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Show i 0 3:90 Of Seeing. BaéifiiT, ilixt-ttly oppolite to the Pupil of the Eye) may fall upon it in a right line, is lnth {Ray is called Orthogonor 5 and being direétly oppofed at the Cornea to the Axis of the Eye, containeth the Third part, or almoit half ofa right Ani- Qlc; lo that the Optick Cone, by which the Obyeél is clearly dilcerned, is a iight Angle, having its Vertex at the center of the (omen; and the-fidescm, taining the Angle in a conick Surface, have their Bafe 1n‘the ambient parts ofthe vilible Objeét ', And by reafon adiltmét fight of its whole Bafemav be made at one glance without the motion of the Eye; it follOWS that all rising-,1:- points of the Bale do emit perpendicular Rays into the Comm, and have iii'iiksnctl'ilic y the fame power which the Axis of the Eye obtaineth; lo that the Rays do V' reprcfent every point of the vifible Obyeét; wherefore ifthe Convex Surface of the Comm be the feat of Vifion, that part of the thing feen,Whieh maketh a right Angle in the center of the Cornea, innit be dil'tinc‘tly difcerned, which oppofeth the received Principles of Experience, approved by Learned M1. thematicians well verfed in Opticks. Having demonllrated how Vilion cannot be ultimately celebrated, as fal. ling in right Lines upon the Cornea, as it is a more denfe Medium then the Air, and thereby giving a refiltance to the vilible Ray, caufeth it to make an Angle of Incidence as well as Refraétion, which are the lubJeéts of my prefent Difcourfe. MR5, my, A Ray making a right progrefs from the Bafe of the vifible Objeét, is Threefuld 3 Firi‘t Direct, when the Ray is carried into a tranfparent limilar IQ J),rfflm Medium, without any infleflion: And Secondly, Reflexe, when the Ray . . . . falleth upon an opaee Body (not havrng Pores receptive ofLight) isreverberated toward the Rays, coming from the feveral points of the thing item. A n-mmd And Lafily, a refracted Ray is carried from one tranfparent Medium ofadimy vers Confillence, .13 having different degrees of Rarity or Denfityg where. upon the lucid Ray being tranlinitted in a right line in the fame fimilar Medium, maketh an Angle in the next Heterogeneous Body, at the point of Incidence, which is called the point of Refraétion, as in it the Ray of Incidence hilt tecetleth from its liraight progrefs, and beginneth its Refradion, as forced to take an angularcourlh FA cry Ray that liiffers a]1efra&ion,in making an Angle, either cometh neater the perpendicular, or recedeth more from it. By the perpendicular is meant a_line erected at the furface ofa diaphanous refringing Medium at the point or Incidence, and different from the perpendicular (called Cat/99W A Mai-Ci Imidmm) which is all'o named Orthogozm, as a lucid Ray runneth in a firaighl :;,',f'c‘f{§"‘l',‘; "Wm conrfe, without the lealt inflection from one Medium to another. But the other perpendicular being called that of Refrafiion , pallflh through the fole point of Incidence : and the Surface making Refraétioni" feared in the beginning, or uppn part of the Surface, relating to theHeterogeneous tranlparent Medium 'lruiiSjisoirct or , The point of Incidence is defigned by the utmofi term of the incident line, falling upon the rCll'il‘zgt‘iit Surface of a diaphanous Medium, «vi-xi. The common point of the inWard Surface, or termination of the former Medium; and the upper part, or Origen of the fubfequent diaphanous Bodym "film" Wherefore when the lower Medium is endued with a DenfitY Elmfiféhh. then the upper, this kind of Refraéiion is made toward thegreater perpendicular, Plug-mm," as the Angle of Infie&ion,approaclieth the Axis of the Eye 5 {0 that the my ,rgmlmfmm falling from the former Medium, is called Incident, as it relateth t0 the my, fubfequent Medium, and as it belongeth to the former, is named Refraéted; whence it happens, ifthere be many Lairs of tranfparent Mediums (throgigh w ic Book III. 0f Steiner. 