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The comparative size of the image depends on the amount of light.

The pupil of the eye, in the open air, changes in size with every degree of motion from the sun; and at every degree of its changes one and the same object seen by it will appear of a different size; although most frequently the relative scale of surrounding objects does not allow us to detect these variations in any single object we may look at.

Taken from The Notebooks of Leonardo da Vinci edited by Jean Paul Richter, 1880.

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Notebooks of Leonoardo da Vinci
I: Prolegomena and General Introduction to the Book on Painting.
. . .
The use of the book on Painting.
18
Necessity of theoretical knowledge.
19,
20
The function of the eye.
21,
22,
23,
24
Variability of the eye.
25
Differences of perception by one eye and by both eyes.
26,
27,
28,
29
The comparative size of the image depends on the amount of light.
30,
31,
32,
33,
34,
35,
36,
37,
38,
39