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the sun. To correct for these irregularities
                                         Copernicus introduced epicycle on epicycle
                                         in the lunar orbit.
                                            This is in its main features the system
                                         propounded by Copernicus. But attention
                                         must, to state the case fully, be drawn to
                                         two points to be found in his first and sixth
                                         books respectively. The first point relates
                                         to the seasons, and it shows a strange ig-
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