Читать книгу The Stones of Venice (Vol. 1-3) - John Ruskin - Страница 10

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§ I. We have lastly to consider the close of the wall’s existence, or its cornice. It was above stated, that a cornice has one of two offices: if the wall have nothing to carry, the cornice is its roof, and defends it from the weather; if there is weight to be carried above the wall, the cornice is its hand, and is expanded to carry the said weight.

There are several ways of roofing or protecting independent walls, according to the means nearest at hand: sometimes the wall has a true roof all to itself; sometimes it terminates in a small gabled ridge, made of bricks set slanting, as constantly in the suburbs of London; or of hewn stone, in stronger work; or in a single sloping face, inclined to the outside. We need not trouble ourselves at present about these small roofings, which are merely the diminutions of large ones; but we must examine the important and constant member of the wall structure, which prepares it either for these small roofs or for weights above, and is its true cornice.

§ II. The reader will, perhaps, as heretofore, be kind enough to think for himself, how, having carried up his wall veil as high as it may be needed, he will set about protecting it from weather, or preparing it for weight. Let him imagine the top of the unfinished wall, as it would be seen from above with all the joints, perhaps uncemented, or imperfectly filled up with cement, open to the sky; and small broken materials filling gaps between large ones, and leaving cavities ready for the rain to soak into, and loosen and dissolve the cement, and split, as it froze, the whole to pieces. I am much mistaken if his first impulse would not be to take a great flat stone and lay it on the top; or rather a series of such, side by side, projecting well over the edge of the wall veil. If, also, he proposed to lay a weight (as, for instance, the end of a beam) on the wall, he would feel at once that the pressure of this beam on, or rather among, the small stones of the wall veil, might very possibly dislodge or disarrange some of them; and the first impulse would be, in this case, also to lay a large flat stone on the top of all to receive the beam, or any other weight, and distribute it equally among the small stones below, as at a, Fig. IV.

Fig. IV.

§ III. We must therefore have our flat stone in either case; and let b, Fig. IV., be the section or side of it, as it is set across the wall. Now, evidently, if by any chance this weight happen to be thrown more on the edges of this stone than the centre, there will be a chance of these edges breaking off. Had we not better, therefore, put another stone, sloped off to the wall, beneath the projecting one, as at c. But now our cornice looks somewhat too heavy for the wall; and as the upper stone is evidently of needless thickness, we will thin it somewhat, and we have the form d. Now observe: the lower or bevelled stone here at d corresponds to d in the base (Fig. II., page 59). That was the foot of the wall; this is its hand. And the top stone here, which is a constant member of cornices, corresponds to the under stone c, in Fig. II., which is a constant member of bases. The reader has no idea at present of the enormous importance of these members; but as we shall have to refer to them perpetually, I must ask him to compare them, and fix their relations well in his mind: and, for convenience, I shall call the bevelled or sloping stone, X, and the upright edged stone, Y. The reader may remember easily which is which; for X is an intersection of two slopes, and may therefore properly mean either of the two sloping stones; and Y is a figure with a perpendicular line and two slopes, and may therefore fitly stand for the upright stone in relation to each of the sloping ones; and as we shall have to say much more about cornices than about bases, let X and Y stand for the stones of the cornice, and Xb and Yb for those of the base, when distinction is needed.

§ IV. Now the form at d, Fig. IV., is the great root and primal type of all cornices whatsoever. In order to see what forms may be developed from it, let us take its profile a little larger—a, Fig. V., with X and Y duly marked. Now this form, being the root of all cornices, may either have to finish the wall and so keep off rain; or, as so often stated, to carry weight. If the former, it is evident that, in its present profile, the rain will run back down the slope of X; and if the latter, that the sharp angle or edge of X, at k, may be a little too weak for its work, and run a chance of giving way. To avoid the evil in the first case, suppose we hollow the slope of X inwards, as at b; and to avoid it in the second case, suppose we strengthen X by letting it bulge outwards, as at c.

Fig. V.

§ V. These (b and c) are the profiles of two vast families of cornices, springing from the same root, which, with a third arising from their combination (owing its origin to æsthetic considerations, and inclining sometimes to the one, sometimes to the other), have been employed, each on its third part of the architecture of the whole world throughout all ages, and must continue to be so employed through such time as is yet to come. We do not at present speak of the third or combined group; but the relation of the two main branches to each other, and to the line of origin, is given at e, Fig. V.; where the dotted lines are the representatives of the two families, and the straight line of the root. The slope of this right line, as well as the nature of the curves, here drawn as segments of circles, we leave undetermined: the slope, as well as the proportion of the depths of X and Y to each other, vary according to the weight to be carried, the strength of the stone, the size of the cornice, and a thousand other accidents; and the nature of the curves according to æsthetic laws. It is in these infinite fields that the invention of the architect is permitted to expatiate, but not in the alteration of primitive forms.

§ VI. But to proceed. It will doubtless appear to the reader, that, even allowing for some of these permissible variations in the curve or slope of X, neither the form at b, nor any approximation to that form, would be sufficiently undercut to keep the rain from running back upon it. This is true; but we have to consider that the cornice, as the close of the wall’s life, is of all its features that which is best fitted for honor and ornament. It has been esteemed so by almost all builders, and has been lavishly decorated in modes hereafter to be considered. But it is evident that, as it is high above the eye, the fittest place to receive the decoration is the slope of X, which is inclined towards the spectator; and if we cut away or hollow out this slope more than we have done at b, all decoration will be hid in the shadow. If, therefore, the climate be fine, and rain of long continuance not to be dreaded, we shall not hollow the stone X further, adopting the curve at b merely as the most protective in our power. But if the climate be one in which rain is frequent and dangerous, as in alternations with frost, we may be compelled to consider the cornice in a character distinctly protective, and to hollow out X farther, so as to enable it thoroughly to accomplish its purpose. A cornice thus treated loses its character as the crown or honor of the wall, takes the office of its protector, and is called a DRIPSTONE. The dripstone is naturally the attribute of Northern buildings, and therefore especially of Gothic architecture; the true cornice is the attribute of Southern buildings, and therefore of Greek and Italian architecture; and it is one of their peculiar beauties, and eminent features of superiority.

