R. ;>•?? ^rj^- .^^ /^Ji-^ I 3 T153 OOObSSlfi 2 Date Due ^^6^'^^ % 1 2 -! 1 Demco 293-5 NATURAL THEOLOGY; OR EVIDENCES OF THE EXISTENCE AND ATTRIBUTES OF THE DEITY, COLLECTED FROM THE APPEARANCES OF NATURE. BY WILLIAM PALEY, D. D. ILLUSTRATED BY A SERIES OF PLATES, AND EXPLANATORY NOTES, BY JAMES PAXTON, MEMBF.R OF THE ROYAL COLLEGE OF SURGEONS, LONDON. VOL. I. THIRD EDITION. OXFORD : PRINTED FOR .T. VINCENT; WHITTAKER AND CO ; AND SIMl'KIN AND MARSHALL, LONDON ; 1836. ■P3 OXFORD : PRINTED BY J. VINCENT. 60 V HONOURABLE AND RIGHT REVEREND ^ SHUTE BARRINGTON, LL.D. lord bishop of durham. My Lord, To your suggestion the world is \ indebted for the existence of Dr. Paley's valuable work on Natural Theology. The universal and ^ permanent esteem in which it has been held in this country, and its favourable reception in France, even after the desolating influence of ^ the Revolution, have abundantly approved your \ ~^ Lordship's selection both of the subject and of the P^ person to whom you intrusted it. In looking round, then, for a patron for these Illustrations, it was natural to have recourse to him who was the original suggestor of the ^ work which it is their object to explain. Nor ^ was I disappointed in my wish ; your Lordship IV DEDICATION. not only condescending to approve of the design but to encourage me in its prosecution, by your very liberal support. For this distinguished ho- nour you will believe me deeply sensible ; and if I may indulge the hope that my humble efforts will increase the utility of so eminent a writer, I shall consider it the highest gratification. I am, My Lord, With great veneration, Your Lordship's most obliged And obedient servant, JAMES PAXTON, Oxford, January 1, 1826. PREFACE. The works of Dr. Paley have acquired that popularity which renders it scarcely necessary to observe that his Natural Theology was written to establish the truth of the agency and wisdom of the Deity from the admirable contrivances and mechanism displayed in natural objects, inferring from thence that the knowledge and power requi- site for the formation of created nature must be infinite. The principal physical arguments made use of, relate to organs destined to mechanical functions, as the bones of man — the muscles — the structure of animals, or comparative anatomy — prospective and compensatory contrivances — insects and plants : with most of these objects the anatomist only can be conversant ; but all admit of graphic represen- tation, and such has been attempted. The designs of the following plates are original, obtained from the most authentic sources, and submitted to the critical examination of the most VI PREFACE. competent judges. It is hoped that the illustra- tions will be found the more interesting from their being simple and unincumbered by parts irrelevant to the subject of the author. These are accom- panied by notes, which are intended to supply de- fective or correct erroneous statements, and to ex- plain the plates. The undertaking originated in the diflficulty of understanding the various descriptions introduced by Paley, not however from his want of clearness, for the subjects in general are plainly and correctly described ; but it is evident that visible represen- tations strike the mind more forcibly than mere descriptions. It is therefore presumed that the subsequent illustrations will be an acquisition, by bringing \-ividly to the imagination, objects of which only an imperfect idea could otherwise be formed ; and that they will consequently render the work more inteUigible to the general reader. PREFACE TO THE SECOND EDITION. X "annot be necessary to insist on the superior characici and merits of the Natural Theology of Dr. Paley. The high estimation in which the original work has been held, from the first publication to the present time, supersedes any encomium. The Illustrations and Notes con- sequently met with a reception proportionably fa- vourable ; its success indeed exceeded every ex- pectation the editor had entertained ; and it be- comes a matter of surprise, that so popular an author had not before received the aid of plates to exhibit animal mechanism, and vegetable forma- tion, with notes to bring the physical statements down to the present advanced stage of natural knowledge ; for it was well known, that with the utmost attention, the fancy could not follow the author in his descriptions of structure and func- tions, especially when complicated contrivance, either in animal or vegetable nature, were to be unfolded. To comprehend the subject thoroughly also required a somewhat deeper acquaintance with the several sciences of anatomy, entomology, and botany, than most persons can be supposed to Vlll PREFACE. possess. The editor therefore trusts, that the illustrations and notes, particularly in their improved state, will be found to meet the difficulty and sup- ply the deficiency. In presenting the second edition to the public, the editor believes that the notes have not been enlarged without giving increasing value and in- terest to the text. The references have been corrected, a number of new figures introduced, and two plates added, containing such objects which have been pointed out as being required to render the book more complete. Several corrections and additions have been made from suggestions in the Edinburgh Review, &c. In the Entomological department the editor begs to acknowledge his obligations to A. Ingpen, Esq. and for several of the Botanical notes he is indebted to Mr. Baxter, of the Botanical Gardens of the University of Oxford. Oxford, Jrnie, 1,1828. CONTENTS. VOL. I. CHAPTER I. STATE OF THE ARGUMENT. Stone. Watch. Description of the parts. Eight statements of the case. CHAPTER II. STATE OF THE AKGUMENT CONTINUED. CHAPTER III. APPLICATION OF THE ARGUMENT Eye and telescope compared. Light — Distance . Mechanism of the iris. Straight muscles. Bony rim of the eyes of birds, Marsupium. Eyes of fishes. of the eel. Minuteness of picture on the retina. Socket — Eye-brow — Eye-lid — Lachrymal apparatus. Nictitating membrane in birds — its muscles. Expedients. Why means used. Human ear. Ear of elephant. b CONTENTS. CHAPTER IV. OF THE SUCCESSION OF PLANTS AND ANIMALS. No account hereby of contrivance. Plants. Oviparous ~j Viviparous > animals. Rational j Instance in a gardener and flowers. CHAPTER V. APPLICATION OF THE ARGUMENT CONTINUED. Repetition from Chapter I. Imperfection. Superfluous parts. Atheistic argument. Remains of possible forms. Use arising out of the parts. A principle of order. Of our ignorance. CHAPTER VI. THE ARGUMENT CUMULATIVE. CHAPTER VII. THE MECHANICAL AND IMMECHANICAL PARTS AND FUNCTIONS OF ANIMALS AND VEGETABLES. Imperfection of knowledge no proof of want of contrivance. Muscular action. Trochlear muscle. Chemistry. Electricity. Secretion. Kidney. CONTENTS. XI CHAPTER VIII. MECHANICAL ARRANGEMENT IN THE HUMAN FRAME. Of Bones. Neck. Fore-arm. Spine. of the serpent. Chest. Knee-pan. Shoulder-blade. Joints. Ball and socket. Gynglymus or hinge-joint. Knee. Ligaments. Ankle. Shoulder. Passage of blood-vessels. Gristle. Synovia. Moveable cartilages. How well the joints wear. Immoveable joints. CHAPTER IX. OP THE MUSCLES. Suitableness to the joints. Sartorius muscle. Oblique muscles of the head. Antagonist muscles in the arm. Not obstructing one another. Action wanted where their substance would be inconvenient. Variety of figure. How many must be right for health. Particular muscles. Celerity of motion. Tongue — Mouth — Nose. Music — Writing. Sphincters. XU CONTENTS. Combination — Delicacy- Mechanical disadvantages. Single muscles. Lower jaw. Perforation of tendons. Bandage at the ankles. Hypothesis from appetency repelled. Keill's enumeration of muscles. Why mechanism not more striking. Description inferior to inspection. Quotation from Sten'o. CHAPTER X. OF THE VESSELS OP ANIMAL BODIES. 