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 Again, Eratosthenes wished to show the ignorance of Deimachus, and his want of information concerning such matters, as proved by his assertion that India lies between the autumnal equinox1 and winter tropic.2 Also in his blaming Megasthenes, where he says that in the southern parts of India the Greater and Lesser Bear are seen to set, and the shadows to fall both ways; assuring us that such is not the case in India.3 These assertions, says Eratosthenes, arise from the ignorance of Deimachus. For it is nothing else than ignorance to suppose that the autumnal equinox is not equally distant from the tropics with the vernal; since in both equinoxes the sun rises at the same point, and performs a similar revolution. Further, [he continues,] the distance from the terrestrial tropic to the equator, between which, according to Deimachus himself, India is situated, has been proved by measurement to be much less than 20,000 stadia, consequently his own statements prove that my assertion is correct, and not his. For supposing India to be twenty or thirty thousand stadia [in breadth] it could not be contained in the given space, but if my estimate be taken it is simple enough. It is another evidence of his want of information, to say that the two Bears are not seen to set, or the shadows to fall both ways, in any part of India, since 5000 stadia south of Alexandria4 both of these phenomena are observable. Thus reasons Eratosthenes; whom Hipparchus again criticises in the same mistaken way. First he substitutes [in the text of Deimachus] the summer in place of the winter tropic; then he says that the evidence of a man ignorant of astronomy ought not to be received in a mathematical question; as if Eratosthenes in the main had actually been guided by the authority of Deimachus. Could he not see that Eratosthenes had followed the general custom in regard to idle reasoners, one means of refuting whom is to show that their arguments, whatever they may be, go only to confirm our views.
1 The equinoctial line.
2 There is no doubt that the expressions which Deimachus appears to have used were correct. It seems that he wished to show that beyond the Indus the coasts of India, instead of running in a direction almost due east, as the Greeks imagined they did, sloped in a direction between the south and the north-east, which is correct enough. As Deimachus had resided at Palibothra, he had had an opportunity of obtaining more exact information relative to the form of India than that which was current at Alexandria. This seems the more certain, as Megasthenes, who had also lived at Palibothra, stated that by measuring India from the Caucasus to the southern extremity of the continent, you would obtain, not its length, as the Greeks imagined, but its breadth. These correct accounts were obstinately rejected by the speculative geographers of Alexandria, because they imagined a certain uninhabitable zone, into which India ought not to penetrate.
3 The truth of these facts depends on the locality where the observations are made. In the time of Alexander the most southern of the seven principal stars which compose the Greater Bear had a declination of about 61 degrees, so that for all latitudes above 29 degrees, the Wain never set. Consequently if Deimachus were speaking of the aspect of the heavens as seen from the northern provinces of India, the Punjaub for instance, there was truth in his assertion, that the two Bears were never seen to set there, nor the shadows to fall in contrary directions. On the other hand, as Megasthenes appears to be speaking of the south of India, that is, of the peninsula situated entirely south of the tropic, it is certain that he was right in saying that the shadows cast by the sun fell sometimes towards the north, at others towards the south, and that accordingly, as we proceeded towards the south, the Bears would be seen to set. The whole of Ursa Major at that time set at 29 degrees, and our present polar star at 13 degrees. β of the Lesser Bear was at that time the most northern of the seven principal stars of that constellation, and set at 8° 45′. So that both Bears entirely disappeared beneath the horizon of Cape Comorin.
4 This would be at Syene under the tropic.
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