PHYSICS. parts whereof, how numerous foever, could none of them be fpared or alter'd, unless for the worse; as may appear from thofe many diseases obferv'd in that small admirable organ: for each of thofe difeafes confifts in this, that the humours, or other parts of the eye, are brought to a state different from that whereto nature had defign'd it. 'Twould be tedious to enumerate the feveral diftempers of the eye; wherefore I fhall only mention two or three particulars, wherein one would scarce imagine that a fmall recefs from the natural state could bring any confiderable or fenfible inconvenience. That which we call the pupil, is not a fubstantial part of the eye, but only an aperture of the uvea; almoft perpetually changing its bignefs, according to the different degrees of light the eye chances to be exposed to. And therefore, it should seem, that whilst this hole remains open, it performs its office, by giving entrance to the incident rays of light. And yet I lately faw a woman, who, after a fever, was not able to dilate the Pupille of her eyes, as before; and tho' they were but very little narrower than ordinary, yet fhe complain'd fhe had thereby almoft loft her fight. The preternatural conftriction of the pupil is indeed no frequent diftemper; yet phyficians have given it a place among the ftated difeafes of the eye. And, on the other fide, tho' a competent widenefs of the pupil be requifite to a clear and distinct vision; yet if its dilatation exceeds the due limits, there is thereby produced a diftemper worfe than the former; because it often almoft totally deprives the patient of fight. It may feem alfo but a flight circumftance, that the tranfparent coats of the eye fhould be devoid of colour; and of as little moment, that the cornea fhould be very fmooth, provided it remain tranfparent: yet when either of thefe circumftances is wanting, the fight may be greatly vitiated. Thus we fee, that in the yellow jaundice, the adventitious colour wherewith the eye is ting'd, makes the patient think he fees many objects yellow, which are of a contrary colour. And I know a gentleman, who having had a fmall puftule excited and broken upon the cornea, tho' the eye has long been cicatriz'd; yet a very little inequality or depreffion, that ftill remains upon the furface of that tranfparent coat, fo affects him, that when he comes into the open fields, or the streets, he for a pretty while thinks he sees objects very glaring, and as many others as men ufually do ftones at the bottom of clear water: which I impute to the want of uniformity in the refraction of thofe reflected rays of light, that fall upon the unequal furface of the cornea. To give a further proof, that the eye was made with defign, I fhall here take notice of an obfervation or two, that do not occur in the diffection of that part, and are therefore often unobserved by anatomists.

which they

I have found in frogs, that, befides thofe parts of the eye which have in common with men, dogs, cats, and most other animals, there is a peculiar membrane or cartilage, which is not commonly perceiv'd; wherewith they can at pleasure cover the eye, without too much hindering the fight, because the membrane is both transparent and strong; fo that it may pass for a kind of moveable cornea, or occafional fafe-guard

to the eye. In furnishing frogs with this ftrong membrane, the providence PHYSICS. of nature seems very confpicuous; for, they being amphibious creatures, defign'd to pafs their lives in watery places, which, for the most part, abound in plants, endow'd with fharp edges, or points; and the progreffive motion of this animal, being not by walking, but by leaping, if his eyes were not provided with fuch a cafe, he muft either fhut them, and fo leap blind-fold; or, by leaving them open, muft run the risk of having the cornea cut, prick'd, or otherwife offended; whilft this membrane, as was faid, is like a kind of fpectacle, that covers the eye, without taking away the fight: and as foon as the occafion for it is over, the animal withdraws it into a little cell, where it refts till its ufe be again required. This membrane becomes vifible, by applying the point of a pin, or any fuch fharp thing, to the eye of a frog, whilft his head is held fteady; for to fcreen his eye, he will presently cover it therewith, and afterwards withdraw it, upon a removal of the fufpected danger. And because many birds are deftin'd to fly among the branches of trees, and bushes; left, by this means, the prickles, twigs, leaves, &c. fhould wound or offend their eyes, nature hath alfo given them fuch another kind of horny membrane, as we find in frogs.

'Tis known that men, and moft four-footed beafts, and birds, have feveral muscles belonging to their eyes, by the help of which, they can turn them any way; and fo obvert the organ of fenfe to the object. But nature, not having given that mobility to the eyes of flies, fhe, in recompence, furnishes them with a multitude of little protuberant parts, finely rang'd upon the convex of their large bulging eyes: fo that by means of these numerous little ftuds, numberless rays of light are reflected from objects placed on either hand, above or beneath the level of the eye, and confequently fall upon that organ, to render the objects they come from, vifible to the animal; and by the help of a good microscope, and a clear light, fome hundreds of thefe little round protuberances may be difcover'd, curiously rang'd, on the convexity of a fingle eye of an ordinary flesh-fly.