1. Circulation of the blood. Disposition of the blood-vessels — Arteries — \'cins. The heart as receiving and returning the blood. As referable to the lungs. Valves of the heart. Vital motions involuntary. Pericardium. 2. Alimentary system. Passage of the food through the stomach to the intestines. of the chyle through the lacteals and thoracic duct to the blood. Length of intestines. Peristaltic motion. Tenuity of the lacteals. Valves of the thoracic duct. Entrance of near the neck. 3. Gall bladder. Oblique insertion of the biliary duct into the intestines. 4. Parotid gland and duct. 5. Larynx. Trachea — Gullet — Epiglottis. Rings of the trachea. Sensibility — Musical instrument. Lifting' the arm to the head. CONTENTS. Xin CHAPTER XI. OP THE ANIMAL STRUCTURE REGARDED AS A MASS. 1. Correspondence of sides. Not belonging to the separate limbs. Nor to the internal contents. Nor to the feeding vessels. 2. Package. Heart. Lungs. Liver. Bladder. Kidneys. Pancreas. Spleen. Omentum. Septa of the brain. Guts. Mesentery. 3. Beauty. In animated nature. In flowers. Whether any natural sense of beauty. 4. Concealment. 5. Standing. C. Interrupted analogies. Periosteum covering all bones except the teeth. Skin terminating at the nails. Solid case for the brain. CHAPTER Xn. COMPARATIVE ANATOMY. 1. Covering of animals. Of man — Of birds. Structure of feathers. Black down. 2. Mouths of animals. Bills of birds. Serrated bills. Affinity of mouths. XIV CONTENTS. 3. Gullets of animals. 4. Intestines of animals. Valvulae conniventes. Length of intestines. 5. Bones of animals. of birds. 6. Lungs of animals. of birds. 7. Birds oviparous. 8. Instruments of motion. Wings of birds. Fins offish. Web-feet of water-fowl. 9. Senses of animals. CHAPTER XIII. PECULIAR ORGANIZATIONS. Pax-wax of quadrupeds. Oil of birds. Air-bladder of fish. Fang of viper. Bag of opossum. Pelvis. Middle claw of heron. Stomach of camel. Tongue of woodpecker. Babyrouessa. VOL. II. CHAPTER XIV. PROSPECTIVE CONTRIVANCES. Teeth. Temporary and permanent. Milk. CONTENTS. XV Eye of the foetus. Lungs of the foetus — Foramen ovale. Ductus arteriosus, &c. CHAPTER XV. RELATIONS, ILLUSTRATED IN A WATCH. Alimentary system. Kidneys, ureters, and bladder. Eyes, hands, feet. Sexes. Teats and mouth. Particular relations. Swan. Mole. CHAPTER XVI. COMPENSATION. Elephant's proboscis. Hook in the bat's wing. Crane's neck. Parrot's bill. Spider's web. Multiplying-eyes of insects. Eye of the chameleon. Intestines of the alopecias. Snail — Muscle — Cockle — Lobster. Sloth — Sheep. More general compensations. Want of fore-teeth — Rumination. In birds, want of teeth supplied by a gizzard. Reptiles. CHAPTER XVII. THE RELATION OF ANIMATED BODIES TO INANIMATE NATURE. Wings of birds — Fins of fish — Air and water. Ear to the air. Organs of speech— Voice and respiration to air. XVI CONTENTS. Eye to light. Size of animals to external things. Of the inhabitants of the earth and sea to their elements. Sleep to night. CHAPTER XVIII. INSTINCTS. Incubation of eggs. Deposition of eggs of insects. Solution from sensations considered. CHAPTER XIX. OF INSECTS. Elytra of the scarabaeus. Borer of flies. Sting of the bee. Proboscis. Metamorphosis of insects. Care of eggs. Observations limited to particular species. Thread of silkworm and spider. Wax and honey of bee. Sting. Forceps of the panorpa tribe. Brushes of flies. Glow-worm. Motion of the larva of the dragon-fly. Gossamer spider. Shell animals. Snail shells. Univalve shell-fish. Bivalve. Lobster shell. Variety of insects. CHAPTER XX. OF PLANTS. Preservation, i)erfection, and dispersing of seed, Trees . CONTENTS. XVll Germination. Tendrils. Particular species. Grasses. Vallisneria. Cuscuta Europaea. Misseltoe. Colchium autumnale. Dionsea muscipula. CHAPTER XXI THE ELEMENTS. Consolidation of uses. 1. Air. Reflecting light. Evaporating fluids. Restoratives of purity. 2. Water. Purity. Insipidity. Circulation. 3. Fire. Dissolvent power. 4. Light. Velocity. Tenuity. CHAPTER XXII. ASTRONOMY. Fixing the source of light and heat in the centre. Permanent axis of rotation. Spheroidicity of the earth. (Jf centripetal forces. Attraction indift'erent to laws. Admissible laws within narrow limits. Of admissible laws, the present the best. United attraction of a sphere, the same as of the constituent particles. C XVin CONTENTS. The apsides fixed. Figures of the planetary orbits. Buffon's hypothesis. CHAPTER XXIII. OF THE PERSONALITY OF THE DEITY. Not the object of our senses. Contrivance proves personality. Misapplication of laws. Mechanism. Second causes. Of generation as a principle. Atheistic suppositions. Buffon's organic nodules. Appetencies. Analogies by which they are supported. Camel's bunch. Crane's thighs. Pelican's pouch. Analogy strained. Solutions contradicted. By ligaments — Valves. By senses of animals. By the parts without motion. By. plants. CHAPTER XXIV. OF THE NATURAL ATTRIBUTES OF THE DEITY. Omnipotence. Omnipresence. Omniscience. Eternity. Self-existence. Necessary existence. Spirituality. CONTENTS. XIX CHAPTER XXV. THE UNITY OP THE DEITY. From the laws of attraction, and the presence of light among the heavenly bodies. From the laws of nature upon our globe. Resemblance of animals. Fish. Insects. CHAPTER XXVI. THE GOODNESS OF THE DEITY. From the parts and faculties of animals. The actual happiness of young animals. — — winged insects. aphides. —fish. Of old age. Of different animal habits. Prepollency of happiness. Causes of not observing it. Quotation. Apparent exceptions. Venomous animals. Animals of prey. . Taste. Adaptation of senses. Property, origin of. Physical evils of imperfection. ■ finiteness. bodily pain. mortal diseases. death. Civil evils of population. distinctions. wealth. idleness. Objections from chance answered. XX CONTENTS. Must be chance in the midst of design. Ignorance of observance. Advantages of chance. Disease. Seasons. Station. Acquirability. Sensible interposition. Probation. CHAPTER XXVII. CONCLUSION. Natural religion prepares the way for revelation. HONOURABLE AND RIGHT REVEREND SHUTE BARRINGTON, LL. D. lord bishop of durham. My Lord, The folio wing- Work was under- taken at your Lordship's recommendation, and, amongst other motives, for the purpose of making the most acceptable return that I could, for a great and important benefit conferred upon me. It may be unnecessary, yet not perhaps quite impertinent, to state to your Lordship, and to the reader, the several inducements that have led me once more to the press. The favour of my first and ever-honoured Patron had put me in posses- sion of so liberal a provision in the Church, as abundantly to satisfy my wants, and much to exceed my pretensions. Your Lordship's munifi- cence, in conjunction with that of some other ex- cellent Prelates, who regarded my services with XXll DEDICATION. the partiality with which your Lordship was pleased to consider them, hath since placed me in eccle- siastical situations, more than adequate to every object of reasonable ambition. In the mean time, a weak, and, of late, a painful state of health, de- prived me of the power of discharging the