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BL 180 .P3 1879
Paley, William, 1743-1805
Natural theology
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PALEY'S THEOLOGY, WITH ILLUSTRATIONS V"
JUN 9 1914
A
tStoem %&0
NATURAL THEOLOGY:
Oil,
EVIDENCES
OF THE EXISTENCE AND ATTRIBUTES OF THE DEFr*
COLLECTED FROM THE APPEARANCES
OF NATURE,
BY
WILLIAM PALEY, D. D.
ILLUSTRATED BY
THE PLATES, AND BY A SELECTION FROM THE NU/jFjS
op
JAMES PA XT ON.
WITH
ADDITIONAL NOTES, ORIGINAL AND SELECTED, FOR THIS EDITION, AND A VOCABULARY OF SCIENTIFIC TERMS.
BY JOHN WARE M D.
NEW YORK:
SHELDON & COMPANY,
No. 8 MURRAY STREET. l879.
Rntered, according to Act of Oungress, in the year 1854, tj
GOULD AND LINCOLN.
la the Clerk's Office of the District Court of the District of M&sstichuMttfc
FUBLISHERS' NOTICE.
Several years since the publishers of this valuable and very popnluf work engaged the services of Dr. John Ware, of this city, to prepare an improved edition, by the addition of forty elegant pages of the illustra- tions of Paxton, with references to the same in the text; extensive notes, original and selected ; a vocabulary of scientific term<s, etc. ; with a view of adapting it more perfectly to the wants of our colleges and schools, so as thereby to increase its circulation and usefulness.
The sale, with these additions and improvements, has been gradually on the increase, until it has become very generally introduced into our best schools and colleges throughout the country; and having passed through some forty or more editions, the publishers found the plates, by constant use, very much worn, and in some cases imperfect. They have consequently procured an entirely new and beautiful set of illus- trations, which, with other improvements, render the work all that can be desired, and in view of which they anticipate a wider and stili more extensive sale of the work.
Boston, January, 1854.
PEEFACE
TO TUB
REVISED AMERICAN EDITION.
The present edition of the Natural Theology of Dr. Paley was andes taken witn the view of making this admirable work more extensively useful than it could ever be under the form in which it has been usuall) circulated. A great proportion of those who have read it must have sensi bly felt the disadvantage under which they labor in comprehending the descriptions; and of course the arguments of the author, from the want of a knowledge of the subjects to which they relate. No man could so well supply the want of this knowledge, by clearness of statement and description, as Dr. Paley; ana it is probable that few other writers would have made a book so intelligible, which relates to subjects remote from common observation, without the aid of plates and illustrations. Still it must be imperfectly comprehended in many important parts, except bv those acquainted with the sciences from which his illustrations are drawn. Enough it is true may be understood by all, to carry them along with the argument, and produce a general conviction of its truth. But the concep- tions even of professional readeis would be much more clear, definite, and aatisfactory, were the description aided by visible representations.
It was the original design of the publishers to ^ave merely attached thp plates and references of Paxton, which have bee.i published in England and in this country in a separate volume, to the t»xt of Dr. Paley. It was, however, suggested to them that the value of their edition might be increased by the addition of Notes, and they had madb arrangements for this purpose and were going on with the work, when Mr. Paxton's edition if the Natural Theology fell into their hands, containing, beside the j. l&tes, a considerable number of Notes. From these Notes a selection has been made of such as seemed most valuable and interesting. A numbei of Notes have also been made up of quotations from the excellent treatise of Mr. Charles Bell on Animal Mechanics, published in the Library of Useful Knowledge ; a tract which cannot be too highly recommended K> the perusal of those who take pleasure in studying the indications of a nrtee and benevolent Providence in the works of creation.
A few additional Notes have also been subjoined, which have aot b©«« befoi 3 published.
W PREFACE.
