Изображения страниц

necessary to provide a cause. This, perhaps, would have been nearly the state of the question, if nothing had been before us but an unorganised, unmechanised substance, without mark or indication of contrivance. It might be difficult to show that such substance could not have existed from eternity, either in succession (if it were possible, which I think it is not, for unorganised bodies to spring from one another), or by individual perpetuity. But that is not the question now. To suppose it to be so, is to suppose that it made no difference whether he had found a watch or a stone. As it is, the metaphysics of that question have no place; for, in the watch which we are examining, are seen contrivance, design; an end, a purpose; means for the end, adaption to the purpose. And the question which irresistibly presses upon our thoughts, is, Whence this contrivance and design? The thing required is the intending mind, the adapted hand, the intelligence by which that hand was directed. This question, this demand, is not shaken off, by increasing a number or succession of substances, destitute of these properties; nor the more, by increasing that number to infinity. If it be said, that, upon the supposition of one watch being produced from another in the course of that other's movements, and by means of the mechanism within it, we have a cause for the watch in my hand, viz. the watch from which it proceeded: I deny, that for the design, the contrivance, the suitableness of means to an end, the adaption of instruments to a use (all which we discover in the watch), we have any cause whatever. It is in vain, therefore, to assign a series of such causes, or to allege that a series may be carried back to infinity; for I do not admit that we have yet any cause at all of the phenomena, still less any series of causes either finite or infinite. Here is contrivance, but no contriver; proofs of design, but no designer.

V. Our observer would farther also reflect, that the maker of the watch before him, was, in truth and reality, the maker of every watch produced from it: there being no difference (except that the latter manifests a more exquisite skill) between the making of another watch with his own hands, by the mediation of files, laths, chisels, &c. and the disposing, fixing, and inserting, of these instruments, or of others equivalent to them, in the body of the watch already made in such a manner, as to form a new watch in the course of the movements which he had given to the old one. It is only working by one set of tools, instead of another.

The conclusion which the first examination of the watch, of its works, construction, and movement, suggested, was, that it must have had, for the cause and author of that construction, an artificer, who understood its mechanism, and designed its use. This conclusion is invincible. A second examination presents us with a new discovery. The watch is found, in the course of its movement, to produce another watch, similar to itself; and not only so, but we perceive in it a system or organisation, separately calculated for that purpose. What effect would this discovery have, or ought it to have, upon our former inference? What, as hath already been said, but to increase, beyond measure, our admiration of the skill, which had been employed in the formation of such a machine? Or shall it, instead of this, all at once turn us round to an opposite conclusion, viz. that no art or skill whatever has been concerned in the business, although all other evidences of art and skill remain as they were, and this last and supreme piece of art be now added to the rest? Can this be maintained without absurdity? Yet this is atheism *.

One of the greatest of chemical philosophers, the illustrious Davy, who brought to the investigation a talent, and a love of truth never excelled, seems to have had this eloquent and logical statement of Paley's in his memory, when he was writing the concluding passages of his chapters" on the Powers and Properties of Matter." "Active powers," said this highly gifted chemist,"must be supposed to be bestowed upon some species of matter, and the impulse must be ultimately derived from the same source. In the universe nothing can be said to be automatic, as nothing can be said to be without design. An imperfect parallel may be found in human inventions; springs may move springs, and wheels, indexes; but the

motion and the regulation must be derived from the artist. Sounds may be produced by undulations of the air, undulations of the air by vibrations of musical strings, but the impulse and the melody must arise from the master."-Chem. Phil. 180.

The watch so fully, so ably, employed by Paley, as an illustration, had been similarly reasoned from many years previously by a French author, translated by a Mr. Dale in his "Philosophical Conversations." But even where our author is deficient in originality, he excels in the mode of application; he had a mental alchemy possessed by few other authors.

No person perhaps ever possessed the power of improv.



