In the latter half of the fourteenth century, Gothic art, both in France and England, again showed symptoms of a change of character. In France the architects seemed to have exhausted their powers of development as regards constructional elements, and were now occupied with the elaboration of details. The earlier geometric tracery now assumed a very flowing character, which, from the flame-like shapes of the bars of the stone work, was called “Flamboyant.” In England, on the other hand, the tracery assumed a rigid form, and from the mullions of the windows being carried up in straight lines from the sill to the arch, the style received the name of “perpendicular.” (Fig. 25.) In many respects, connected with ornament and decoration, the styles of the two countries resembled each other, but in one respect they differed widely. In France the simple intersecting pointed vault was never departed from, but in England the development of the vaulting into new forms made great progress at this period. It has been mentioned that in their “decorated” work the English had begun, in the thirteenth century, to introduce “liernes” or intermediate ribs into the vaults. This process still continued and advanced till the vaulting surface became covered with ribs. (Fig. 26.) The ribs were latterly used as ornamental features, spread over the surface of the vault, which again became the supporting arched surface, as it was before the introduction of Gothic bearing ribs in the twelfth century. A favourite form of this kind of vaulting is known from its appearance as fan vaulting. In working out this kind of vaulting, it was found desirable to bring all the ribs to the same level at the apex, and in order to accomplish this it was found convenient to use arches of double curvature, or four centred arches, a depressed form which is characteristic of perpendicular work. [Illustration: FIG. 25.--York Cathedral. View of the East End. (From Britton’s _Cathedrals_.)]