Alhacen's Theory of Visual Perception (First Three Books of by A. Mark Smith

By A. Mark Smith

Someday among 1028 and 1038, Ibn al-Haytham accomplished his enormous optical synthesis, Kitab al-Manazir ("Book of Optics"). through no later than 1200, and maybe a little prior, this treatise seemed in Latin less than the identify De aspectibus. In that shape it used to be attributed to a undeniable "Alhacen." those alterations in name and authorial designation are indicative of the profound transformations among the 2 types, Arabic and Latin, of the treatise. in lots of methods, in reality, they are often appeared now not easily as varied types of a similar paintings, yet as assorted works of their personal correct. for this reason, the Arab writer, Ibn al-Haytham, and his Latin incarnation, Alhacen, signify particular, occasionally even conflicting, interpretive voices. And a similar holds for his or her respective texts. To complicate concerns, "Alhacen" doesn't characterize a unmarried interpretive voice. there have been no less than translators at paintings at the Latin textual content, certainly one of them adhering faithfully to the Arabic unique, the opposite content material with distilling, even paraphrasing, the Arabic unique. as a result, the Latin textual content offers no longer one, yet at the least faces to the reader. quantity This two-volume serious version represents fourteen years of labor on Dr. Smith's half. provided the 2001 J. F. Lewis Award. quantity Two--English Translation

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Additional info for Alhacen's Theory of Visual Perception (First Three Books of Alhacen's De Aspectibus), Volume Two - English Translation (Transactions of the American Philosophical Society)

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38] Furthermore,the form of any point facing the eye reaches the entiresurfaceof the eye; hence it will be refractedat the entiresurfaceof the eye. 74But,afterbeing refracted,no refracted form meets the normal at whose endpoint it was refracted,nor does it pass through it, nor does it pass out of the plane within which it was refracted. And all of these points become clear with experimentation. Therefore, [when] the form of a single point on a visible objectreachesthe surface of the glacialis through refraction,[it] will not reach it at a single point but, rather,at an area on the surface of the glacialis that has some dimension.

However, the sensation of differentcolors and of the TRANSLATION:BOOKONE 379 arrangementof the parts of a visible objectis not of the natureof pain. 103 Therefore,the sensation that reachesthe common nerve includes the sensation of light and color and of the arrangement[of parts],and it is by means of some form that the final sensor perceives light and color. 83]Wearenow left to addressthe following issue: Whenthe formsof light and color extend through air as well as through [other]transparent bodies to reach the eye, since air and [other]transparentbodies accept all colors, and since the forms of any light that are present at the same time extend through the same air at the same time and pass through the transparency of the tunics of the eye when they reach a single eye, then these colors and light ought to mingle in the air and in the [other] transparent bodies and arriveat the eye completely mixed, and so the colors of visible objectswill not be [individually]discernedby sight.

77Also, celestial bodies move along circularlines ratherthan along straightlines or lines of other kinds. And when we examine natural motions, we will find that each of them takes place accordingto specific lines. So it is not impossible for sight to be constituted in such a way as to suffer the effects of light and color along a specific set of straight lines that alone intersect at its center and are perpendicularto its surface. 78These lines are called "radiallines"by them. 44]Since this is possible, and since forms of light and color reachthe eye and pass through the transparencyof the tunics of the eye, and since vision is achieved upon the reception of these forms only when the eye receives them along perpendicularlines, sight perceives the light and colors of the surfacesof visible objectsonly throughforms reachingit from the surfaces of visible objects.

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