It seems to be supposed by some, that the progress made in science
*5nce the writing of this work must have furnished ample materials foi
valuable additions to it. It will readily appear, however, upon reflection.
that this is not likely to be the case, and that no particular advantage tu
the argument is to be expected from bringing it down, as it is often ex
pressed, to the present state of science, O he object of the work is, nol
to teach science in its connexion with Natural Theology, a plan entirely
different, and one upon which distinct works may, and have been written,
t>ut to gather materials from the knowledge communicated by science,
wherewith to construct an argument for the existence and attributes of I
God. The excellence of such a work, then, will not consist in the num- Der of illustrations, or in the copiousness and completeness of the materi- als, but in the judgment with which they are selected, and the aptness with which they are made to bear upon the question at issue.
So far, therefore, as the argument is concerned, no additional strengtn will be given to it by new" discoveries in science. As Dr. I'aiey has him- self admitted, a single case thoroughly made out, proves all that can be proved, and, generally speaking, the most familiar instances which cat, be selected and made intelligible are the best for this purpose, and win have the greatest inlluence u jon men's minds. All the knowledge, there- fore, which is necessary for the completeness and strength of the argu- ment was possessed long ago.
Still there is an advantage in selecting and arguing from a variety of examples, arising out of the different constitutions of men's minds, or their different habits of thinking and reasoning. Some are more affected Dy examples of one kind, and some by those of another. In this way much more might be done in the way of illustrating and enforcing the argument, and holding it up in every possible light, than has been attempt- ed in the present edition. The principal object here had in view, has been to make such additions, as with tne help of the engraved views, would bring the argument, as stated by the author, clearly within reach of all readers.
To give a correct edition, various English and American copies have been consulted, in which variations have been found; but those readings have been adopted, which appeared best to comport with that familiarity, and originality of expression, which gives its principal charm, and ita great force and clearness to Dr Paley's style.
J W
TO THE RIOriT HONORABLE AND RIGHT REVEREND
iHUTE BARRINGTON, LL I
LORD BISHOP OF DURHAM.
MY LORD,
The following work was undertaken at your Lordship's recom- mendation; and amongst other motives, for the purpose of making the most acceptable return I could make 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 favor of my first and ever honored patron had put me in possession of so liberal a provision in the church, a9 abundantly to satisfy my wants, and much to exceed my pretensions. Your Lordship's munificence, in conjunction with that of some other ex- cellent Prelates, who regarded my services with the partiality with which your Lordship was pleased to consider them, hath since placed me in ecclesiastical situations, more than adequate to every object of reason- able ambition. In the meantime, a weak, and, of late, a painful state of health, deprived me of the power of discharging the duties of my sta- tion, in a manner at all suitable, either to my sense of those duties, or to my most anxious wishes concerning them. I\Ty inability for the public functions of my profession, amongst other consequences, left me much at leisure. That leisure 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 pres9 tr.at I could speak. These circumstances, in particular, entitled your Lordship 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 reter, either to the supreme importance of the subject, or to any skepticism concerning 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 discussion alone was wanted to make up my works into a system : in which works, such as diej are, the public have now before them, the svidences of natural reli
A
2 DEDICATION.
gion, the evidences of revealed religion, and an account of the duties thai 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 rea<2. I commend therefore the present volume to your Lordship's protection, not only as, in all probability, my last labor, but as the completion of a c>5!\ sislent and compiehensive design.
Hitherto, my Lord, I have been speaking of myself and not of my Pa- tron. Your Lordship wants not the testimony of a dedication, nor any testimony from me : I consult therefore the impulse of my own minJ alone when I declare, that in no respect has my intercourse with vour Lordship been more gratifying to me, than in the opportunities, whici* it has afforded me, of observing your earnest, active, and unwearied solicitude, for the advancement of substantial Christianity: a solicitude, nevertheless, accompanied with that candor of mind, which suffer> no subordinate differences of opinion, when there is a coincidence in the main intention and object, to produce an alienation of esteem, or diminution of favor. It is fortunate for a country, and honorable to its government, when qualities and dispositions like these are placed in high and influential 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, »! beg leave to subscribe myself, with great respect and gratitude,
My Lord, Your Lordship's faithful
And most devoted servant,
WILLIAM PALEY
TO THE HONORABLE AND RIGHT REVEREND
SHUTE BARRINGTON, LL D
LORD BISHOP OF DURHAM.
