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imagine that reasoners so acute as the Chaldasanastronomers failed to recognize how all the phasescould be explained by the varying amount of themoon’s illuminated hemisphere turned at differenttimes towards the earth.*
Quite early, then, the moon must have been recog-nized as an opaque globe illuminated by the sun. Itwould be understood that only one half of her surfacecan be in light. And apart from the fact that themoon was early recognized as causing solar eclipsesby coming between the earth and the sun, it wouldbe understood by the fineness of her sickle when nearthe sun’s place on the celestial vault, that she travelsin a path lying within the sun’s. That fine sickle oflight shows that at such times the illuminated halfis turned almost directly away from the earth ; andtherefore the illuminating sun must at such times lienot far from the prolongation of a line carried fromthe earth’s centre to the moon’s.
It is not improbable, indeed, that the acute Chal-dseans deduced similar inferences respecting themoon’s nature from a careful study of her face;for the features of the moon when horned or gibbous
* It is remarkable, however, that Aratus , writing about 230 b.c,,long after the time when the Chaldaeans established their system ofastronomy, refers to the lunar phases in a way which implieseither ignorance or forgetfulness of their real cause; for hespeaks of the significance of the position in which the horns of thenew moon are seen, regarding this position, though obviously anecessary consequence of the position of the sun and moon, as initself a weather portent.