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That it has the form of a perfect globe we learn from the name which has been uniformly given to it, as well as from numerous natural arguments. For not only does a figure of this kind return everywhere into itself2 and sustain itself, also including itself, requiring no adjustments, not sensible of either end or beginning in any of its parts, and is best fitted for that motion, with which, as will appear hereafter, it is continually turning round; but still more, because we perceive it, by the evidence of the sight, to be, in every part, convex and central, which could not be the case were it of any other figure.

1 I may remark, that the astronomy of our author is, for the most part, derived from Aristotle; the few points in which they differ will be stated in the appropriate places.

2 This doctrine was maintained by Plato in his Timæus, p. 310, and adopted by Aristotle, De Cœlo, lib. ii. cap. 14, and by Cicero, De Nat. Deor. ii 47. The spherical form of the world, οὐρανὸς, and its circular motion are insisted upon by Ptolemy, in the commencement of his astronomical treatise μεγάλη σύνταξις, Magna Constructio, frequently referred to by its Arabic title Almagestum, cap. 2. He is supposed to have made his observations at Alexandria, between the years 125 and 140 A.D. His great astronomical work was translated into Arabic in the year 827; the original Greek text was first printed in 1538 by Grynæus, with a commentary by Theon. George of Trebisond published a Latin version of it in 1541, and a second was published by Camerarius in 1551, along with Ptolemy's other works. John Muller, usually called Regiomontanus, and Purback published an abridgement of the Almagest in 1541. For an account of Ptolemy I may refer to the article in the Biog. Univ. xxxv. 263 et seq., by Delambre, also to Hutton's Math. Diet., in loco, and to the high character of him by Whewell, Hist. of the Inductive Sciences, p. 214.

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