Allow me to speak geometrically in terms of proportion. Here are three bodies approached by the sun’s light, earth, moon, air; we see that the moon is illuminated like the earth, not like the air; but bodies naturally affected in the same way by the same must be themselves similar.’ XIX. When all had applauded Lucius, ‘Bravo!’ said I, [Sidenote: D] ‘a beautiful proportion fitted to a beautiful theory; for you must not be defrauded of your own.’ ‘In that case,’ he said, with a smile, ‘I must employ proportion a second time, in order that we may prove the moon like the earth, not only as being affected in the same way by the same body, but also as producing the same effect on the same. Grant me that no one of the phenomena relating to the sun is so like another as an eclipse to a sunset, remembering that recent concurrence[337] of sun and moon, which, beginning just after noon, showed us [Sidenote: E] plainly many stars in all parts of the heavens, and produced a chill in the temperature like that of twilight. If you have forgotten it, Theon here will bring up Mimnermus and Cydias, and Archilochus, and Stesichorus and Pindar[338] besides, all bewailing at eclipse time “the brightest star stolen from the sky” [Sidenote: F] and “night with us at midday”, speaking of the ray of the sun as “a track of darkness” and, besides all these, Homer[339] saying that the faces of men are “bound in night and gloom” and “the sun is perished out of the heaven”, i.e. around the moon, and how this occurs according to Nature, “when one moon perishes and one is born”. The remaining points have been reduced, I think, by the accuracy of mathematical methods to the one[340] certain principle that night is the shadow of earth, whereas an eclipse of the sun is the shadow of the moon when it falls within our vision. When the sun sets he is blocked from our sight by the earth; when he is eclipsed, by the moon. [Sidenote: 932] In both cases there is overshadowing; in his setting it is caused by the earth, in his eclipses by the moon, her shadow intercepting our vision. From all this it is easy to draw out a theory as to what happens. If the effect is similar, the agents are similar; for the same effects upon the same body must be due to the same agents. If the darkness of eclipses is not so profound, and does not affect the atmosphere so forcibly, let us not be surprised; the bodies which cause respectively night and eclipse are similar in nature, but unequal in size. The Egyptians, I believe, say that the moon’s bulk is one two-and-seventieth part of the earth’s, Anaxagoras made her as large as Peloponnesus; but [Sidenote: B] Aristarchus[341] proves that the diameter of the earth bears to that of the moon a ratio which is less than sixty to nineteen, and greater than a hundred and eight to forty-three. Hence the earth because of its size removes the sun entirely from our sight, the obstruction is great and lasts all night;