This is a mechanical device that draws an ellipse. It is based on the
Trammel of Archimedes. The shuttles appear to be, but, they are not the
fixed points (the foci) described in the definition of an ellipse: the
locus of points for which the sum of the distances from each point to two
fixed points is equal. This a special device for drawing ellipses. The
relationship to the formula, (x2
) + (y2
) = 1, for an ellipse centered around (0,0) is not readily
apparent. The semi major axis and the semi minor axis are represented,
though. Do you see them?
Do you know how to draw an ellipse using a string and two pins? Do you
want to know? See Ellipse Foci for an animation of the method.
Do you know that a circle is a special ellipse where the foci are one
point? Think about it. The semi major and semi minor axes are the same
Edwin Attaway <edwin222@EdwinsAnimatedImages.com>