This section is from the book "The Tinman's Manual And Builder's And Mechanic's Handbook", by Isaac Ridler Butt. Also available from Amazon: The Tinman's Manual And Builder's And Mechanic's Handbook.

[Simple Method.]

Fig. 3.

At a given distance, equal to the required eccentricity of the ellipse, place two pins, A and B, and pass a string, ACB, round them; keep the string stretched by a pencil or tracer, C, and move the pencil along, keeping the string all the while equally tense, then will the ellipse CGLFH be described. A and B are the foci of the ellipse, D the centre, DA or DB the eccentricity, EF the principal axis or longer diameter, G H the shorter diameter, and if from any point L in the curve a line be drawn perpendicular to the axis, then will LK be an ordinate to the axis corresponding to the point L, and the parts of the axis EK, KF into which LK divides it are said to be the abscissae corresponding to that ordinate.

NOTE. - Oval. A curve line, the two diameters of which are of unequal length, and is allied in form to the ellipse. An ellipse is that figure which is produced by cutting a cone or cylinder in a direction oblique to its axis, and passing through its sides. An oval may be formed by joining different segments of circles, so that their meeting shall not be perceived, but form a continuous curve line. All ellipses are ovals, but all ovals are not ellipses; for the rerm oval may be applied to all egg-shaped figures, those which are broader at one end than the other, as well as those whose ends are equally curved.

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