Читать книгу The Stones of Venice - John Ruskin - Страница 19

Table of Contents

§ I. We have hitherto supposed ourselves concerned with the support of vertical pressure only; and the arch and roof have been considered as forms of abstract strength, without reference to the means by which their lateral pressure was to be resisted. Few readers will need now to be reminded, that every arch or gable not tied at its base by beams or bars, exercises a lateral pressure upon the walls which sustain it—pressure which may, indeed, be met and sustained by increasing the thickness of the wall or vertical piers, and which is in reality thus met in most Italian buildings, but may, with less expenditure of material, and with (perhaps) more graceful effect, be met by some particular application of the provisions against lateral pressure called Buttresses. These, therefore, we are next to examine.

§ II. Buttresses are of many kinds, according to the character and direction of the lateral forces they are intended to resist. But their first broad division is into buttresses which meet and break the force before it arrives at the wall, and buttresses which stand on the lee side of the wall, and prop it against the force.

The lateral forces which walls have to sustain are of three distinct kinds: dead weight, as of masonry or still water; moving weight, as of wind or running water; and sudden concussion, as of earthquakes, explosions, &c.

Clearly, dead weight can only be resisted by the buttress acting as a prop; for a buttress on the side of, or towards the weight, would only add to its effect. This, then, forms the first great class of buttressed architecture; lateral thrusts, of roofing or arches, being met by props of masonry outside—the thrust from within, the prop without; or the crushing force of water on a ship’s side met by its cross timbers—the thrust here from without the wall, the prop within.

Moving weight may, of course, be resisted by the prop on the lee side of the wall, but is often more effectually met, on the side which is attacked, by buttresses of peculiar forms, cunning buttresses, which do not attempt to sustain the weight, but parry it, and throw it off in directions clear of the wall.

Thirdly: concussions and vibratory motion, though in reality only supported by the prop buttress, must be provided for by buttresses on both sides of the wall, as their direction cannot be foreseen, and is continually changing.

We shall briefly glance at these three systems of buttressing; but the two latter being of small importance to our present purpose, may as well be dismissed first.

§ III. 1. Buttresses for guard against moving weight and set towards the weight they resist.

The most familiar instance of this kind of buttress we have in the sharp piers of a bridge, in the centre of a powerful stream, which divide the current on their edges, and throw it to each side under the arches. A ship’s bow is a buttress of the same kind, and so also the ridge of a breastplate, both adding to the strength of it in resisting a cross blow, and giving a better chance of a bullet glancing aside. In Switzerland, projecting buttresses of this kind are often built round churches, heading up hill, to divide and throw off the avalanches. The various forms given to piers and harbor quays, and to the bases of light-houses, in order to meet the force of the waves, are all conditions of this kind of buttress. But in works of ornamental architecture such buttresses are of rare occurrence; and I merely name them in order to mark their place in our architectural system, since in the investigation of our present subject we shall not meet with a single example of them, unless sometimes the angle of the foundation of a palace set against the sweep of the tide, or the wooden piers of some canal bridge quivering in its current.

§ IV. 2. Buttresses for guard against vibratory motion.

The whole formation of this kind of buttress resolves itself into mere expansion of the base of the wall, so as to make it stand steadier, as a man stands with his feet apart when he is likely to lose his balance. This approach to a pyramidal form is also of great use as a guard against the action of artillery; that if a stone or tier of stones be battered out of the lower portions of the wall, the whole upper part may not topple over or crumble down at once. Various forms of this buttress, sometimes applied to particular points of the wall, sometimes forming a great sloping rampart along its base, are frequent in buildings of countries exposed to earthquake. They give a peculiarly heavy outline to much of the architecture of the kingdom of Naples, and they are of the form in which strength and solidity are first naturally sought, in the slope of the Egyptian wall. The base of Guy’s Tower at Warwick is a singularly bold example of their military use; and so, in general, bastion and rampart profiles, where, however, the object of stability against a shock is complicated with that of sustaining weight of earth in the rampart behind.

§ V. 3. Prop buttresses against dead weight.

This is the group with which we have principally to do; and a buttress of this kind acts in two ways, partly by its weight and partly by its strength. It acts by its weight when its mass is so great that the weight it sustains cannot stir it, but is lost upon it, buried in it, and annihilated: neither the shape of such a buttress nor the cohesion of its materials are of much consequence; a heap of stones or sandbags, laid up against the wall, will answer as well as a built and cemented mass.

