CIHM Microfiche Series (l\/lonographs) ICMH Collection de microfiches (monographies) Canadian Institute for Historical Microreproductlons / Instltut canadien de microreproductions historiques Technical and Bibliographic Notes / Notes techniques et bibliographiques The Institute has attempted to obtain the best original copy available for filming. 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OSLER UBR*M REPWNT COLU STEREOSCOPIC VISION. BY (i. P. (ilKDWOOl), M.I).. M.IJ.C.S.. Knir., I'rofessor i)f Clifiiii^tr.v, McGill .Modiciil Kficulty ; Consiiltiiiv?8iirK<'iiii .Montreiil Geiv iT.il Hospital ; late A-ssL-SurKcoiiGrfnadierGuarils, F.H.S.C. !•".('. K., F.I.C, etc. Rrjiriiitril from llir. ^flmtrl•(ll Mrdlriil Jon.-ntil, July, 1900. STEKEUSCOl'JC VISION. II V G. P. (iiKDWooK, M.I)., M.Il.U.S., Kn^., I'loli-HHor of Cln-iiiislry, Miliill Mcdiciil Kiuully ; CniiHultinn SnrKPon Montreal Jion- eral llu.vipititl ; li.le An>'t. Siiwini (in-imdifrCinurds, F.H.S.C, l''.(M';., K.I.I'., etc Wlion looking around us, if wo luivc good vision witli hotli oyts, we Bee surrounding ubjeeLs in tlii'ir nonnal position as regards disUiU'i! l'ron\ us, and are able to .-ay that one ol)jrct is iitanT than llie otlur; l)ut if wo liavc only one eye, the other being blind or teni|)orarily comtihI, the picture presented to us ai)l)ears flat, and the relative distanee of objects is not preserved to us. Un investigating this phenomenon, we lind that the two eyes are normally about 2\ inelies ai)art from cent re to centre, and that we converge the axis of the two eyes on diiferenl objects, and thus view the whole picture, the object converged upon beiug the prominent feature in the picture for the moment, and we really see two pictures, one with each eye, the central ol)ject of which is the object on which convergeiue is made, and that these two pictures are blended by means of the perceptive faculty of the brain, and we see oidy one picture. The two pictures as presented by the two eyes are not identical, and this may be readily shown by taking two pictures with a lens placed iu t-wo positions 2^ inches apart and comparing the t.vo pictures. They wdl not be tracings one of the other, but tlie point of eoiivcrgeiice will lie the centre of each, and other objects will take their place accordingly. Tiiis will be easily proven if we place two objects in line with our nose, and alternately converge on the nearer object and the distant one. If we converge the eyes on the distant object, it will be seen that there are two images of the nwir object visible, and in like manner, if we con- verge our eyes on the near object, two of tho distant objects will bo visible. If now, whilst converging the eyes on the distant object, and the two images of the near object are both visible, one eye, say the right eye, be closed or covered, the left-hand image of the near object vdll be obliter- ated, and if the left eye be clo.sed or covered, the right-hand inuige of the near object disappears. (Fig. 1.) Again, if whilst converging the eyes on the near ol, • t two images of the distant object are visible, and if, whilst converging on he near ol)ject, and the two images of the di.stant object are visible, the right eye be closed or obscured, the right-hand image of the distant object disap- pears, and if the left eye, the image on the left disappears. If now two objects be placed in line with the nose and the eyes con- \( !■;.'<■• I on the ili.-tilllt iiliji'cl, 11 (iinl iiiiiy lie lli'lil lip on the mimii' lili«' so as to iil>lit('nil(' llic iK'iir (ilijccl iiltii<.M'ili('i', ami llii' ilistaiit uliji'ct rcinains \ isible us one dbjcet. (I'ig. 1.) \U\\ if eyes arc ciMivxTgcd on near Dhjuct, l\v<) iiiiajrcs of (he (li.-liiiil olijrct will lii' scfii, iiiiil if till' ri}.'lit eve Ik' clo-rd or iili^iiifi'il, ilic ri,Lrlil iiiui^c oj' di-liiiil ulijccl will In' olililcrati'd, iiiiii if till' ji'l'l cvi'. iIh' III! iiiiii;i(' will lir nl)lit('riitc(l. Mini' il' twii canls lie j;ra liir iiii'dinn line, lioili dis- tant iiiia;;,i>i cm |„. nlililriali'il uliiUl llic iirar olijcct rciiiaiiis visjlilf. (I'i^'. '.'•) Tlit'sc ('\|iiTiiiii'iits .-how lliiil Iwodi-liini |iir| iirc^ hit -ci'ii liy the two iliirci'ciit I'vcs, and tliiit. tlicrcrori'. lo olitniii line stcrcoscoiiic vi,-ioii, (wo dislinct |>ictiircs must, he iircscnti'd to tlir two eyes, (Ik- left to tlic left and tilt' ri^'lit to tlic rifriit cyi'. If. lloWrMT. llh' ipii'llircs he rcVi'l'scd Mild lllr Irlt |iirtni'i' |IU| to tllC li^ilil eye, and tlic ri;,dit piiliin' to the Icl't cyi'. the reverse pfl'i'ct is pro- • liieed, and tlie distant olijcct or portion of oltjci't a|i|iears near, in-lead of distant. In l'ostcr"s i'liysiold^/y a drawiiij,' is <(ivcii, from which the •Irawiiiffs pnidneed are cupied A. In liiis the forcshortciiinjr is given on tlie inside nf ihe tuu pictures, ami in IS. I liavi' reversed the sides ; tiiiil i-, I have pill ilic rij.dit picture (d' A to tlie left eye in M, and the lefl eye picture id' .