duties of my station in a manner at all suitable, either to my sense of those duties, or to my most anxious wishes concerning them. My inability for the public functions of my -profession, amongst other consequences, left me much at leisure. That lei- sure was not to be lost. It was only in my study that I could repair my deficiencies in the Church ; it was only through the press that I could speak. These circumstances entitled your Lordship in particular to call upon me for the only species of exertion of which I was capable, and disposed me without hesitation to obey the call in the best manner that I could. In the choice of a subject I had no place left for doubt : in saying which, I do not so much refer, either to the supreme im- portance of the subject, or to any scepticism con- cerning it with which the present times are charged, as I do to its connexion with the subjects treated of in my former publications. The following DEDICATION. XXlll discussion alone was wanted to make up my works into a system : in which works, such as they are, the public have now before them, the Evidences of Natural Religion, the Evidences of Revealed Religion, and an account of the duties that result from both. It is of small importance that they have been written in an order the very reverse of that in which they ought to be read. I commend, therefore, the present volume to your Lordship's protection, not only as, in all probability, my last labour, but as the completion of a regular and com- prehensive design. Hitherto, my Lord, I have been speaking of myself, and not of my Patron. Your Lordship wants not the testimony of a Dedication ; nor any testimony from me : I consult, therefore, the im- pulse of my own mind alone when I declare, that in no respect has my intercourse with your Lord- ship been more gratifying to me, than in the op- portunities which it has afforded me, of observing your earnest, active, and unwearied solicitude, for the advancement of substantial Christianity ; a soUcitude, nevertheless, accompanied with that can- dour of mind, which suffers no subordinate dif- XXIV DEDICATION. ferences of opinion, when there is a coincidence in the main intention and object, to produce any alienation of esteem, or diminution of favour. It is fortunate for a country, and honourable to its government, when qualities and dispositions like these are placed in high and influencing stations. Such is the sincere judgment which I have formed of your Lordship's character, and of its public value : my personal obligations I can never forget. Under a due sense of both these considerations, I beg leave to subscribe myself, with great respect and gratitude. My Lord, Your Lordship's faithful And most devoted servant, WILLIAM PALEY. Bishop- Wearmo2ith, Jiili,, 1802. NATURAL THEOLOGY CHAPTER I. STATE OF THE ARGUMENT. In crossing a heath, suppose I pitched my foot against a stone^ and were asked how the stone came to be there ; I might possibly answer, that, for any thing I knew to the contrary, it had lain there for ever ; nor v»^ould it perhaps be very easy to show the absurdity of this answer. But suppose I had found a ivatcli upon the ground, and it should be inquired how the watch happened to be in that place ; I should hardly think of the answer which I had before given, that for anything I knew, the watch might have always been there. Yet why should not this answer serve for the watch as well as for the stone ? why is it not as admissible in the second case, as in the first? For this reason, and for no other, viz. that, when we come to inspect the watch, we perceive (what we could not discover in the stone) that its several parts are framed and put together f v a purpose, 2 STATE OF e. g. that they are so formed and adjusted as to produce motion, and that motion so regulated as to point out the hour of the day : that if the different parts had been differently shaped from what they are, of a different size from what they are, or placed after any other manner, or in any other order than that in which they are placed, either no motion at all would have been carried on in the machine, or none which would have answered the use that is now served by it. To reckon up a few of the plainest of these parts, and of their offices, all tending to one result : — we see a cylin- drical box containing a coiled elastic spring, which, by its endeavour to relax itself, turns round the box.* We next observe a flexible chain (artifi- cially wrought for the sake of flexure) communi- cating the action of the spring from the box to the fusee. t We then find a series of wheels,^ the * Tab. I. Fig. 1. The box, or barrel, containing the main spring, which is the first power ; and the chain which communi- cates the power to — ■j- Fig. 2. The fusee and great wheel. The fusee is tapered at the top to correct the irregular recoil of the spring. The great wheel turns — X Fig. 3. The centre wheel and pinion, which makes one revolu- tion in an hour, carries the minute hand, and turns — Fig. 4. The third wheel and pinion, which turns the contrite wheel. Fig. 5. The contrite vvheel, which makes one revolution in a minute, and turns the balance or escape wheel. Fig. 6. The balance wheel, which acts upon the pallets of the verge, and escapes, or drops from one pallet to another alternately, thereby keeping the balance in constant vibration. TAB o I Puhlislu-d h J.ri-netnl.O.rford,. THE ARGUMENT. 3 teeth of which catch in, and apply to, each other, conducting the motion from the fusee to the ba- lance,* and from the balance to the pointer; t and at the same time, by the size and shape of those wheels, so regulating that motion, as to terminate in causing an index, by an equable and measured progression, to pass over a given space in a given time. We take notice that the wheels are made of brass in order to keep them from rust: the springs of steel, no other metal being so elastic ; that over the face of the watch there is placed a glass, a ma- terial employed in no other part of the work, but in the room of which, if there had been any other than a transparent substance, the hour could not be seen without opening the case. This mechanism being observed (it requires indeed an examination of the instrument, and perhaps some previous know- ledge of the subject, to perceive and understand it ; but being once, as we have said, observed and un- derstood,) the inference, we think, is inevitable, * Fig. 7. The balance verrje, and balance or pendulum spring, which regulates the whole machine. -|- Fig. 8. The cannon jrinion, affixed to the centre wheel ar- bour, on which the minute hand is placed. Fig. 9. The minute wheel. Fig. 10. The hour wlieel. The two last mentioned wheels are turned by the cannon pinion, and having a greater number of teeth, move much slower than the cannon pinion, and mark the hour by the hand on the dial. The above is a description of the several wheels alluded to by Paley. Their relative situation, and combined movement, may be seen by the simple inspection of a v. atch. 4 STATE OF that the watch must have had a maker : that there must have existed, at some time, and at some place or other, an artificer or artificers, v/ho fijrmed it for the purpose which we find it actually to answer j who comprehended its construction, and designed its use. I. Nor would it, I apprehend, weaken the con- clusion, that we had never seen a watch made ; that we had never known an artist capable of making one : that we were altogether incapable of