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s i(le of j®\ erse piece so as to bring the mark upon the upperPt(>ce e( j . ln a line with the straight-edge. Tiiis being done,lines (j ,' n tk e sa me manner witli tiie other end, and the twoyitl m a l' V " on , the vertical sides of the intermediate piecehy wor^ tbe shonlders of the tenons. This process is called'Wien th rn ^ n tumbling - in joists, a nd is particularly usefulIlavinV' 1 ' 1 ^ 61 ' >s W!U 'ped or twisted.

Stpt!ll gth ^ . s h° w n the principles of lengthening timber andat ttt, gles n ' n " °* beams, also the methods of joining timbersIn g r 1 We s l' a H now proceed to construction in general.Sl,1- face / n Center ing, the boarding which forms the exteriotimber ,°J\ b uildin g upon is supported by transverse ribs of

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llCc ° r< li'n IU ' b are either constructed simply, or with trusses,®'sts „ ® to f he magnitude of the work ; and as a groin eon-I s “livav i ^ °1 two vaults crossing each other, one of them“'Ivin,,' b °arded over, the same as a plain vault, withoutat >d hon r a^ 1 res P eo(; to t l |e other, which is afterwards ribbed• ’rimi )ei ed ’ - So as t0 make out the regular surface.

Pitied tocf ^* s P 0se( I in walls and at returns or angles, are^Posuref 11 "" w bere the magnitude of the building, orV°, Strain ’ may require. These are of three denomi-i I'loori^bond-tiinber, lintels, and wall-plates.

• <iilr,ls > call J 8 su PP° r ted by one or more rows of parallelS j n j naked or carcase-flooring, and is denominatedaccordingly. The manner of joining

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Pave already spoken of.construction of the building

Pcntry ip ie cons truction of the building, the flooring ofs , ’ “ n °t supported by brick or stone partitions, isI cot lst ^° rt ? ( I V the partitioning of timber or by shores.j?Pcjn] s lUc tion of the flooring, whether single or double,i '"^"sions 01 } ^' e ma g n >tude of the building, the horizontal"bty i ° t be apartments, or the weight which the board-^Uir e ,j t ^ e required to support. When the flooring is° '' k -i's be very stiff, it becomes necessary to use truss

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S( ;^ >!Uld 00 ''">g for dancing upon should be made verypi ilS f ° hend° C0lltl ’ived that the upper part of it may spring,"ustai ' t0 tbe biipression of the force, while the lowerli,, in t ’Uo tls ln '’ the ceiling, remains immovable.

of ‘ Ue constructed of a row of timbers, or if theh'ir °I ft'.!; bearing require very great stiffness, they aretii.o'"^ truss-work, and afterwards filled in with" ssi *t in ers ‘. The

^bpPortmi ving support to the floors, where they ared *Hch a - bel ° VV - .

trussing of ])artitions may be madeiport to the floors, where they arecv e ■•"eiiam. ' The framing ought to be so managedVir^ioftl' 6 office of hanging up the floor, in what->i,°Ith e le doors are placed. Truss partitions are

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use in supporting the superior floor.

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to ti par'd! 1 • ' le ro °f’ s sustained by one

^^veH-btnbe,,each row being in a plane parallelu ponTi ^ be force of the timbers, which would act“■« i>» »• i!!'! 11 *' is generally restrained by tie-beamsCot ltj V VV(! r einjjj .bites on the top of the walls, and fixed to%o'ti anee s may'i tile rafters - In roofing, many ingenious' v ' 1 icl 1 • Pitch of 6 resorte< I t0 ’ their application dependingCot 11 be i- tbe roof > the number of compartments intor ®of ' If an lv 'ifled, or whether there are to be tie-beamsIWeq 1 . 1,J Xgitud' Pan " lent ' s re( iuired to be coved into the''uftfcj. 111 a verp 1 '^ truss > supported at the ends, may betl le 1>la y be ], ' Ca * P} l, ne under the ridge, by which the''[Cold d^' ter 8 'vve Un ° ’ ior * s evident) that if the upper endscir cl es .^cenq ^ le held in their situation, their lower endsjSter V( -i'ti Ca i'' j' 1 ' gravity, and would describe arcs ofl c \y. l |, °5P-t]i< 3r P an cs, and in their descent would approachb l cr_ h ' v ould h> ’ conse quently, instead of pushing out■^Kl if , ave a tendency to draw them towards each41118 were placed transversely immediately3 E

under the longitudinal truss, and fixed to the opposite rafters,they would act as straining pieces, and prevent the exteriorsides of the roof from getting hollow. If the whole spacewithin, under the rafters, were required, that is, to have nointermediate work of trussing, the sides of the roof may beprevented from descending by arching them with cast iron,or trussing them with wood in the inclined planes of theirsides ; and to restrain the pressure of the rafters, whichwould be discharged at the extremities of the building, a strongwall-plate, well connected in all its parts, must'be introduced,which acting as a tie, would prevent the lateral pressureforcing out the walls.

In this construction, as well as in the former, the rafterswould have a tendency, from their gravity, to become hollow;in this case straining beams should be introduced at a con-venient height, which would have a good effect in counter-acting that tendency. If it be required to occupy very littlespace by the wood-work, cast-iron arches, abutting upon eachother, and screwed with their planes upon the upper side?of the rafters, will answer the purpose best.

The idea of trussing roofs upon these principles wasdiscovered, many years ago, by Mr. P. Nicholson, in con-sequence of a dispute concerning a roof which had beenconstructed upon a chapel, and which had pushed out thewalls to such an alarming degree as to threaten the demo-lition of the whole fabric : Mr. Nicholson was chosen asarbiter, but the principle which the architect adopted wasso incompatible with the nature of the design, that, thoughchosen by the architect himself, he was under the disagree-able necessity of giving judgment in favour of the constructor.This roof was truncated, or flat, and the ceiling withincylindrical, extending horizontally the whole clear of thewalls, and in height to the under sides of the camber-beams,so that there were no ties between opposite rafters. Theprinciple consisted, therefore, of two sloping sides and ticamber-beam, which were only tied together by angle-braces,and as the ceiling came in contact with the under side of therafters and the under sides of the camber-beams, the braceswere also disposed so that the middle of their under sidescame in contact with the ceiling, and thus, to maintain theroof in its position, depended entirely upon the resistance ofthe walls, or upon the inflexibility of the timbers, or both ;all of which were of unusual strength.

The lesson which every architect ought to learn from this,is, always to construct his roof in such a manner as to makeit entirely dependent on itself.

In the year 1802, two years subsequent to the above dis-pute, a model of a roof was exhibited before a numerousmeeting of the Philosophical Society at Glasgow , whereinthe timbers consisted simply of rafters abutting at the topupon a ridge-piece, leaving the wholo space under the raftersclear, and, of course, forming a triangular hollow prism, withthe two upper sides parallel to the inclined planes of theexterior. The wall-plates were unsupported, except atthe four corners, which were sustained by uprights or posts ;the pieces let in upon the upper sides of the rafters consistedof small arcs, almost straight, forming on each inclined planea parabolic curve, and extending from post to post. Ironi the ridge-piece equal and very considerable weights weresuspended, one from the meeting of every pair of rafters,without producing any visible effect upon the wall-plates.

The form of a parabolic curve is best adapted to that ofequal weights suspended at equal distances. Instead of arcs,simple trusses may be used, and the rafters may bridgeover them.

In many cases, where space is required, we cannot lieipthinking, that the disposition and fixing of the boarding in