At this point, the earth’s surface is tilted, as it were, like a plate that receives light. It is important to note that the world is not tilted at this point because the shadow does not come out on either side of the well in Saigon. But in Alexandria, farther from the equator than in Ceylon, the shadow is moving north, and the earth is tilted north. So what’s happening as the world tilts? So the surface of the earth is definitely curved. For one thing, the stick may have been tilted, and the ground may have been tilted. But mathematicians are not so bad. He believed that the scales and water scales had existed since their time, so he believed that they were accurate.