Draw

C

B

2080. A cornice bracket of any form being given, to make another similar one, or one that shall have the same proportions in all its parts. Let A ABCDEF (fig. 723.) be the given bracket. lines from the angular points CDE, and let Ab be the projection of the required bracket. The lines AC, AD, AE, being drawn, draw be parallel to the edge BC, cutting AC in c; draw cd parallel to CD, cutting AD in d. Draw de parallel to DE, cutting AE in e, and draw ef parallel to EF, cutting AF in f. Then Abcdef is the bracket required.

2081. To form an angle bracket to support the plastering of a moulded cornice. Let fig. 724. X be the plan of the bracket. Draw the straight line AE equal to the projection ab of the bracket on the plan X, and Aa perpendicular to AE, to which make it equal. Join Ea, and on AE describe the given form AFGHIKLE of the bracket which stands perpendicular to the line of concourse of the wall and the ceiling. From the angular points FGHIKL, draw the lines Fa, Gb, Ie, He, Kd, Ld, cutting AE in the points BCD, and aE in the points r. a, b, c, d. Draw af, bg, ci, dk, perpendicular to a E. Make af. bg. ch, ci, dk, dl, each respectively equal to AF, BG, CH, CI, DL, DK. Join fg, gh, hi, ik, kl, lE. afghiklE is the angle bracket required.

2082. An angle bracket for a cove (fig. 725.) may be described in exactly the same

manner.

Fig. 725.

E

Fig. 723.

Then

2083. When cove brackets have different projections, the method of describing the angle one is shown in fig. 726. Let AB, BC be the wall lines. Draw any line GD perpendicular to AB and HF perpendicular to BC. Make GD equal to the projection of the bracket from the wall represented by the line AB, and make HF equal to the projection of the bracket from the wall represented by BC. Then, as one of the brackets must be given, we shall suppose the bracket GAD described upon GD. Draw DE. parallel to AB, and FE parallel to BC, and join BE. In the curve AD take any number of points Q, S, and draw QP, SR cutting GD in P, R and BE in p, r. From the points p, r draw the lines pq, rs parallel to BC, cutting HF in the points p,r. Draw pq, rs perpendicular to BE. pq, rs also pq, rs respectively equal to PQ, RS, &c. and HC equal to GA, then through the points aqs, &c. draw a curve which forms the bracket for the angle. Also C through the points C, q, s draw another curve, and this will form the cove bracket.

Make
Ba

2084. The angle bracket of a cornice or cove may be formed by the method shown in X and Y (fig. 727.), whether the angle of the room or apartment be acute or obtuse, external or internal. Let ABC be the angle. Bisect it by the line BE. Draw GF perpendicular to BC, and make GF equal to the projection of the bracket, GC equal to its height, and FC the curve of the given bracket or rib. In the curve FC, take any number of points PQ, and parallel to BC draw the lines Pr, Qs, cutting BE in the points r, s, and GF in the points R, S. Draw rp, sq perpendicular to BE, and make the ordinates rp, sq respectively equal to RP, SQ, and through all the points pq, draw a curve, which will be the bracket as required.

2085. When the angle is a right angle, it may be drawn as at fig. 728., which is an ornamental bracket for the string of a stair, and traced in the same manner as that on a rightangled triangle.

E

F

2086. In coved ceilings, the coves meeting at an angle are of different breadths, and the plan of the angle is a curve to construct the brackets. Let ABC (fig. 729.) represent the angle formed by the walls of the room, and let Bdefg be the plan of the bracket in the angle of a curvilinear form. Draw HM, and thereon describe the bracket HOPQ intended for that side, and in the curve HOQ take any number of points NOP, and draw the lines NR, OS, PT perpendicular to AB, cutting it in the points R, S, T. Let MQ be the height of the bracket, and draw QA perpendicular to BA, and through the points NOPQ draw the straight lines Nd, Oe, Pf, cutting HM at IKLM. Draw hm perpendicular to BC. Make hr, hs, ht, ha respectively equal to HR, HS, HT, HA, and draw rn, so, tp, aq perpendicular to BC; also from the points defg draw the lines du, eo, fp, gq, and through the points hnopq draw a curve, which will form the other bracket required.

When

2087. Whether brackets occur in external or internal angles, the method of describing them is the same, and when the brackets from the two adjacent walls have the same projection, one of them must be given to find the angle bracket. the brackets from these walls have unequal but given projections, then the form of one of the brackets must be given in form to find the angle bracket.

