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1 is, i n( ^ a ^ tr 'b u t e d much of the grandeur of the building.

' m P oss 'bl e to enter this magnificent room, with-8 ^ Ce ) tie S , truc ^ with admiration. An uninterrupted open^entejj e< l ua l to the size of a large cathedral church, is*ith ^li ' n on e view, and the scientific spectator, gazingart ' s t-li] l '®^ ,: on its lofty roof, admires the elaborate andg* 10 ® the 6 arran o ement of its timbers. These serving at[.t ) Pare nt | PUr P os es of utility and decoration, and uniting the'8i‘tne Ss ^ °Pposite qualities of massive solidity and airy

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is formed on what country workmen

ter^. n ^ e the roof

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a, " ,; 'r°n r ^i >rarnon P>tch, the length of the rafters being about, tie-h e . 18 °f the entire span. The cutting off the girders,i .°ts,r es 't r 8 ’which, crossing from wa 'l t0 wa ^ ' n common; 111 a " biteral expansion, was the first circumstance

^ >Ur e ° 'I 1 ' 8 construction. To provide against lateralJ tj^'SHate^ 6 trusses, or principals, as they are technically! al 1 I '° ll alioi,t 1 a ' se< i ot the distances of about eighteen feet; hJ 11 Ogning^'^ w ' 10 ' e length of the building.

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These trusses

'’s. ih. 1“”' the solid parts of the walls between the win-1 are strengthened in those parts by arch-buttressesIt “Sin» p '^ e ‘ Every truss comprehends one large arch,tip r ° m cor l )e l 9 of stone, which project from the walls

CHe nefeet below the base-line of the roof, and at

^ IS ar cli C SaTne height from the floor. The ribs formingI, P cts’tf re f |ame -d at its crown into a collar-beam, whichV* ’ s in’ 6 ra *' ters ,n the middle of their length. A smallerI ,,! 1 rne< ^ within this large one, springing from the! l bg Sl, Ppor| lt ^* * s l eve l with the base-line of the roof,

bp 8 I"'ino.p V two brackets or half-arches, issuing from°f the main arch. By this construction of thel^getg ° n e acts like an arch, and by placing these

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far below the top of the walls, a more firm

Detained. The main arched

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rib is constructed

Jesses, somewhat after the principle of Philibertn r ° m *' le extremity of the hammer-beam risesallyj St which supports the end of the collar-beamp 0s[ to, and this again, by means of two otherfiiPast ’ su PPorts a second collar-beam, and a central orV ‘»t8 ve

\vb'' rS ’ maT1 y roofs have been constructed of iron,Kill s ) sn"! ' 1 at f“' s t began to be introduced for particular'Hjp er Hpl C * as t ' e an< ^ suspension-rods, but afterwardst 0 i) S j 1,| g liljg 0 ^. 6 ^ f° r the entire truss, and sometimes for thelf|, : l r 1 | l ' [1<: tiori ' V,Se ‘ Eon roofs are for the most part of similarWli’ 4 ? t ' 10se already described of timber, thoseVS/c. are su fijected to tension, such as ties andCo, epre *’ k ft ing of wrought-iron rods, and those which' v 0 r] {g rf) of s such as principals and struts, of cast-iron.

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■ 0l> tli^ 6 ^ een very extensively employed in railway'Ite. e covering of passenger and engine sheds, and

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S S( at| Grr 0V g ,^' e passengers’ arrival and departure shed at/V^tfed c ! as a very light and elegant appearance ; it isand r ' nc 'f a Hy °f wrought-iron, the bressumers,([boh 1 ** ^0 f e ^ uttei- s, only being of cast-iron. The entiref° rt ned in two spans of 40 feet each, a rowontl: a od bressumers supporting the rafters in theand on the opposite side by iron corbels

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V„' n tii e ° ats ’ de >

^O ls ; tt, a ^’ an< l further secured thereto by strong bolts°’ight - e ratv — - - -

In fwrm °f t,ie

N, #r tli 8 V? Ca -fled,

'»f,’a fafterg.

s are six feet eight inches apart, and anletter T ; the slate battons,are of angle-iron, firmly riveted to theat such a distance as the slates require,fled are secured by strips of copper. Thereof

* a art er s ‘de to side by a tension-rod of one inch

at neter, to each pair of rafters, and is further

supported and braced by struts of T iron and suspension-rods,with nuts and screws to adjust their length. The entirelength of the roof is 200 feet; the gutters are cast in lengthsof 10 feet each, joined together by flanges and bolts, and sofixed as to form an incline towards each column, which, beingcast hollow, and having a pipe connected with a drain, theyform a convenient and easy conveyance for rain from theroof.

The truss consists of two principals—a tie-beam, which issustained by three suspending rods and four struts, two oneither side ; one from the head of the central suspending-rod to the foot of the outer one, and another thence to theprincipal.

The roof of the locomotive engine-house at Camden Townis of very similar construction to the one above described :the rafters are of T iron, and the slates are supported byangle-iron riveted to the rafters. There are cast-iron chairssecured down to a stone coping on the walls, and from whichthe rafters spring ; each pair of rafters is tied by meansof a tension-rpd, and otherwise supported and braced bystruts of T iron, and suspension-rods of round iron, whichmake the whole very firm, and gives it a light and pleasingappearance.

Both these roofs were manufactured and erected byMessrs. Cubitt, of Gray’s Inn Eoad, under the direction ofC. Fox, Esq., the engineer to the Company.

Of the numerous roofs of this material which have beenerected over railway works, the following examples will givesome of the principal varieties. The first, for a roof 30 feetspan, consists of two principals, with tie-rod, which is sus-pended at two points, by two oblique rods meeting at theapex, by which means the king-rod is dispensed with. Atthe meeting of the suspension-rods with the tie-rod, a strutbranches out at right angles to the principal, which it meetsat half way. The rafters and rods are connected at the ridgein a separate casting, or the two ends of the rafters may be castto half lap over each other, and the rods secured by wroughtpins and nuts.

The rafters are of cast-iron of the K section, the dimen-sions of the lower table or flange being, in the centre of thelength, 3^ inches wide, and at the two extremities, 1^ inch,with a thickness of -ij? inch; and those of the upper table 2^inches throughout the entire length, and § inch thick. Thedepth is the same throughout, being 4J inches.

The tension-rods are 1 inch round at the outer ends, and| inch midway ; and the oblique suspension-rods f inch roundthroughout.

The second example for the same span consists of twoprincipals and tie-rod, which is suspended at three points bya king-rod and two queen-rods, dividing the bearings intothree equal parts : struts rise from the foot of the king-rodto the heads of the queen-rods.

The rafters are formed of two parallel bars, 3 inches by•J inch, having a wooden rib 1£ inch thick between them.The struts are of T iron, 2£ inches wide over the toptable, and f inch thick; rib, 2^ inches deep, and inch inthickness.

The tension rod is lj-inch round, the king-rod § inch, andthe queen-rods inch round.

The timber between the bars in the rafters serves to fixbattens for the covering.

The third example is for a roof 35 feet wide, constructedwholly of malleable iron. It consists of rafters and tie-rod,suspended at three points by king-rod and queen-rods, withstruts from the bottom of the king-rod to the top of thequeen-rods, and from the foot of the latter to the rafters.

The rafters and struts are of T iron, the rafters being 2i