In forming the naked flooring, over rooms of very large dimensions, it is found necessary to introduce large strong timbers, in order to shorten the bearing of the binding-joists; such strong timbers are called girders, and are made with mortises, in order to receive the tenons at the ends of the binding-joists, which, by this mean, are greatly stiffened, being much shorter.

The bridging-joists are frequently notched down on the binding-joists, in order to render the whole work more steady.

Figure 1, pl. X, is the plan of a naked floor; b, b, b, &c. are the bindingjoists; a, a, a, &c. are the bridging-joists; d, a timber close upon the stair-case. This piece of timber is called a trimmer: its use is to receive and secure the ends of the joists, e, e, e, &c. upon the landing.

C, C, C, &c. are wall-plates, upon which the ends of the binding-joists rest. In the construction of floors, great care must be taken that no timber come near to a chimney; therefore, the ends of the timbers, as here shown, have no connection with the fire-place, nor with the flues.

The flues, in this plan, are indicated by their being shadowed darker than the other parts of the plan.

Figure 2, pl. X, is the plan of naked flooring with a girder.

Figure 3, shows the manner of framing joists into a girder, with the form of the mortise and tenon. No. 1, is the part of a joist framed into the girder; and No. 2 is a joist out of the mortise.

Figure 4, shows the connection of binding-joists, bridging-joists, and ceiling-joists; as, also, the manner of fixing the binding-joists upon the wallplates, which manner is called cocking, or cogging. The long dark parts represent the mortises, into which one end of the ceiling-joists are fixed. These long mortises are called pulley-mortises, or chase-mortises. The ceiling-joists are introduced into common mortises at one end, and the other end of them are let into these long mortises obliquely, and slide along until they are perpendicular.

Figure 5, shows how the bridging-joist is let down upon the binding-joist,

TUMBLING IN A JOIST, is to frame a joist between two timbers, of which the sides, which ought to be vertical or square to the upper edges, are oblique to these edges.

Figure 6, shows the method of fitting in a joist between the sloping sides of two others. The first thing done is, to turn the upper edge of the joist upon the top of the two pieces into which it is to be fitted, and brought over its proper place. The next thing is to turn the joist on its under edge, so as to lie over its place; then apply a rule, or straight edge, upon the side of the one piece where the shoulder of the joist is intended to come; then slide the joist until the line drawn come to the straight edge of the rule so applied; then draw a line by the edge of the rule. Do the same at the other end, and the two lines thus drawn will mark the shoulder of the tenon at each end.

LENGTHENING TIMBERS.

TIMBERS may be lengthened in various ways, either by making the piece of timber in two or more thicknesses; or by securing one piece to another, with a piece on each side, in order to cover the joint; and by spiking or bolting each piece on both sides of the joint. Sometimes the pieces that are applied on the sides are made of wood; in this case, it is called fishing the beam: such modes are used in ships, when their masts, beams, or yards, are broken, in order to mend them. Other modes of continuing the length of timbers or beams is, by splicing them with a long bevel-joint, ending in a sharp edge at the end of each piece. Sometimes the sharp edge of the end of each piece is cut off, so as to form an obtuse angle at the top. Sometimes the splice is so formed as that the two surfaces which come into contact are reciprocally indented into each other, which will add greatly to their security, when firmly bolted together. Every kind of scarf should have a strong iron-strap upon each opposite side, extending in length considerably beyond each joint.

Figure 7, pl. X, shows the manner of building a beam in three thicknesses; which, being strapped with iron across every joint, and bolted, will be exceedingly strong and firm.

Figure 8, exhibits the method of joining timbers by two tables and a key. Figure 9, the method of lengthening timber by a plain scarf, being cut only with an obtuse angle at the ends.

Figure 10, the same kind of scarf, with two tables and a key.

Timbers that are scarfed and strapped ought to be so applied, that the sides which are strapped should be the horizontal sides; for, if otherwise applied, they will be liable to split at the bolting.

But, if the surfaces of the joints are to be placed in a vertical position, there ought to be two straps upon the top and two upon the bottom; each strap being brought close to the vertical face. By this method it will be much stronger than when set in the other position, or with the joint of the scarf horizontal.

THE ROOFING.

