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would not have compensated for the additional labour required in building the former.


By referring to the general plan, you will see that in it are shown three large buildings parallel to each other, the refreshment rooms, the nave, and the picture gallery. These are connected at their ends by transepts, and thus two vast oblong spaces are enclosed, one to the north, and the other to the south of the nave.

On both sides of the nave and the inner sides of the transepts, are aisles 50 feet wide. Another aisle, 25 feet feet wide, is carried olong the outer sides of the transepts and along the back wall of the south front.

After deducting the space occupied by all these aisles from the oblongs above referred to, we have remaining two smaller ones, that north of the nave 750 feet by 87, and that at the south of it 750 by 200 feet. Each of these is subdivided into three courts by two 50 feet aisles. The centre courts are 150 feet long, and those at the ends 250 feet. The dividing aisles on the north lead to the refreshment rooms, on the south to the entrance vestibule. Twenty-five feet above the ground floor are the galleries, following the same line as the aisles; they give an additional exhibiting space of 203,000 square feet. Particular care has been taken to make these galleries amply strong for the heavy moving loads they will have to bear. The floors are supported on cast iron girders fixed to the

Section of One-half of a Nave Rib, showing the cross-bracing in the Gallery,

columns; over them are laid two strong suspended trusses which carry the joists and boarding.

Supposing a floor to be loaded with 140 lbs. to the square foot, which, being more than the weight of a dense crowd of people, is heavier than any weight it can have to bear, the greatest load that can thus be placed on a girder is 84 tons. The breaking weight of the girders used is 88 tons, and every one of them is proved in a hydraulic press, spe

cially constructed for the purpose, to a load of 38 tons, to avoid all risks of bad castings being used. Over each gallery is a flat roof covered with felt, supported like the floor, but of much lighter construction. Sixteen flights of steps, 10 feet wide, give ample means of ascending from the ground to the upper floor.

The galleries play a very important part in the construction of the building; they are made to form an abut

ment to the nave and transept roof, and the particular wooden principals going straight across, has two iron form of bracing by which this is effected is the in- diagonal ribs crossing it, forming as it were a groined genious suggestion of Mr. Ordish. The roof thrust-arch, whose apex is a point in the centre of the bay and ing outwards tends to throw the columns out of the per- in a line with the roof ridge. By joining the apices of pendicular; strong iron braces are, therefore, anchored to these groins and the points in the octagon already deterthe foundation of the inner column, and carried up to the mined, we get a nearly regular dodecagon, having its top of the opposite outer column, which are thus made to opposite sides parallel and equal, and with eight sides in counteract the thrust of the roof. Another bracing, an- pairs each equal to 43′ 9′′, and the four remaining chored to the footing of the outer column, is carried up to sides coming between these pairs, each equal to 35′ 5′′ the top of the inner column, to secure it from being acted This dodecagon forms the base of the dome, which will on by the force of the wind. This vertical cross bracing thus have eight sides over the nave and transepts, and is repeated at every 100 feet, or every fourth bay, and by four sides over the corners of the aisles, equal respectively introducing horizontal diagonal bracing under the roof to the dimensions just given, and a diameter of 160 feet. flats, they are turned, as it were, into a deep horizontal Each groined rib transmits the weight on it to two girder, supported at two ends by the columns vertically columns outside the octagon, so that the dome may be braced as just described. This horizontal girder, therefore, said to rest on 16 points, its pressure on the angles of the takes the thrust of the three intervening ribs. The way octagon being nearly five times (4) as much as it is in which the bracing is introduced is very clever, and is an on the adjacent columns of the nave and transepts. admirable example of the perfect control which the By the very ingenious and novel plan of the groined simplest mechanical means, properly applied, gives us in roof ribs a dodecagon dome is made to seem to stand on dealing with enormous inasses. The bracing is all ad- an octagon; no additional columns of support but those justed by connecting screw links, on a plan very similar actually coming in the sides of the nave and transepts are to the method of joining railway carriages; by this means used, and thus an uninterrupted vista is obtained through it can be tightened at pleasure, and the position of the both, and a very beautiful architectural effect produced. columns corrected to the minutest fraction of an inch. The drawing of the rib also shows the vertical cross bracing, which will, I hope, be thus made perfectly clear to you. (See woodcut p. 47.)