execut- ing such a piece of workmanship ourselves, or of understanding in what manner it was performed ; all this being no more than what is true of some exquisite remains of ancient art, of some lost arts, and, to the generality of mankind, of the more cu- rious productions of modern manufacture. Does one man in a million know how oval frames are turned ? Ignorance of this kind exalts our opinion of the unseen and unknown artist's skill, if he be unseen and unknown, but raises no doubt in our minds of the existence and agency of such an ar- tist, at some former time, and in some place or other. Nor can I perceive that it varies at all the inference, whether the question arise concerning a human agent, or concerning an agent of a dif- ferent species, or an agent possessing, in some re- spects, a different nature. II. Neither, secondly, would it invalidate our conclusion, that the watch sometimes went wrong, or that it seldom went exactly right. The pur- THE ARGUMENT pose of the machinery, the design and the de- signer, might be evident, and in the case supposed would be evident, in whatever way we accounted for the irregularity of the movement, or whether we could account for it or not. It is not necessary that a machine be perfect, in order to shew with what design it was made : still less necessary, where the only question is, Vv'hether it were made with any design at all. III. Nor, thirdly, would it bring any uncer- tainty into the argument, if there were a few parts of the watch, concerning which we could not dis- cover, or had not yet discovered, in what manner they conduced to the general effect ; or even some parts, concerning which we could not ascertain, whether they conduced to that effect in any man- ner whatever. For, as to the first branch of the case ; if by the loss, or disorder, or decay of the parts in question, the movement of the watch were found in fact to be stopped, or disturbed, or re- tarded, no doubt would remain in our minds, as to the utility or intention of these parts, although we should be unable to investiofate the manner ac- cording to which, or the connexion by which, the ultimate effect depended upon their action or as- sistance ; and the more complex is the machine, the more likely is this obscurity to arise. Then, as to the second thing supposed, namely, that there were parts which might be spared, without prejudice to the movement of the watch, and that 6 STATE OF we had proved this by experiment — these super- fluous parts, even if we were completely assured that they were such, would not vacate the reason- ing which we had instituted concerning other parts. The indication of contrivance remained, with respect to them, nearly as it was before. IV. Nor, fourthly, would any man in his senses think the existence of the watch, with its various machinery, accounted for, by being told that it was one out of possible combinations of material forms ; that whatever he had found in the place where he found the watch, must have contained some internal configuration or other ; and that this configuration might be the structure now ex- hibited, viz. of the works of a watch, as well as a different structure. V. Nor, fifthly, would it yield his enquiry more satisfaction to be answered, that there existed in things a principle of order, which had disposed the parts of the watch into their present form and situation. He never knew a watch made by the principle of order ; nor can he even form to him- self an idea of what is meant by a principle of order distinct from the intelligence, of the watch- maker. VI. Sixthly, he would be surprised to hear that the mechanism of the watch was no proof of contrivance, only a motive to induce the mind to think so. VII. And not less surprised to be informed. THE ARGUMENT. that the watch in his hand was nothing more than the result of the laws of metallic nature. It is a perversion of language to assign any law as the efficient, operative cause of any thing. A law pre-supposes an agent ; for it is only the mode according to which an agent proceeds : it implies a power ; for it is the order, according to which that power acts. Without this agent, without this power, which are both distinct from itself, the law does nothing ; is nothing. The expression " the law of metallic nature," may sound strange and harsh to a philosophic ear ; but it seems quite as justifiable as some others which are more familiar to him, such as "the law of vegetable nature," *'the law of animal nature," or indeed as "the law of nature" in general, when assigned as the cause of phenomena, in exclusion of agency and power ; or when it is substituted into the place of these. VIII. Neither, lastly, would our observer be driven out of his conclusion, or from his confidence in its truth, by being told that he knew nothing at all about the matter. He knows enough for his argument : he knows the utility of the end : he knows the subserviency and adaptation of the means to the end. These points being known, his ignorance of other points, his doubts concern- ing other points, affect not the certainty of his reasoning. The consciousness of knowing little need not beget a distrust of that which he does know. STATE OF Tin: CHAPTER II. STATE OF THE ARGUMENT CONTINUED. Suppose, in the next place, that the person who found the watch, should, after some time, discover that, in addition to all the properties which he had hitherto observed in it, it possessed the unexpected property of producing, in the course of its move- ment, another watch like itself, (the thing is con- ceivable;) that it contained within it a mechanism, a system of parts, a mould for instance, or a com- plex adjustment of laths, files, and other tools, evidently and separately calculated for this pur- pose ; let us inquire, what effect ought such a dis- covery to have upon his former conclusion, I. The first effect would be to increase his ad- miration of the contrivance, and his conviction of the consummate skill of the contriver. Whether he regarded the object of the contrivance, the dis- tinct apparatus, the intricate, yet in many parts intelligible mechanism, by which it was carried on, he would perceive, in this new observation, nothing but an additional reason for doing what he had already done, — for referring the construc- tion of the watch to design, and to supreme art. If that construction without this property, or, ARGUMENT CONTINUED. 