. An encyclopaedia of architecture, historical, theoretical, & practical. New ed., rev., portions rewritten, and with additions by Wyatt Papworth. CBAr. III. DOORWAYS. ;)j7 where it crosses tlie line A D, as at F, will be the centre of the required circle or circle witii the radius A F being drawn, the other centres on the lines of division, asA G, A H, &c., are readily found. Another usual geometrical problem in tracery work consists in finding the centre of acircle placed in the head of anarch. This has been eluci-dated by E. \V. Tarn, in the Builder for 1863, p. A B C in fg.
. An encyclopaedia of architecture, historical, theoretical, & practical. New ed., rev., portions rewritten, and with additions by Wyatt Papworth. CBAr. III. DOORWAYS. ;)j7 where it crosses tlie line A D, as at F, will be the centre of the required circle or circle witii the radius A F being drawn, the other centres on the lines of division, asA G, A H, &c., are readily found. Another usual geometrical problem in tracery work consists in finding the centre of acircle placed in the head of anarch. This has been eluci-dated by E. \V. Tarn, in the Builder for 1863, p. A B C in fg. 1202. be an equilateral arch, and thewidth A B be divided into three equal portions A D £ the arches D F and E G be drawn with the sameradius as those of A and B, as D H. Then it is re-quired to find the centre of the circle which shall touchthe four arcs. Make E I equal to ^ih of E B, and with *the centre A and radius A I draw an arc cutting theperpendicular or centre line of the window in K; then K is the required centre, and K Lthe radius of the circle.
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