You will recollect that in describing the position of the aisles and galleries, I explained to you how they enclosed six courts, three north of the nave, two of which are 250 by 87 feet, and the other 150 by 87 feet-three south of the nave, two of which are 250 by 200 feet, and the other 150 by 200 feet. These form the open or glass covered courts, and are the only portions of the building which in this particular resemble the Crystal Palace of 1851. They have only a ground-floor, and the roof, which is on the ridge and valley plan, but in spans of 50 feet, is entirely covered with glass. The roof is carried on square iron columns 50 feet apart each way, at the top of which, 50 feet above the ground, wrought-iron trellisgirders are fixed on lines running east and west. The columns and trellis-girders carry the principles of the roof, which are all of iron, on the trussed rafter plan, eight feet apart. The roofs are drained by channels in the vallies conducting the water down the hollow iron columns. The effect of these courts with their light glass roofs admitting floods of light into the building will give a pleasing variety to the interior, and afford most valuable exhibiting space. The whole of the S. W. court, with a portion of the adjoining aisles and galleries, has been allotted to France, which will have the greatest space of any foreign country.


We now come to the great domes, which, from their stupendous size, will form one of the most prominent and interesting features in the building.

I have before explained that they are situated at the intersection of the nave and transepts. Their form and position have been thus determined. The intersections of the lines of columns in the nave and transept aisles form two octagons, which, though not mathematically regular, are regular in this one respect-their opposite sides are parallel and equal, the length of the sides being alternately 85 feet and 35' 5". The points at the angles of these octagons are the chief supports of the domes. For this purpose there is a column at each angle, 2 feet in diameter, and for architectural effect, as well as for carrying the groined ribs, the object of which I shall presently explain, the lower portion of these 2-feet columus is clustered with two round and one square column of smaller dimensions.

But though the chief points of support are at the eight angles of the octagon, the dome is a dodecagon, the other four points being thus obtained. The last bay of the nave and transept, instead of having a roof resting on

You will see a drawing showing a projection of one of the groined ribs on a line at right angles to the nave, its curve forms a semicircle, to correspond with the curve of the other ribs, but its actual elevation will show a semiellipse, whose diameter, 88 feet, is the diagonal of the rectangle formed by the four supports of the groins.


Each rib is two feet deep, with a web of in. plate-iron, to the edge of which is rivetted a top and bottom flange formed of angle-iron in such a way as to give the top flange an area of 10 in., and the bottom flange an area of 19 in. The principal rafter and its upright are also made of wrought iron, having a web 12 in. deep, with an equal top and bottom flange of angle iron rivetted to it so as to give it a sectional area of 20 Radial pieces of iron 8 X in., connecting the upright and principal rafter with the circular portion of the rib, are introduced every 5 feet. At the intersections the ribs are strengthened by additional plates of iron, and here, for a short distance, they assume the form of a box girder. A drawing, showing the details of these portions on a large scale is provided, and will, I hope, fully explain their construction.

The intersections of the principal rafters and semi-ellipses are connected together by a cast-iron standard, which is continued up above the ridge of the roof to a point 107 ft. from the nave floor line, this being the level of the bed on which the dome ribs rest.

The large columns at the angles of the octagon are two feet in external diameter with seven-eighths of an inch of metal, and they are raised in three lengths to a height of 95 feet, their ends being joined together by flanges and screwed nuts on the inside. To fasten the bolts, a man is lowered down inside the columns, the diameter of which is sufficient to give room for him to screw up the nuts. The columns are thus kept perfectly smooth on the outside, and appear like one casting 95 feet long. To the top of each two-feet column is bolted a cast iron stanchion 12 feet high, whose summit is therefore just 107 feet above the nave floor. On the tops of these stanchions, and resting on ornamental brackets, a gallery three feet wide is carried round the outside and inside of the drum. It will not, however, be accessible to the public, but only to men employed in opening the louvres which are here placed for ventilation. To the upper side of the gallery, and through it to the stanchions, the double wrought-iron tie-plate acting as the dome's hoop, is securely bolted. It consists of an inner plate of iron x 6"X" 6 × 1, which is connected with an outer plate 10" X 10 X, so that both these plates take the thrust of the dome. The dome ribs are bedded on the top of them, with their feet bolted through to the heads of the stanchions.

Each dome rib is an iron girder made of boiler plate and

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ing line. The top flange follows the curve traced by a radius of 91' 9", the centre being a point 12' 3" beyond the centre of the dome; the bottom flange is on a curve whose radius is 90' 1", and centre 14' 0", beyond the dome's centre.

angle iron. The top and bottom flanges are nearly equal in section, the former being 198", the latter 203" 204. There is no continuous web between the two flanges, but they are joined at 8 feet intervals by two pieces of boiler plate, having a 3" wood spacing piece between. The first seven feet of each rib is vertical, and the girder is The two flanges thus come nearer each other as they here 3 feet deep. At the summit of the vertical portion, approach the apex, where they are only two feet apart. which is 114 feet above the nave floor level, is the spring-This point is 91 feet above the springing line, and the




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Elevation of Diagonal Ribs, supporting the Rib of Dome over Nave and Transepts.