\ to the lijilil eye of li. ami mnv they appear reversed ill A. The olijcct w hen viewed ill the stereoscope appears n.s a solid trnn- catcd cdiie. wliiNt in l'> llie cll'ect of lookin_u into a hollow truncated eono is priiiliiced. On viewing' any of these jiiciuns with the stereoscope, they np]iear as if seen in relief or as solid ohjects. Iiecaiise the instnimciit gives to eai'li eye its proper picture and the lirain hleiids the two pictures into one. il is (piite possihlc. and most pco|ilc with a little practice can see thc>e jiicturos sli'reoseopically, the centres are jilneed '2\ indies apart, ami if lield opposite their resjiective cye.«, and the axis of the two eyes ho made i>aralle!. each eye will sec its own ]iicture, and the hrain will lilcnd them to!_M'thcr. On looking at one of these pictures with the eyes ])ar- allel. that is. converged on intinity. three jiictures will he seen, a central picture which ap]icars solid, and a ]iicture on either side which ai)pears Hat and wanting in solidity. If whilst looking at one of these cards and seeing the tlirec jiietures. a card he jiasscd up hetwcen Ihe eyes, it will he I'ouml that the two outside ineturcs are cut olT Init the cenii'al one remains visihie and a|i))ears solid. If when looking at llie lanl and Ihe three jHcturcs arc visihie. either eye he ohsciired. the centre solid olijcct lieconies Hat and loses its rotun- dity and the third image on the side opposite to the ohscurul eye is lost. If when looking at the card and the three pictures are visible, the card bo altered in its horizontal level so as to raise one picture above the ;i iillicr, tlic cfiilrc |iiiliirf im lip|i;.'cr .iiiiicarH sn'' I, Iml i> seen In fi>ii>i-t (if twfi imii^'c.-i. which iiinvc a.^ the level is altered. I'"niiu tlit'so t'.\|ieriiiieiits it i< clear thai when ilie card i^ lonked at with the axis (if the twit f\f^ coiiver^nii;; mi inlinity. in reality an inia;,'e of eat'li drawinf,' is seen by oaeii eye, so that, in reality there are fi.ur pictiircs presented in the Imiin, Imt the two whieli are oppo-iie t<> tlic ^e^|n■(■|i^•e eyes are Ijjeiided into ime Milid idijeit, hy the hrain. and the iitller \\\n |iictlires are seen hy ihe respective eyes Id the in«i(le (if the |»ictuie which is opposite to the eye, and licnce when tlie card is placed hetween the two i-\i'>^ it is the Iwo lateral pictnre- which are cut oil', and tilt' c'critral solid nlijc«crvalions is thai ifa picture he laken ster- eosc()|)i(*ally and mounted .so as to have left picture opjMisile left eye .'.nd ri;j;hl picture (ippo.-itc iij;ht eye, the -olidily will appear as correct troiu the point of view lakcM. luil il' the piciures he reversed, the view appears to he Ironi the opposite sidi-. .\nil if Ihe i'\f> can he practiced to look .straight lad'ore them, that is, parallel axes or even a little diverf,'ent, and ail (diject he jdaced hefore one eye and ;i hiank sheet of paper liefore the other eye, it will he perfectly possihle with a little practice to draw on Iho hIank sheet wdh one eye what is seen with the other eye; hence il is possible to look down a microscope with the left eye and draw on a sheet of pajicr hy Ihe side of the inicro.seoiie with the right eye what is seen hy the left; and in like manner, if a mark lie made on a piece of paper opposite Ihe left eye, and looked at stereoscopically, that is with paralleled vision, a line can lie drawn on the paper exactly under the line seen hy the left eye which will lie found to he '.'.l inches a|iarl from the first line, a see(uid and a third, or as many as an' de-ircd can he drawn equidistant. In skiaf^rajihy the advania^'e of ihe-e observations is that a jiiclure may be taken stereoscopically, and by reversing the picture a. view of both sides may be obtained as the parts, even the boiu's are so largely transparent. {■Hi. I. 1 .uiil li lire cyt!-*, 2.|. ii>i;lirs ,i|iiirt, H a iii'iir iiti.irrt, I ii (littmit ulijt'ct in liiK! with llic nose, '.■oiivcru''"''*' I'f cyi's (III ili>'iiiil oli.ii'cl t, ■! iiimp'H (if iiciirdlijcct lire visililc in iil o iiiid (1. Ciiid |iln(C(l fil A (Ills (if I iiiid 5 fniiii -, li'ii\ inn 1 "•'"' •' vUililc liy 1, ifciird pliiccil III H, I iindtlarH cul ()tr fiiiiii 1, lint 5 and I lire viMililc. ("iird iiliiccd lit IJ cuts olV "i mid (i liiit I n visililc til liutli cji'S. 1 1/ Kid. II. 1 and 2 iiio eyes, 'I\ inithcH apiirt, 11 a near (ili.icct, I a'distaiit (ilijfrt in line with iKisc. Kycs (•(iiivcii^c on :i, I wi) imiiircs of I iiiv Hci'ii out! (jh I'itlici' sidcdf ;i. Card plaii'd 111 .\, 1 and •') will 111! cut dll' from '1, if al Ii t aii(l II willliiMiil oirfidin I, if beards are liidd ai I), I will lie cut i- siti' to il iiikI also spi's (I to the iii.Hi and II l.s NiM'ii liy I Kliiiilnrly to llu- tIkIiI of roii- joliiril pirturi'. Canl at A cuIh oiroaiiil .'i from 'i, at M cuts of Aainl II fioin I. At I) '-i'ts oil" side pii'tni-i's of 5 anil II from op|H)Hiie eyi's 2 ami 1, liiit '■ anil II ore seen Holid around the eiinen of cord. \ i zzk B