9 which is the same thing, before this property had been noticed, proved intention and art to have been employed about it ; still more strong would the proof appear, when he came to the knowledge of this further property, the crown and perfection of all the rest. II. He would reflect, that though the watch before him were, in some sense, the maker of the watch which was fabricated in the course of its movements, yet it was in a very different sense from that in which a carpenter, for instance, is the maker of a chair ; the author of its contrivance, the cause of the relation of its parts to their use. With respect to these, the first watch was no cause at all to the second : in no such sense as this was it the author of the constitution and order, either of the parts which the new watch contained, or of the parts by the aid and instrumentality of which it was produced. We might possibly say, but with great latitude of expression, that a stream of water ground corn ; but no latitude of expression would allow us to say, no stretch of conjecture could lead us to think, that the stream of water built the mill, though it were too ancient for us to know who the builder was. What the stream of water does in the affair, is neither more nor less than this ; by the application of an unintelligent im- pulse to a mechanism previously arranged, arranged independently of it, and arranged by intelligence, an effect is produced, viz. the corn is ground. But c 10 STATE OF THE the effect results from the arrangement. The force of the stream cannot be said to be the cause or author of the effect, still less of the arrangement. Understanding and plan in the formation of the mill were not the less necessary, for any share which the water has in grinding the com ; yet is this share the same as that which the watch would have contributed to the production of the new watch, upon the supposition assumed in the last section. Therefore, III. Though it be now no longer probable, that the individual watch, which our observer had found, was made immediately by the hand of an artificer, yet doth not this alteration in any-wise affect the inference, that an artificer had been originally em- ployed and concerned in the production. The ar- gument from design remains as it was. Marks of design and contrivance are no more accounted for now than they were before. In the same thing, we may ask for the cause of different properties. We may ask for the cause of the colour of a body, of its hardness, of its heat ; and these causes may be all different. We are now asking for the cause of that subserviency to a use, that relation to an end, which we have remarked in the watch before us. No answer is given to this question, by telling us that a preceding watch produced it. There can- not be design without a designer ; contrivance, without a contriver ; order, without choice ; arrange- ment, without any thing capable of arranging: sub- ARGUMENT CONTINUED. 11 serviency and relation to a purpose, without that which could intend a purpose ; means suitable to an end, and executing their office in accomplishing that end, without the end ever having been con- templated, or the means accommodated to it. Ar- rangement, disposition of parts, subserviency of means to an end, relation of instruments to a use, imply the presence of intelligence and mind. No one, therefore, can rationally believe, that the in- sensible, inanimate watch, from which the watch before us issued, was the proper cause of the me- chanism we so much admire in it ; — could be truly said to have constructed the instrument, disposed its parts, assigned their office, determined their order, action, and mutual dependency, combined their several motions into one result, and that also a result connected with the utilities of other beings. All these properties, therefore, are as much unac- counted for as they were before. IV. Nor is any thing gained by running the difficulty farther back, i. e. by supposing the watch before us to have been produced from another watch, that from a former, and so on indefinitely. Our going back ever so far brings us no nearer to the least degree of satisfaction upon the subject. Contrivance is still unaccounted for. We still want a contriver. A desio^nino- mind is neither supplied by this supposition, nor dispensed with. If the difficulty were diminished the farther we went back, by going back indefinitely we might 12 STATE OF THE exhaust it. And this is the only case to which this sort of reasoning applies. A¥here there is a tendency, or, as we increase the number of terms, a continual approach towards a limit, there^ by supposing the number of terms to be what is called infinite, we may conceive the limit to be attained : but where there is no such tendency, or approach, nothing is effected by lengthening the series. There is no difference, as to the point in question, (whatever there may be as to many points,) be- tween one series and another ; between a series which is finite, and a series which is infinite. A chain, composed of an infinite number of links, can no more support itself, than a chain composed of a finite number of links. And of this we are assured, (though we never can have tried the ex- periment,) because, by increasing the number of links, from ten for instance to a hundred, from a hundred to a thousand, &c. we make not the smallest approach, we observe not the smallest tendency, towards self-support. There is no dif- ference in this respect (yet there may be a great difference in several respects) between a chain of a greater or less length, between one chain and another, between one that is finite and one that is infinite. This very much resembles the case be- fore us. The machine which we are inspecting demonstrates, by its construction, contrivance and desig-n. Contrivance must have had a contriver ; design, a designer; whether the machine imme- ARGUMENT CONTINUED. 13 diately proceeded from another machine or not. That circumstance alters not the case. That other machine may, in hke manner, have proceeded from a former machine : nor does that alter the case ; contrivance must have had a contriver. That for- mer one from one preceeding it ; no alteration still ; a contriver is still necessary. No tendency is perceived, no approach towards a diminution of this necessity. It is the same M^ith any and every succession of these machines ; a succession of ten, of a hundred, of a thousand ; v^^ith one series as with another ; a series which is finite, as with a series which is infinite. In whatever other re- spects they may differ, in this they do not. In all, equally, contrivance and design are unac- counted for. The question is not simply, how came the first watch into existence ? which question, it may be pretended, is done away by supposing the series of watches thus produced from one another to have been infinite, and consequently to have had no such Jirsty for which it was necessary to provide a cause. This, perhaps, would have been nearly the state of the question, if nothing had been before us but an unorganized, unmechanized substance, with- out mark or indication of contrivance. It miffht 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 unor- ganized bodies to spring from one another) or by li STATE OF THE 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, adaptation to the purpose. And the question w^hich irresisti- bly presses upon our thoughts, is, whence this con- trivance and design ? The thing required is the intending mind, the adapting hand, the intelli- gence by which that hand was directed. This question, this demand, is not shaken off, by in- creasing a number or succession of substances, destitute of these properties ; nor the more, by in- creasing that number to infinity. If it be said, that upon the supposition of one watch being pro- duced 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 suitable- ness of means to an end, the adaptation of instru- ments 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, stiU less any series of causes either finite or infinite. Here is con- ARGUMENT CONTINUED. 