Treasury of Optics

OPTICAE LIBER I.

of its surface, and does not comprehend that point of the viewed object from the remainder of the form arriving at its surface from the remainder of the surface of the eye, then vision will be completed, and the parts of the viewed object will be ordered, and the things themselves will be distinguished by the eye. And vision will not be completed except according to this mode. And this cannot be so unless one of the points that are on the surface of the eye, through which the form of one point of the surface of the viewed object passes, is distinct from the remaining points that are on the surface of the eye, and there is a line upon which the form comes to that point of the surface of the eye, distinct from the remaining lines upon which the form comes. And because of this, the glaciale can comprehend the form coming along that line, and from the point of the surface of the eye that is upon that line, and it cannot comprehend it through another.

17. Perpendicular light penetrates through any different media; oblique light is refracted. 42. 43. 44. 45. 47 p 2.

A decorative initial "E" marks the beginning of this paragraph.And when lights are introduced and the quality of their passage and their extension in transparent bodies is tested, it is found that light extends through a transparent body according to straight lines, provided the transparent body is of similar transparency. And when it encounters another body of different transparency from the transparency of the preceding body in which it was extending, it will not pass through according to the straightness of the lines upon which it was extending before, except when those lines are perpendicular to the surface of the second transparent body. And if those lines are oblique to the surface of the second body, and not perpendicular, the light will be bent at the surface of the second body and will not extend straightly. And when it is bent, it will extend in the second body according to those straight lines upon which it was bent. And the lines upon which the light was bent in the second body will also be declining toward the surface of the second body, and not perpendicular. And if there are some lines upon which light comes in the first body that are perpendicular to the surface of the second body, and some that are declining, the light that was on the perpendicular lines will extend in the second body according to straightness, and that which was on the declining lines will be bent at the surface of the second body according to the declining lines, and it will extend in it according to the straightness of those declining lines upon which it was bent. And this we will declare in the discussion on refraction, and we will show the way through which one can test this arrangement; and it will appear to the sense, and certainty will fall upon it.

18. Distinct vision is made by straight lines perpendicular from the visible object to the surface of the eye. Thus, individual points of the visible object obtain the same position on the surface of the eye as they have in the visible object. 17 p 3.

A decorative initial "E" marks the beginning of this paragraph.And since this is so, then regarding the form of light and color that comes from any point of the viewed object to the surface of the eye, when it arrives at the surface of the eye, nothing will pass through the transparency of the tunics of the eye according to right angles, and that which is upon another will be refracted and will not pass through straightly; for the transparency of the tunics of the eye is not like the transparency of the air touching the surface of the eye. And that which is refracted from these forms will also be refracted along declining lines, not along the perpendicular lines extended from the place of refraction. And one single straight line goes to a point of the surface of the eye from one point of the surface of the viewed object, such that it is perpendicular to the surface of the eye [per 13 p 11], and infinite lines declining toward the surface of the eye go out to it. And the form coming according to the straightness of the perpendicular passes through the tunics of the eye according to the straightness of the perpendicular. And all forms coming along declining lines to that point are refracted at that point, and pass through the tunics of the eye along declining lines. And nothing of them passes according to the extension of the lines upon which they came, nor even according to the straightness of the lines standing perpendicularly upon that point. And to every point of the surface of the eye come, at the same time, the forms of all the points that are on the surfaces of all the visible and illuminated objects opposite to it at that time; for between it and every point opposite to it is a straight line. And from every one of the points that are on the surfaces of the illuminated visible objects, forms extend along every straight line that can be extended from that point. And the form of only one point, out of the number of all the points opposite the eye, that comes to that point of the surface of the eye at that time, comes along the perpendicular raised upon that point of the surface of the eye. And the forms of all the remaining points come to that point of the surface of the eye along declining lines. And in every point of the surface of the eye there pass, at the same time, the forms of all the points that are on the surfaces of all the visible objects opposite at that time. And the form of only one point passes straightly through the transparency of the tunics of the eye, and it is the point that is at the extremity of the perpendicular going out from that point of the surface of the eye. And the forms of all the remaining points are refracted at that point of the surface of the eye and pass through the transparency of the tunics of the eye along lines declining toward the surface of the eye. And from every point of the surface of the glaciale crystalline humor there goes out one line only, perpendicular to the surface of the eye; and from the same there go out infinite lines to the surface of the eye, and they are declining toward it. Therefore, from the point of the surface of the glaciale from which the perpendicular to the surface of the eye goes out, and which passes through the hole of the uvea, there go out infinite lines that pass into the hole of the uvea and arrive at the surface of the eye, besides that perpendicular. And the extremities of all the lines going out from any point of the surface of the glaciale and passing through the hole of the uvea and arriving at the surface of the eye, and declining toward it, when they are...