THIS is atheism; for every indication of contrivance, every manifestation of design, which existed in the watch, exists in the works of nature; with the difference, on the side of nature, of being greater and more, and that in a degree which exceeds all computation. I mean that the contrivances of nature surpass the contrivances of art, in the complexity, subtilty, and curiosity, of the mechanism; and still more, if possible, do they go beyond them in number and variety: yet, in a multitude of cases, are not less evidently mechanical, not less evidently contrivances, not less evidently accommodated to their end, or suited to their office, than are the most perfect productions of human ingenuity.

I know no better method of introducing so large a subject, than that of comparing a single thing with a single thing: an eye, for example, with a telescope *. As far as the examination of the instrument goes, there is precisely the same proof that the eye was made for vision, as there is that the telescope was made for assisting it. They are made upon the same principles; both being adjusted to the laws by which the transmission and refraction of rays of light are regulated. I speak not of the origin of the laws themselves; but such laws being fixed, the construction, in both cases, is adapted to them. For instance; these laws require, in order to produce the same effect, that the rays of light, in passing from water into the eye, should be refracted by a more convex surface, than when it passes out of air into the eye. Accordingly we find that the eye of a fish, in that part of it called the crystalline lens, is much rounder than the eye of terrestrial animals. What plainer manifestation of design can there be than this difference? What could a mathematical instrument-maker have done more to shew his knowledge of his principle, his application of that

ing upon the writings of others to a happier degree than Paley; of making the driest materials become popular and eloquent; of modernising phrases, and polishing the coarsest diction.

Thus the materials for this great work were almost entirely derived from the writings of Derham, especially from the "Physico-Theology;" the very titles of some of Derham's chapters indicate the similarity of plan followed by both these talented authors, as for instance, in the "Physico-Theology," we find "Of Animals in general," " Of the Eye," "Of the Sense of Hearing, and of Sound," "Of the Sense of Smelling," " Of the Taste," "Of Respiration," "Of the Balance of Animals, or the due Proportion in which the World is stocked with them," "Of the Consent between the Parts of Man's Body," "Of the Variety of Men's Faces, Voices, and Handwriting," "Of the Incubation of Birds," "Of the Shape and Structure of Insects," "The Sagacity of Insects to secure themselves against Winter," "Of the Inhabitants of the Waters," "Of Vegetables, Flowers, and Seeds," &c. &c.

This excellent Christian philosopher, the friend of Ray, and of all lovers of science, was born in 1657, was appointed in 1711 to preach the lecture in Bow church, founded by the great Boyle, the substance of which he afterwards published under the title of " Physico-Theology, er a demonstration of the Being and Attributes of God, from his Works of Creation:" he published also, "Astro-Theology, or a demonstration of the Being and Attributes of God, from a Survey of the Heavens;" a work on "Watch and Clock Work," and many curious papers in the Royal Society's Transactions, of which he was one of the most indefatigable members.

He also edited some of Ray's works; died in 1735, and lies buried at Upminster, in Essex, of which parish he was long the beloved vicar.-Ray's Letters. Philosophical Transactions, numbers 236 to 411. Biographia Britannica.

The eye, says Dr. Young, exhibits to an attentive observer, an arrangement of various substances, so correctly and delicately adapted to the purposes of vision, that we cannot help admiring, at every step, the wisdom by which each part is adjusted to the rest, and made to conspire in effects, so remote from what the mere external appearance promises, that we have only been able to understand by means of laborious investigation, the nature and operations of this wonderful structure, while its whole mechanism still remains far beyond all rivalship of human art.-Lectures on Natural Philosophy.

