The way in which the octagon and lantern combine in producing a perfectly harmonious composition is in great part due to two points of difference, points which very few observers detect. These are, firstly, that the lantern is a regular octagon, having all its sides equal, in this respect being unlike the stone octagon beneath it; and, secondly, that the eight faces of the lantern are not parallel to the eight faces of the octagon. The new windows of the lantern are similar to the large ones below, but are not mere copies of them. The upper stage of the lantern, above the roof as seen from within, was once a bell-chamber; its lights are not, and never have been, glazed. The whole of the lantern is of wood, covered with lead. Two flying buttresses rise from the corners of the nave and transept aisles to the corbel table of the clerestory range. There are also eight elegant flying buttresses, one to each of the angles of the lantern. These are part of the new work, the originals having long disappeared. #The North Transept# retains its original Norman windows in the lower stage of its western aisle, though we must remember that the north-western angle of this transept fell down in 1699, and was rebuilt[9] under the superintendence of Sir Christopher Wren. It is said that an earthquake had occurred some few years before, and had caused some damage which was not suspected at the time. However much we may admire Wren's constructive genius, we cannot justify the incongruous door in the north wall of the transept, for which we take it for granted he was responsible. It is in the classical style, utterly out of keeping with the architecture near. The arch and jambs of the Norman window above it were replaced; but this again is spoilt by the insertion of rude unadorned mullions. The corresponding window over the eastern aisle is original and unaltered. The north end of the transept has also Norman lights, larger than those below, on the second range; while above are two large Perpendicular windows, each of three lights, with transoms. To see the east wall of the transept we have to go round the lady-chapel. Here both triforium and clerestory are in their original Norman condition. The lower windows are Decorated.