Figs. 1 and 2 show one method of setting out an elliptic Gothic arch. Referring to Fig. 1, bisect the span AP by the perpendicular line D C E, and make CD and CE each equal to the given rise of the arch. Draw AF and BG parallel to C D; and draw D Fand D G, making the angles CDF and CDG each-equal to half the given vertical angle. Take CII, equal to the difference between C D and A F, and join All. Divide A H and A F each into six or more equal i arts at the points 1, 2,3, 1, 5. Through these point-, on the line A II, draw the lines E J, E K.EL, etc.; and through those on the line AF draw the lines D J, P K, D L, etc., cutting the former in the points 3, K,L, etc.: a curve drawn through these points with a bender will give half of the Gothic arch required. Referring to Fig. 2, having constructed the arch, make AO equal to A F, and draw D I' perpendicular to D F. Make D Q equal to A 0, and join 0 Q; bisect OQ by a perpendicular line meeting D P in P, and produce PO to meet the curve in R. Divide the curve A R D into equal parts, corresponding to the number of arch stones or bricks; then O will be the centre for drawing the joints to the portion A R,, and P the centre for drawing the joints to the portion R D. Figs.:; and 4 show other methods of setting out an elliptic Gothic arch. A given rise is not required with these methods, and the arch may be filled from the centres. Referring to Fig. 3, set off on the span three equal parts, and describe a square on the centre division and with the corners of square as centres describe the curves as shown. Fill in from the striking centres. In Fig.4 the span C D is divided into four equal parts, and a square is described on the two centre ones, the corners of the square being taken as centres and the curves described from them, as before. The arch may be filled in from the centre as shown.

Fig. 2.

Setting out an Elliptic Gothic Arch.