As for those that are necessary for the turning joints of great engines constructed of timber, they make no part of the art of carpentry. (See Note IL) After having attempted to give a' syatetnatic view of the principles of framing carpentry, we shall conclude, by giving some examples which *ill 'illus trate and confirm theforegoing principles.
Pig. 88. Plate LH. is the roof Of the ohapel of the Royalllespital at Greenwich, constructed by Mr S. Wyatt.
EE, Srtutv, • • 8 X 71 PP, AuxiliaryVaftett Cat bottbm), • 10 x 81 HE, Principal rafter (at'besttom), - 10 x 81 g g, Stilds eupporting the rafter, • 8 X 8 The trusses are about 10 feet 6 inches spare and the dotted lines in the -middle compartment show the manner in which the roof is frained•under the cupola. .
This -roof far excels •the •origiaal one put up by Inigo Jones. One of its *wises Contains 198 feet of timber. One of • the old •roof bad Es, but had many inactive timbers, and 'others 'ill disposed. The internal truss•FCF iendniirablreentriveil forme. porting the aey-pressare en the. far•prejecting•ends theSie.baaar. The former soof had bent them greatly, so ea to appearungrace ful. '(See Note KK.) We •think that the cribber (six •inches) of the titAream is rather huitiltl; because 'by settling, the beam lengthens; and this must be accompanied by a considerable sinking of the roof. This will seem by calculation. (See NotelL.) Fig. 40. Plate LIII. the rookif Birtalisghatothestre, constructed • by Mr Geo. &tinders. The span•s 80 feet clear, and the trusses are 10 feet•part.
The trusses are 7 feetapart, and the whole is covered with lead, the boarding being suppoited by horizontal ledgers h, of 6 by 4 inches.
This is a beautiful roof, and timber than most of its dimensions. The parts are all dis posed with •great • judgment. Perhaps the iron rod is unaecestairy ; but it adds great stiffness to the *ale.
/4;km-straps aethe rafter feet would have had more-effect if not so oblique. Those at the head of the, post are very effective.
We-may observe, however, that the joints between the atrainmg basin and its braces are not of the best kind, and tend to bruise both the straining beam and the truss beam above it.
Fig. 3g. The roof of St Paul's, Covent Garden, designed by Mr Hardwick, and constructed by Mr Nilapabot•n 1796.
AA, Tie-beam+ spanning 'am iset winches • 1,11,41treen poets, .9%X '8 • C, Straining beam, 10 X 8 D, King post (14 at the joggle), • 9 X 8 This tootle siftee'speeinten of -British carpentry, and krone of•thelboldeet 'and•lighteet roofs in Eu. rope. The' straining sill Q, gives a•finn abutment to the principal braces, and• the space between the posts is 191 feet wide, affording 'roomy workshops for the carpenters and other workmen connected with a theatre. The contrivancUthr taking double hold of the wall, which is very thin, is excellent. There is also added a beam (marked It), bolted down to the tie-beams. The intention of this was to prevent the total failure of so bold a truesing,if any of Lbe tiebeams should fail at•the end. by rot.
Akin to'this roof is fig. 41.-Plate LIII. the roof] of DrurpLane theatre, 80 feet 3 inches lathe clear,' and•the-trusses 15 feet apart, constructed by Edward Grey Saunders.
8 x SAralumg.iNglus. 42. X. 12., The main, beams are trusped. in the middle space with oak, trusses 5 inches square, This, was neces sary for, its width of 32, feet, occupied by the carr penters,painters, &c. The greatspace between the trusses afford good store, rooms, dressing rooms, &c.
It is probable, that this roof has not its equal in the world for ligtne,ss,,stiffeess, mid strength. The main trims, is so.jutliciettaly &WO, that each of them will sakly bear a,legd, of tons se it is not like. ly that they will, QM be quarter loaded. Thq divir sion of the whole, into three part. makes the exterior roofings very light. The strains. are, admirably kept from die mut the walls are, eien 6rmly bound together by the roof: . They also, take, off tbe,dead weight, from the, main . tr,uss, one third.
The_ intelligent reader will perceive that ail. dm* roofs are on. one principle, depending on, a trips, of three. and q,straight This is, indeed the great principle, of a truss,, and is a step be.yosd the roof with two.raftsrs,arkl, a icing post, It,a4mits of much,grcitler vertel.); of forms, acil,of greater ex. tent. WO. Ism see,,6114,t, even the pact mow carriq4 ku, spugg.,.urifl, yet flat at, tow, for the,tross:heam ins': be sumitorteti .iq tie mbidie.b anioveKtati., kiug post. (0 r, tiltnber kr"), cwie by icon qr, wooden, ties Irmo, its extremitin: alai the some ties spry,04e, boriSpata,1 for411 X, be, 4VA eSttetleKt9c.b4h anA bP:cri117 Piga, , Pgthin4 The, roof of St. blark.e..:0- 0%40 01 the 11 ieenetruaeit up. pad, Rriuf tkluth Anti perly tlis,potsetts. OPtino.t.ex' euea 40 ftt.Crumsuluuntu.culwau.klieuuttuus,TP9C41 timber in g.trius then, thers• is theatre.. T.h4 roof of the ORO PreAntfAche, thnA of St Nut's. Cevent-.G.ardeci, that of and that of Pgury-Lane. theatre*, form a dually more, perfect., Suck specimen afro q?cgall lent lessons. to the artists, We therefore *Roan; them a useful present to the pnbjic, There is a, very iegeoious projeet, effeFe4, to dA9 public tw Mr P. Nicbolsux (Curpentar's 4,14i4ant, p. 68.) He proposes. iron rods, or king posts,, (peva posts,, and eit other situatioes.where beams perform the office of ties.. This, is in prosecutien of the no tions, which, we published in, the article ROOF or the Eney4oeflie, Ile. receives the feet, of the bra and in a socket, very, wejl connected, w,itb, the foot of iron. irjug post;, NA he secures the feet of his wo.9 posts, am* bAwg by interposing a, straiainsill. kl 4P98 4%.everiN mortise, the foot, of his priecipai mto the end of the tie-obeign,, hut sets, it ig is socket bite ;shoe rte. bait bold into tie-breanka.gpow4.w.iy.b440 .All-tIK park are form ed, and, disposed. with- the precision 'V a. person' thPra.ughly acquainted with the subject; and we have not the.. smallest doubt of the success of the pmoject, and the complete security and durability of roofs. We abound in iron,. but we must send abroad for building timber. This is therefore a valuable project ; at the same. time, however,, let us not over-rate its value. Iron is but about 12 times stronger than red fir, and. is.more than 1.2 times hea vier ; nor is it cheaper, weight for or strength for strength.