Join the extremities a and b (Fig. 191), and from f, the given projection of the moulding, draw/0 at right angles to the fillets; from b draw bh at right angles to a b; bisect a b in c; join f and c, and upon c, with the radius cf, describe the arc fh, cutting bh in h; through c draw de parallel with the fillets; make dc and ce each equal to bh; then de and a b will be conjugate diameters of the required ellipse. To describe the curve by intersection of lines, proceed as directed at Art.
551 and note; by a trammel, see Art. 549; and to find the foci, in order to describe it with a string, see Art. 548.