yet it is neglected by our great mafter* of natural knowledge in this kind, in his beft enumeration of the diseases of age. And thofe that look out of the windows be darkened. That by this clear expreffion the eyes and the infirmities of them in old age, is intimated unto us, was never yet, and I perfuade myself never will be, in the least measure doubted or queftioned. Forafmuch as they are the only true, and proper organs of feeing; however, it will be well worth our labour to confider, how the eyes may be called, the lookers out of the windows. One may be faid to look out of a window in a double fense, either when he looks thro' the glafs of the window, and thro' the pellucidity of that most refined body, discerneth those things which are without; or when he looks thro' the open cafement, or thro' fome open hole of the window, wherein there is nothing at all interposeth between him and the object. Now in both these senses may our interpretation well be made. For the explication of it in the first sense, we must take notice of all those transparent parts, through which the visible species muft of neceffity pass before vifion can be perfected for as a man could fee nothing thro' a window, were it not made of glass, or of fome body alike diaphanous: So neither could he perceive any thing with his eye, were not * Hippo. 1. 3. Apho. ult. the the parts thereof, through which paffage is made, of the very fame nature. Now, the parts of the eye, through whofe bodies the vifible fpecies muft pafs that they may be dif cerned, are either the humours, or the tunicles; the humours are three, the watry, the chrystalline, and the glay humour, fo called by anatomists; and you may perceive by their names that the substance of them all is diaphanous; all which, howsoever they wonderfully differ among themselves, and several ways contribute to the use and benefit of the eye, and confequently are made variously inftrumental unto vision, yet they all agree in this one thing, that they are transparent; and that they must of neceffity do, forafmuch as into their bodies, and thro' their bodies, muft the vifible fpecies pafs, before they can perfectly be difcerned by any man. And if one opacous, or darkfome body interpofeth, they can go no further, but there they must determine their course. The tunicles or coats, through which the fight is made, are only two; for although there are other tunicles of the eye, which conduce wonderfully to the fight, (as you fhall hear beneath) yet those through which the fpecies pass, are only the tunica aranea, and the cornea. The firft is fo called from the fimilitude of a fpider's web, because it is most fine and fubtile, and being derived from the brain and optick nerve, it becomes a most tenuous E 3 veft vestment for the humours; and is fo pellucid, and tranfparent, that among the learned it bears the name of speculum. The other is called, fclerotica, or cornea; and that is, that hard and horny membrane, which being derived from the dura mater, encompasseth the whole body of the eye, without any perforation; and on the back part, behind the fight of the eye, is more obfcure and dark; but on the forepart, is far more plain, polite, and diaphanous, that the fpecies may pass thro' its body most pure and unaltered. And now I am come to that part of the eye, that doth moft aptly resemble the glass of the window, by reason of which a man may be truly faid to look through a window, and an old man, to fee through a glass darkly, a Cor. xii. 12. without the use of fpectacles, which fome would fain have here to be understood; of whofe opinion I cannot perfuade myself to be, because it is uncertain to me, whether thofe helps of nature were then, and there, in ufe: And most certain it is, that they are without the compass of the allegory, and are not part of that house or body of man, whofe decay is here fo livelily reprefented. Befide, this tunicle hath the fame use to man, in his perfect state, that spectacles have in his imperfect. And this be confident of, that there is nothing that art hath found out to help man in his decays, that hath not its footsteps firft in nature, and is not an imidation of thofe things in man, that were most com compleatly in him in his perfection. And here I muft of neceffity go one step farther than our common oculists; who afcribe to this part but a low and a mean office, which is only to keep the humours in their place, or at the best, to defend the inward parts from external injuries; but without all queftion, it hath this farther, and more noble ufe, viz. fo to difpofe and order the visible species, that they may in the most convenient manner, make their impreffion upon the proper organ of fight; and this their craffitude or thicknefs, together with their convexity or bending outward, doth fufficiently. make appear. I here all along retain the terin of the ancients, viz. vifible fpecies, as being most known, and that by which I may be better understood among moft, to whom this para phrafe may comé, though it be not fo proper, and the conceptions which they had about them, are not to be admitted; for there is no new entity, either material, or immaterial,. caft off from the object, diftinct from it, and from the light, which is the cause of vifion in: the eye; by the vifible fpecies therefore, I mean no more than the feveral beams of light being so reflected from the object, as that they become fully fraught with the representation of it; (not only in respect of the proper objects of fight, which we call colour, but of these common ones alfo, which we call fituation, figure, distance, bignefs, and the like) and have a E 4 com compleat power of impreffing the fame upon the retina, which is the ftrict and proper organ of fight, and is nothing else than the dilatation of the optick nerve all about the bottom of the eye. For the bettter understanding of alb which, we must know that the fpecies pafs along the medium in a pyramidical figure, and as they are caft off from one point of the fuperficies of the object in a cone, so they must be reduced again in the fame conical figure upon one and the same point of the organ; which reduction is performed by that collection, refraction, and direction, which happeneth to them in those several pellucid bodies through which they pass, and primarily (while the eye remains in its vigour) in the tunica cornea; but as age enfeebleth the eye, the form and figure of it becomes more piane and depreffed than it was before; and the cryftalline humour, which had a power of reducing itself, and confequently the whole body of the eye, to a more oblong and convex fhape, becomes dry, and altogether unable for fuch an end; fo that now the species caft off from the object at a convenient distance, cannot be brought to a cone upon the organ, which must needs breed a confufion in the fight: To avoid which confufion, old men hold the object that they look upon at a greater diftance from the eye, because fo, the prefent conftitution of the eye can better regulate the species; and thus alfo fpec tacles |