On the JffeBicns afid Properties ef Light. I49 



{ube was (lOwly introduced into the light, and fo held that none of the rays migJit be re- 

 frafted, a ftreak, chiefly white, was feen, fimilar in (hape and pofition to thofe defcribcd 

 before *. When narrowly infpe£ted, it was found to contain many images by reflexion in it. 

 But ihefe were much diluted by the abundance of white light, reflected without dccom- 

 pofition in the manner above-mentioned f . This ftreak lay wholly on one fide of the tube j 

 but I moved the tube onward a little, and another ftreak darted through the fhadow, and 

 extended all round on both fides : and now, when the tube was in the middle of the rays, 

 there were two ftreaks on both fides, one a little feparated from the other and continued 

 through the ftiadow, the other on each fide of the fhadow : the former was evidently pro- 

 duced by refraction : it contained many images very like thofe by reflexion, only more vivid 

 in the colours, which were all in the inverted oAder, the violet being outermoft, and the 

 reft neareft the point of incidence. Images fimilar to thefe are alfo producible on the re- 

 tina, as mentioned before %. 



Ohfervation 6 — I now placed a prifm at the hole, and made the fame images by re- 

 fraiStion, out of homogeneal light. Thefe inclined to the red, not (like images by re- 

 flexion) to the violet; but they were broadeft in the red, and grevlf narrower towards the 

 violet parts. In (hort, when viewed befide the images by reflexion, except in point of 

 brightnefs and inclination, they differed from them in no refpeft. 



The three firll experiments fliew, that when homogeneal light is refledled, fome rays arft 

 conftantly difpofed into larger images than others arc, that is, into images more diftended 

 in length, though of the fame breadth. The fourth experiment {hews, that the fame takes 

 place when light is infle£led and deflefted ; and the two laft fhew that the fame happens 

 when the rays are refrafled in a way fimilar or analogous to that in which the other 

 images were produced by reflexion and flexion. 



We are now to ftiew, that this difference of fize is not owing to the different rcflexibi- 

 lities and flexibilities of the rays. In order to this we fliall both dempnftrate, and then 

 prove by experience, "that inflexion and deflexion do not decompound heterogeneous' 

 rays, whofe dire£lion is fuch, tliat they fall on the bending body." In fig. 2. let A B be ' 

 the body, GH, EF, CD, the limits of its fpheres of deflexion, iiiflexion, and reflexion, re- 

 fpe£lively ; and let I P be a white ray of dlretl light entering at P the fphere of deflexion : 

 'through P draw LK at right angles to GH ; IP will be feparated into PR red, and PV 

 violet, and the five other colorific rays according to their deflexibilities; at R and V dravp 

 the perpendiculars ST and QO; then the alternate angles PRT, RPL; and PVQ, VPL 

 are equal each to each. But TRP and QVP are the angles of incidence, at which the 

 red and violet enter the fphere of inflexion 5 and RPL, VPL are the angles of deflexion of 

 the red and the violet \ therefore the difference of the two latter, that is RPV, is like- 

 wife the difl^erence of thc'two former. Suppofe this difference equal to nothing; or that 

 PV and PR are parallel;' then rRS the angle of the red's inflexion will be lefs than vVO 

 the angle of the violet's inflexion, by the angle RPV: (when not evanefcent) add RPV 

 to rRS; then rRS will be equal to vVO : that is, the divergence will be deftroyed, and the . 

 rays enter the fphere of reflesion, parallel and undecompounded. It is evident, therefore, 

 that t>he effe^ arifing from the different deflexibilities of the rays is deftroyed by the equal 



* Phil. Tranf. 1796, page 236. or Philof, Journal i. 555. f Ibid. p. 237. or Phil, Journali. 556. 



X Ibid. p. 143- or Phil.' Journal i. 559. 



