, and is brought to a smooth surface with the plane wherever it is likely to be seen, while the carpenter’s work is left rough as it comes from the saw. The principal cutting tools used by the Joiner are, saws, planes, and chisels. The _saws_ are of various sizes, and are called rippers, half rippers, hand saws, and panel saws, according to their shape, and the number of teeth to each inch. [Illustration: Chisel. Gouge. Screw Driver. Screw. Tenon Saw. Narrow Saw.] The _tenon saw_ is used for cutting tenons, or flat slices from the ends of beams, that other beams cut in the same way may rest upon them and yet leave a flat surface. The thick back of the tenon saw keeps the blade from “buckling,” or twisting; as it would be very likely to do while sawing in a horizontal direction.