15 trivance, but no contriver j proofs of design, but no designer. V. Our observer would further 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, lathes, chisels, &c. and the disposing, fixing, and inserting of these instru- ments, 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 move- ments which he had given to the old one. It is only working by one set of tools instead of another. The conclusion which the Jirst examination of the watch, of its works, construction, and move- ment, suggested, was, that it must have had, for the cause and author of that construction, an arti- ficer, 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 organization, 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, 10 APPLICATION OF 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 op- posite 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 with- out absurdity ? Yet this is atheism. CilAPTER III. APPLICATION OF THE ARGUMENT. This is atheism: for every indication of contriv- ance, every manifestation of design, which existed in the w^atch, exists in the works of nature ; with the difference, on the side of nature of being greater or more, and that in a degree which exceeds all computation. I mean, that the contrivances of nature surpass the contrivances of art, in the com- plexity, 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. TAB.Oo ruNUIuxi M .ir,neaii (Kriord . J^.lJf^f jf^UfiSiFv^J THE ARGUMENT. 17 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 in- strument 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 ad- justed 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 re- quire, 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. Accord- ingly 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 dif- ference ? What could a mathematical instrument- maker have done more, to shew his knowledge of his principle, his application of that 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 ? * Tab. II. 1. The crystalline lens of a fish; it is propor- tionably larger than ia other animals, and perfectly spherical. 18 APPLICATION OF 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 em- ployed, and even as to the kind of it, this circum- stance varies not the analogy at all. For, observe what the constitution of the eye is. It is neces- sary, 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 some- * Fig. 2. A section of the human eye. It is formed of various coats, or membranes, containing pellucid humours of different degrees of density, and calculated for collecting the rays of light into a focus upon the nerve situated at the bottom of the eye- ball. The external membrane, called sclerotic, is strong and firm, and is the support of the spherical figure of the eye ; it is deficient in the centre, but that part is supplied by the cornea, which is transparent and projects like the segment of a small globe from one of larger size. The interior of the sclerotic is lined by the choroid, which is covered by a dark mucous secretion, termed pig- mentum nigrum, intended to absorb the superfluous rays of light. The choi-oid is represented in the plate by the black line. The the third and inner membrane, which is marked by the white line, is the retina, the expanded optic nerve. THE ARGUMENT. 19 thing which is not mechanical, or which is inscru- table. But this affects not the certainty of our in- vestigation, as far as we have gone. The difference between an animal and an automatic statue, con- sists in this, — that, in the animal, we trace the mechanism to a certain point, and then we are stopped ; either the mechanism becoming too sub- tile for our discernment, or something else beside the known laws of mechanism taking place : where- as, in the automaton, for the comparatively few mo- tions 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, af- fects the distinctness of the vision. The forma- tion then of such an image being necessary (no matter how) to the sense of sight, and to the ex- ercise 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 '20 APPLICATION OF same. The purpose in both is ahke ; the contriv- ance for the accompHshing that purpose is in both ahke. The lens of the telescope,* and the lens of the eye,t bear a near resemblance to one another, in their figure, their position, and in their power over the rays of light, viz. in bringing each pencil to a point at the right distance from the lens; viz. 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 con- trivance 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 tele- scopes, there is an imperfection of this nature. Pen- cils of light, in passing through glass lenses, are se- parated into different colours, thereby tinging the * See Fig. 3. f Fig. 4. The crystalline lens, or, as it has been called, the crystalline humour, of the eye. The comparison with the lens of the telescope is not perfectly exact, for the crystalline lens is a substance composed of concentric layers, of unequal density, the hardness of which increases from the surface to the centre ; and hence possesses a more refractive power than any artificial lens. Mr. Ramsden sujiposes that this texture tends to correct the aberration occasioned by the spherical form of the cornea, and the focus of each oblique pencil of rays falls accurately on the concave surface of the retina. THE ARGUMENT. • 21 object, especially the edges of it, as if it were viewed through a prism. To correct this incon- venience had been long a desideratum in the art. At last it came into the mind of a sagacious opti- cian, to inquire how this matter was managed in the eye ; in which, there was the same difficulty to contend with, as in the telescope. His obser- vation taught him, that, in the eye, the evil was cured by combining lenses composed of different substances, i. e. of substances which possessed dif- ferent refracting powers. Our artist borrowed thence his hint ; and produced a correction of the defect by imitating, in glasses made from different 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 further; there are other points, not so much perhaps of strict resemblance between the two, as of superiority of the eye over the telescope ; yet * Within the coats of the eye which have been mentioned, are the humours. Fig. 2. a, the aqueous humour, which is a thin fluid like water ; b, the crystalline lens, of a dense texture ; c, the vitreous humour, a very delicate gelatinous substance named from its resemblance to melted glass. Thus the crystalline is more dense than the vitreous, and the vitreous more dense than the aqueous humour ; they are all perfectly transparent, and together make a compound lens, which refracts the rays of light issuing from an object, d, and delineates its figure, e, in the focus upon the retina, inverted. ^22 AITLICATION OF 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 as 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 eye, 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 open- * As the rays of light flowing from all the points of an object through the pupil of the eye, by the refraction of the lens and humours of the eye, form an exact representation at the bottom of the eye on the retina ; so the camera obscura, by means of a lens refracting the rays, exhibits a picture of the scene before it on the opposite wall. THE ARGUMENT. *23 ing ; when too strong, can again contract it ; and that without any other assistance than that of its own exquisite machinery. It is further 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 will 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.t II. The second difficulty which has been stated, * The pupil of the eye is the aperture formed by the inner margin of the iris. See Fig. 5, 6 ; which shew the arrangement of the fibres of the iris. ■f Some eminent anatomists have doubted the muscularity of the iris, and have given very ditferent explanations of its motions at- tributing the contraction and dilatation either to the varied im- pulse of the blood in its vessels, or to its own vita propria. The enlightened physiologist Magendie affirms, that the latest researches upon the anatomy of the iris proves its muscular structure, and that it is composed of two layers of fibres, the external (Fig. 5.) radiated, which dilate the pupil, the other (Fig. 6.) circular, which contract the pupil. The external circular fibres appear to be supported by a species of ring, which each of the radiated fibres contributes to form, and in which they slide during the alternate contractions and relaxations of the pupil. See a beautiful plate in Dr. A. Monro's Elements of Anatomy, vol. ii. p. 543. 