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tion). By this third motion the earth, he
held, made a revolution on itself and on the
poles of the ecliptic once a year ... Coperni-
cus did not know that motion in a straight
line is the natural motion, and that motion
in a curve is the resultant of several move-
ments. He believed, with Aristotle, that cir-
cular motion was the natural one.
Copernicus made this rotation of the earth’s
138
