(2) That the moon derived her light from the sun was a discovery due to Anaxagoras (fifth century B.C.). (3) The true cause of eclipses was known to the Pythagoreans, and is stated by Aristotle, and, with more precision, by Posidonius. (4) The inclination of the equator to the sun’s path is stated by Oenopides of Chios (a little after Anaxagoras). (5) That the moon revolves round the earth at a moderate distance is stated by Empedocles. (6) The other planets (including the sun) revolve round the earth at a distance vastly less than that of the fixed stars. (No actual estimate of the distances or sizes is given even by Ptolemy, who is not able to state a parallax for any, or an angular diameter.) (7) That the planets share in the (apparent) daily motion of the stars, and also have an (apparent) motion of their own in the reverse direction was held by Pythagoras. All these refer to physical facts and can be stated without the use of mathematical language, though many of the discoverers were expert mathematicians. Gradually, and certainly from the time of the great astronomer Hipparchus (about 130 B.C.), attention came to be fixed upon the accurate mathematical interpretation of observed _apparent_ facts; in a favourite phrase, the object was ‘to save the phenomena’, irrespective of physical and actual fact. In the case of the moon, the two lines of inquiry are less sharply divided than in that of other bodies. Very correct statements as to her size and distance from the earth may be gathered from Plutarch’s Dialogue. A guess is even hazarded that she is lighter than the earth, bulk for bulk, because of the action of fire in the past.