Figure 4-43.-Conic sections: ellipse, parabola, and hyperbula (left to right).
Figure 4-44.-Ellipse by pin-and-string method.
ELLIPSE BY
C as a center, strike
PIN-AND-STRING METHOD
F and F´. The points
arcs intersecting AB at
F and F´ are called the
foci of the ellipse. Set a pin at point C,
The dimensions of an ellipse are given in terms
another at F, and a third at F´. Tie the
of the lengths of the major (longer) and minor
end of a piece of string to the pin at F, pass the
(shorter) axes. Figure 4-44 shows a method of con-
string around the pin at C, draw it taut, and fasten
structing an ellipse that is called the pin-and-string
it to the pin at F´. Remove the pin at C, place the
method. The problem is to construct an ellipse
pencil point in the bight of the string, and draw
with a major axis, AB, and a minor axis, CD. Set
the ellipse as shown in view C, keeping the string
a compass to one-half the length of AB, and, with
taut all the way around.
4-15