The camera obscura, invented by Baptista Porta, in 1560, gave the first idea how the actual images of external objects might be conveyed into the eye, but it was not until after the lapse of years, that Kepler, the immortal discoverer of those great laws which regulate the periods and motions of the planets, pointed out distinctly the offices performed by the several parts of the eye in the act of vision. From this to the invention of the telescope and microscope, there seems but a small step, yet these were the discoveries of accident, rather than of design, and the re-invention of the telescope by Galileo, on a mere description of its effects, serves among a thousand similar instances to show that inestimable practical applications lie open to us, if we can only bring ourselves to conceive their possibility.-Herschel, on the Study of Natural Philosophy.

knowledge, his suiting of his means to his end; I will not say to display the compass or excellence of his skill and art, for in these all comparison is indecorous, but to testify counsel, choice, consideration, purpose?

To some it may appear a difference sufficient to destroy all similitude between the eye and the telescope, that the one is a perceiving organ, the other an unperceiving instrument. The fact is, that they are both instruments. And, as to the mechanism, at least as to mechanism being employed, and even as to the kind of it, this circumstance varies not the analogy at all. For observe, what the constitution of the eye is. It is necessary, in order to produce distinct vision, that an image or picture of the object be formed at the bottom of the eye. Whence this necessity arises, or how the picture is connected with the sensation, or contributes to it, it may be difficult, nay, we will confess, if you please, impossible for us to search out. But the present question is not concerned in the inquiry. It may be true, that, in this, and in other instances, we trace mechanical contrivance a certain way; and that then we come to something which is not mechanical, or which is inscrutable. But this affects not the certainty of our investigation, as far as we have gone. The difference between an animal and an automatic statue, consists in this,-that, in the animal, we trace the mechanism to a certain point, and then we are stopped; either the mechanism becoming too subtle for our discernment, or something else besides the known laws of mechanism taking place; whereas, in the automaton, for the comparatively few motions of which it is capable, we trace the mechanism throughout. But, up to the limit, the reasoning is as clear and certain in the one case, as in the other. In the example before us, it is a matter of certainty, because it is a matter which experience and observation demonstrate, that the formation of an image at the bottom of the eye is necessary to perfect vision. The image itself can be shewn. Whatever affects the distinctness of the image, affects the distinctness of the vision. The formation then of such an image being necessary (no matter how) to the sense of sight, and to the exercise of that sense, the apparatus by which it is formed is constructed and put together, not only with infinitely more art, but upon the self-same principles of art, as in the telescope or the camera-obscura. The perception arising from the image may be laid out of the question; for the production of the image, these are instruments of the same kind. The end is the same; the means are the same. The purpose in both is alike; the contrivance for accomplishing that purpose is in both alike. The lenses of the telescope, and the humours of the eye, bear a complete resemblance to one another, in their figure, their position, and in their power over the rays light, viz. in bringing each pencil to a point at the right distance from the lens; namely, in the eye, at the exact place where the membrane is spread to receive it. How is it possible, under circumstances of such close affinity, and under the operation of equal evidence, to exclude contrivance from the one; yet to acknowledge the proof of contrivance having been employed, as the plainest and clearest of all propositions, in the other?


The resemblance between the two cases is still more accurate, and obtains in more points than we have yet represented, or than we are, on the first view of the subject, aware of. In dioptric telescopes there is an imperfection of this nature. Pencils of light, in passing through glass lenses, are separated into different colours, thereby tinging the object, especially the edges of it, as if it were viewed through a prism. To correct this inconvenience, had been long a desideratum in the art. At last it came into the mind of a sagacious optician, to inquire how this matter was managed in the eye; in which, there was exactly the same difficulty to contend with, as in the telescope *. His observation taught him, that, in the eye, the evil was cured by combining lenses composed of different substances, i. e. of substances which possessed different refracting powers. Our artist borrowed thence his hint; and produced a correction of the defect by imitating, in glasses made from different

This discovery of the achromatic telescope is not quite accurately stated by Paley. Dollond, the optician alluded to, was discussing with Klingenstierna, an eminent Swedish philosopher, and the celebrated geometer Euler, some abstract theoretical investigations of the latter, which led him to speculate on the possibility of improving the telescope, and terminated in our countryman's

complete and happy execution of the idea.
"It is,"
observes Mr. Herschel," a memorable case in science,
though not a singular one, where the speculative geometer
in his chamber, apart from the world, and existing among
abstractious, has originated views of the noblest practical
application."-On the Study of Natural Philosophy.

materials, the effects of the different humours through which the rays of light pass before they reach the bottom of the eye. Could this be in the eye without purpose, which suggested to the optician the only effectual means of attaining that purpose?

