On the eye of man.

The small size of the pupil is the cause of making the image of the sun appear a tiny thing on the surface of the water.

The image of the sun is single across the whole sphere of the water that sees and is seen by that sun, but it appears divided into as many parts as there are eyes of animals that from different positions look at the surface of the water. What is here proposed is proved thus: however much the eyes of sailors, carried by ships across the world, move about, at one and the same moment they see the image of the sun in all the waters of their hemisphere, through every motion made and from every aspect.

If the eye were as large as the sphere of the water, then, when it was seen by the sun, it would all be a single image of that sun.

If the eye were as large as the sphere of the water, it would see the image of the sun occupy a great part of the Ocean. This is shown thus: if you move along a bridge from which you see the image of the sun in the waters of its river, and you move about 25 braccia or so, you will see the sun's image move across the surface of that water; and so, if one put together all the images seen during that motion, you would have made a single image having the form of a fiery beam. Now imagine making a circle of which that beam is the diameter, and that the whole circle is filled with such images: without doubt you would see a single image whose diameter would be 25 braccia. Now understand that if a pupil had its diameter of the same 25 braccia, then without moving it would see in the same water an image of the sun spanning 78 braccia and 4/7.

How, if the sphere of the water were diminished by great distance to the appearance of a star, the image of the sun would occupy the whole of it.

If, through the great distance of the eye from the sphere of the water, the sphere of the water were diminished to the size of an ordinary image of the sun, as is shown in perspective, you would see the sphere of that water which is seen by the sun to be a single image of that sun.

How the stars, many times larger than the earth, are made to appear tiny by distance.

This is proved by perspective, showing how things remote from the eye, even though they be very great, are shown of the smallest figure. And this without too many demonstrations: if you raise your eyes to the starry sky, you will see in it many stars very many times larger than the earth, yet through the great distance appearing tiny; and the light you see in them is not their own power, but a single image of the sun mirrored in them, because of themselves those stars have no light, but they do have a surface, like the sphere of the water, fit to receive and return the light of the sun that is mirrored in them.