The Geometry of the North Transept Plan
The distance ab, in feet, between the line of the glass and the exterior surface of the north wall is easily calculated:
ab = 43.5 (cos22.5 – cos 30)
= 43.5 (0.9239 – 0.8660)
= 43.5 x 0.0579
= 2.518 feet
If the glass stands at one third of the thickness of the wall this gives a wall thickness of 7.55 feet, which is in accord with the wall thickness as measured on Peers’ plan.
On the west transept wall the geometry of the glass, fg is seen to lie at about one fifth of the wall thickness, and again this is in close accord with the position provided in Britton, Detail 4, page 3, which, by Britton’s scale is at one foot within a wall six feet thick. It may be noted that although Britton’s smaller scale for the whole plan is inaccurate by about ten per cent, the larger scale for details appears to be accurate.