Now when our comrade, in his dissertation, was expounding the proposition of Anaxagoras, that “the sun places the brightness in the moon”, he was highly applauded. But I am not going to speak of things which I learned from you or with you, I will gladly pass on to the remaining points. It is then probable that the moon is illuminated not as glass or crystal by the sunlight shining in and through her, nor yet by way of accumulation of light and rays, as torches when they multiply their light. For then we should have full moon at the beginning of the month just as much as at the middle, if she does not conceal or block the sun, but allows him[332] to pass through [Sidenote: C] because of her rarity, or if he, by way of commixture, shines upon the light around her and helps to kindle it with his own. For it is not possible to allege any bending or swerving aside on her part at the time of her conjunction, as we can when she is at the half, or is gibbous or crescent. Being then “plumb opposite”, as Democritus puts it, to her illuminant, she receives and admits the sun, so that we should expect to see her shining herself and also allowing him to shine through her. Now she is very far from doing this; she is herself invisible at those times, and she often hides him out of our sight. _So from above for men_, as Empedocles says, [Sidenote: D] _She quenched his beams, shrouding a slice of earth Wide as the compass of the glancing moon_; as though his light had fallen, not upon another star, but upon night and darkness. ‘The view of Posidonius, that it is because of the depth of the moon’s body that the light of the sun is not passed through to us, is wrong on the face of it. For the air, which is unlimited, and has a depth many times that of the moon, is filled throughout with sunlight and brightness. There is left then that of Empedocles, that the illumination which we get from the moon [Sidenote: E] arises in some way from the reflexion of the sun as he falls upon her. Hence her light reaches us without heat or lustre, whereas we should expect both if there were a kindling by him or a commixture of lights. But as voices return an echo weaker than the original sound, and missiles which glance off strike with weaker impact, _E’en so the ray which smote the moon’s white orb_ reaches us in a feeble and exhausted stream, because the force is dispersed in the reflexion.’ XVII. Here Sylla broke in: ‘All these things no doubt [Sidenote: F] have their probabilities; but the strongest point on the other side was either explained away or it escaped our comrade’s attention; which was it?’ ‘What do you mean?’ said Lucius. ‘The problem of the half-moon, I suppose?’