De praecipius visus symptomatis eorumque causis Physica & Medica contemplatio

XXX.
Finally, the mode of vision is not one and the same among the philosophers. Plato thought that colors, plucked from bodies externally, were carried into the eye by an emissary visual spirit. Galen agreed with this, with a truly excellent effort of genius, to defend the authority of the greatest philosopher against the subtlety of the Peripatetics: though, as it appears, to the great injury of the truth.

XXXI.
For no spirit flying outside the limits of the body is still in the power of the soul, nor can it diffuse itself into immense spaces of places without being absorbed by the surrounding air, nor can it animate the air with new light and summon the already common viduum likely referring to the 'widowed' or detached air into a society of labor, so that it might represent the species of things to the sense as if it were a traducer. The absurdity of this invention drove physicians back into the opinion of the Peripatetics, although the prince of them, Aristotle, sometimes forgetting himself, left the controversy suspended in a kind of doubtful epoche suspension of judgment.

XXXII.
They, having rejected the aporrhoai emanations of colored corpuscles which Empedocles established as being intercepted in their course by the meeting middle spirit and carried straight to the eyes, define the form of vision relying on two hypotheses.

XXXIII.
The first is that a perennial sympathy exists between light and transparent media, by which the latter immediately drink up the flashing rays from a bright body and store them in their entire substance. For light does not float on the surface of the air, but coheres with the whole substance, mixed in from every side.

XXXIIII.
Colors claim the same right for themselves, as a certain offspring of light, or shadowed simulacra, which continuously dye the surrounding air with their familiar species and transmit them to the eye by that ruler. Nor, however, should this tincture be referred to a material impression, as if the intermediate air were thoroughly obscured by the color of the object, as if from the irradiation of red coral, a red air might emerge: for then many species of colors, and those contrary, could not be perceived at one and the same time, as one would destroy the other.

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