If you keep observed the small parts of the spots of the moon, you will often find great variety in them, and of this I have made proof myself by drawing them. And this arises from the clouds that rise from the waters of that moon, which interpose themselves between the sun and this water, and with their shadow take the sun's rays from that water, whence this water comes to remain dark for being unable to mirror the solar body.

These 2 proportionalities serve for the finding of the angle of incidence.

direct (straight) proportionality.

intersected proportionality. a b is in the same proportion with c d as is e f with f g, and likewise a f with f d, and so b f with f c, and so the whole triangle a b f with the triangle f c d, and the halves of such triangles each do the like to their corresponding one, as a e f with f c g. The triangle a e f is not in that proportion of its sides to sides as is c g f with its sides; and the triangles below the line e f g do the like. Therefore this is not called direct or inverse proportionality, but is conversed or intersected, because the proportion that the triangle a e f has with the triangle g d f, which are similar, is not the same that a e f has with c g f, but is similar to the proportion that e b f has with f c g. The surface of the sphere of the water does not move from the circuit of the center of the world which it clothes with equal distance, and would not move from that equality even if the earth, the support and vessel of this water, went entirely out of that center 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 the water is moved by a small droplet of water, and into it it descends.

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