But a buttress acting by its strength is not of mass sufficient to resist the weight by mere inertia; but it conveys the weight through its body to something else which is so capable; as, for instance, a man leaning against a door with his hands, and propping himself against the ground, conveys the force which would open or close the door against him through his body to the ground. A buttress acting in this way must be of perfectly coherent materials, and so strong that though the weight to be borne could easily move it, it cannot break it: this kind of buttress may be called a conducting buttress. Practically, however, the two modes of action are always in some sort united. Again, the weight to be borne may either act generally on the whole wall surface, or with excessive energy on particular points: when it acts on the whole wall surface, the whole wall is generally supported; and the arrangement becomes a continuous rampart, as a dyke, or bank of reservoir.

§ VI. It is, however, very seldom that lateral force in architecture is equally distributed. In most cases the weight of the roof, or the force of any lateral thrust, are more or less confined to certain points and directions. In an early state of architectural science this definiteness of direction is not yet clear, and it is met by uncertain application of mass or strength in the buttress, sometimes by mere thickening of the wall into square piers, which are partly piers, partly buttresses, as in Norman keeps and towers. But as science advances, the weight to be borne is designedly and decisively thrown upon certain points; the direction and degree of the forces which are then received are exactly calculated, and met by conducting buttresses of the smallest possible dimensions; themselves, in their turn, supported by vertical buttresses acting by weight, and these perhaps, in their turn, by another set of conducting buttresses: so that, in the best examples of such arrangements, the weight to be borne may be considered as the shock of an electric fluid, which, by a hundred different rods and channels, is divided and carried away into the ground.

§ VII. In order to give greater weight to the vertical buttress piers which sustain the conducting buttresses, they are loaded with pinnacles, which, however, are, I believe, in all the buildings in which they become very prominent, merely decorative: they are of some use, indeed, by their weight; but if this were all for which they were put there, a few cubic feet of lead would much more securely answer the purpose, without any danger from exposure to wind. If the reader likes to ask any Gothic architect with whom he may happen to be acquainted, to substitute a lump of lead for his pinnacles, he will see by the expression of his face how far he considers the pinnacles decorative members. In the work which seems to me the great type of simple and masculine buttress structure, the apse of Beauvais, the pinnacles are altogether insignificant, and are evidently added just as exclusively to entertain the eye and lighten the aspect of the buttress, as the slight shafts which are set on its angles; while in other very noble Gothic buildings the pinnacles are introduced as niches for statues, without any reference to construction at all: and sometimes even, as in the tomb of Can Signoria at Verona, on small piers detached from the main building.

§ VIII. I believe, therefore, that the development of the pinnacle is merely a part of the general erectness and picturesqueness of northern work above alluded to: and that, if there had been no other place for the pinnacles, the Gothic builders would have put them on the tops of their arches (they often did on the tops of gables and pediments), rather than not have had them; but the natural position of the pinnacle is, of course, where it adds to, rather than diminishes, the stability of the building; that is to say, on its main wall piers and the vertical piers at the buttresses. And thus the edifice is surrounded at last by a complete company of detached piers and pinnacles, each sustaining an inclined prop against the central wall, and looking something like a band of giants holding it up with the butts of their lances. This arrangement would imply the loss of an enormous space of ground, but the intervals of the buttresses are usually walled in below, and form minor chapels.

Fig. XLII.