But farther; there are other points, not so much perhaps of strict resemblance between the two, as of superiority of the eye over the telescope; yet of a superiority which, being founded in the laws that regulate both, may furnish topics of fair and just comparison. Two things were wanted to the eye, which were not wanted (at least in the same degree) to the telescope; and these were the adaptation of the organ, first, to different degrees of light; and secondly, to the vast diversity of distance, at which objects are viewed by the naked eye, viz. from a few inches to as many miles. These difficulties present not themselves to the maker of the telescope. He wants all the light he can get; and he never directs his instrument to objects near at hand. In the eye, both these cases were to be provided for; and for the purpose of providing for them, a subtile and appropriate mechanism is introduced.


I. In order to exclude excess of light, when it is excessive, and to render objects visible under obscurer degrees of it, when no more can be had, the hole or aperture in the through which the light enters, is so formed, as to contract or dilate itself for the purpose of admitting a greater or less number of rays at the same time. The chamber of the eye is a camera-obscura, which, when the light is too small, can enlarge its opening: when too strong, can again contract it: and that without any other assistance than that of its own exquisite machinery. It is farther also, in the human subject, to be observed, that this hole in the eye, which we call the pupil, under all its different dimensions, retains its exact circular shape. This is a structure extremely artificial. Let an artist only try to execute the same; he will find that his threads and strings must be disposed with great consideration and contrivance, to make a circle which shall continually change its diameter, yet preserve its form. This is done in the eye by an application of fibres, i. e. of strings similar, in their position and action, to what an artist would and must employ, if he had the same piece of workmanship to perform *.

II. The second difficulty which has been stated, was the suiting of the same organ to the perception of objects that lie near at hand, within a few inches, we will suppose of the eye, and of objects which are placed at a considerable distance from it, that, for example, of as many furlongs (I speak in both cases of the distance at which distinct vision can be exercised). Now this, according to the principles of optics, that is, according to the laws by which the transmission of light is regulated (and these laws are fixed), could not be done without the organ itself undergoing an alteration, and receiving an adjustment, that might correspond with the exigency of the case, that is to say, with the different inclination to one another under which the rays of light reached it. Rays issuing from points placed at a small distance from the eye, and which constantly must enter the eye in a spreading or diverging order, cannot, by the same optical instrument in the same state, be brought to a point, i. e. be made to form an image, in the same place with rays proceeding from objects situated at a much greater distance, and which rays arrive at the eye in directions nearly (and physically speaking) parallel. It requires a rounder lens to do it. The point of concourse behind the lens must fall critically upon the retina, or the vision is confused; yet, other things remaining the same, this point, by the immutable properties of light, is carried farther back when the rays proceed from a near object, than when they are sent from one

The exclusion of too great an excess of light was not the only difficulty, humanly speaking, that had to be overcome in the formation of an organ, to be usefully employed by all animals, for some of these are in motion only during the hours of darkness. A change of apparatus was here required to render it available during the greatest absence of light. It has been found the nocturnal animals have eyes with very dilatable pupils; and very little of that dark substance (pigmentum nigrum), so abundant between the retina and the choroid coat of those creatures that appear most in the sunlight hours. The consequences are obvious, the eyes of the former

are better adapted to receive, and more susceptible of the influence of light. Moreover, the eyes of nocturnal animals have an organisation which reflects light from the back of the eye upon the pupils, and thus gives them the repeated benefit of every ray. It is certain, that those of the cat are luminous in the dark; and there are not wanting examples of men in very early periods, as well as in modern times, who, under certain cirer mstances of excitement, or after long confinement in darkness, could see during the almost total privation of light.-Pliny, Dr. Willis, Dr. Briggs, Mr. Boyle.