Ml «.ORD„
To your suggestion the world is indebted for the existence of Di. Paley's valuable work on Natural Theology. The universal and perma- neix* esteem in which it has been held in this country, and its favorable reception in France, even after the desolating influence of the Revolution, ha\c abundantly approved your Lordship's selection both of the subject ?nd of the person to whom you intrusted it.
lu booking 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 wich; your Lordship not only condescending to approve of the design, but to encourage me in its prosecution, by your very liberal support. Fo» this distinguished honor you will believe me deeply sensible ; and if I may indulge the hope that my humble efforts will increase the utility of »c eminent a w riter, I shall consider it the highest gratification.
I am, -my Lord,
With great veneration, Your Lordship's most obliged,
And obedient servant,
JAMES PAXTON,
CONTENTS
Chapter P«*
1. Sta.e of the Argument, . . • • • 6
2. State of the Argument, continued, • • .8
3. Application of the Argument, . ... 13
4. Of the succession )f Plants and Animals, ... 31
5. Application of the Argument, continued, .... 35
6. The Argument cumulative, ..... 44
7. Of the mechanical and immechanical parts and functions of
Animals and Vegetables, ...... 45
8. Of mechanical Arrangement in the human Frame— Of the
Bones, ......... 52
9. Of the Muscles, ....... 74
10. Of the Vessels of animal Bodies, .... 90
11. Of the animal Structure, regarded as a Mass, . . 109
12. Comparative Anatomy, • 122
13 Peculiar Organizations, . 137
14. Prospective Contrivances, . . . . . • 145
15. Relations, 149
16. Compensation, • 157
17. The Relation of animated Bodies to inanimate Nature, . 166
18. Instincts, 170
19 Of Insects, ....... .180
20 Of Plants, . 193
21 Of the Elements, .... . 207
22 Astronomy, .... , . 212
23. Personality of the Deity, . . . 229
24. Of the Natural Attributes of the Deity, . . 246
25. The Unity of the Deity, . 249
26 The Goodness of ths Deity, 252
27. Conclusim, . . . . . ; . 292
Vocabulary. . . .... . 29^
NATURAL THEOLOGY.
CHAPTER I.
STATE OF THE ARGUMENT.
In ci :ssing a heath, suppose I pitched my foot against % stoAe, and were asked how the stone came to be there; i might possibly answer, that, for anything 1 knew to the contrary, it had lain there forever: nor would it perhaps uc very easy to show the absurdity of this answer. But suppose I had found a watch 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 be- fore given, that, for anything I knew, the watch might have always been there. Yet why should not this answer seive 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 dis- cover in the stone) that its several parts are framed and put together for a purpose, e. g. that they are so formed and ad- justed as to produce motion, and that motion so regulated 19 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 olaced, 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 res.: t: [See Plate I.] — We see a cylindrical box containing h. coiled elastic spring, which, by its endeavor to relax itself, turnis round the box. We next observe a flexible chain (ar- tificially wrought for the sake of flexure) communicating the aetiou of the s\ ring from the box to the fusee. We then
A*
b STATE OF THE ARGUMENT.
find a series of wheels, the teeth of which catch in, and apply to each other, conducting the motion from the fusee to the balance, and from the balance to the pointer; 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 material employed in no other part of the work; but in the room of which, if there had been any other than a transparent sub- stance, 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 pre- vious knowledge of the subject, to perceive and understand it; but being once, as we have said, observed and under- stood,) the inference, we think, is inevitable ; that the watch must have had a maker; that there must have exist- ed, at sometime, and at some place or other, an artificer or artificers, who formed it for the purpose which we find it actually to answer ; who comprehended its construction, and designed its use.
