+OCTAGON AT ELY.+ The magnificent +Octagon+ of Ely Cathedral, at the intersection of the nave and transepts, belongs in the same category with these polygonal chapter-house vaults. It was built by Alan of Walsingham in 1337, after the fall of the central tower and the destruction of the adjacent bays of the choir. It occupies the full width of the three aisles, and covers the ample space thus enclosed with a simple but beautiful groined and ribbed vault of wood reaching to a central octagonal lantern, which rises much higher and shows externally as well as internally. Unfortunately, this vault is of wood, and would require important modifications of detail if carried out in stone. But it is so noble in general design and total effect, that one wonders the type was not universally adopted for the crossing in all cathedrals, until one observes that no cathedral of importance was built after Walsingham’s time, nor did any other central towers opportunely fall to the ground. +WINDOWS AND TRACERY.+ In the Early English Period (1200-1280 or 1300) the windows were tall and narrow (_lancet_ windows), and generally grouped by twos and threes, though sometimes four and even five are seen together (as the “Five Sisters” in the N. transept of York). In the nave of Salisbury and the retro-choir of Ely the side aisles are lighted by coupled windows and the clearstory by triple windows, the central one higher than the others--a surviving Norman practice. Plate-tracery was, as in France, an intermediate step leading to the development of bar-tracery (see Fig. 110). The English followed here the same reasoning as the French. At first the openings constituted the design, the intervening stonework being of secondary importance. Later the forms of the openings were subordinated to the pattern of the stone framework of bars, arches, circles, and cusps. Bar-tracery of this description prevailed in England through the greater part of the Decorated Period (1280-1380), and somewhat resembled the contemporary French geometric tracery, though more varied and less rigidly constructive in design. An early example of this tracery occurs in the cloisters of Salisbury (Fig. 132); others in the clearstories of the choirs of Lichfield, Lincoln, and Ely, the nave of York, and the chapter-houses mentioned above, where, indeed, it seems to have received its earliest development. After the middle of the fourteenth century lines of double curvature were introduced, producing what is called _flowing_ tracery, somewhat resembling the French flamboyant, though earlier in date (Fig. 111). Examples of this style are found in Wells, in the side aisles and triforium of the choir of Ely, and in the S. transept rose-window of Lincoln. [Illustration: FIG. 132.--CLOISTERS, SALISBURY CATHEDRAL (SHOWING UPPER PART OF CHAPTER-HOUSE).] [Illustration: FIG. 133.--PERPENDICULAR TRACERY, WEST WINDOW OF ST. GEORGE’S, WINDSOR.]