If you keep the little particles of the moon's spots under observation, you will often find great variety in them, and I myself have proved this by drawing them. And this arises from the clouds that rise from the waters of that moon, which interpose themselves between the sun and that water, and with their shadow take the sun's rays away from that water, whereby the water is left dark because it cannot mirror the solar body.

These two proportionalities serve for finding the angle of incidence.

straight proportionality.

intersected proportionality. a b is in the same proportion to c d as e f is to f g, and likewise a f to f d, and so b f to f c, and so the whole triangle a b f to the triangle f c d; and the halves of these triangles each do the like with their counterpart, as a e f with f c g. The triangle a e f is not in that proportion of its sides to the sides that c g f is with its own; and the triangles below the line e f g do the like. Therefore this is not called straight or inverse proportionality, but converse or intersected, because the proportion the triangle a e f has to the triangle g d f, which are similar, is not the same as it has to c g f, but is similar to the proportion that e b f has to f c g. The surface of the sphere of water does not move from the circuit of the centre of the world, which it clothes at an equal distance, and it would not move from that equality even if the earth, the support and vessel of that water, were to pass wholly out of that centre of the world. The earth is moved from its place by the weight of a small bird that alights upon it. The surface of the sphere of water is moved by a little drop of water that descends into it.

That sector of a circle will have the less curvature which contains the smaller quantity of the circumferential line of its circle.