Then said Lucius: These are the principal points, and the summary of what is said. But in the first place, if you please, take the argument drawn from the form and figure of the shadow. For this is a cone, as it must be when a great fire or light that is spherical encompasses a mass that is also globular but less; whence it comes that, in the eclipses of the moon, the circumscriptions of the black and dark from the clear and luminous have their sections always round. For the sections given or received by one round body applied to another, which way soever they go, do by reason of the similitude always keep a circular form. Now as for the second argument, I suppose you understand that the first part which is eclipsed in the moon is always that which looks towards the east, and in the sun that which regards the west. Now the shadow of the earth moves from the east to the west, but the sun and moon from the west eastward. The experience of the appearances gives us a visible knowledge of this, nor is there need of many words to make us fully understand it; and from these suppositions the cause of the eclipse is confirmed. For, inasmuch as the sun is eclipsed by being overtaken, and the moon by meeting that which makes the eclipse, it probably or rather necessarily follows that the one is surprised behind, and the other before. For the obstruction begins on that side whence that which causes it first approaches. Now the moon comes upon the sun from the west, as striving in course with him and hastening after him; but the shadow of the earth comes from the east, as that which has a contrary motion.