De praecipius visus symptomatis eorumque causis Physica & Medica contemplatio

called it Aspect, whence comes horaton visible, visible, aspectable. Vision is properly the notation of the action itself.

V.
Many things, however, concur in this place, joined among themselves by a certain similarity, which fluent Greece, prodigal of names, has distinguished with appellations beyond the scarcity of the Latin language. Indeed, a phasis appearance, phasma apparition, phantasma phantom, is a certain vision or spectrum, as also an emphasis appearance/reflection, an apparition or species represented from elsewhere, to which Aristotle opposes the hypostasis substance/underlying reality. These sometimes designate the images of external things, sometimes they are accommodated to internal images, which the free mind, or the mind hindered by dreams original: "præpes", fashions and stirs, whence they are called both visas and visions, whether true and express, as those which appear "in waking" original: "καθ’ ὕπαρ", or feigned and erroneous, as those which are accustomed to appear "in sleep" original: "κατ’ ὄναρ". But leaving these aside, the discussion will be only about external [things], and that, with the definition having been premised.

VI.
Vision is the perception and discernment of visible things: or it is the function of the eyes, perceiving color as a proper object, but magnitude, figure, motion, rest, and position as common objects, through a medium that is actually transparent, prepared for the utility of life and for discerning the differences of things.

VII.
Although one and the same method of seeing exists everywhere in the reception of visible species, nevertheless a distinction can be constituted not unwisely by the diversity of "the things between" original: "τῶν μεταξὺ". For either colors shine through an interval of air or water: or they enter the view of the eyes through bodies that are solid but nonetheless transparent original: "διαφανῆ", such as glass, scraped horn, crystal, and similar things, which, polished by nature or art, are pellucid.

VIII.
With the same consideration, opticians have also distinguished vision into Direct and Oblique. Direct vision original: "ἀπ’ εὐθείας" perceives the form of the visible thing simply, through one transparent medium, and through one axis and perpendicular of the object and the sensory organ. Oblique [vision] receives the "appearances" original: "ἐμφάσεις" of things expressed and formed in different ways, and that in two ways, namely, by anaplasis refraction and diaklasis deflection/refraction.