Although, however, the pointed arch was actually adopted from simple necessities of construction, its advantages in all points of view soon became apparent. In an essentially arcuated style it becomes necessary not only to have the command of a form of arch capable of carrying the greatest weights and of requiring the least abutment, but it is essential to have at command an arch of variable proportions. It carries absurdity on the very face of it that, while able to give our piers a greater or a less degree of height at pleasure we should have no such power over the arch they sustain; not to mention the numerous cases in which we have to bring together arches of unequal span, and which nevertheless demand an equal height. The rules of harmony imperatively demand that the arch should be equally capable of modification in its proportions of height to width, with all other features of the architecture.
Fig. 12.
In the above outline of the history of vaulting I have, for the sake of simplicity, omitted two modes actually adopted to avoid the difficulty of oblong groining over naves. The first, which was common in German round-arched churches, was to make the vaulting of the nave simply to comprise two bays of the aisles, thus bringing the main vault equally into squares with those of the aisles. The second was the use of what Dr. Whewell has entitled sexpartite vaulting, and which is common both in France, Germany, and England ([Fig. 12]). It adopts the system last named, but subdivides the double bay by a triangular slip of vaulting ([Figs. 13], [14]). The real solution arose, however, from the free and simple use of the pointed arch, which gave the result which is seen at Westminster[7] and in nearly all the vaulted churches of the thirteenth century—the simple groined vault with arches of equal height, though the side arches are sometimes stilted, not from necessity, but merely to afford greater space for clerestory windows.
Fig. 13.