I. Nor would it, I apprehend, weaken the conclusion, that we had never seen a watch made: that we had never known an artist capable of making one ; that we were alto- gether incapable of executing such a piece of workman- ship 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 curious produc- tions of modern manufacture. Does one man in a million know how oval frames are turned? Ignorance of thir; 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 artist, at gome 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 different species, or an agent possessing, in some respects, a different nature.
II. Neither, secondly, would it invalidate our conclu sion, that the watch sometimes went wrong, or that it sel- dom went exactly right. The purpose of the machinery, *he design and the designer, might be evident, and in the case supposed would be evident, in whatever way we tw«
STATE OF THE ARGUMENT
counted for the irregularity of the movement, or whethc* we could accou.it for it or not. It is not necessary that ♦» machine be perfect, in order to show with what design ii was made: still less necessary, where the only question is, whether it were made with any design at all.
III. Nor, thirdly, would it bring any uncertainty into the argument, if there were a few parts of the watch, concern- ing which we could not discover, or had not yet discovered, in what manner they conduced to the general effect; or even some parts, concerning which we could not ascer- tain whether they conduced to that effect in any manner 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 retarded, no doubt would remain in our minds as to the utility or intention of these parts, although we should be unable to investigate the manner according to which, or the connexion by which, the ultimate effect depended upon their action or assistance ; 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 pre- judice to the movement of the watch, and that we had prov- ed this by experiment — these superfluous parts, even if we were completely assured that they were such, would not vacate the reasoning 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, ac- counted 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, m-ist have contained some internal configuration or other; and tha*. this configuration might be the structure now exhibited, viz. of the works of a watch, as well as a different structure.
V. Nor, fifthly, would it yield his inquiry moie satisfac- tion to be answered, that there existed in things a principle of order, which had disposed the parts of tlie watch into their present form and situation. He neve* knew a watch
A
made by the principle of order; nor can Le even foim to himself an idea of what is meant by a principle of order distinct from the intelligence of the watchmaker.
VI. Sixthly, he would be surprised to hear that the mechanism of the watch was no proof of contrivance, only a motive t induce the mind to think so.
3 STATE OF THE ARGUMENT.
VII. And not less surprised to be informed, that the v/atch 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 anything A law presupposes an agent; for it is only the mode ac- cording 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 dis- tinct from itself, the law does nothing ; is nothing. The expression, "the law of metallic nature," 'xiay sound strange and harsh to a philosophic ear; but it seems quite as justi- fiable as some others which are more familiar to him, such as "the law of vegetable nature," "the law of animal na- tire," or indeed as "the law of nature" in general, when assigned as the cause of phenomena, in exclusion of agen- cy and power; :>r 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 igno- rance of other points, his doubts concerning other points, affect not the certainty of his reasoning. The conscious- ness of knowing little need not beget a distrust of that which he does know.
CHAPTER II.
STATE OF THE ARGUMENT CONTINUED.
Suppose, in the next place, that the person who found •he watch, should, after sometime, discover, that, in ad- dition to all the properties which he had hitherto observed (n it, it possessed the unexpected property of producing, in the course of its movement, another watch like itself, (the thing is conceivable ;) that it contained within it a mechanism, a system of parts, a mould for instance, or a complex adjustment of lathes, files, and other tools, evident- ly and separately calculated for this purpose; let us in- quire, what effect ought such a discovery to have uoonhis forme conclus'jn.