that is remote. A person who was using an optical instrumeut would manage this matter by changing, as the occasion required, his lens or his telescope; or by adjusting the distance of his glasses with his hand or his screw: but how is this to be managed in the eye? What the alteration was, or in what part of the eye it took place, or by what means it was effected (for if the known laws which govern the refraction of light be maintained, some alteration in the state of the organ there must be), had longed formed a subject of inquiry and conjecture. The change, though sufficient for the purpose, is so minute as to elude ordinary observation. Some very late discoveries, deduced from a laborious and most accurate inspection of the structure and operation of the organ, seem at length to have ascertained the mechanical alteration which the parts of the eye undergo. It is found, that by the action of certain muscles, called the straight muscles, and which action is the most advantageous that could be imagined for the purpose,-it is found, I say, that whenever the eye is directed to a near object, three changes are produced in it at the same time, all severally contributing to the adjustment required. The cornea, or outermost coat of the eye, is rendered more round and prominent: the crystalline lens underneath is pushed forward; and the axis of vision, as the depth of the eye is called, is elongated. These changes in the eye vary its power over the rays of light in such a manner and degree as to produce exactly the effect which is wanted, viz. the formation of an image upon the retina, whether the rays come to the eye in a state of divergency, which is the case when the object is near to the eye, or come parallel to one another, which is the case when the object is placed at a distance. Can any thing be more decisive of contrivance than this is? The most secret laws of optics must have been known to the author of a structure endowed with such a capacity of change. It is as though an optician, when he had a nearer object to view, should rectify his instrument by putting in another glass, at the same time drawing out also his tube to a different length.

Observe a new-born child first lifting up its eyelids. What does the opening of the curtain discover? The anterior part of two pellucid globes, which, when they come to be examined, are found to be constructed upon strict optical principles; the self-same principles upon which we ourselves construct optical instruments. We find them perfect for the purpose of forming an image by refraction; composed of parts executing different offices: one part having fulfilled its office upon the pencil of light, delivering it over to the action of another part; that to a third, and so onward: the progressive action depending for its success upon the nicest and minutest adjustment of the parts concerned yet these parts so in fact adjusted, as to produce, not by a simple action or effect, but by a combination of actions and effects, the result which is ultimately wanted. And forasmuch as this organ would have to operate under different circumstances, with strong degrees of light and with weak degrees, upon near objects and upon remote ones, and these differences demanded, according to the laws by which the transmission of light is regulated, a corresponding diversity of structure; that the aperture, for example, through which the light passes, should be larger or less; the lenses rounder or flatter, or that their distance from the tablet, upon which the picture is delineated, should be shortened or lengthened; this, I say, being the case and the difficulty to which the eye was to be adapted, we find its several parts capable of being occasionally changed, and a most artificial apparatus provided to produce that change. This is far beyond the common regulator of a watch, which requires the touch of a foreign hand to set it but it is not altogether unlike Harrison's contrivance for making a watch regulate itself, by inserting within it a machinery, which by the artful use of the different expansion of metals, preserves the equability of the motion under all the various temperatures of heat and cold in which the instrument may happen to be placed. The ingenuity of this last contrivance has been justly praised. Shall, therefore, a structure which differs from it chiefly by surpassing it, be accounted no contrivance at all? or, if it be a contrivance, that is without a contriver *?

The motions of the eye, multitudinous in variety, and rapid as they are, are not among the phenomena least worthy of remark in this wondrous organ. The immediate action of the recti-muscles are simply those of

directing the axis of the eye towards different points. According to their attachments they will elevate or depress the pupil, turn it towards the nose or the temple. By the different combined actions of these muscles, the

« ПредыдущаяПродолжить »