The Gothic bay
One bay of a High Gothic nave in perspective section: pier, arcade, triforium, clerestory, rib vault, aisle, flying buttress and pinnacle.
The rules it illustrates
Arcade, triforium, clerestory. Divide the elevation of the nave into three storeys: a tall arcade opening into the aisles, a low triforium passage in the thickness of the wall against the aisle roof, and a clerestory of large windows reaching up into the vault.
The width of the choir is the measure of all. Proportion every member of a vaulted choir from its clear width: the wall a fixed fraction of the width (a tenth, as the rule is usually read), and buttresses, window jambs, mullions and ribs as simple multiples or fractions of the wall.
Ever taller, ever narrower. Within a generation the nave vaults of the French cathedrals rose from about 37 m to 48 m while their spans stayed near 15 m: the ratio of height to width climbed from about 2.3 to over 3, until at Beauvais part of the choir vault fell.
Where it appears in the book
In the styles Gothic.
In the chapters Romanesque and Gothic.