Description
"Join A and D. Lay off DF equal to AC-DC. Bisect AF by a perpendicular crossing AC at G and intersecting DE produced at H. Make CG' equal to CG and CH' equal to CH. Then G, G', H, and H' will be centers for four arcs approximating the ellipse. The half of this ellipse when used in masonry construction is known as the three-centered arch." —French, 1911