THE ROOF is that part of a building raised upon the walls, and extending over all the parts of the interior, in order to protect its contents from depredation, and from the severities and changes of the weather.

The ROOF, in CARPENTRY, consists of the timber-work which is found necessary for the support of the external covering.

The most simple form of roofs is that consisting of a level plane; but this description of roofs is adapted only to short bearings, and is not at all calculated to resist or prevent the torrents of rain or moisture from penetrating into the interior.

The next simple form is that which consists of an inclined plane; and, though well calculated to resist the injuries of the weather, and to afford greater strength than a level disposition of the timbers would supply, it is far from admitting of the utmost strength that a given quantity of timber is

capable of affording: it occasions an inequality, and a want of uniformity and correspondence in the proportions of the fabric, and an unnecessary and unpleasant height of walling. The best figure for a roof is that which consists of two equal sides, equally inclined to the horizon, terminating in the summit, over the middle of the edifice, in a horizontal line, or the ridge of the roof, as it is called: so that the section made by a plane, perpendicular to the ridge, is every where an isosceles triangle, the vertical angle of which is the top of the roof. This form is very advantageous, as it regards saving of timber; for it may be executed with the same scantlings, to span double the distance, that the simple sloping roof admits; or, in buildings of the same dimensions, the scantlings of the timbers will be very much diminished.

The antient Egyptians, Babylonians, and other eastern nations, of the remotest antiquity, constructed their roofs flat, as do likewise the present inhabitants of these countries. The antient Greeks, though favoured with a mild climate, yet sometimes liable to rain, soon found the inconvenience of a platform covering for their houses, and accordingly raised the roof in the middle, declining towards each side of the building, by a gentle inclination to the horizon, forming an angle of from 13 to 15 degrees, or the perpendicular height of from one-eighth to one-ninth of the span.

In Italy, where the climate is still more liable to rain, the antient Romans constructed their roofs from one-fifth to two-ninth parts of the span.

In Germany, where the severities of the climate are still more intense than in Italy, the antient inhabitants, as we are informed by Vitruvius, made their roofs of a very high pitch. When the pointed style of architecture was introduced into Europe, high pitched roofs were thought consonant with its principles; and they therefore formed, externally, one of the most striking characteristics of the Gothic style.

In their usual proportions, the rafters were equal to the breadth or span of the roof, or the rafters were the sides of an equilateral triangle, of which the spanning line was the base.

During the middle ages this form prevailed, not only in public but in private buildings, from the most stately and sumptuous mansion down to

the humble cottage of the common labourer; and this equilateral triangular roof continued in request until, finally, the pointed style came into

disuse.

When the celebrated INIGO JONES introduced Roman architecture, the rafters were made three-quarters of the breadth of the building; and this proportion, which was called true pitch, still prevails in some parts of the country where plain tiles are used; subsequently, also, the square seems to have been considered as true pitch: but, in large mansions, constructed in the Italian style, roofs of a pediment pitch, covered with lead, were introduced.

In the present day, where good slates are to be obtained in abundance, roofs may be covered with them, from the pyramidal equilateral Gothic down to the gently inclined Greek pediment.

With regard to the present practice, the proportion of the roof depends on the style of the architecture of the edifice; the usual height varying from one-third to one-fourth part of the span.

There are, doubtless, some advantages in high pitched roofs, as they discharge the rain with greater rapidity; the snow does not lodge so long on their surface; also, they may be covered with smaller slates, and even with less care, and are not so liable to be stripped by high winds as the low roofs are; but the low roofs bear less weighty on the walls, and are considerably cheaper, since they require shorter timbers, and, of course, smaller scantlings.

The roof is one of the principal ties to a building, when executed with judgement, as it connects the exterior walls, and binds them together as one mass; and, besides the protection it affords the inhabitant within, it preserves the whole work from a state of decay, which would soon inevitably ensue, from the violence of rain or frost, which would operate in a way of rotting the timbers, of destroying the connection in the walls, and would cause them ultimately to fall.

The several timbers of a roof are, principal rafters, tie-beams, king-posts, queen-posts, struts, collar-beams, straining-sils, pole-plates, purlins, ridgepiece, common-rafters, and camber-beams. The uses of these will

appear from