899 which fome new vilible point doth pals; all the intermedial Rays may be fiyled Incident 3 and refrafted under a different refpeé‘t to feveral tranlparem Mediums ; and the lafi Ray is only refraéted. Andthe Firfi lucid Line may have the appellative of Incident, and [he hit Refraéted; and the interhtedial line is named Incident, in reference to the fubfequent Medium, and refraéted in relation to the former. Divers points have feveral Appellatives, and proper Ollices; A Lucid point may truly alliime the Title of Incidence and Refraction : But as it endetli in the furface ofthe lal't Medium, it cannot be called either the point of Incidence or Refraaion, but of termination, and as a lucid point is trajeéted through the firfl Plane ofthe following Medium, it obtaineth the name of Incidence only; but the line paliing down from the refringing furface of the former, through all the fubfequent Mediums in altraight progtefs, is called the perpendicular. And becaufe one rightIncident upon another right Line, maketh either two right, or two oblique Angles; and the line of In~ cidence with the perpendicular, doth make two unequal Angles, ofwhicli the lal't is called that of Incidence, as the Angle coming from the incident Ray: And the lcalt Angle derived from the refracted Ray, hath the Anule ofrefraéted. \ D Every Ray {lreaming from the object to the Eye, and being trajeéled through the Comm, and not {topped in its progrefs by the liq/ca, doth infinuate it felf through all the Coats and Humors, to the Tum'mz C/Joroider : For inftance, Take an Eye out ofthe Head ofany Animal, and you may difcern rays of Light through the whole body of the Eye 5 or in a living Eye you may fee its bottom, which is the (/Joraider. Wherefore if 3. Ray be ob- liquely tranlinitted to a furface of any diaphanous Coat or Humor bf the Eye, it muf't neceflarily admit a Refraétion ; but if the Ray be carried in a right Line, it paflbth without any Refraétion. And the oblique Ray (refracted at the furface of any tranfparent Tuniele, rm mm] or Humor of the Eye ) proceedeth from the different degrees of their Rarity ""r" "a" Iraélion. - . and Denfity, and Excentrick Situation. And it may be truly affirmed, that the Ray pulling from the point ofa ,Thcthayrgf' ' . . _ In! nun Vlfible Obyeét, through the Air. Into the Cornea, lS rcfraéled according to the [hi/airmail: perpendi Cornea. is rev cular; becaufe the Tunicle of the Cornea is endued with a greater l'raflcdac~ ' then the. Air. cording tolhe perpendicular But the vifible Ray trajeéted through the Comm into the watry Humor, is {The Ray rafeither not refraéted e nfity ing Fromthe at all, or maketh its Angle of Refraélion frotri the per- cgmmom PmdlcUlar , as the watry Humor obtaineth a greater degree of Rarity then 333,513" the Cornea. from the per. . . . . . ptndicular. .And the lucrd Line (Howm g from a paint ofa Vifible ob}eét, and tranll iii: gyof mitted from the watry into the Cril'talline Humor) is become refracte d to"imam?" ward the perpendicular, as the Crifialline Humor is affeéted with more Den- ""‘Hmm" flt)' then the watry. And if a Beam of Light, be trajeéted through the tranfparen Body of Thcmn nsr the Ctiflalline to the ConcaVe Surface of the vitreous Humor, ittfuflie tha :iiiifiiii‘f efraflion toward the perpendicular, as the vitreous Humor hath a lefs de- "mm" 8ch of Rarity then the Oril'talline. Ray arifing out of any point of a vifible objeét, is carried by an A-ngU- Tlieman ncr lat emitfc‘ through the Criflalline and vitreous Humo r, and is brought into $532635" order by the Retina, by reafon it is endued with a greater Denfity then W 1W" any him of the Eye , whereupon the Vifory Ray is refraéted toward ‘he Perpendicular, to that it is reduced to its true fituation, in reference to the X 10 true |