But fome may here pretend, that all organs of fight ought to be conform'd to thofe of men; thefe being the best and most perfect. And, indeed, man being juftly reputed the moft perfect of animals, it is not ftrange he should prefume, that his eyes, and other parts of his body, are the beft contriv'd of any to be found in nature; yet we cannot, from hence, fafely conclude, that all eyes, which, in other animals, are of different stru&tures from thofe of man, fhould, for that reafon, be defective. For, firft, the admirable wisdom difplay'd by the author of nature, in fitting the eyes, and other organical parts of animals, to their feveral uses, and the respective functions we fee them exercife, may juftly perfuade us, that the things whose reafons and ufes we do not alike difcern, are, nevertheless, moft wifely conftituted: God having too much knowledge to do any thing unskilfully; and we having too much prefumption, if we fuppofe he had no ends in framing his creatures beyond the reach of our difcovery. And, fecondly, the eye is not to be confider'd abftractedly, as an inftrument of

Y 2

vifion;

PHYSICS. vifion; but as an inftrument belonging to an animal, that is to make use of it in particular circumftances. And therefore it ought highly to recommend the wisdom and providence of the great author of things, that he has furnish'd various fpecies of animals with organs of fight, very differently framed and placed; fince this diverfity nobly manifefts his great providence and knowledge, in having fo admirably fuited the eyes of all animals, both to the rest of their bodies, and to thofe parts of the great theatre of the world, on which he defign'd they fhall live and act. Thus, tho' several beasts, as horses, oxen, &c. have their eyes furnish'd with a feventh muscle, befides the fix they fhare in common with men; we must not conclude that either the organs of vifion are imperfect in men, or that those of these beafts have fomething fuperfluous: for they being to feed, for the most part, on the grafs of the field; and that they may the better chufe their food, being obliged to turn their eyes, for a long time together, downwards; the feventh mufcle excellently ferves them for that purpofe, by enabling them to continue unwearied by fuch a posture; whilst man, who has no fuch neceffity of looking affiduoufly downwards, would be only incumber'd by a feventh muscle.

On the other hand, the deficiency obfervable in the eyes of fome animals, compared to thofe of man, may be ascribed to the just contrivance of nature, that, on most occasions, declines doing what is unneceffary to the particular ends fhe aims at in the fabric of a part. Thus moles, being deftin'd to live, for the moft part, under ground, have their eyes fo little, in proportion to their bodies, that 'tis commonly believ'd they have none at all; but tho' I have found the contrary, yet their eyes are very different from thofe of other four-footed beafts; which need not be wonder'd at, confidering that nature defign'd thefe creatures to live under ground, where fight is of no use, and where large eyes would be more expos'd to danger; befides, their fight, as dim as it is, ferves them to perceive when they are no longer under ground; which feems to be the most neceffary intelligence they want from their eyes.

'Tis obferved, that the organs of vifion in a camelion are of a very uncommon structure, fince, to omit other confiderable peculiarities, his eyes often move independently on each other; fo that, for inftance, he can look directly forward with the right eye, and at the fame time directly backward, towards his tail, with the left; or may turn the pupil of the former, ftrait upwards, whilft the other is turn'd directly downwards. This peculiar power feems to have been granted him by providence, that as he is a very low animal, and deftin'd to live, for the most part, in trees and bufhes, and there to feed chiefly on flies; he may perceive them, which way foever they chance to come, within the reach of his tongue, which, being of a great length, he fuddenly darts out, and therewith catches his

prey.

Many fish have the cryftalline humour of their eyes almost spherical, and confequently much rounder than it is found in man, and other terreftrial animals. And this difference of figure, tho' it would be inconvenient

for us, is very well accommodated to them; fince they, living in the wa- PHYSICS. ter, which, as a thicker medium, much more refracts the rays of light than the air, thro' which they pafs to our eyes; 'twas fit their cryftalline humour should be of that figure, to refract the rays already refracted by the water, and thereby make them converge, fo as to paint the images of objects at the bottom of the eye.

