DISTANCE, SIZE, AND MASS.

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obviously correspond with those presented by the fullmoon, in such sort that no one who considers thephenomenon attentively can doubt for a moment thatthe moon undergoes no real change when passingthrough her phases. It may also be imagined thatthe same astronomers who recognized the fact thatMercury is a planet, though he is never visible exceptin strong twilight, must have repeatedly observedthat the whole orb of the moon can be seen whenthe bright part is a mere sickle of light. Nay, it iseven possible that in the clear skies of ancient Chal-dica * the chief lunar features might be discerned whenthe dark half of the moon is thus seen.

The comparative nearness of the moon was pro-bably inferred very early from her rapid motion ofrevolution around the earth. Almost as soon asobservers noticed that the celestial bodies have dif-ferent apparent motions, they must have learned thatthe moon’s daily change of place among the stars ismuch greater than that of any other orb in theheavens. It would seem almost, from the distinctiondrawn in Job between the sun and the moon, that forsome time the moon was regarded as the only body

* It is not very easy to determine what was the true site of theregion spoken of in Judith (v. 6), as the land of the Chaldaeans.The verse here referred to shows clearly that the region was not inMesopotamia . From astronomical considerations I have been ledto suppose that the first Chaldtean observers occupied a regionextending from Mount Ararat northward as far as the Caucasianmnge. See Appendix A to “ Saturn and its System,” and theIntroduction to my Gnomonic Star-atlas.