Bk. II. Ch. X. BUTTRESSES. 573 was sparingly used, its place being supplied by constructive carving. Whatever may have been the com])arative merits of the two methods when first used, the Englisli vaults have a great advantage now, inasmuch as the carving remains, while the paintings of the others have perished, and we have no means left of judging of their original effect. One of the most beautiful features of French vaulting, almost entirely unknown in this country, is the great polygonal vault of the semi-dome of the chevet, Avhich as an architectural object few will be disinclined to admit is, Avith its walls of painted glass and its liglit constructive roof, a far more beautiful thing than the plain semi- dome of the basilican apse, notwithstanding its mosaics. Still, as the French used it, they never quite surmounted the difficulties of its construction ; and in their excessive desire to do away Avith all solid Avail, and to get the greatest possible surface for painted glass, they often distorted these vaults in a very unpleasing manner. The chevet of Pontigny (Woodcut No. 409) j^resents a good ex- ample of the early form of vault, Avhich, OAving to the small size of the windoAvs and general sobriety of the composition, avoids the defects aboA'C alluded to. Of the latter examples there are fcAv, except that of Souvigny, represented in Woodcut No. 427, where the difficulty has been entirely conquered by constructing the spandrils Avitli pierced tracery, so that the A^ault virtually springs from nearly the same height as the arch of the windows, and a Aery sliglit improvement Avould have made this not only constructiA'ely, but artistically perfect. This is a solitary specimen, and one Avhich, though among the most beautiful suggestions of Gothic art, has found no admirers or at least no imitators. Notwithstanding this difficulty of construction, these pierced semi- domes are not only the best specimens of French vaulting, but ere among the most beautiful inventions of the Middle Ages, and form a finer termination to the cathedral A-ista than either the great windows of the English, or the wonderful rose windows of the French cathedrals. Buttresses. The employment of buttresses was a constructive expedient that folloAved almost indispensably on the use of vaults for the roofing of churches. It Avas necessary either to employ enormously thick Avails to resist the thrust, or to support them by some more scientific arrange- ment of the materials. The theory of the buttress will be easily under- stood from the diagram (Woodcut No. 428), representing seven blocks or masses of masonry, disposed first so as to form a continuous Avail, but which evidently affords very little resistance to a tlirust or push tending to overturn it from within. The left-hand arrangement is,
