De praecipius visus symptomatis eorumque causis Physica & Medica contemplatio

XLIIII.
Furthermore, as it is necessary for forming a figure to have many lines terminating a surface, so its autotypon self-image/copy in another will not be easily expressed without a doubled thesis position/arrangement, which occurs in optics by the repercussion of rays. The eye, however, does not perceive a point or a line in act, but a surface composed from them. Whence formerly color was defined as of a surface and an extremity, not indeed from its own essence, but from its proximate and therefore inseparable adjunct in the physical body. For every color is on the surface.

XLV.
Therefore, in vision, three things concur: first, the object body, tinctured with its colors and removed by a due interval from the sensorium; second, the transparent medium, acting in place of a vehicle; third, the healthy constitution of the eye in due symmetria symmetry/proportion of the humors, the tunics, and also the spirit for vision.

XLVI.
How the other common objects are also perceived in a certain respect with colors can be easily gathered from the preceding, as also those which are painted with various colors; and why they do not represent so many bodies, torn bit by bit, but coalesce into one schema.

XLVII.
Furthermore, the affinity of the optic spirit with the phasei chromaton appearance of colors declares the reason for perception. For just as these are contained by the most thin light and are submitted to the eyes in a certain hidden way, so that spirit, hos elampsis rhe eso photos as a shining of the light within, illuminates all things and, by a perennial reciprocation, communicates the received species to and fro to the innermost sense, itself being without law. Whence it is not diffused like the rest in the body through the hollow passages of the nerves, although Galen’s error conjectured something of this kind in the eyes, where the tenuity of spirits of all kinds least required it. It is more beautiful that he compares the same to a solar ray passing through the whole region of the air in a very brief moment; so, indeed, the animal aura is scattered from the brain, conferring sense and notification to the limbs.

XLVIII.
Thus far, in the manner of physicists, we have pursued the reason for seeing in general; it remains to transfer it from the present institution to medicine.