eye, the exercise of its office, as an optical inftrument, depends; the further provifion for its defence, for its conftant lubricity and moisture, which we fee in its focket and its lids, in its gland for the fecretion of the matter of tears, its outlet or communication with the nofe for carrying off the liquid after the eye is washed with it; thefe provifions compofe altogether an apparatus, a fyftem of parts, a preparation of means, fo manifeft in their defign, fo exquifite in their contrivance, fo fuccefsful in their iffue, fo precious and fo infinitely beneficial in their ufe, as, in my opinion, to bear down all doubt that can be raised upon the subject. And what I wish, under the title of the present chapter, to obferve, is, that, if other parts of nature were inacceffible to our enquiries, or even if other parts of nature prefented nothing to our examination but diforder and confufion, the validity of this example would remain the fame. If there were but one watch in the world, it would not be lefs certain that it had a maker. If we had never in our lives feen any but one fingle kind of hydraulic machine; yet, if of that one kind we understood the mechanism and ufe, we should be as perfectly affured that it proceeded from the hand, and thought, and fkill, of a workman, as if we vifited a museum of the arts, and faw collected there twenty different kinds of machines for drawing water, or a thousand different kinds for other purposes. Of this point each machine is a proof, independently of the reft. So it is with the evidences of a divine agency. The proof is not a conclufion, which lies at the end of a chain of reafoning, of which chain each inftance of contrivance is only a link, and of which, if one link fail, the whole falls; but it is an argument separately supplied by every separate example. An error in ftating an example affects only that example. The argument is cumulative in the fulleft fenfe of that term. The eye proves it without

the ear; the ear without the eye. The proof in each example is complete; for when the defign of the part, and the conducivenefs of its ftructure to that defign, is fhewn, the mind may set itself at reft: no future confideration can detract any thing from the force of the example.

CHAPTER VII.

OF THE MECHANICAL AND IMMECHANICAL PARTS AND FUNCTIONS OF ANIMALS AND VEGETABLES.

Ir is not that every part of an animal or vegetable has not proceeded from a contriving mind; or that every part is not conftructed with a view to its proper end and purpose, according to the laws belonging to, and governing, the fubftance or the action made ufe of in that part; or that each part is not so constructed, as to effectuate its purpofe whilft it operates according to thefe laws: but it is, because these laws them felves are not in all cafes equally underflood; or, what amounts to nearly the fame thing, are not equally exemplified in more fimple proceffes, and more fimple machines; that we lay down the diftinction, here propofed, between the mechanical parts, and other parts, of animals and vegetables.

For inftance; the principle of mufcular motion, viz. upon what cause the fwelling of the belly of the mufcle, and confequent contraction of its tendons, either by an act of the will or by involuntary irritation, depends, is wholly unknown to us. The fubftance employed, whether it be fluid, gaseous, elastic, electrical, or none of these, or nothing resembling thefe, is alfo unknown to us: of courfe the laws be

longing to that fubftance, and which regulate its action, are unknown to us. We fee nothing similar to this contraction in any machine which we can make, or any process which we can execute. So far (it is .confelfed) we are in ignorance: but no further. This power and principle, from whatever cause it proceeds, being affumed, the cellocation of the fibres to receive the principle, the difpofition of the mufcles for the ufe and application of the power, is mechanical; and is as intelligible as the adjustment of the wires and frings by which a puppet is moved. We fee therefore, as far as refpects the fubject before us, what is not mechanical in the animal frame, and what is. The nervous influence (for we are often obliged to give names to things which we know little about)-I fay the nervous influence, by which the belly or middle of the muscle is fwelled, is not mechanical. The utility of the effect we perceive; the means, or the preparation of means, by which it is produced, we do not. But obfcurity as to the origin of mufcular motion brings no doubtfulness into our obfervations upon the fequel of the process. Which obfervations relate, 1ft, to the conftitution of the muscle; in confequence of which conflitution, the fwelling of the belly or middle part is neceffarily and mechanically followed by a contraction of the tendons: 2dly, to the number and variety of the mufcles, and the correfponding number and variety of useful powers which they fupply to the animal; which is aftonishingly great: 3dly, to the judicious (if we may be permitted to ule that term, in fpeaking of the author, or of the works, of nature,) to the wife and well contrived difpofition of each muscle for its specific purpose; for moving the joint this way, and that way, and the other way; for pulling and drawing the part, to which it is attached, in a determinate and particular directio; which is a mechanical operation, exemplified

in a multitude of inftances. To mention only one; The tendon of the trochlear mufcle of the eye, to the end that it may draw in the line required, is paffed through a cartilaginous ring, at which it is reverted, exactly in the fame manner as a 1ope in a fhip is carried over a block or round a ftay, in order to make it pull in the direction which is wanted. All this, as we have faid, is mechanical and is as acceffible to inspection, as capable of being afcertained, as the mechanifm of the automaton in the Strand. Suppose the automaton to be put in motion by a magnet, (which is probable,) it will fupply us with a compar ifon very apt for our prefent purpose. Of the magnetic effluvium we know perhaps as little as we do of the nervous fluid. But magnetic attraction being affumed (it fignifies nothing from what cause it proceeds,) we can trace, or there can be pointed out to us, with perfect clearness and certainty, the mechanifm, viz. the steel bars, the wheels, the joints, the wires, by which the motion fo much admired is communicated to the fingers of the image: and to make any obfcurity, or difficulty, or contraverfy in the doctrine of magnetifm, an objection to our knowledge or our certainty concerning the contrivance, or the marks of contrivance, difplayed in the automaton, would be exactly the fame thing, as it is to make our ignorance (which we acknowledge) of the cause of nervous agency, or even of the fubftance and ftructure of the nerves themselves, a ground of question or fufpicion as to the reafoning which we inftitute concerning the mechanical part of our frame. That an animal is a machine, is a propofition neither correctly true, nor wholly falfe. The diftinction which we have been difcuffing will ferve to fhew how far the comparifon, which this expreffion implies, holds; and wherein it fails. And, whether the diftinction be thought of importance or not, it is certainly of importance to e

member, that there is neither truth nor juftice in endeavoring to bring a cloud over our under ftandings, or a diftruft into our reafonings upon this fubject, by fuggefting that we know nothing of voluntary motion, of irritability, of the principle of life, of fenfation, of animal heat, upon all which the animal functions depend; for our ignorance of thefe parts of the animal frame concerns not at all our knowledge of the mechanical parts of the fame frame. I contend, therefore, that there is mechanism in animals; that this mechanism is as properly fuch, as it is in machines made by art; that this mechanism is intelligible and certain; that it is not the lefs fo, because it often begins or terminates with fomething which is not mechanical; that whenever it is intelligible and certain, it demonftrates intention and contrivance, as well in the works of nature as in thofe of art; and that it is the best demonstration which either can afford.

But, whilft I contend for thefe propofitions, I do not exclude myfelf from afferting that there may be, and that there are, other cafes, in which, although we cannot exhibit mechanism, or prove indeed that mechanism is employed, we want not fufficient evidence to conduct us to the fame conclufion.

There is what may be called the chymical part of our frame; of which, by reafon of the imperfection of our chymistry, we can attain to no distinct knowledge: I mean, not to a knowledge, either in degree or kind, fimilar to that which we poffefs of the me chanical part of our frame. It does not therefore afford the fame fpecies of argument as that which mechanifm affords; and yet it may afford an argument in a high degree fatisfactory. The gastric juice, or the liquor which digefts the food in the ftomachs of animals, is of this clafs. Of all menftrua it is the moft active, the most univerfal. In the human.ftom