Part 4
As Mr. Paxton himself has stated, the design for a building of such magnitude could not have been produced in so short a space of time without the aid of the experience he had gained in constructing other great buildings of a somewhat similar character; the progress of this experience Mr. Paxton has described in the lecture he delivered to the Society of Arts on the 13th of November, 1850, from which we have made the following extracts; and we hope to be excused by the reader for their copiousness, on the ground that no man can so well relate his own doings as the actor himself:--
"The Great Industrial Building now in the course of erection, and which forms the subject of the present paper, was not the production of a momentary consideration of the subject. Its peculiar construction, in cast-iron and glass, together with the manner of forming the vast roof, is the result of much experience in the erection of buildings of a similar kind, although on a smaller scale, which has gradually developed itself through a series of years. It may not, therefore, be uninteresting to give a brief account of the reasons which led me to investigate the subject of glass roofs and glass structures generally, and which have resulted in the Exhibition Building.
"In 1828, when I first turned my attention to the building and improvement of glass structures, the various forcing-houses at Chatsworth, as at other places, were formed of coarse thick glass and heavy woodwork, which rendered the roofs dark and gloomy, and, on this account, very ill suited for the purposes they were intended to answer. My first object was to remove this evil, and, in order to accomplish it, I lightened the rafters and sash-bars, by bevelling off their sides; and some houses which were afterwards built in this manner proved very satisfactory. I also at this time contrived a light sash-bar, having a groove for the reception of the glass; this groove completely obviated a disadvantage connected with the old mode of glazing, namely, the putty becoming continually displaced by sun, frost, and rain, after the sashes had been made for a short time, and the wet by this means finding its way betwixt the glass and the wood, and producing a continual drip in rainy weather.
"About this period the desire for metallic roofs began to extend in every direction; and as such structures had a light and graceful appearance, it became a question of importance as to the propriety of using metal sashes and rafters, instead of wooden ones, for horticultural purposes. After carefully observing the effects of those built by various persons, it became apparent to me that the expansion and contraction of metal would always militate against its general adoption, as at no season of the year could the sashes and rafters be made to fit.
"The extra expense, also, of erecting metallic-roofed houses was a consideration. In 1833 I contemplated building a new range of hot-houses; and being desirous of knowing how much they would cost, if erected of metal, a plan of the range was prepared and sent to Birmingham, and another to Sheffield, with a desire to be furnished with estimates for that purpose. The estimate from Birmingham was 1,800_l._; and the other, from Sheffield, was 1,850_l._ These appeared to me such enormous sums, that I at once set about calculating how much the range would cost if built of wood under my own inspection; and the result was, that I was able to complete the whole range, including masonry (which was omitted in the metal estimates), for less than 500_l._
"Besides the extra cost of metallic roofs, we must add the extreme heat of such houses in hot weather, and their coldness in times of frost; the liability to breakage of glass from expansion and contraction of the metal; the very limited duration of the smaller portions, as sash-bars, from corrosion, by exposure to the alternations of heat, cold, and moisture, inseparable from gardening operations, and which could only be prevented by making use of the expensive material, COPPER; and the difficulty, when compared with wood, of repairing any damages, as a wooden roof could at any time be set to rights by a common carpenter. These different items formed in my mind so many objections to its use, and the same disadvantages soon became generally apparent.
"It was now thought advisable by some parties that, in order to obviate the many disadvantages in the use of metal, the rafters and frame-work of the sashes ought to be made of wood, and the sash-bars of metal. This plan certainly presented more advantages than the other, yet it was quite obvious that materials so incongruous could never give satisfaction; and accordingly, in a few years, as I had anticipated, the rage for these structures gradually subsided, and the use of wood again became resorted to by most persons, as the best material for horticultural purposes.
[Illustration: COMMON MODE OF GLAZING ROOFS.]
