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of a cone. It is an oval curve, which may
be drawn by fixing two pins in a sheet of
paper at S and H, fastening a string, SPH,
to the two pins, and stretching it with a
pencil point at P, and moving the pencil
point, while the string is kept taut, to trace
the oval ellipse, APB. S and H are the foci .
Kepler found the sun to be in one focus, say
S. AB is the major axis . DE is the minor
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