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The Bornholm Method
By Niels Lind
The Earth is positively curved in all directions. As you
travel north, the Pole Star moves steadily closer to Zenith.
And on clear days a ship that sails away can be seen
gradually to disappear below the horizon hull first,
followed by the sails. This has been known since antiquity,
or even before.
Celestial
bodies seem to move in perfect circles about an axis
pointing to the Pole Star, so it was quite reasonable to
conjecture that Heaven is spherical with Earth at the
center. However, a further conjecture was that Earth, being
positively curved in all directions, is also spherical
(approximately, neglecting mountains and valleys). Indeed,
it would reflect perfection and simplicity if Earth and
Heaven were concentric spheres.
The motions of the Sun, Moon and Planets presented an
anomaly; only by introducing a complicated system of
(perfectly circular) epicycles was it possible to extend the
apparent simplicity to include these objects. And, after
careful observations had revealed further apparent
imperfections in their motion, the hypothesis of the
Ptolemaic World Model became untenable. With this the idea
of perfection was lost, and with it also the notion that the
earth would have to be approximately spherical.
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