#Exterior of Nave.#--Those portions of the precincts near the western end of the cathedral are known as the Upper Close; and, walking round the exterior of the cloisters, we come to the Lower Close. The nave on the south side can be seen well either from the upper or lower Close, and can be better examined in detail from the interior of the cloisters. Its elevation consists of fourteen bays divided by flat Norman buttresses. In height it is composed of what, at first sight, appears a bewildering confusion of arches, arcades, and windows. Over the aisle windows, hidden by the north walk of cloisters, comes a Norman wall arcading; and over this the Norman triforium windows blocked up, and again, above the later Perpendicular triforium, superimposed on the old, and finished with a battlemented parapet. Behind this come the triforium roof, and then beyond the original Norman clerestory, each bay with a triple arch formation, the centre arch pierced for a window. And then above all, the lead roof over nave vault. The radical changes that have taken place since the nave was built by Bishop Eborard (1121-45) consist of the insertion in the aisles of later "Decorated" traceried windows in place of the original Norman ones, and of the superimposition, before referred to, at triforium level of a whole range of "Perpendicular" windows over the old Norman work, which were blocked up at this period. The pristine aspect, then, of this elevation of the nave would have shown a sloping roof over the aisles where now the later addition occurs. The battlementing, too, over the clerestory to the nave is later work, to correspond with battlementing over the triforium windows. It will be noticed that the two bays next the transept in the triforium are higher than the others, in order to throw additional light into the choir. Also on this same south side, in the seventh and eighth bays from the west end, two very late windows occur, inserted in the Norman arcading under the original triforium windows; these were inserted by Bishop Nykke to light the chapel he built in two bays of the south aisle of the nave. The curious raking of the lead rolls to the nave roof is noticeable; the mediaeval builders did this with a view of counteracting the "crawl" of the lead. Lead, under the variations of temperature of the atmosphere, expands and contracts considerably; and from its own weight, and the steepness of the roofs, the contraction takes place in a downward direction, and starts the joints, letting in the weather. This raking of the vertical rolls was a device whereby the old builders in some measure got over their difficulty by inducing a fixed expansion and contraction. [Illustration: The Clerestory and Triforium of Choir (South Side).]