That at Gloucester is a work of extraordinary magnificence. Its great specialty lies in its having two sets of diagonal ribs ([Fig. 388]), the one on the ordinary system, the other comprising two bays each, and by their intersection defining the position of the “Welsh” groins. Thus the whole of the ordinary diagonal ribs, and half of the others, become mere ornamented mouldings on the surface of the barrel-vault, while to them is added a vast network of liernes, cutting it into an infinity of panels, whose angles are marked by a perfect army of carved bosses. The same was imitated at a later period in the Lady Chapel.
Fig. 387.—Oriel, Eltham Palace, Kent.
Fig. 388.—Gloucester Cathedral. Choir Vaulting.
In many cases, as in the western portals at Winchester, the upper portion of the groining assumes forms in which the lines of the true ribs seem almost forgotten. This is done to a very vicious extent in the choir at Wells. I may mention, as a late example of this manner of vaulting, an exquisitely beautiful chamber adjoining the cloister at Windsor.
During this period two practices crept into use, to which it is not easy to assign precise dates, but which worked great changes in the art of vaulting. The one is the use—especially at first for diagonal ribs—of a curve drawn from two centres, which gradually brought down the arches to excessively low proportions. The other practice was the use of portions of the same curve for several, or even all, of the ribs, either throughout their height, or at least for their lower part. The first-named custom was very natural in cases where the height of the vaults was limited by circumstances, as in St. Stephen’s crypt. The diagonal ribs here were struck from three centres to the double rib, and in the next ribs from two to each single rib, and were also slightly segmental; that is to say, that they made an angle with the vertical line. They may be said to be a sort of imitation of the ellipse, as also is the case with the diagonals in the vaulting of the south and west cloisters at Westminster.
The other practice (i.e. the repetition of the same curve for different ribs) is very curious and important in its results. It influenced in an extraordinary degree the plan of the vaulting at its intermediate heights. Professor Willis has called special attention to these half-height plans, as a matter of much importance to the effect.