Storied windows; a traveller's introduction to the study of old church glass, from the twelfth century to the renaissance, especially in France (1914)
Bushnell, Arthur J. de Havilland · Edinburgh, W. Blackwood and sons · leaf 43
Tympanum pierced by a Cusped Circle lined with a Trefoil. … Transition from Geometrical to Flowing Tracery. Pointed Trefoils with no enclosing circles.
Glass painting and staining · Cathedrals
Internet Archive · Getty Research Institute · Public domain (published before 1931). Free to use for anything.