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r /. ^-B. The purlins are those pieces into which the smallraf> erS t 16 tenante( i) and they are tenanted into the principal• -length of purlins is generally from six to eleven feet,^exceeding that length.
fou • ra ftcrs: their scantlings two inches and a half, andthr 1 ” C ' les > three inches, and four inches and a half; andee an( j j ia |^ anr j g ve ; nc i, es . according to the
J'aff nUUde *^ le r0 °f and length of the rafters. Smallra should not exceed seven feet in length in a purlined^ happen that the length of the principal be abovelo„ e ?, n ^ eet > 't is best to put in two tier of purlins in theen f n th of the rafter.”
foil ^ es P ect to the construction of roofs for coves, he has theside ^Nervations : “ The use of coving a room of con-it , height, is, first, the making of it much lighter thanl;„i . d otherwise be, if level in the ceiling; the rays of* ’" a cove are reflected back again into the room, which
c eilin otherwise lost and confused in a roof with a flat
xewise, all rooms with circular roofs or ceilings are
&c £? mm °dious and useful for entertainment, for music,refle *• 6 an ff^ es of incidence are always equal to those ofS ph e . Ion > 80 the undulation of sounds flying on any cove orif r ‘ ca ! Port of a building, reverberate on the audience; andj t eri p a U no part of the sphere can receive the vibration,Ondul ' V *^ ret urn in the same direction from whence thereverh ^ 0n> ^ rst began. The reflecting rays of light, and thefrom • erat ' on of sounds, proceed from the same cause, andjj. lnc 'dents naturally affecting the eye and the ear.”of sq 1113 / ,^ e proper here to state, that though the reflectionanq an '*.' s analogous to that of the rays of light, the laws*re j eg 0al doations by which sound is propagated to the ear,that i 3 Nd'eetly understood: it may, however, be observed,of tj, vau lted apartments, it is necessary to reduce the pitch^rit e !! V0 ' c e, and to speak slowly and distinctly. The besthas b 3 reeomr nend the ceilings of theatres to be arched, as°f Practised in some of the most distinguished edifices
This k ' n<1 in Eur °P e -
leritr^ij aut j'or likewise gives the method of finding theGodfj. °‘ b'Ps, both with and without a plan, as shown by3ooh of 7 j C ' lar d s , at the end of his Translation of the FirstTjj * Palladio.
of Ca] ? Wor ^ of Mr. Smith contains, in all, thirty-three platesthe Su |y ntl 7> arranged in the same order as he has treated^Wh ^ eCt " these, twenty are plates of roofs, some ofPlates a J e . toler ably good examples, and at the end are five*h°w n j n tlm ber bridges. His methods of joining-work are^’ a ?rams t lG lowing descriptions and their corresponding
the \vah3T" s ^ ows his method of cocking beams down upontbre e d ^ a ^ es » Figure 1, by two dovetails, and Figure 2, bybest; f ° Vetails - Dovetailing is a very bad method at thebriber aU W ^ len the taper is small, the shrinking of theP r °Portion° WS l ^ le beam to be drawn out of the socket inbteafitb r pu t ' le quantity to which it is reduced in itsthe weake • fewer the number of dovetails in the breadth,• tlUst have r U1 enc * °f tb e beam be, or otherwise theyltl . Cr eased s ta P er > an d if the number of dovetails arebe a f 6 P arts °f them formed on the end of the beamea Ut can f t0 °ff - But, in modern Carpentry, the^rts are \ ever be drawn from the wall-plate, as the abutting^nis. la a plane perpendicular to the length of thea f O .
with 3 if Ws ^' s me tbod of framing wall-plates at the'^berg t be diagonal and dragon pieces, where all theis muff 31 to . b e ^ et ' n flush with each other. Thisc inferior to the present practice, where both the
angle-tie and dragon-piece are fixed above the plates, whichposition not only allows a much firmer hold one to another,but also a much better support for the hip-rafter to standupon.
Figure 4, represents four different methods, shown by him,for naked flooring. “ The first method of framing is thatmarked a, where the joists are framed flush with the top ofthe girder; the two cross joists, marked a and h, are calledtrimming-joists; that marked a is supposed to come againsta chimney; that marked h is the stairs.’’ Here he showsthat the joists a and h, should be thicker than the commonjoists, because of the mortising; but with equal reason heshould have allowed the joists c, d, e, into which the joists aand b are framed, to have also been stronger ; for one mortisein the middle of a beam will weaken the beam as much as ifit had been cut full of mortises. He gives no name to thejoists c, d, e, which should have been named, in order to trans-fer the idea from one to another, without circumlocution, orhaving recourse to description. His next manner of framingfloors is that shown at n. “ The six joists marked b are thebinding-joists framed flush with the under side of the girder,and about three or four inches below the top of the girder, toreceive the bridgings, which are those marked m in the floor,and which lie across the binding-joists,” at c. In the othercompartment, L>, are shown the ceiling-joists, n, the bridgingsbeing supposed’ to be removed for the purpose of showingthem.
Figures 5, 6, 7, 8, he says, show the manner of tenoningthe binding-joists, the tenons being generally made double,
Figures 9, 10, 11, 12, he observes, are common tenoning,which seems to imply a less sufficient method than the former.These last four examples, with the single tenons on the endof each, are much to be preferred to the double ones on theends of Figures 5, 6, 7, 8, which are not only difficult toexecute, but are calculated to weaken the mortised piece,which is to receive them, by the slanting shoulders of thetenons; his observation is the very reverse of what is nowasserted, as he observes, in page 17 of his work, “thestrongest way being double tenanting and tusking, as is shownin the binding-joists.”
Figures 13, 14, 15, and 16, are exhibited in the third plateof his work, but he does not describe them ; we suppose themto show the method of lengthening beams. The two methods,Figures 15 and 16, are extravagant ideas, being not onlydifficult to execute, but weak as a tie, and incapable of makinga sufficient resistance to a longitudinal strain.
Figures 17, 18, 19, 20, 21, 22, 23, 24, 25, are variousmethods which he shows for trussing girders. He observes,that the trussing pieces or cores are let half into each flitch,and the scantlings of these pieces to be about 4£ or 5 incheswide, and 4 inches thick. Figure 18, he says, “is anotherway, which is by cutting the girder through, and driving awedge against the ends of the trusses, as the wedge d; whenthese are thus prepared, bolt them together with iron boltsand keys, or, much rather, a screw at the end of the bolt.”This method, though not the best, is certainly a tolerableapproximation to what may be called good. He does notmention how the pieces a, a, are to be tightened in Figure 17.He observes, that “ some in trussing girders, make use ofother trusses,” as in Figures 20 and 21. These hardly de-serve comment, being the wmakest forms that can be con-ceived. The trussed girders, represented by Figures 24 and25, he claims as his invention, with one inverted arch, whichhe proposes to be of iron. Nothing could be more unmean-ing than these examples.
The observation which he makes in respect to Figure 24,is void of principle, and contrary to mechanical strength;
2 A