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That the earth also has a curvature from the north to the south and vice-versa is shown in this way. For those living toward the north, certain stars are of perpetual appearance, namely those that are close to the arctic pole. Others, however, are of perpetual occultation, such as those that are close to the antarctic pole. If, therefore, someone were to travel from the north toward the south, they could travel so far that the stars which were previously of perpetual appearance to them would now begin to set. And the further they approached the south, the more they would move toward setting. Furthermore, that same person would be able to see stars which had previously been of perpetual occultation to them. The reverse would happen to someone traveling from the south toward the north. The cause of this thing is the curvature of the earth. Also, if the earth were flat from east to west, the stars would rise as quickly for those in the West as for those in the East, which is clearly false. Likewise, if the earth were flat from north to south and vice-versa, the stars which were of perpetual appearance to someone would always appear to them no matter where they traveled, which is also false. But the reason the earth appears flat to human sight is because of its immense size.