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 Posidonius informs us that Parmenides was the first to make this division of the earth into five zones, but that he almost doubled the size of the torrid zone, which is situated between the tropics, by bringing it beyond these into the temperate zones.1 But according to Aristotle the torrid zone is contained between the tropics, the temperate zones occupying the whole space between the tropics and the arctic circles.2 Both of these divisions Posidonius justly condemns, for the torrid zone is properly the space rendered uninhabitable by the heat. Whereas more than half of the space between the tropics is inhabited, as we may judge by the Ethiopians who dwell above Egypt. The equator divides the whole of this space into two equal parts. Now from Syene, which is the limit of the summer tropic, to Meroe, there are 5000 stadia, and thence to the parallel of the Cinnamon region, where the torrid zone commences, 3000 stadia. The whole of this distance has been measured, and it may be gone over either by sea or land; the remaining portion to the equator is, if we adopt the measure of the earth supplied by Eratosthenes, 8800 stadia. Therefore, as 16,800 is to 8800, so is the space comprised between the tropics to the breadth of the torrid zone. If of the more recent measurements we prefer those which diminish the size of the earth, such as that adopted by Posidonius, which is about 180,000 stadia,3 the torrid zone will still only occupy half, or rather more than half, of the space comprised between the tropics; but never an equal space. [Respecting the system of Aristotle, Posidonius farther says,] ‘Since it is not every latitude which has Arctic Circles,4 and even those which do possess them have not the same, how can any one determine by them the bounds of the temperate zones, which are immutable?’ Nothing however is proved [against Aristotle] from the fact that there are not Arctic Circles for every latitude, since they exist for all the inhabitants of the temperate zone, on whose account alone the zone receives its name of temperate. But the objection that the Arctic Circles do not remain the same for every latitude, but shift their places, is excellent.5
1 According to Plutarch, both Thales and Pythagoras had divided the earth into five zones. Since Parmenides lived one hundred and fifty years after the first of these philosophers, he cannot be considered the author of this division. As Posidonius and Strabo estimated the breadth of the torrid zone at 8800 stadia, and Parmenides is said to have nearly doubled it, this would give 17,600 stadia, or 25° 8′ 34″, taking this at 25° it would appear that Parmenides extended the torrid zone one degree beyond the tropics.
2 The Arctic Circles of the ancients were not the same as ours, but varied for every latitude. Aristotle limited the temperate zone to those countries which had the constellation of the crown in their Arctic Circle, the brilliant star of that constellation in his time had a northern declination of about 36° 30′, consequently he did not reckon that the temperate zone reached farther north or south than 53° and a half. We shall see that Strabo adopted much the same opinion, fixing the northern bounds of the habitable earth at 54° 25′ 42″. Gosselin.
3 For the circumference.
4 Viz. none for those who dwell under the equator, or at the poles.
5 Strabo's argument seems to be this. It matters but little that there may not be Arctic Circles for every latitude, since for the inhabitants of the temperate zone they do certainly exist, and these are the only people of whom we have any knowledge. But at the same time the objection is unanswerable, that as these circles differ in respect to various countries, it is quite impossible that they can fix uniformly the limits of the temperate zone.
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