12 ribs meet there, abutting against a strong cast-iron they approach the summit, and those in the larger tripipe, one foot in diameter, to which they are bolted. angles are slightly heavier, on account of their longer Eight wrought iron purlins between the springing and bearing. The first purlin of a large triangle is 1' 818" the apex are bolted to the ribs, and the divisions thus deep, and its T-iron flanges are 3 X 3"X". The formed are strongly cross-braced, so as to make the whole upper purlin has a continuous web plate 1018" deep, with as rigid as possible. These purlins are formed of two top and bottom flanges made of four pieces of iron, pieces of T-iron, joined together at six-feet intervals by a 2" X 2" X". These dimensions are altered in a small half-inch plate. They vary in section, decreasing as triangle, the depth of the lower purlin being 1' 818",

Plan of the top of the Groined Rib.

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Section on Line ab in elevation, showing junction of Diagonal Ribs at crown of Arch.

The crown of the dome, for about thirty-two feet down, has an ornamental zinc covering, but the whole of the remainder is glazed. From the apex rises the finial to a height of fifty feet, resting on a concave base, which, being

Top Plate to receive Column.



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Section on Line c d in elevation, showing junction of Top of
Diagonal Ribs.

prettily ornamented with cast-iron brackets, windows, and
mouldings, is terminated by a globe surrounded by three
great circles intersecting each other, from the top of which
rises a gilded pinnacle.

Section of Seat of Diagonal Rib, separated from Square Ribs. exterior diameter, the dome of St. Peter's is 157 feet, and that of St. Paul's 112 feet. But, although our domes are in themselves larger in every way than any yet constructed, they will not rise to so great a height above the ground as either of those with which I have compared them. The Exhibition domes spring from a height of 114 feet, which makes the top of the finial 260 feet above the ground, while the cross on St. Peter's is 434 feet, and that of St. Paul's 340 feet above the pavement.


The scaffolds for the construction of these domes are on a greater scale than anything of the kind ever executed. They are literally forests of timber, occupying nearly the whole interior space of the domes, cross-braced and bolted together in every possible way, so as to give them sufficient strength, for they will have to bear the weight of the whole of the iron in the domes, 120 tons in each.

The scaffold is carried up in eight different stages, between which are horizontal beams. The central portion is a square of 24 feet, rising to a height of 200 feet. As this ascends each stage is cross-loraced vertically. From the centre radiates a scaffold into each triangle of the dome, to which it is in shape si nilar, though not quite so large. These radiating scaffolds have independent vertical bracing, while at each stage they are cross-braced horizontally, and connected with the central scaffold as well as with each other. The main timbers in the scaffold are from 14" to 12" square. while the cross-bracing is, on an average, 12" x 6". This work was put up by Mr. Clemence, the contractor's clerk of works, and must be considered a chef-d'œuvre in scaffolding; it is of immense strength, and so skilfully constructed, that very little of the timber in it has been spoiled by cutting, so that when taken down, every particle of wood used, amounting to 40,672 cubic feet in each scaffold, will be as available for any other work as if it had just come from the builder's yard.

Section on Line e ƒ in elevation, showing Section of Seat of Diagonal which will show you all the details of construction.

Among the drawings you will see a plan of the scaffold,

Rib on corner column of Dome.

They were completed in eight weeks, and every beam in them was hoisted by the steam-winch before described, without the aid of which they would have required at least double the time, and have been far more costly to



interesting section of the Exhibition, for here will be grouped alongside each other the most cunningly devised machines in the world. What endless occupation and suggestive thought will a careful comparison of them all give rise to!

The building itself will be worthy of its contents, for in ingenuity, economy, and simplicity, it is allowed to be a triumph of construction. It requires no fram

Having now gone through the various portions of the permanent buildings, I shall proceed to a description of the annexes or temporary buildings adjoining the Ex-ing; any person of ordinary intelligence, able to drive hibition.

The plan of having detached buildings for machinery will be a great improvement on the 1851 Exhibition, where everything was under the same roof; for, admirably arranged and ventilated as that building was, yet the smell of oil and grease inseparable from machinery, occasionally intruded itself on those who were examining objects which might have been expected to afford an exemption from that unpleasantness.

