ON THE WONDERS OF THE WORLD,

Ninth, on the influences of the heavens.

¶ On the errors of sight. Chapter I.

For the first point, it is notable that vision does not occur merely through the reception of a likeness original: "speciei" in the eye, unless the internal faculty concurs. Thus, it happens that you do not see with open eyes if the internal faculty is occupied elsewhere and does not pay attention. This is common to all senses: that without the internal faculty attending, the likeness received in the organ does not cause sensation. Second, note that sight does not perceive a single bodily form in isolation; for it perceives no color without magnitude, nor magnitude without shape, nor shape without position, for it is impossible for these to be separated from one another by nature. Third, note that deception is caused by an undue proportion of visible forms to the sight. Besides the object, the medium, and the conversion of the power, there are eight things required for sight: light, distance, position, magnitude, solidity, transparency original: "diaphanitas", competent time, and a healthy disposition of the sight. For because of the diversity of these, different vision is caused. Therefore, due to an error regarding sight, and due to an undue proportion regarding it, wonders appear. For through experience, one thing is seen as two because of the placement of a finger upon or near the corner of the eye; and because of the motion of the eye with the finger, the object appears to move, although it is still. Furthermore,