““it is clear that in the study of beings this aim can be fulfilled by us perfectly only through successive examinations of them by one man after another,41 the later ones seeking the help of the earlier in that task, on the model of what has happened in the mathematical sciences. For if we suppose that the art of geometry did not exist in this age of ours, and likewise the art of astronomy, and a single person wanted to ascertain by himself the sizes of the 15 heavenly bodies, their shapes, and their distances from each other, that would not be possible for him—e.g. to know the proportion of the sun to the earth or other facts about the sizes of the stars—even though he were the most intelligent of men by nature, unless by a revelation or something resembling revelation.42 Indeed if he were told that the sun is about 150 or 160 times43 as great as the earth, he would think this statement madness on the part of the speaker, although this is a fact which has been demonstrated in 20 astronomy so surely that no one who has mastered that science doubts it.””
