Among the images of the sun that are retained within the eye, that one will appear the more luminous which has been the less retained by the eye.

... the whiter it is, the more it will be tinged with the colour of the illuminated or luminous object.

b c a; e o a — Pupil of the owl; Pupil of man. The pupil c is its size during the daytime, that is in the greatest brightness of day. a c is how it grows in the greater darkness of night; and so it goes changing from greater to lesser size according to the greater or lesser darkness of the night.

If the darkness of night is a hundred degrees darker than the evening, and the eye of man doubles its pupil in that darkness, that darkness is halved for that eye, because it has doubled by half its visual power. There remain to it, then, fifty degrees of darkness. And if the eye of the owl enlarges its pupil a hundred times in the aforesaid darkness, its visual power grows a hundredfold, which is a hundred degrees of visual power gained; and because things equal to one another do not surpass each other, the bird sees in the darkness with its pupil increased a hundredfold in size as [it sees] by day with its pupil diminished by 99/100. And if you should say that such an animal does not see light by day and therefore stays shut away, to this it is answered that the bird shuts itself away by day only to free itself from the flocking of the birds, which in great multitude always surround it with great clamour, and would often be killed if they did not hide themselves in the grottoes and caverns of the high rocks.

Pupil of the cat. Of the nocturnal animals only the leonine species enlarges and diminishes its pupil while varying it in shape, since, when it is at its utmost contraction it is of an elongated shape, when it is middling it is of an oval shape, and when it is at its utmost size it is of a circular shape.

a – d – e c – b; n a – S – o – t – r – m. It is to be doubted whether, when this pupil is of an elongated shape, round and spherical things appear elongated or round. It is proved that as great as are the distances of the spherical object, so many are the varieties into which the figure of that spherical body is transformed to the eye. It is true that after the convergence of the pyramidal rays they arrive from a r at o and pass across into n m, and the parts of the shadow of that spherical body are exchanged, because t, the lower part of that body, becomes the upper part at n, and S, the upper part of such body, becomes the lower part at m.

To make a fine green. Take the green and mix it with mummy and you will make the shadow darker. Then for the lighter part, green and ochre; and for lighter still, green and yellow; and for the highlights, plain yellow. Then take green and turmeric together and glaze over everything. To make a fine red. Take cinabrese mixed with burnt ochre for the dark shadows; and for the lighter parts, hematite and minium; and for the highlights, minium alone; then glaze with fine lake. To make good oil for painting. One part of oil, one of first turpentine and one of second. Monies I have had from ser Matteo. First 20 grossoni, then in 3 times 3 ducats, and then 6(?) grossoni and then 3, then 3, 3, 40 soldi, 12 grossoni.

20 . 8 . 6 . 9 — 6 12 20(?)