"In the construction of glass-houses requiring much light, there always appeared to me one important objection, which no person seemed to have taken up or obviated; it was this. In plain lean-to or shed roofs, the morning and evening sun, which is on many accounts of the greatest importance in forcing fruits, presented its direct rays at a low angle, and, consequently, very obliquely to the glass. At those periods most of the rays of light and heat were obstructed by the position of the glass and heavy rafters, so that a considerable portion of time was lost both morning and evening; it consequently became evident that a system by which the glass would be more at right angles to the morning and evening rays of the sun would obviate the difficulty, and remove the obstruction to rays of light entering the house at an early and late hour of the day.
[Illustration: METHOD BY RIDGE-AND-FURROW.]
"This led me to the adoption of the ridge-and-furrow principle for glass roofs, which places the glass in such a position that the rays of light in the mornings and evenings enter the house without obstruction, and present themselves more perpendicularly to the glass at those times when they are the least powerful; whereas at mid-day, when they are most powerful, they present themselves more obliquely to the glass. Having had this principle fixed in my mind, and being convinced of its importance, I constructed a pine-house in 1833 as an experiment, which still exists unimpaired, and has been found fully to answer the purpose.
"In 1834 I resolved to try a further experiment on a larger scale, on the ridge-and-furrow principle, in the construction of a green-house of considerable dimensions, which also remains and answers admirably. For this building I made a still lighter sash-bar than any I had previously used; on which account the house, when completed (although possessing all the advantages of wood), was as light as if constructed of metal. The whole length of this structure is 97½ feet, and its breadth 26 feet; the height at the back is 16 feet 9 inches, and in the front 12 feet 3 inches. A span so large as 26 feet could not be safely covered with a roof constructed in the ordinary way, unless the sash-bars were stronger, and the assistance of heavy rafters and numerous supports was afforded. The house presents a neat and light appearance, and consists of 15 bays, and pediments in front, supported by 16 slender reeded cast-iron columns. Whilst it makes an admirable green-house, it is also an economical building; for, at the period of its construction, notwithstanding the heavy tax on glass (since removed), it only cost at the rate of twopence and a fraction per cubic foot. At the present time, considering the change in the price of material, and the removal of the glass-tax, it could be constructed at a considerably smaller amount.
"Having in contemplation the erection of the Great Conservatory in its present form, it was determined, in 1836, to erect a new curvilinear hot-house 60 feet in length and 26 feet in width, with the elliptical roof on the ridge-and-furrow principle, to be constructed entirely of wood, for the purpose of exhibiting how roofs of this kind could be supported. The plan adopted was this: the curved rafters were composed of several boards securely nailed together on templets of wood cut to the exact curve; by this means a strength and firmness were obtained sufficient to support an enormous weight.
"In 1837 the foundations of the Great Conservatory were commenced; and in constructing so great a building it was found desirable to contrive some means for abridging the great amount of manual labour that would be required in making the immense number of sash-bars requisite for the purpose. Accordingly, I visited all the great workshops in London, Manchester, and Birmingham, to see if anything had been invented that would afford the facilities I required. The only apparatus met with was a grooving-machine, which I had at once connected with a steam-engine at Chatsworth, and which was subsequently so improved as to make the sash-bar complete.
[Illustration: CUTTERS OF MR. PAXTON'S SASH-BAR MACHINE.]
"For this apparatus the Society of Arts, in April, 1841, awarded me a medal; and this machine is the type from which all the sash-bar machines found in use throughout the country at the present time are taken. As the Conservatory was erected under my own immediate superintendence, I am able to speak accurately as to the advantages of the machine: it has, in regard to that building alone, saved in expenses 1,400_l._ The length of each of the bars of the Conservatory is 48 inches; only one inch shorter than those of the Exhibition Building. The machine was first used in its present form in August, 1838; and its original cost, including table, wheels, and everything complete, was 20_l._ The motive power is from a steam-engine employed on the premises for other purposes; and any well-seasoned timber may be used. The attendants required are only a man and a boy, and the expense of the power required for it when in use is comparatively trifling. The sash-bars may be made of any form, by changing the character of the saws.
"There is one particular feature in working the machine, namely, the bar is presented to the saws below the centre of motion, instead of above it (as is usual); and to the sides of the saw which are ascending from the table, instead of those which are descending. These arrangements were necessary to suit the direction of the teeth to the grain of the wood; for when the bars were presented to the saws in the usual way, the wood was crushed instead of being cut and cleaned. It is essential that the machine should revolve 1,200 times in a minute to finish the work in a proper manner.
