¶Of the vertue visible. Cap. 17.
THe sight is most simple, for it is firie,* and diserueth sodainely things that are farre off. The sight is formed after this manner. In the middle of the eye, that is the blacke thereof, is a certaine humour most pure and cleare. The Phi∣losophers call it Christalloides, for it taketh sodainly diuers formes & shapes of colours, as Christall doth. The sight is a wit of perceiuing and knowing of colours, figures, & shapes, and vtter pro∣perties. Then to make the sight perfect, these things are néedfull, that is to wit, the cause efficient, the lymme of the eye conuenient to the thing that shall bée séene, the aire that bringeth the likenesse to the eye and taking héede, & easie moo∣uing. The cause efficient, is that vertue that is called Animalis. The instrument and lymme is the humor lyke Christall in either eye cléere & round. It is cléere that by the cléerenesse thereof, the eye may shine about the spirite and aire: It is round, that it be stronger to withstand griefes, for a rounde shape hath no sides or corners, that containeth superfluityes that should grieue it. The vtter thing, helping to worke, is the aire, without which being a meane, the sight maye not be perfect. In some beastes to profit the sight, néedeth the cléerenes of aire, and in some the darknesse, and in some the meane, not too darke nor too cléere. For in Cats néedeth darknesse, in Reremice, or Bats and in other flieng beasts née∣deth meane, as it shall be shewed heere∣after. And it néedeth to take héede, for if the soule be occupied about other things then belongeth to the sight, the sight is the lesse perfect, for it déemeth not of the thing that is séene. And easie mouing is néedfull, for if the thing that is seene, moueth too swiftly, the sight is combred and disparced with too swifte and conti∣nuall mouing, as it is in an oare, that séemeth broken in the water, through the swifte mouing of the water. Like∣wise also an euen long trée moued swift∣ly séemeth rounde. How the sight is made, olde men had diuers opinions.
Page 18In 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,
Page [unnumbered]And thereto agreeth Austen super Ge∣nesis, lib. pri. & VI. musice, wher he saith, that nought commeth from the thing that is seene, but the likenesse thereof, nor from the sight to the thing that is seene, but the lykenesse of the sight. For nothing of the substance of the eye com∣meth out, but out of the eye commeth a small appearaunce, that is shapen as a stéeple or a top, and the broad end there∣of is spread vpon all the vtter parte of the thing séene. Also the Author of Per∣spectiue, li. i.proueth, That nothing is séene, but by sight that ariseth vpon the thing that is séene, & is multiplyed spée∣delye from the wide thing to the eye. Therefore néedes is required the thirde stéeple of the same light. And of all these thrée stéeples, the poynts are in the eyen, and the broad endes in the things that be séene. Therefore when the lykenesse of the thing commeth to the sight vpon these thrée stéeples, then the likenesse of lyght and colour, passe by the small for∣tells and humors of the eye, euen to the humor that is called Christallinus, like Christall, and there the soule beginneth to giue iudgement of the thing that is séene by that lykenes, but there it is not fulfilled and complete, but the lykenesse is multiplied forth, euen to the sinewe, that is called Obticus,* an hollow sinew, that is hid in the vtter part of ye braine: and ther is the vertue of sight in maure and roote in the first and principalll sub∣iects, and is one: for els euery thing that is seene should séeme two things, because of the two eyen, if they continued not to one lymnie, in the which is the onely well of the vertue of sight, and springeth to the blacknesse of the eye. The Author of Perspectiue sheweth all this. Hée sheweth & expresseth another reson of the sight. li. 3. ca. 11. He saith, that ye spirit vi∣sible, ye eye & the aire, be cléere bodies, the whith lyghten euery other, & make eue∣ry like to other. For the aire, that is next the thing that shall be séene, taketh a likenesse of the propertie of that thing: and in that lykenesse the aire prosereth it selfe to the eye, whereof the spirit vi∣sible taketh a lykenesse. For this vertue of sight, shewing it selfe to the vtter∣most part of the black of the eye, is ioy∣ned to the aire, and is likened and made as it were one therewith: & by meane of the aire, the color is brought and pre∣sented to the iudgement of the soule. For the aire is lightly chaunged and li∣kened by diuersitie of shapes, that are therein. As we sée, that the aire that is nigh the Sunne beame, is coloured and dyed, by red cloath set betwéene. And therefore it is no wonder, though ye eye take likenesse and shape of a cléere thing that is next thereto. Then touching this worke it is now to gather shortly, that the sight or vertue visible is more sub∣till and more liuely than the ether wits, and Visus, the sight, hath the name of Viuacitas, that is, liuelinesse, as saith I∣sidore. Also it is more worthie than the other wits, and therefore it is set aboue the other. Also in effect, as it were a vertue of fire, it is more mightie than the other wits: For the other wits knewe things that be néerer, but this wit by his vertue comprehendeth things farthest of, vnder a right corner and stéeple sight, iudgeth and discerneth after the nobler kinde and disposition of the organe, and discerneth in an easie manner betwéene things to be séene. Wherefore Aristotle lib. 12, saith, that good sight and sharp, is of temperate humour. And therefore Fowles (as the Eagles) with crooked clawes, be sharpe of sight. And that is through the pure and subtill humour, and temperate being, and purifieth that that is in the organe of the sight. And such Fowles sée their pray out of farre and more high places. And such Fowles fiye higher in ye aire than other fowles. But Fowles that remaine on ye ground, be not sharpe of sight: therefore they sée their meate nigh and not farre. Also, Lib. 19. he saith, that yeolow eyen be not sharpe of sight by daye, nor blacke by night, for scarsitie of humors. The yeo∣low eye moueth greatlye, and therefore the vertue of sight is féebled. Blacke cy∣en moue lesse, for multitude and plentie of humors, and the sight of the night is feeble, and the humour by night moueth heauely. Therefore the spirite visible is closed in, and by humor letted. Also the Page 19 sight of olde men is not sharpe, because their skins are riueled. Whereby it ap∣peareth, that the vertue of the sight is feeble or strong, by goodnes or feeblenes of the lymme. And he saith, When the eyen of beasts haue lyds, and the humor in the blacke of the eye is cleane and temperate, and soft mouing, and the skin vpon the blacke, tender, supple or thinne, then the sight is sharpe and may sée far. But yet he discerneth not perfectly farre off betwéene coulours and difference of the body: but yet the sight of such beasts is better, than the sight of them that haue much humour in the eyen, & haue no heling nor eye lyddes. For by conti∣nuall opening, the spirite Visibilis is to diminish, and the blacke of the eye is lyghtly grieued and hurt, and so the sight is let. But in men helyngs and eye lids cause the contrarie. Also there it is sayd, that cause of a sharpe sight, in séeing a farre, is for the place of the eyen: For big and ouerswellyng eyen, be féeble of sight, and sée not so well a farre: but déepe eyen see perfectlye a farre of. For the mouing thereof is not departed, nor consumed, but goeth foorth right, and the spirite visible passeth straight forth to the things that be seene. And so if there bée no heling nor couering without the eye, néedes the sight must be féebled, and shal not sée a farre. Hetherto speketh Aristo∣tle lib. 12, & 19. And this that is said ge∣nerally of the properties of the sight, shal suffice at this time. For other things shall be knowen héerafter, wher we shal treate of the propertie of the eye.