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vival by Copernicus of the notion of a mov-
ing earth was a help to Kepler. No one
who reads Kepler’s great book could hold
such an opinion for a moment. In fact, the
excellence of Copernicus’s book helped to
prolong the life of the epicyclical theories
in opposition to Kepler’s teaching.
All of the best theories were compared
by him with observation. These were the
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