STATE OF THE ARGUMENT. 9
I. The first effect would be to increase his admiration of the contrivance, and his conviction of the consummate skill of *he contriver. Whether he regarded the ob- ject of t'.ie contrivance, the distinct apparatus, the intri- cate, yet in many parts intelligible mechanism, by which it was carried on, he would perceive, in this new observa tion, nothing but an additional reason for doing what he had already done, — for referring the construction of the watch to design, and to supreme art. If that construction without this property, or, 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 farther 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 con- trivance, 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 pos- sibly say, but with great latitude of expression, that a stream of water ground corn; but no latitude of expres- sion 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 impulse to a mechanism previously arranged, arranged independently of it, and arranged by intelligence, an effect is produced, viz. the corn is ground. But the effect results from the arrangement. The force of the stream cannot be said to be the cause or author of tne effect, still less of the arrangement. Understanding and plan in the formation of the mill were not the less neces* sary, for any share which the water has in grinding the corn ; 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. There- fore,
III. Though it be now no longer probable, that the individual watch which our (bserve*1 had found was mad a
10 STATE OF THE ARGUMENT.
immediately by the hand of an artificer, yet doth not Lis alteration in any-wise affect the inference, that an artificei had been originally employed and concerned in the pro- duction. The argument from design remains as it was. Marks of design and contrivance are no more accounted for n)w 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 color of a body, of its hardness, of its heat; ai.d these causes may be all different. We arc now asking for the cause of that subserviency to a :se, 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; arrangement, without anything capable of arranging; subserviency and relation to a purpose, without that which could intend a purpose; means suitable to an end, and executing their office ir. accomplishing that end, without the end ever having been contemplated, or the means accommodated to it. Arrange- ment, disposition of parts, subserviency of means to an end, relation of instruments to a use, imply the presence of in- telligence and mind. No one, therefore, can rationally be- lieve, that the insensible, 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, assign ed their otfice, determined their order, action, and mutual dependency, combined their several motions into one re- sult, and that also a result connected with the utilities of other being3. All these properties, therefore, are as much unaccounted for as they were before.
IV. Nor is anything gained by running the difficulty farther back, i. e. by supposing the watch before us to have )een 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 designing mind is neither supplied by this supposition, nor dispensed with. If the difficulty w< re diminished the farther we went back, by going back indefinitely we might exhaust it. And this is the only case to which this sort of reasoning applies. Where there is a tendency, or, as we increase the number of terms, a continual approach towards a limit, there, Dy supposing the number of terms to be what is tailed infinite, we may con-
STATE OF THE ARGUMENT 11
c*,ive the limit to be attained: but where there is n: such tendency, or approach, nothing is effected by lengthening the series. There is no difference, as to the point in ques- tion, (whatever there may be as to many points,) between 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 inci easing the number of links, from ten, for instance, to a hundred, from a hundred to g thousand, &c. we make not the smallest approach,. we ob- serve not the smallest tendency, towards self-support. There is no difference in this respect (yet there may bo 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 before us. The machine which we are inspecting demonstrates, by its construction, contrivance and design. Contrivance must have had a contriver; design, a designer; whether the machine immediately proceeded from another machine or not. That circumstance alters not the case. That other machine may, in like manner, have proceeded from a for- mer machine: nor does that alter the case; contrivance must have had a contriver. That former one from one preceding it: no alteration still; a contriver is still neces- sary. No tendency is perceived, no approach towards a diminution of this necessity. It is the same with any and every succession of these machines; a succession of ten, of a hundred, of a thousand; with one series as with an- other; a series which is finite, as with a series which is infinite. In whatever other respect* they may differ, in this they do not. In all, equally, ccntrivance and design are unaccounted 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 pro- duced from one another to have been infinite, and conse- quently tc have had no such first, for which it was neces- sary to provide a cause. This, perhaps, would have been nearly the state of the question, it' nothing had been before us but an unorganized, unmechanized substance, without mark or indication of contrivance. It might be difficult tc show that such substance could not have existed from eter- nity, either in succession (if it were possible, which I think