"The glass and glazing of the Chatsworth Conservatory caused me considerable thought and anxiety, as I was very desirous to do away altogether with the numerous overlaps connected with the old system of glazing with short lengths. This old method, even under the best of management, is certain, in the course of a few years, to render unsightly any structure, however well built.
"In the course of my inquiries, I heard that Messrs. Chance and Co., of Birmingham, had just introduced from the Continent the manufacture of sheet glass. Accordingly, I went to see them make this new article, and found they were able to manufacture it three feet in length. I was advised to use this glass in two lengths, with one overlap; but to this I could not assent, as I observed, that since they had so far advanced as to be able to produce sheets three feet in length, I saw no reason why they could not accomplish another foot; and, if this could not be done, I would decline giving the order, as, at that time, sheet glass was altogether an experiment for horticultural purposes. These gentlemen, however, shortly afterwards informed me that they had one person who could make it the desired length, and, if I would give the order, they would furnish me with all I required.
"It may just be remarked here that the glass for the Exhibition Building is forty-nine inches long--a size which no country except England is able to furnish in any large quantity, even at the present day.
"In 1840 the Chatsworth Conservatory was completed and planted. The whole length of this building is 277 feet; its breadth, 123 feet over the walls; and the height, from the floor to the highest part, 67 feet.
"Notwithstanding the success which attended the erection of these buildings, it became to me a question of importance how far an extensive structure might be covered in with _flat_ ridge-and-furrow roofs; that is, the ridge-and-valley rafters placed on a level, instead of at an inclination, as in the green-house, or curvilinear, as in the Great Conservatory. I therefore prepared some plans for an erection of the kind for the Earl of Burlington, somewhere about ten years ago; but, on account of the lamented death of the Countess, the design of erection was abandoned. However, from that time I felt assured, not only that it could be done satisfactorily, but that the most appropriate manner to form and support level glass roofs, to a great extent, was that adopted this year for the New Victoria House at Chatsworth, which may be considered a miniature type of the Great Industrial Building.
"Before describing this house, however, it may be well to notice two instances in which the flat roofs had been previously tried, and in both cases with the most perfect success.
"The first of these was a conservatory attached to a villa in Darley Dale, only a short distance from Chatsworth. This building is divided into five bays, with a glass door in the centre, and glass pilasters separating the bays; the ridge-and-furrow roof covers an opening of seventeen feet in the clear. The ventilation is simultaneously effected by a lever connected with a rod, which is attached to all the ventilators....
[Illustration: THE VICTORIA REGIA HOUSE, CHATSWORTH.]
"The second instance is this. In the spring of 1848, plans were prepared for the erection of an ornamental glass structure, to cover the conservatory wall at Chatsworth. This wall was previously a plain flued structure, devoted to the growth of rare and choice plants. The new erection is 331 feet in length, and 7 feet in width. It is divided into ten bays, with an ornamental centre projecting beyond the general line of the building. Each bay is subdivided by smaller bays, which are separated by glass pilasters; the glass sashes are so arranged that they can be removed in summer, and the whole thrown open to the gardens, whilst in winter the building affords an extensive promenade under cover. The ground on which this structure is built has a fall of 25 feet 6 inches in its whole length; consequently, there is a proportionate fall at each bay, which gives great variety, and obviates the monotony that would be exhibited in a building of such length and dimensions placed on a uniform level. The lower side of each bay is finished by a glass pilaster, three feet in width, and surmounted by a vase on the wall behind. The roof is on the ridge-and-furrow principle, with the rafters on a very slight inclination; and the ventilation is effected in a similar but more perfect manner than that already described as in use at the conservatory at Darley Dale.
"The new Victoria Regia House, which presents a light and novel appearance, is 60 feet 6 inches in length, and 46 feet 9 inches in breadth. Although, when compared with the Great Industrial Building, the Victoria House is a very diminutive structure, yet the principles on which it is constructed are the same, and may be carried out to an almost unlimited extent. The form of the roof, the general elevation, the supports, and the mode of construction, are all quite simple, and yet fully answer the purposes for which they were intended.
