The flying buttress
Half-arches of stone carry the outward thrust of a high vault over the aisle roof to a massive pier weighted by a pinnacle.
The rules it illustrates
The flying buttress. Carry the outward thrust of a high vault across the aisle roof by a half-arch of stone (the flyer) that leans against the clerestory wall at the level of the vault’s haunches and springs from a massive buttress pier outside the aisle, which takes the thrust down to the ground.
The pinnacle is a weight. Load the top of a buttress pier with a heavy pinnacle: the added weight steepens the resultant of the flyer’s thrust and the pier’s own weight, keeping it well inside the base of the pier.
Art without science is nothing. A building’s form must follow the geometrical rules of the craft (scientia) as well as the experience of the builder (ars); neither is sufficient alone.
Where it appears in the book
In the chapters Romanesque and Gothic.