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 centre, but the least honourable member, of the Universe, the all-embracing circumference being the most noble, and the heavenly bodies having a dignity in inverse ratio to their approach towards the centre. The guesses, or intuitions, of the ancient Greeks in Aristotle's time, or soon afterwards, hit upon something very like an anticipation of the Copernican system. And this was especially the case with Aristarchus of Samos, who announced the double movement of the earth, round its own axis and round the sun. But Aristotle certainly contributed nothing towards the adoption of such ideas. He unfortunately committed himself, on fancied grounds of symmetry, to an opposite view.

Aristotle argued that if the earth were to move it could only do so "unnaturally," by the application of external force in contradiction to its own natural tendency to rest round the centre, and that no such forced movement could be kept up for ever, whereas the arrangements of the Cosmos must be for all eternity. Therefore the earth must be at rest! As to its shape, Aristotle was more correct: he proved it to be spherical—(1) by the consideration that all heavy bodies are by nature always tending to the centre, and that this process must result in the production of a spherical mass; (2) by the fact that the earth's shadow cast on the moon in an eclipse is circular. He considered the bulk of the earth to be small when compared with that of "the other stars;" he accepts the calculations of the geometers of his time that its circumference was 400,000 stades; and he says that "we must not treat with incredulity the opinion of those who say that