In pri. cap. Perspectiue, the Philosopher saith, that in thrée manners the sight is made. One manner by straight lynes, vpon the which, the lykenesse of ye thing that is séene, commeth to the sight. Ano∣ther manner vpon lynes rebounded a∣gaine: when the lykenesse of a thing commeth there from to a shewer, and is bend, and reboundeth from the shewer to the sight. The thirde manner is by lynes, the which though they be not bent and rebounded, but stretched betwéene the thing that is séene and the sight: yet they passe not alwaye foorthright, but other while they swarue some whether aside from the straight waye. And that is when diuers manner spaces of diuers cléerenesse and thicknesse, be put betwéen the sight and the thing that is séene: and sometime the spaces be of diuers kindes, as when one is thicker, another thin∣ner. And sometime there commeth a meane of another kinde, but the beame or bright likenes is broke, but if it come vpon a line that falleth straight, & Per∣pendiculariter vppon the same middle second occurring. And I cal a line to fall Perpendiculariter vpon a plaine thing, Ad angulos rectos, that is straight and a crosse wise: and vpon a round thing, if it fall into the middle thereof.
To the sight, for to speake in the first manner, néed nine things principally, as they be rehersed ther. The first is firm∣nesse or good disposition of the organe or instrument of sight. The seconde is a thing that may be séene set afore ye sight: for in ye manner the sight séeth nothing. but if the same thing, from the partes, wherof commeth likenes vpon ye straight lynes, that fall into the middle of the eye. All which lynes drawen from all the parts of the thing that is séene, make one stéeple, the poynt whereof is in the blacke of the eye, and the broad end in the thing that is séene as appeareth in this figure.
A and B be the Aristrées,
when the séeing direct lye beholdeth the poynt, C. when it beholdeth y
e point D. Then these two B C procéeding frō the eyes, be called axiltrees, for they pro∣céede immediatelye from the eyes, by meane to the thing seene. The third is distance proportional. The fourth D C is a certaine stede or place, not too farrre from the lyne of the sight. For though a thing be right before the eye, if it be too far ther from, it is not distinctly known.
Axis visualis is the cléere beame or line, the whichlis vnderstood to be deduct from the middle of the sight, to the poynt of the thing séene directly to the opposite, in the mids of the sight, as appereth in this figure A B. The fift is sadnes or thick∣nesse of the thing that is séene. For
〈…〉〈…〉 be all cleare and without thicknesse,
〈…〉〈…〉 the aire is, then that is not séene, as saith the Author of the science
Perspectiue, that is, the science of the sight. The sixt, is due greatnesse of the thing y
t is séene. For a thing may be so lyttle, y
t it cannot be séene in no space: for there is no sight but by appearance shapen top wise, that commeth to the eye, y
t which if it be ve∣ry little, it shal occupie a very smal part of the sight, & the sight may not sée, but when a part of the vttermost thereof is changed to the likenes of the thing that is séene. The vii. is clearnesse of y
e space, that is betwéene the eye & the thing that is séene: for if the space be thick, it letteth the likenesse of that thing, that it may not come lightly & in due manner to the black of the eye. The viii. is light: for the visible lykenesse of the thing, can not chaunge the sight without lyght. The ninth is time for the sight must haue time, as it is proued in
Perspectiue: for though a thing come sodainly before the sight: it is not knowne readily and di∣stinctly without some aduisement had, the which needeth time and leasure. And therefore it needeth also that the soule take heede, as it is sayde before. Also the Philosopher sayeth, That not onelye the lykenesse of the thing seene commeth to the sight after a steeple wise, but also the lykenesse of the sight, strotcheth to the thing that is spread, vp∣pon such a steeple in the same place.
In lib. 19.
De Animalibus, Aristotle saith, That seeing is nought els, but that the sight passeth out to the thing that is seene.