2088. To form a bracket for a moulded cornice. On the drawing of such cornice, draw straight lines, so as to leave sufficient thickness for the lath and plaster, which should in no case be less than three-fourths of an inch. Thus the general form of the bracketing will be obtained.

DOMES.

2089. We have, in a foregone page, mentioned a method of constructing domes with ribs in thicknesses. We here present to

the reader two designs for dome-framing, wherein there is a cavity of framed work between the inner and outer domes; with moderate spans, however, simple framing is all that is required. Fig. 730. A is a design for a domical roof. B exhibits the

method of framing the curb for it to stand upon, the section of the curb being shown upon fig. A. The design here given is nearly the same as that used for the dome of the Pantheon in Oxford Street, which was destroyed by fire. Cis another design for a domical roof, which is narrow at the bottom part of the framing, for the purpose of gaining room within the dome.

A

Our object

The reader will immediately perceive that many varieties may be formed. here is merely to show how the carpenter is to proceed in making his cradling, as it is called, when pendentives are to be formed in wood.

2091. To cove the ceiling of a square room with conical pendentives. Let ABC (fig. 732.) be half the plan of the room, and DFE the half plan of the curb, at whose top the ribs are all fixed. The hyperbolical arches agb, bhe on each of the four sides are of equal height. The straight ribs bf, ik, lm, &c. are shown on the plan by FB, IK, LM, &c. The method of finding the hyperbolical curves agb, bhe will be explained in the following figure.

2092. To find the springing lines of the preceding pendentives, the section in one of the vertical diagonal planes being given. Bisect the diagonal LK (fig. 733.) at the point N by the perpendicular NW, which make equal to the height of the cone, and draw the sides LW and KW. Bisect the side MK of the square at a, and on N, with the radius Na, describe an arc a A, cutting the diagonal LK at A. Then take any points B, C, D, between A and K, and with the several radii NB, NC, ND, describe the arcs Bb, Ce, and Dd, cutting KM at the points d, c, and b. From the points A, B, C, and D, draw AE, BF, CG, and DH perpendicular to the diagonal KL, cutting the side WK of the section of the cone at E, F, G, H. At the points abcd erect perpendiculars ae, bf, cg, and dh to the side ML, making each equal to their corresponding distances AE, BF, CG, and DH, which will be one half of the curve for that side from which the other may be traced. The dark parts show the feet of the ribs.

2093. Fig. 734. shows the method of coving a square room with spherical pendentives, which a few words will sufficiently describe. CD, DE are two sides of the plan; AFB is half the plan of the curb. In the elevation above is shown the method of fixing the ribs (which, in projection, are portions of ellipses) on two sides of the plan. ab is the elevation of the curb AFB; cfd and dge are ribs on each side of the plan supporting the vertical ribs that form the spherical surface, which vertical ribs support the curb afb. On afb may, if necessary, be placed a lantern or skylight; or, if light be not wanted, a flat ceiling or a dome may be placed. This pendentive is to be finished with plaster; hence the ribs must not be farther apart than about 12 inches.

C

c

A

B

Fig. 734.

E

2094. For finding (fig. 735.) the intersection of the ribs of a spandrel dome, whose section is the segment of a circle, and whose plan is a square ABCD. Let DEFB be the section on the plane of the diagonal. First plan one quarter of the ribs, as at UC, TN, SL, RI, and QG, this last being parallel to DC or AB, the sides of the square; on V, with the radii VG, VI, VL, VN, and VC, describe the arcs GPg, Iti, Lul, Non, &c. cut

ting the base DB of the angular rib in g, i, l, and n. Draw gh, ik, lm, and no, each perpendicular to DB, cutting the diagonal rib at h, k, m, and o. Then making the distances GH, IK, IM, and NO equal to the corresponding distances gh, ik, lm, and no, through the points H, K, M, O draw a curve which will be the under edge of that for the bottom of the ribs QG, RI, SL, TN, and UC, shown complete on each side of the square plan. If each of the circular segments on each side of the square plan be turned up at right angles to the plan ABCD, the ribs will then stand in their true position.

BRIDGES.

Fig. 735.

