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positing of the stones of the vault between the ribs, which, instead of being parallel to each side of the plan, as in Roman groined vaults, take a mean direction between the groined rib and the ribs of the arches over the sides ; whence they meet at the vertex at an acute angle, and are received by stones running along the vertés, cut in the form of a ratchet. The advantage of this method consists in requiring less centering, and originates in the position of the ribs at the springing." “ From these beginnings vaulting began to assume those practical advantages which the joint adaptation of the pointed arch and ribs was cal. culated to produce." " The second step differed from the first, inasmuch as at the vertex of the vault a continued keystone or ridge projects below the surface of the vault, and forms a feature similar to the ribs. But here it was necessary that the ridge should be a stone of great length, or having artificially that property, because its suspension by a thinner vault than itself would be unsafe, unless assisted by the rib arches over the diagonals and side, a distance equal to half the width of the vault. To obviate this objection, other ribs were introduced at intervals, which may be conceived to be groined ribs over various oblongs. one side continually decreasing. This practice had a further advantage, as the panels or vaults hetween the ribs might become proportionally thinner as the principal supports increased. It is now that the apparent magic hardiness of pointed vaulting and the high embowered roof began to display itself; from slender columns to streti h shades as broad as those of the oak's thick branches, and, in the levity of the panel to the rib, to imitate that of the leaf to the branch.” “ On comparing rib-pointed vaulting with Roman vaulting, it will be invariably found that the rib itself is thinner than the uniform thick ness of the Roman vault under similar circumstances; and that the panel, which is the principal part of the vault in superficial quantity, sometimes does not exceed one ninth part of the rib in thickness. The Gothic architects, it has been expressively said, have given to stone aa apparent flexibility equal to the most ductile metals, and have made it forget its nature, Weaning it from its fondness to descend to tbe centre."
Fig. 590h1499y. In the second example (fig. 590g.), another rib, a b, is introduced, which on plan produces the form of a star of four points. The forms of these thus inserted ribs result from curves of the lines on the plan in the space to be vaulted. As many radii are drawn
engage to build another" (vault like it). The vault of the chapel in question is divided into oblong severies, whose shorter sides are placed longitudinally (fig. 5900.) It must be evident that the curves of the inverted quadrants must intersect each other previous to the whole quadrant of the circle being completed. Hence these intersections form a curved summit line lowest against the windows or smaller sides of the oblong. This summit line of the vaulting of the building in the direction of its length forms a series of curves, though from the angle under which it is seen it is scarcely perceptible. Mr. Ware says, “ It is observable, in the construction of this vault, that the prin: eiple of using freestone for the ribs, and tufa for the panels, has not been followed; but the whole vault has been got out of the same deseription of stone, and with an uniform face, and the panels worked afterwards, and 10 dueed to a tenuity hardly credible except from measurement. The artists of this building might be trusted in the decoration of a vault with what is now called tracery; they knew how to render it the chief support, and what was the superfluous stone to be taken away : every part has a place, not only proper, but necessary; and in the ribs which adorn the vault we may in vain look for false positions. This is the ocular music which atfords universal pleasure.”
1499dd. We now return to the consideration of two more modes of simple vaulting. In England, the summit ribs of the vault are almost always found running longitudinally and transversely in the various examples. In Germany the summit ribs are more frequently omitted than introduced. Thus in the example fig. 5901, the scheme is merely a square diagonally placed within the severy, subdivided into four parts and connected with the basepoints of the groins by ribs not parallel to the alternate sides of the inserted square. This, bowever, sometimes occurs in English buildings, as in the monument of Archbishop Stratford, at Canterbury Cathedral ; though in that the central portion is not domical. It is to be remarked that the intersecting arches are not of equal height, otherwise the arrangement could not occur.
1499ee. In the example fig. 590p, the arrangement completely assumes what Mr. Willis calls the stellar form. Here in the soffit a star of six points is the figure on which the projection depends, the points radiating froin the angles of an hexagon, and thus forming a cluster of lozenges whose middle longitudinal sides produce another longitudinal lozenge to connect the centres of the pattern. The longitudinal arches are, as in the preceding figure, lower than the transverse arches. Mr. Willis says, “ the principal distinction between these and our own fansaulting is the substitution of lozenge-headed compart. ments in the fans, for the English horizontal transom
We have also lozenge-headed compartments in our early vaulting, but they are never so symmetrically arranged in stars throughout.”
1499ff. From the simple lines or principles above given, it is easy to perceive through what numberless ramifications of form they may be carried. Another form is that called hexpartite vaulting, where the ribs spring from the angles, and two others from a shaft placed in the middle of each long side, thus making sis divisions. This is a step beyond the quadripartite groining shown in fig. 590f. Examples of herpartite vaulting are scarce in England, but it may be seen in the chapel of St. Blaise in Westminster Abbey, the choir of Canterbury Cathedral, and in many parts of Lincoln Minster.
14999g. It would be difficult to find a system of vaulting more unlike any English etample than that in Anjou generally, of which the Hospital at Angers is a fair specimen. It is always excessively donuical in its sections, both longitudinal and transverse ; and has eight ribs, the cells being filled in with stones exactly parallel with the centre or ridge of Each cell : the ribs are edge-roll mouldings.
1499hh. Besides the books named above, Prof. Willis On Vaulting, and by T. Eagles, 1874, both read at the Royal Institute of British Architects, the Dictionnaire by Viollet. le-Duc, the Lectures by Sir G. G. Scott, R.A., and the paper by W. H. Wood, in Buililer for 1883, xliv., 55, should be referred to. A very complete outline of the subject has been printed by Prof. Babcock, of the Cornell University, Ithaca, New York, for his courses of lectures.