2-i Arr-LICATION OF was the suiting of the same organ to the percep- tion of objects that he 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 with- out 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 consequently 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 ob- jects 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 re- * The focus of the refracted rays must fall exactly on the retina, so that the point of vision may be neither produced beyond it, nor shortened so as not to reach it. The latter defect exists in short- THE ARGUMENT. 25 maining the same, this point, by the immutable properties of hght, is carried farther back when the rays proceed from a near object than when they are sent from one that is remote. A per- son who was using an optical instrument, 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 it 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 ef- fected, (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 long 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 as- certained the mechanical alteration which the parts of the eye undergo. It is found, that by the ac- tion of certain muscles * called the straight mus- sighted persons, from too great convexit}' of the cornea or lens. The former is the defect of long-sighted persons, in whom there is an opposite conformation of those parts. * Fig. 7. There are four straight muscles a, a, a, «, belonging to the globe of the eye. These muscles resemble each other, each arising from the bottom of the orbit, where they surround c, the optic nerve ; they are strong and fleshy, and are inserted by broad thin tendons at the fore part of the globe of the eye, into the tunica ^() APPLICATION' OF cles, 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 pro- minent ; 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, w^hich is the case when the object is near to the eye, or come pa- rallel 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 rec- tify his instrument by putting in another glass, at sclerotica. The internal changes of the ej'e are chiefly accom- plished by the pressure of these muscles on the ball. The more ob- vious use of the straight muscles, and the action which is assigned to them by anatomical writers, is, to turn the eye in different direc- tions : hence they are severally named — levator oculi, depressor oculi, adductor oculi, and abductor oculi. THE ARGUMENT. 27 the same time drawinsf out also his tube to a dif- ferent lens'th. Observe a new-born child first lifting up its eye- lids. What does the opening of the curtain dis- cover ? 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 per- fect for the purpose of forming an image by refrac- tion ; composed of parts executing different offices : one part having fufilled its office upon the pencil of light, delivering it over to the action of another part ; that to a third, and so onward : the pro- gressive action depending for its success upon the nicest and minutest adjustment of the parts con- cerned ; 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, ac- cording 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 de- 28 Ari'LICATlON OF lineated, should be shortened or lengthened ; this, I say, being the ease 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 re- gulator 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 contri\ance has been justly praised. Shall, therefore, a struc- ture which differs from it, chiefly by surpassing it, be accounted no contrivance at all ? or, if it be a contrivance, that it is without a contriver ? But this, though much, is not the whole ; by different species of animals the faculty we are de- scribing is possessed, in degrees suited to the dif- ferent range of vision which their mode of life, and of procuring their food, requires. Birds, for in- stance, in general, procure their food by means of their beak : and, the distance between the eye and the point of the beak being small, it becomes ne- cessary that they should have the power of seeing very near objects distinctly. On the other hand, from being often elevated much above the ground. T A;B , I I'lihli.th.J /.. Jliti,,nl 0.i/hrd THE ARGUMENT. 29 living in air, and moving through it with great ve- locity, they require, for their safety, as well as for assisting them in descrying their prey, a power of seeing at a great distance ; a power of which, in birds of rapine, surprising examples are given. The fact accordingly is, that two peculiarities are found in the eyes of birds, both tending to facili- tate the change upon which the adjustment of the eye to different distances depends. The one is a bony, yet in most species, a flexible rim or hoop,* surrounding the broadest part of the eye ; which, confining the action of the muscles t to that part, increases the effect of their lateral pressure upon * Tab. III. Fig. 1, 2. The flexible rim, or hoop, consists of bony- plates, vvliich in all birds occupy the front of the sclerotic ; lying close together and overlapping each other, These bony plates in general form a slightly convex ring, Fig. 1, but in the accipitres they form a concave ring, as in Fig. 2, the bony rim of a hawk. It is a principle in optics, that the rays of light, passing through a lens, will be refracted to a point or focus beyond the lens, and this focus will be less distant in proportion as the lens approaches to a sphere in shape. This principle is very naturally applied to the ex- planation of the use of this apparatus. These scales partly lying over each other, so as to allow of motion, will, on the contraction of the straight muscles inserted into and covering them, move over each other, and diminish the circle of the sclerotica ; and thus the cornea, which is immediately within the circle made by these scales, must be pressed forwards and rendered more convex, from the focus of the eye becoming altered, by its axis being elongated. This consequent convexity of the cornea renders small objects near the animal very distinct. Without this structure a bird would be con- tinually liable to dash itself against trees when flying in a thick forest, and would be unable to see the minute objects on which it sometimes feeds. ■j- These muscles resemble the straight muscles of the human eye, and the eyes of all animals possess similar moving powers. 