12 STATE OF THE ARGUMENT.
it is viot, for unorganized 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 mad6 no difference whether we 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 con- trivance, design; an end, a purpose; means for the end, adaptation to the purpose. And the question which ir- resistibly presses upon our thoughts, is, whence this con- trivance and design? The thing required is the intending mind, the adapting hand, the intelligence by which that hand was directed. This question, this demand, is lot shaken off, by increasing a number or succession of sub- stances, 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 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 adaptation of instruments to a use, (all which we discover in a watch,) we have any cause what- ever. 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 eithei 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 ex- quisite 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 movements which he had given to the old one. It is only working by one set of tools in- stead 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 con- struction, 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
APPLICATION OF THE ARGUMENT 13
is found, in the course of its movement, to produce anoth- er watch, similar to itself: and not only so, but we perceive in it a system or organization, separately calculated for thai purpose. What effect would this discovery have or ought it to bive, upon our former inference? What, as hath al- ready been said, but to increase, beyond measure, our ad miration of the skill which had been employed in the for- mation of such a machine! Or shall it, instead of Inis 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 re- main 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.
CHAPTER III.
APPLICATION OF THE ARGUMENT.
This is atheism: for every indication of contrivance, ev- ery manifestation of design, which existed in the watch, ex- ists in the works of nature; with the difference, on the side of nature, of beirg greater and more, and that in a degree which exceeds all computation. I mean, that the contriv- ances 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 an'" variety: yet, in a multitude of cases, are not less evidently mechanical, not less evidently contrivances, not less evi- v dently 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 sub- ject , than that of comparing a single thing with a single thing ; an eye, for example, with a telescope. As far as the ex- amination of the instrument go as, there is precisely the same proof that the eye was made for vision, as there la 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. 1 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 tays of light, in passing from water into the eye, should bo
H
1*1 AFFLlCATlOfl OF THE ARGUMENT
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. [Plate II. fig. 1.] What plainer manifestation of design can there be than thi9 difference ? What could a mathematical instrument-make; have done more, to snow 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 excel- lence 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 instru- ment. 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 circumstance va- ries not the analogy at all. For, observe what the consti- tution of the eye is. [Plate II. fig. 2.] 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 "ft'ill 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 in- scrutable. But this affects not the certainty of our inves- tigation, as far as we have gone. The difference between in 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 foo subtile for our discernment, or something else beside "iie known laws of mechanism taking place: whereas, in :ie automaton, for the comparatively few motions of which \ is capahJe, we trace the mechanism throughout. But, ap 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 lin- age at the bottom of the eye is necessary to perfect vision The image itself can be shown. Whatever affects the dis- tinctness of the image, affects the distinctness of the vision. The fo?mation then ot such an image being necessary (n*«
APPLICATION OF THE ARGUMENT. 15
matter how) to the sense of sight, ana to the exercise of that sense, the apparatus by which it is formed is con- structed and put together, not only with infinitely more art, but upon the selfsame 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 pur- pose in both is alike, the contrivance for accomplishing that purpose is in both alike.* The lenses of the telescope, [Plate II. fig. 3, 4.] 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 of light, viz. ir bringing each pencil to a point at the right distance from the lens; namely, in the eye, at the exact place where ihe membrane is spread to receive it. How is it possible, un- der 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 hav- ing been employed, as the plainest and clearest of all pro- positions, in the other?
