Next for the impression they make on the Retina, we will further examine this Hypothesis: Suppose therefore ABCDEF, in the fifth Figure, to represent the Ball of the eye: on the Cornea of which ABC two Rays GACH and KCAI (which are the terminating Rays of a luminous body) falling, are by the refraction thereof collected or converg’d into two points at the bottom of the eye. Now, because these terminating Rays, and all the intermediate ones which come from any part of the luminous body, are suppos’d by some sufficient refraction before they enter the eye, to have their pulses made oblique to their progression, and consequently each Ray to have potentially superinduc’d two proprieties, or colours, viz., a Red on the one side, and a Blue on the other, which notwithstanding are never actually manifest, but when this or that Ray has the one or the other side of it bordering on a dark or unmov’d medium, therefore as soon as these Rays are entred into the eye and so have one side of each of them bordering on a dark part of the humours of the eye, they will each of them actually exhibit some colour; therefore ADC the production of GACH will exhibit a Blue, because the side CD is adjacent to the dark medium CQDC, but nothing of a Red, because its side AD is adjacent to the enlightned medium ADFA: And all the Rays that from the points of the luminous body are collected on the parts of the Retina between D and F shall have their Blue so much the more diluted by how much the farther these points of collection are distant from D towards F; and the Ray AFC the production of KCAI, will exhibit a Red, because the side AF is adjacent to the dark or quiet medium of the eye APFA, but nothing of a Blue, because its side CF is adjacent to the enlightned medium CFDC, and all the Rays from the intermediate parts of the luminous body that are collected between F and D shall have their Red so much the more diluted, by how much the farther they are distant from F towards D.
Now, because by the refraction in the Cornea, and some other parts of the eye, the sides of each Ray, which before were almost parallel, are made to converge and meet in a point at the bottom of the eye, therefore that side of the pulse which preceded before these refractions, shall first touch the Retina, and the other side last. And therefore according as this or that side, or end of the pulse shall be impeded, accordingly will the impressions on the Retina be varied; therefore by the Ray GACH refracted by the Cornea to D there shall be on that point a stroke or impression confus’d, whose weakest end, namely, that by the line CD shall precede, and the stronger, namely, that by the line AD shall follow. And by the Ray KCAI refracted to F, there shall be on that part a confus’d stroke or impression, whose strongest part, namely, that by the line CF shal precede, and whose weakest or impeded, namely, that by the line AF shall follow, and all the intermediate points between F and D will receive impressions from the converg’d Rays so much the more like the impressions on F and D by how much the nearer they approach that or this.