Greek. One authority to whom Plutarch twice refers by name requires special mention. This was Aristarchus of Samos, who belongs to the middle or later part of the third century B.C. He is the author of a work on ‘The Sizes and Distances of the Sun and Moon’ which is extant. It was well edited by Wallis for the Oxford Press in 1688, and more recently (1913) and in a modern form, by Sir Thomas Heath, F.R.S., who has prefixed an invaluable history of astronomy prior to Aristarchus. The book is rigorously mathematical, and contains six ‘hypotheses’, and eighteen propositions deduced from them. The second of the hypotheses, ‘That the earth is in the relation of a point and centre to the sphere in which the moon moves’, is quoted by Plutarch, apparently as being accepted by Hipparchus. The sixth, ‘That the moon subtends one-fifteenth part of a sign of the Zodiac (i. e. 2°)‘, raises a curious point which is fully considered by Sir T. Heath. That Aristarchus should at any time have thus exaggerated (multiplied by four) a measurement which seems open to some sort of simple observation, and have based good work upon it, seems very strange, firstly, because he must have considered the matter, (since he is aware that the same figure may stand for sun and moon); and, secondly, because Archimedes (287-212 B.C.), whose knowledge and good faith are beyond question, says that ‘Aristarchus discovered that the sun appeared to be about one seven hundred and twentieth part of the circle of the Zodiac (30´)‘, which is roughly correct.[302]