§ VII. Before passing to the dripstone, however, let us examine a little farther into the nature of the true cornice. We cannot, indeed, render either of the forms b or c, Fig. V., perfectly protective from rain, but we can help them a little in their duty by a slight advance of their upper ledge. This, with the form b, we can best manage by cutting off the sharp upper point of its curve, which is evidently weak and useless; and we shall have the form f. By a slight advance of the upper stone c, we shall have the parallel form g.

These two cornices, f and g, are characteristic of early Byzantine work, and are found on all the most lovely examples of it in Venice. The type a is rarer, but occurs pure in the most exquisite piece of composition in Venice—the northern portico of St. Mark’s; and will be given in due time.

§ VIII. Now the reader has doubtless noticed that these forms of cornice result, from considerations of fitness and necessity, far more neatly and decisively than the forms of the base, which we left only very generally determined. The reason is, that there are many ways of building foundations, and many good ways, dependent upon the peculiar accidents of the ground and nature of accessible materials. There is also room to spare in width, and a chance of a part of the arrangement being concealed by the ground, so as to modify height. But we have no room to spare in width on the top of a wall, and all that we do must be thoroughly visible; and we can but have to deal with bricks, or stones of a certain degree of fineness, and not with mere gravel, or sand, or clay—so that as the conditions are limited, the forms become determined; and our steps will be more clear and certain the farther we advance. The sources of a river are usually half lost among moss and pebbles, and its first movements doubtful in direction; but, as the current gathers force, its banks are determined, and its branches are numbered.

§ IX. So far of the true cornice: we have still to determine the form of the dripstone.

Fig. VI.

We go back to our primal type or root of cornice, a of Fig. V. We take this at a in Fig. VI., and we are to consider it entirely as a protection against rain. Now the only way in which the rain can be kept from running back on the slope of X is by a bold hollowing out of it upwards, b. But clearly, by thus doing, we shall so weaken the projecting part of it that the least shock would break it at the neck, c; we must therefore cut the whole out of one stone, which will give us the form d. That the water may not lodge on the upper ledge of this, we had better round it off; and it will better protect the joint at the bottom of the slope if we let the stone project over it in a roll, cutting the recess deeper above. These two changes are made in e: e is the type of dripstones; the projecting part being, however, more or less rounded into an approximation to the shape of a falcon’s beak, and often reaching it completely. But the essential part of the arrangement is the up and under cutting of the curve. Wherever we find this, we are sure that the climate is wet, or that the builders have been bred in a wet country, and that the rest of the building will be prepared for rough weather. The up cutting of the curve is sometimes all the distinction between the mouldings of far-distant countries and utterly strange nations.

Fig. VII.

Fig. VII. representing a moulding with an outer and inner curve, the latter undercut. Take the outer line, and this moulding is one constant in Venice, in architecture traceable to Arabian types, and chiefly to the early mosques of Cairo. But take the inner line; it is a dripstone at Salisbury. In that narrow interval between the curves there is, when we read it rightly, an expression of another and mightier curve—the orbed sweep of the earth and sea, between the desert of the Pyramids, and the green and level fields through which the clear streams of Sarum wind so slowly.

Fig. VIII.

And so delicate is the test, that though pure cornices are often found in the north—borrowed from classical models—so surely as we find a true dripstone moulding in the South, the influence of Northern builders has been at work; and this will be one of the principal evidences which I shall use in detecting Lombard influence on Arab work; for the true Byzantine and Arab mouldings are all open to the sky and light, but the Lombards brought with them from the North the fear of rain, and in all the Lombardic Gothic we instantly recognize the shadowy dripstone: a, Fig. VIII., is from a noble fragment at Milan, in the Piazza dei Mercanti; b, from the Broletto of Como. Compare them with c and d; both from Salisbury; e and f from Lisieux, Normandy; g and h from Wenlock Abbey, Shropshire.

§ X. The reader is now master of all that he need know about the construction of the general wall cornice, fitted either to become a crown of the wall, or to carry weight above. If, however, the weight above become considerable, it may be necessary to support the cornice at intervals with brackets; especially if it be required to project far, as well as to carry weight; as, for instance, if there be a gallery on top of the wall. This kind of bracket-cornice, deep or shallow, forms a separate family, essentially connected with roofs and galleries; for if there be no superincumbent weight, it is evidently absurd to put brackets to a plain cornice or dripstone (though this is sometimes done in carrying out a style); so that, as soon as we see a bracket put to a cornice, it implies, or should imply, that there is a roof or gallery above it. Hence this family of cornices I shall consider in connection with roofing, calling them “roof cornices,” while what we have hitherto examined are proper “wall cornices.” The roof cornice and wall cornice are therefore treated in division D.

We are not, however, as yet nearly ready for our roof. We have only obtained that which was to be the object of our first division (A); we have got, that is to say, a general idea of a wall and of the three essential parts of a wall; and we have next, it will be remembered, to get an idea of a pier and the essential parts of a pier, which were to be the subjects of our second division (B).