Should a perfon of curiofity furvey and confider the various structures of the organs of vifion, in different animals, and compare them with the other parts of the refpective animal; the fcene he is defign'd to act on, and the ufes each of them is to make of his eyes, in the most ordinary circumstances; he might, doubtless, offer a probable reason of the differences in those organs, which, to a common obferver, would seem to be errors, or defects in nature. Thus, tho' the pupil of the eye be oblong in horfes, oxen, and fome other quadrupeds, as well as in cats; yet, in the former kinds of animals, it lies tranfverfly from the right fide of the eye to the left, whilft in cats its fituation is perpendicular; for horfes and oxen, being usually obliged to find their food on the ground, they the more conveniently receive the images of the grafs, &c. in a horizontal view, by having their Pupille tranfverfly placed; whilft cats, being to live chiefly on rats and mice, which are animals that ufually climb, and run upon steep places; the most commodious fituation of their pupil, for difcovering and pursuing thefe objects, is the perpendicular. But, to proceed: the different ftructures, and fituations of the eye, in different animals, wonderfully fhew a great variety in the skill of the divine author. And, indeed, if I might prefume to guefs at any of God's ends, that are not manifeft; 1:fhould think that the delightful variety, we may observe, not only in animals themselves, confider'd as entire systems; but in those parts of them which appear destin'd for the fame function; as particularly, that the organ of vifion was defign'd, at least, among other ends, to difplay the great creator's manifold wifdom, and to fhew that his skill is not confined either to one fort of living engines, or in their parts of the fame kind, to the fame contrivance; but is able to make a multitude of furprizing organs, all of them curious, and exquifite in their kind, with regard to their different uses.

To be able to frame clocks and watches, fhips, mills, &c. manifefts a far greater skill in an artificer, than the power of making but one of those engines, how perfectly foever he contriv'd it. And the fame fuperiority of knowledge would be difplay'd, by contriving engines of the fame kind, or for the fame purposes, after very different manners.

Thus weights are of great use and neceffity in the famous clock of Strafburg; and therefore it recommends the contrivers of watches, that they give them a very little and portable bulk, which is wanting in the Strasburg machine; and ftill more, that they can make a clock without weights, and fubftitute a spring to perform their office.

And thus tho' it seems abfolutely neceffary that an animal fhould be furnish'd with feathers in order to fly, yet the wife creator hath fhewn, that he is

not

PHYSICS. not confined to apply them for that purpose; fince a flying-fifh is able to move a great way in the air. And the Indies have lately afforded a fort of flying fquirrels, one whereof I faw, alive, at Whitehall. And tho' the flight of thefe is fmall, yet there is another kind of animal, without feathers, that long continues upon the wing, and that is the bat; fome whereof I have feen but little lefs than hens: and was affur'd, by a credible eyewitness, that, in the kingdom of Golconda, he had feen much bigger.

Chance an imaginary Being.

This confideration is alone fufficient to juftify the wisdom of the creator; who, being a moft free, as well as a moft wife agent, men ought not to find fault, if he think fit to recommend his wifdom, by difplaying it in very different manners: tho' there are many cafes wherein the lefs perfect fabric, or fituation, of an eye, or other organical part, may be more convenient than the correspondent organ of man, to obtain the ends for which it was given to an animal defign'd to act upon its respective stage, and live by its peculiar provifion. Befides, an organical part may, in fome animals, be intended for more uses than in others; and, therefore, require a different ftructure: as, in moles, the feet are differently framed, or fituated, from thofe of other quadrupeds; because the chief use they are to måke of them, is not to walk upon the ground, but to dig themfelves ways under it; provident nature wifely fuiting the fabric of the parts to the uses wherein they were to be employ'd: as, a mechanic employs one contrivance of his wheels, pinions, &c. when he makes a mill to be driven by water; and another, when it is to be mov'd by the wind. The camelion has a tongue, both peculiarly fhaped, and of a length difproportionate to that of his body; becaufe, as we before obferved, he is to take his prey, which are flies, by fhooting out that inftrument; and could not often, otherwise, approach very near them, without frighting them away. And, in many cafes, where this reflection does not fo properly take place, we may obferve, there is a wonderful compenfation made for that which feems a defect in the parts of an animal, of a particular fpecies, compar'd with the correspondent ones of an animal of fome other species. Thus birds, which want teeth to chew their food, are not only furnish'd with hard bills to break it; and, birds of prey, with crooked ones to tear it; but, which is more confiderable, have crops to prepare and foften it, and very strong muscular stomachs, to digeft and grind it in which work, they are ufually affifted by gravel, and little ftones, that they are led, by instinct, to swallow; great quantities whereof are often found in their stomachs.

And let it be here obferv'd, that chance is really no natural cause, or agent, but a creature of man's own making. For the things that are done in the corporeal world, are really done by the parts of the univerfal matter, acting and fuffering according to the laws of motion, established by the author of nature. But we men, looking upon fome of these parts as directed in their motions by God, or nature, and as difpofed to the attainment of certain ends; if, by the intervention of other caufes, that we are not aware of, an effect be produced, very different from that which