80 APPLICATION OF the orb, by which pressure its axis is elongated for the purpose of looking at very near objects. The other is an additional muscle, called the marsu- pium,* to draw, on occasion, the crystalline lens back, and to fit the same eye for the viewing of very distant objects. By these means, the eyes of birds can pass from one extreme to another of their scale of adjustment, with more ease and rea- diness than the eyes of other animals. The eyes o1 fishes also, compared with those of terrestrial animals, exhibit certain distinctions of structure adapted to their state and element. We have already observed upon the figure of the crys- talline compensating by its roundness the density of the medium through which their light passes. To which we have to add, that the eyes of fishes, in their natural and indolent state, appear to be ad- justed to near objects, in this respect differing from the human eye, as well as those of quadrupeds and birds. The ordinary shape of the fish's eye being * The marsKpiiim arises from the back of the eye ; proceeding apparently through a slit in the retina, it passes obliquely into the vitreous humour, and terminates in that part, as in the eagle. Fig. 3. a section of the eye of the falco chrysaetos. In some species it reaches the lens, and is attached to it, as in Fig. 4. 6. In the plate the marsupium is marked with an *. We have now seen the form, but it is very much questioned whether it has the office here as- signed to it : no muscular fibres are apparent, and its oblique situa- tion seems unfavourable to the conjecture of its having muscular power. The marsupium has a structure resembling the choroid coat, is covered by the same black pigment, and answers the same purpose ; that of absorbing the rays of light when too strong, and intercepting some of the rays in their course to the retina. THE ARGUMENT. 31 in a much higher degree convex than that of land animals, a corresponding difference attends its mus- cular conformation, viz. that it is throughout cal- culated for Jlattening the eye. The iris also in the eyes of fishes does not admit of contraction. This is a great difference, of which the probable reason is, that the diminished light in water is never too strong- for the retina. In the eel, which has to work its head through sand and gravel, the roughest and harshest sub- stances, there is placed before the eye, and at some distance from it, a transparent, horny, convex case or covering, which, without obstructing the sight, defends the organ.* To such an animal, could any thing be more wanted, or more useful ? Thus, in comparing the eyes of different kinds of animals, we see, in their resemblances and dis- tinctions, one general plan laid down, and that plan varied with the varying exigencies to which it is to be applied. There is one property, however, common I be- lieve to all eyes, at least to all which have been examined, namely, that the optic nerve enters the bottom of the eye, not in the centre or middle, but a little on one side : not in the point where the * Fig. 5. The skin of the head of an eel is represented turned back : and as the transparent horny covering of the eye a, a, is a cuticular covering-, it is separated with it. Other fish, have a simi- lar, insensible, dense, and thick adnata, which is designed to pro- tect the eye ; and it seems especially necessary as fish have no eye-lids. 3'2 APPLICATION OF axis of the eye meets the retina, but between that point and the nose. The difference which this makes is, that no part of an object is un perceived by both eyes at the same time. In considering vision as achieved by the means of an image formed at the bottom of the eye, we can never reflect without wonder upon the small- ness, yet correctness of the picture, the subtilty of the touch, the fineness of the Hnes. A landscape of five or six square leagues is brought into a space of half an inch diameter ; yet the multitude of ob- jects which it contains, are all preserved ; are all discriminated in their magnitudes, positions, figures, colours. The prospect from Hampstead- hill is compressed into the compass of a sixpence, yet circumstantially represented. A stage-coach, travelling at its ordinary speed for half an hour, passes, in the eye, only over one-twelfth of an inch, yet is this change of place in the image dis- tinctly perceived throughout its whole progress ; for it is only by means of that perception that the motion of the coach itself is made sensible to the eye. If any thing can abate our admiration of the smallness of the visual tablet compared with the extent of vision, it is a reflection, which the view of nature leads us, every hour, to make, viz. that, in the hands of the Creator, great and little are nothing. * * The magnitude of the image formed on the retina, is propor- tional to the angle which the two extremities of the olyect viewed THE ARGUMENT. S3 Sturmius held, that the examination of the eye was a cure for atheism. Besides that conformity to optical principles which its internal constitution displays, and which alone amounts to a manifesta- tion of intelligence having been exerted in the structure ; besides this, which forms, no doubt, the leading character of the organ, there is to be seen, in every thing belonging to it and about it, an extraordinary degree of care, an anxiety for its preservation, due, if we may so speak, to its value and its tenderness. It is lodged in a strong, deep, bony socket, composed by the junction of seven different bones,* hollowed out at their orbitary processes. In some few species, as that of the coatimondi,t the orbit is not bony throughout ; but whenever this is the case, the upper, which is the deficient part, is supplied by a cartilaginous ligament ; a substitution which shews the same care. Within this socket it is imbedded in fat, of all animal substances the best adapted both to its repose and motion. It is sheltered by the eye- brows ; an arch of hair, which, like a thatched penthouse, prevents the sweat and moisture of the forehead from running down into it. But it is still better protected by its lid. Of subtend with the centre of the eye. Hence the more remote the object, the smaller the image. * The frontal, maxillary, malar, lachrymal, ethmoid, palatine, and sphenoid bones. f Mem. R. Ac. Paris, p. 117. 34 APPLICATION OF the superficial parts of the animal frame, I know none which, in its office and structure, is more de- serving of attention than the eyelid. It defends the eye ; it wipes it ; it closes it in sleep.* Are there, in any work of art whatever, purposes more evident than those which this organ fulfils ? Or an apparatus for executing those purposes more intel- ligible, more appropriate, or more mechanical ? If it be overlooked by the observer of nature, it can only be because it is obvious and familiar. This is a tendency to be guarded against. We pass by the plainest instances, whilst we are exploring those which are rare and curious ; by which con- duct of the understanding, we sometimes neglect the strongest observations, being taken up with others, which, though more recondite and scien- tific, are, as solid arguments, entitled to much less consideration. In order to keep the eye moist and clean, (which qualities are necessary to its brightness and its use,) a wash is constantly supplied by a secretion for the purpose ; and the superfluous brine is conveyed to the nose through a perforation in the bone as large as a goose-quill. t When once the fluid has * The muscles which accomplish these actions are seen in Tab. XIV. Fig. 1, 2. The eyelids also moderate the force of a too bril- liant light, and exclude, by a partial closure, that excess of it which would offend the eye. The eyelashes have a similar office, that of regulating the quantity of light : and it is believed, that they pro- tect the eye from the small particles of dust that float in the air. f Tab. IV. Fig. I. a, is the organ which supplies this fluid, TAB.W Pul:lijlir,t I,. n„„,nl ll.i-,;