Letters

⁶ There is in this another mystery, and you are not to be distressed if perhaps it be not so readily perceived by you, because of your being less versed in such studies; nor are you to think me any better than you, because I learned these things in early years: for the Lord says, “Let him that glories glory in this, that he understands and knows Me, that I am the Lord.” Some men who give attention to such studies, have investigated many things concerning the numbers and motions of the heavenly bodies. And those who have done this most ably have found that the waxing and waning of the moon are due to the turning of its globe, and not to any such actual addition to or diminution of its substance as is supposed by the foolish Manichæans, who say that as a ship is filled, so the moon is filled with a fugitive portion of the Divine Being, which they, with impious heart and lips, do not hesitate to believe and to declare to have become mingled with the rulers of darkness, and contaminated with their pollution. And they account for the waxing of the moon by saying that it takes place when that lost portion of the Deity, being purified from contamination by great labours, escaping from the whole world, and from all foul abominations, is restored to the Deity, who mourns till it returns; that by this the moon is filled up till the middle of the month, and that in the latter half of the month this is poured back into the sun as into another ship. Amid these execrable blasphemies, they have never succeeded in devising any way of explaining why the moon in the beginning or end of its brightness shines with its light in the shape of a horn, or why it begins at the middle of the month to wane, and does not go on full until it pour back its increase into the sun.

7. Those, however, to whom I refer have inquired into these things with trustworthy calculations, so that they can not only state the reason of eclipses, both solar and lunar, but also predict their occurrence long before they take place, and are able to determine by mathematical computation the precise intervals at which these must happen, and to state the results in treatises, by reading and understanding which any others may foretell as well as they the coming of these eclipses, and find their prediction verified by the event. Such men,— and they deserve censure, as Holy Scripture teaches, because “though they had wisdom enough to measure the periods of this world, they did not much more easily come,” as by humble piety they might have done, “to the knowledge of its Lord,” — such men, I say, have inferred from the horns of the moon, which both in waxing and in waning are turned from the sun, either that the moon is illuminated by the sun, and that the farther it recedes from the sun the more fully does it lie exposed to its rays on the side which is visible from the earth; but that the more it approaches the sun, after the middle of the month, on the other half of its orbit, it becomes more fully illuminated on the upper part, and less and less open to receive the sun's rays on the side which is turned to the earth, and seems to us accordingly to decrease: or, that if the moon has light in itself, it has this light in the hemisphere on one side only, which side it gradually turns more to the earth as it recedes from the sun, until it is fully displayed, thereby exhibiting an apparent increase, not by the addition of what was deficient, but by disclosing what was already there; and that, in like manner, going towards the sun, the moon again gradually turns from our view that which had been disclosed, and so appears to decrease. Whichever of these two theories be correct, this at least is plain, and is easily discovered by any careful observer, that the moon does not to our eyes increase except when it is receding from the sun, nor decrease except when returning towards the sun.