Vision, mirrors and the anatomy of the eye
'O mathematicians...'; the flea and the man; sections of the eye and a glass eye
The verso pursues vision and the science of images. It opens with the celebrated appeal, 'O mathematicians, shed light on this error,' arguing that the spirit has no voice and that a body fills the surrounding air with its images (species). Leonardo asks why a flea and a man entering the eye at equal angles are still judged at their true sizes, notes that mirrors reverse right and left, and distinguishes two natures of reflected and projected images. Lettered sections of the eye then debate whether the image lies in the uvea or the crystalline sphere and propose making a large glass model eye 'as in nature.'
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'O mathematicians, shed light on this error'
The appeal to mathematicians argues that the spirit has no voice, for voice requires a body, and a body occupies space and blocks the eye's view of what lies behind it. Therefore such a body fills all the surrounding air with itself, that is, with its images (species).
Why a flea and a man are judged at true size
A flea and a man may come to the eye and enter it at equal angles, yet the judgment is not deceived into making the man seem no larger than the flea. Leonardo poses the puzzle and asks for its cause.
Mirrors reverse right and left; two kinds of image
On a mirror's surface the image of the real thing exchanges right for left and left for right. Images are of two natures: the first, reflected from flat mirrors along parallel lines, keeps the true likeness; the second, entering a dark room through a small hole, keeps the same likeness but with confused edges.
Sections of the eye and a glass model eye
Lettered sections of the eye ask whether the image (idol) lies in the concavity of the uvea or in the crystalline sphere, concluding it is not in the uvea. Leonardo proposes making such an eye large and of glass, as in the natural one, and notes that a sees the surface of its sphere n S t tinged with the darkness of the uvea.