Ellipse Device
Ellipse Device
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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 / a2) + (y2 / b2) = 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 length.