Page:A history of architecture on the comparative method for the student, craftsman, and amateur.djvu/347

 ENGLISH GOTHIC. 289 systems are found, as at King's College Chapel, Cambridge ; in others, as Henry VII. 's Chapel, Westminster, the whole vault is of jointed masonry. The difficulty of supporting the flat lozenge-shaped space in the top portion of the vault surrounded by the upper boundaries of the hollow cones was comparatively easy in the cloisters, where this type of vaulting was hrst introduced, because the vaulting spaces to be roofed were square or nearly so, but when it was attempted to apply it to the bays of the nave, which were generally twice as long transversely as longitudinally, difficulties occurred. In King's College Chapel (a.d. 15 13) the conoid was continued to the centre, but the sides were cut off", thus forming an awkward junction transversely. In the nave of Henry VIl.'s Chapel pendants supported by internal arches were placed away from the walls and the conoids supported on these, thus reducing the size of the flat central space, and changing it from an oblong to a square on plan. At Oxford Cathedral a somewhat similar method was adopted, the pendants also placed some distance from the wall, being supported on an upper arch, and a polygonal form of ribs adhered to. Fan vaulting is confined to England, and other examples beyond those already mentioned are in the Divinity Schools, Oxford; Trinity Church, Ely; Gloucester Cathedral (No. 112 K, s) ; S. George's Chapel, Windsor ; the retro-choir, Peter- borough, and elsewhere. The depressed four -cent red arch (No. 299 m) is typical of the architecture of the Tudor period, although it seems to have been used in the vaulting of earlier churches (No. iii d). It is not found out of England, and appears to have been first used largely in fan vaulting, to which the reason for its adoption is held to be due. For example, if the diagonal rib is to be a pointed two- centred arch, each portion must obviously be less than a quadrant, and the transverse and wall ribs, being shorter, must be con- siderably less than quadrants, especially if the compartment is oblong, and this would make the window arch in the nave wall of acute lancet form ; but the window arch was made equilateral or even less in height compared to its span in this period, and so the segments of a diagonal arch of two centres preserving the same curvature would not meet at their summit without becoming horizontal or possibly bending downwards to each other. To obviate this the transverse and diagonal ribs in an oblong com- partment were sometimes made as four-centred arches, all the ribs starting with the same curvature, but at a certain height the portions above this level were drawn with a longer radius in order that they might meet the ribs from the opposite side of the vault at the required height. These four-centred arches were afterwards applied to other parts of the buildings in England, as in arches to