Let ab and cd (Fig. 407) be given axes. With ce or ed for radius describe the quadrant fgh; divide fh, ae, and eb, each into a like number of equal parts, as at 1, 2, and 3; through these points draw ordinates parallel to cd and fg; take the distance I i and place it at 1 l, transfer 2j to 2 m, and 3 k to 3n; through the points a, n, m, l, and c, trace a curve, and the ellipsis will be completed.

550 To Describe An Ellipsis By Ordinates 584

Fig. 407.

The greater the number of divisions on a, e, etc., in this and the following problem, the more points in the curve can be found, and the more accurate the curve can be traced. If pins are placed in the points n, m, l, etc., and a thin slip of wood bent around by them, the curve can be made quite correct. This method is mostly used in tracing face-moulds for stair hand-railing.