[Illustration: INTERIOR OF VICTORIA REGIA HOUSE.]
"The Victoria House, however, was so built as to retain as much moisture and heat as possible, and yet to afford a strong and bright light at all seasons; whilst, on the contrary, the Industrial Building, being intended to accommodate a daily assemblage of many thousands of individuals, and a vast number of natural and mechanical productions, many of which would be destroyed by moisture and heat, is constructed so as fully to answer that end."
This, then, was the experience which enabled Mr. Paxton to conceive his design for the "Crystal Palace," a description of which as it has subsequently been carried out we must now proceed with.
General Description of the Building.
The plan forms a parallelogram, 1,848 feet long and 408 feet wide, besides a projection on the north side, 48 feet wide and 936 feet long. A main avenue, 72 feet wide and 66 feet high, occupies the centre through the whole length of the building. Flanking this on either side are smaller avenues alternately 24 feet and 48 feet wide; the two first on either side of the centre are 43 feet, and the remainder 23 feet high. About the centre of the entire length, at a point determined by the position of a row of large trees, which it was resolved to inclose, these avenues are crossed by a transept of the same width as the main avenue, or 72 feet, and 108 feet high; two other groups of trees on the ground give occasion for open courts, which are inclosed within the building. The area thus inclosed and roofed over amounts to no less than 772,784 square feet, or about 19 acres;[4] the building is, therefore, about four times the size of St. Peter's at Rome, and more than six times that of St. Paul's, London. Three entrances lead to this vast interior, one in the centre of the principal or south front, and one at either end of the building. The number of these is necessarily small, in order to facilitate the arrangements for the money-taking, and to avoid having too large a staff of officers; on the other hand, it was equally desirable to afford the most ample opportunities of egress for visitors, and accordingly fifteen exit doors are placed at frequent intervals.
GROUND-PLAN OF THE BUILDING.
[Illustration]
A. Principal Entrance. B. West Entrance. C. East Entrance. D. Refreshment Courts. E. Entrance. F. Gentlemens' Ante-rooms. G. Ladies' Ante-rooms. H. Pay Place. I. Accountant. K. Exits. L. Ante-rooms. M. Committee Waiting-room. N. Royal Commission. O. Clerks. P. Stairs. Q. Engine House.
It will be well to mention here that the horizontal measure of 24 feet, which we have seen as the unit in the plan of the Building Committee, is also preserved in the present plan; every horizontal dimension of which is either a certain number of times or divisions of twenty-four feet.
The avenues into which the plan is divided are formed by hollow cast-iron columns twenty-four feet apart, which rise in one, two, and three storeys respectively, to support the roof at the different heights given above; in the lower storey these columns are nineteen feet high, and in the two upper ones seventeen feet. Between the different lengths of the columns short pieces are introduced, called "connecting-pieces," from the office they perform; these are three feet long, and are so contrived that they serve to support girders in horizontal tiers, dividing the greatest height into three storeys as already mentioned. The girders, of which some are of cast and some of wrought iron, are all of the same depth, namely, three feet, with the exception of four, to be specially named hereafter, and by this arrangement the same horizontal lines are preserved throughout the whole of the building. They are also all similar in appearance, forming a kind of lattice-work, by which construction they do not look too heavy for the slight supports; and large solid masses are avoided, practically showing how great strength may be combined with elegance and lightness. The first or lower tier of these girders, in parts of the building more than one storey in height, forms the support for the floor of the galleries, which are twenty-four feet wide, and extend the whole length of the building in four parallel lines, intercepted only by the transept, round the ends of which they are continued. Numerous cross galleries connect each pair of longitudinal lines on either side of the centre avenue, which remains uninterrupted from end to end, and can only be crossed on the gallery-floor at the extremities.
These galleries are reached by eight double staircases, of easy ascent and ample width, which are placed between the lines of gallery so as to communicate equally readily with either, and are so distributed as to give two to each quarter of the building; in the eastern or foreign half two supplementary staircases of smaller dimensions have been added.