§ IX. The science of this arrangement has made it the subject of much enthusiastic declamation among the Gothic architects, almost as unreasonable, in some respects, as the declamation of the Renaissance architects respecting Greek structure. The fact is, that the whole northern buttress system is based on the grand requirement of tall windows and vast masses of light at the end of the apse. In order to gain this quantity of light, the piers between the windows are diminished in thickness until they are far too weak to bear the roof, and then sustained by external buttresses. In the Italian method the light is rather dreaded than desired, and the wall is made wide enough between the windows to bear the roof, and so left. In fact, the simplest expression of the difference in the systems is, that a northern apse is a southern one with its inter-fenestrial piers set edgeways. Thus, a, Fig. XLII., is the general idea of the southern apse; take it to pieces, and set all its piers edgeways, as at b, and you have the northern one. You gain much light for the interior, but you cut the exterior to pieces, and instead of a bold rounded or polygonal surface, ready for any kind of decoration, you have a series of dark and damp cells, which no device that I have yet seen has succeeded in decorating in a perfectly satisfactory manner. If the system be farther carried, and a second or third order of buttresses be added, the real fact is that we have a building standing on two or three rows of concentric piers, with the roof off the whole of it except the central circle, and only ribs left, to carry the weight of the bit of remaining roof in the middle; and after the eye has been accustomed to the bold and simple rounding of the Italian apse, the skeleton character of the disposition is painfully felt. After spending some months in Venice, I thought Bourges Cathedral looked exactly like a half-built ship on its shores. It is useless, however, to dispute respecting the merits of the two systems: both are noble in their place; the Northern decidedly the most scientific, or at least involving the greatest display of science, the Italian the calmest and purest, this having in it the sublimity of a calm heaven or a windless noon, the other that of a mountain flank tormented by the north wind, and withering into grisly furrows of alternate chasm and crag.

§ X. If I have succeeded in making the reader understand the veritable action of the buttress, he will have no difficulty in determining its fittest form. He has to deal with two distinct kinds; one, a narrow vertical pier, acting principally by its weight, and crowned by a pinnacle; the other, commonly called a Flying buttress, a cross bar set from such a pier (when detached from the building) against the main wall. This latter, then, is to be considered as a mere prop or shore, and its use by the Gothic architects might be illustrated by the supposition that we were to build all our houses with walls too thin to stand without wooden props outside, and then to substitute stone props for wooden ones. I have some doubts of the real dignity of such a proceeding, but at all events the merit of the form of the flying buttress depends on its faithfully and visibly performing this somewhat humble office; it is, therefore, in its purity, a mere sloping bar of stone, with an arch beneath it to carry its weight, that is to say, to prevent the action of gravity from in any wise deflecting it, or causing it to break downwards under the lateral thrust; it is thus formed quite simple in Notre Dame of Paris, and in the Cathedral of Beauvais, while at Cologne the sloping bars are pierced with quatrefoils, and at Amiens with traceried arches. Both seem to me effeminate and false in principle; not, of course, that there is any occasion to make the flying buttress heavy, if a light one will answer the purpose; but it seems as if some security were sacrificed to ornament. At Amiens the arrangement is now seen to great disadvantage, for the early traceries have been replaced by base flamboyant ones, utterly weak and despicable. Of the degradations of the original form which took place in after times, I have spoken at p. 35 of the “Seven Lamps.”

§ XI. The form of the common buttress must be familiar to the eye of every reader, sloping if low, and thrown into successive steps if they are to be carried to any considerable height. There is much dignity in them when they are of essential service; but even in their best examples, their awkward angles are among the least manageable features of the Northern Gothic, and the whole organisation of its system was destroyed by their unnecessary and lavish application on a diminished scale; until the buttress became actually confused with the shaft, and we find strangely crystallised masses of diminutive buttress applied, for merely vertical support, in the northern tabernacle work; while in some recent copies of it the principle has been so far distorted that the tiny buttressings look as if they carried the superstructure on the points of their pinnacles, as in the Cranmer memorial at Oxford. Indeed, in most modern Gothic, the architects evidently consider buttresses as convenient breaks of blank surface, and general apologies for deadness of wall. They stand in the place of ideas, and I think are supposed also to have something of the odor of sanctity about them; otherwise, one hardly sees why a warehouse seventy feet high should have nothing of the kind, and a chapel, which one can just get into with one’s hat off, should have a bunch of them at every corner; and worse than this, they are even thought ornamental when they can be of no possible use; and these stupid penthouse outlines are forced upon the eye in every species of decoration: in St. Margaret’s Chapel, West Street, there are actually a couple of buttresses at the end of every pew.

§ XII. It is almost impossible, in consequence of these unwise repetitions of it, to contemplate the buttress without some degree of prejudice; and I look upon it as one of the most justifiable causes of the unfortunate aversion with which many of our best architects regard the whole Gothic school. It may, however, always be regarded with respect when its form is simple and its service clear; but no treason to Gothic can be greater than the use of it in indolence or vanity, to enhance the intricacies of structure, or occupy the vacuities of design.