The western annexe is 975 feet long; for a length of 720 feet, it is 200 feet wide, the remaining 255 feet being 150 feet wide. The east side is enclosed by the back wall of the west arcade of the gardens, and the west side, which adjoins the road, has a plain lath and plaster front. It is covered by a ridge and valley roof, supported on most ingeniously constructed light wooden ribs of 50 feet span, placed at 15 feet intervals. These ribs are similar in construction to those of the nave, that is, they are formed of planks nailed together, but they are very much lighter. The circular portion springs at a height of 10 feet above the ground line. Its elevation is nearly half of a regular polygon, described about a semicircle, whose diameter is 50 feet; it consists of 3 planks 9 in. wide, the centre plank is 1 in. thick, and has nailed to it on either side ain. plank, the ends breaking joint all through. The principal rafters, which are composed of two in. planks, rise from a point 28 feet above the ground, and ineet above the curved ribs, so as to make the ridge 5 feet above the crown of the arch. The upright, which has its foot morticed into a sleeper resting on piles, is formed of an inch and a quarter centre plank, with a in. plank on each side, having a strengthening piece 4 in. x 3 in. spiked to it on either side to prevent its bending. The principal rafter and upright are connected with the curved rib by radial pieces of 14 in. plank, which are brought rather below the intrados of the curve, and finished off, for the sake of ornament, by a spear head. The roof frames are therefore merely planks nailed together, and so disposed that the weight comes on their edge. One half of the roof is covered with boards and felt, and the other half has a glazed skylight, with louvres for ventilation throughout the whole length. The span of each rib is 50 feet, so that in the 200 feet width there are four spans, and in the 150 feet, three.

The west annexe will be devoted to the exhibition of machinery in motion, for which purpose steam pipes, water pipes and shafting will be led through it. There will be a boarded floor all through, but the heavy machinery, will, of course, be bedded on the ground, independent of the floor, which will only be used for passages. The entrance to it will be through the north end of the west transept, from whence the successive ribs of the roof afford a beautiful perspective view from end to end, and produce a singularly light and elegant effect.

The superficial extent of the west annexe is 184,000 square feet, or about 4 acres; it will of itself be a perfect exhibition of its kind, and contain the most ingenious mechanical contrivances of this inventive age. Here we shall see some of the most ponderous marine engines in comparative miniature, but yet sufficiently powerful to drive shafting to work full-sized machines employed in various branches of manufacture. The many uses to which water power can be applied will be shown, and we shall have specimens of the most interesting machines from every part of Europe and America performing the office for which they were designed.

To a mechanical mind this will doubtless be the most

a nail, could construct the ribs, which have nothing in them but nails and sawn planks. Each rib was made in a horizontal position, over a full-sized drawing, marked on a platform, and, when complete, hoisted vertical by means of a derrick; to prevent it from wabbling, which, from its extreme thinness, it was very liable to do; it was stiffened while being raised by having scaffold-poles tied across the angles, which themselves formed the scaffolding for finishing the roof.

The frames are braced together at the top of the uprights, and the ribs are strutted from the wall-plate, to prevent buckling.

The rain water is let off by pipes, attached to every third rib, to drains under the floor. I have prepared very full detail drawings of this shed, as well as a model of two bays of roofing, by the aid of which you will clearly understand its construction. These roof frames were first of all used in the roof of a drill shed designed by Capt. Fowke two years ago for the 1st Middlesex Engineer Volunteers, at South Kensington. The span of this is 40 feet, and the boards are even lighter than in the annexe-roof. The roof to the entrance to the Royal Horticultural Society's Board-room was the next made, and its ribs are exactly of the same dimensions as in the machinery shed, except that in the latter they are stilted up six feet higher, and are 15 feet apart instead of 10 feet.

I believe it has since been copied for several volunteer and other sheds, and it is doubtless capable of very general application, whether used in temporary or permanent buildings, for it can be made of any required strength by merely increasing the planks; its leading feature is no bolting and no framing.

The eastern annexe is exactly similar to the western in its construction, but by having a large open court 350 ft. by 100 ft. left in it, its covered area is only 96,000 ft. Its total length is 775 ft., and it will be entered from the east transept by means of a covered communication or tunnel under the porch of the Horticultural Gardens.

This annexe is intended for large agricultural implements, and any other heavy machines which do not require to be put in motion to show them off.

Large metallurgic, mineralogical, and geological specimens will also be placed here, and 30,000 square feet at the north end has been most judiciously set apart for a third-class refreshment-room.


The laying out of the works was commenced on 9th March, by three independent agencies-Mr. Marshall on the part of the contractors, while Mr. Wakeford and Sergeant Harkin, Royal Engineers, acted for the Commissioners.

Great care had to be taken with the measurements, for the slightest error would have thrown out the work considerably, and have occasioned great difficulty in fitting the girders. In the three separate measurements made, the mean variation was only three-eighths of an inch, a difference quite imperceptible in a piece of ground 1,200 feet by 600 feet. A glance through any of the aisles will show how accurately the work has been conducted; and whether they be examined on the square or diagonally, the columns will be found to range in line as perfectly as they would show in a plan.

About two weeks were occupied in making the measurements, so that the building may be said to have been actually commenced in the beginning of April, since when its progress has been uninterrupted and rapid.

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