2095. We shall in this work confine ourselves to the simplest forms of timber bridges, which, as well as those of stone, will be found fully treated of in the Encyclopædia of Engineering, by Mr. Cresy, which forms one of the series. As they mostly depend on the principle of the truss, where the span is large, and this combination of timbers we have already explained; so in stone bridges the principle of construction of the arch is the chief matter for consideration, and to that a large portion of this work has been devoted; hence, on the part of the architect, we do not resign his pretension to employment in such works, for which, indeed, as respects design, his general education fits him better than that of the engineer.

2096. The bridge over the Brenta, near Bassano, by Palladio, is an example of a wooden bridge (fig. 736.), which is not only elegant as a composition, but one which is economical

and might be employed with advantage where it is desirable that the piers should occupy a small space, and the river is not subject to great floods. The same great architect, in his celebrated Treatise on Architecture, has given several designs for timber bridges, the principles of whose construction have only been carried out further in many modern instances He was the earliest to adopt a species of construction by which numerous piers were rendered unnecessary, and thus to avoid the consequences of the shock of heavy bodies against the piers in the time of floods. Of this sort was the bridge he threw over the rapid torrent of the Cismone (fig. 737.) whose span was 108 feet.

2097. Palladio has given a design for a timber bridge (fig. 738.) which is remarkable as having been the earliest that has come to our knowledge, wherein the arrangement is in what may be called framed voussoirs, like the arch stones of a bridge, a principle in later days carried out to a great extent, and with success, in iron as well as timber bridges.

Fig. 737.

Fig. 738.

2098. We shall conclude our section on practical carpentry with a method of constructing timber bridges proposed by Price in his Treatise on Carpentry, and one not dissimilar in principle to the method of Philibert de Lorme, before mentioned. The bridge (fig. 739.) is sup

posed to consist of two principal ribs ik. The width of the place is spanned at once by an arch rising one sixth part of its extent. Its curve is divided into five parts, "which," says Price, "I purpose to be of good seasoned English oak plank, of 3 inches thick and 12 broad. Their joint or meeting tends to the centre of the arch. Within this rib is another, cut out of plank as before, of 3 inches thick and 9 broad, in such sort as to break the joints of the other. In each of these ribs are made four mortices, of 4 inches broad and 3 high, and in the middle of the said 9-inch plank. These

Fig. 759.

mortices are best set out with a templet, on which the said mortices have been truly divided and adjusted. Lastly, put each principal rib up in its place, driving loose keys into some of the mortices to hold the said two thicknesses together; while other help is ready to drive in the joists, which should have a shoulder inward, and a mortice in them outward; through which keys being drove keep the whole together. On these joists lay your planks, gravel, &c. ; so is your bridge compleat, and suitable to a river, &c. of 36 feet wide."

2099. "In case the river, &c. be 40 or 50 feet wide, the stuff should be larger and more particularly framed, as is shown in part of the plan enlarged, as I. These planks ought to be 4 inches thick and 16 wide; and the inner ones, that break the joints, 4 inches thick and 12 broad; in each of these are six mortices, four of which are 4 inches wide and 2 high; through these are drove keys which keep the ribs the better together; the other two mortices are 6 inches wide and 4 high; into these are framed the joists of 6 inches by 12; the tenons of these joists are morticed to receive the posts, which serve as keys, as shown in the section K, and the small keys as in L; all which inspection will explain. That of M is a method whereby to make a good butment in case the ground be not solid, and is by driving two piles perpendicularly and two sloping, the heads of both being cut off so as to be embraced by the sill or resting plate, which will appear by the pricked lines drawn from the plan I and the letters of reference." Price concludes: "All that I conceive necessary to be said further is, that the whole being performed without iron, it is therefore capable of being painted on every part, by which means the timber may be preserved; for though in some respects iron is indispensably necessary, yet, if in such cases where things are or may be often moved, the iron will rust and scale, so as that the parts will become loose in process of time, which, as I said before, if made of sound timber, will always keep tight and firm together. It may not be amiss to observe, that whereas some may imagine this arch of timber is liable to give way, when a weight comes on any particular part, and rise where there is no weight, such objectors may be satisfied that no part can yield or give way till the said six keys are broke short off at once, which no weight can possibly do."

SECT. V.

JOINERY.

2100. Joinery is that part of the science of architecture which consists in framing or joining together wood for the external and internal finishings of houses, such as the linings of walls and rough timbers, the putting together of doors, windows, stairs, and the like.