The resemblance between the two cases is still more ac- curate, and obtains in more points than we have yet repre- sented, 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 colors, 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 cur- ed by combining lenses composed of different substances, i, e. of substances which possessed different refracting powers. Our artist borrowed thence his hint, and pro- duced a correction of the defect by imitating, in glasses
* 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 th« centre/ and hence possesses a more refractive power than any artificial lens. Mr. Ramsden supposes that this texture tends to correct the aber- ration occasioned by the spherical form of the cornea, and the focus of each oblique pencil of rays falls accurately on the co icaNe surface of the retiia — Pax ton
16 APPLICATION OF THE ARGUMENT
made from different materials, the effects of the diffeiein humours through which the rays of light pass before they .each 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 ot the eye over the telescope, which being found in the laws that regulate both, may furnish topics of fair and just com- parison. Two things were wanted, to the eye, which were not wanted (at least in the same degree) to the teles cope: 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: —
* " It does not appear that the hint of this discovery was taken by Mr. Dollond from the structure of the eye, as supposed by our author, but was obtained in a different manner. This circumstance does not however lessen the force of the reasoning. The principle thus applied in the construction of achromatic telescopes, has been since carried still farther, and in its new application, illustrates more strongly, if possible, the point so well insisted on by Dr. Paley, namely, the resemblance be- tween the eye and our optical instruments. In the best achromatic tei?- Bcopes, composed of the different kinds of glass, according to the discov • ery of Mr. Dollond, white or luminous objects are not shown perfectly free from color, their edges being tinged on one side with a claret colored, and on the other with a greenish fringe. This remaining imperfection has been got rid of by the combination of solid and fluid lenses in the object and eye-glasses of telescopes. For this beautiful discovery science is indented to Dr. Blair of Edinburgh, who found that by placing a con- cave lens of muriatic acid with a metallic solution, between two convex lenses of glass, a combined lens was formed which refracted rays with perfect regularity and equality. A lens like this has been used with great advantage. The most important point is, however, to consider this improvement in its application to the argument, and it will be seen how much nearer this construction brings the telescope to the eye. In Dollond's telescope there is a combination of solid lenses of different substances. — In Blair's, a combination of fluid and solid ; which is ex- actly the case in the human eye. The only difference is, that in the eve there is a solid lens between two fluid ones ; and in tn/3 telescope a fluid between two solid. The combination is closely similar, ?nd the final causo in both, probably the same, namely, to correct the unequal refraction of light, (see Edinburgh Journal of Science, No. VIII., p. 212, and Library of Useful Knowledge, Nos. I. and II.) Ed.
APPLICATION OF THE ARGUMENT. 17
I. In order to exclude excess of light, when it is ex cessive, 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 great- er or less number of rays at the same time. The cham- ber 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 assist- ance than that of its own exquisite machinery. It is far- ther abo, in the human subject, to be observed, that this hole in the eye, which we call the pupil, under all its dif- ferent dimensions, retains its exact circular shape. Tr.ja 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 con- trivance 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 per- form. [Plate II. Fig. 5 & 6.] |
* As the rays of light flowing from all the points of an object through (he pupil of the eye, by the refraction of the lens and humours of the aye, form an exact representation at the bottom of the eye on the retina ; bo the camera obscura, by means of a lens refracting the rays, exhibits a picture of the scene before it on the opposite wall. — Paxton.
t Some eminent anatomists have doubted the muscularity of the iris, and have given very different explanations of its motions, attributing the contraction and dilatation either to the varied impulse of the blood in its vessels, or to its own vita propria. The enlightened physiologist Magen- die 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, Plate II. (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 ra- diated fibres contribute to form, and in which they slide during the- alter- nate contractions and relaxations of the pupil. — Paxton.
There is a curious circumstance in the way in which light produces thp contraction of the opening of the iris, which strengthens very much the ar gurnent derived from design manifested in its structure and adaptation to its purpose. The object of the iris, it is to be observed, has reference to the quantity of light to be admitted upon the retina or expansion of *he optic neive. It is the state of the retina then which regulates the motions of the iris, an J it is the action of the lijihton the retina which causes those mo- tions and not its action upon the iris itself This has been shown by a very delicate experiment. If a ray of light be accurately thrown in such a diiection, that it shall fall upon the circle of the iris itself, and not pa* through its aperture, no contraction of the aperture takes place; but if il
B*
IS -APPLICATION OF rHE ARGUMENT
II. The second difficulty which has been stated, was the suiting of the same organ to the perception of objects tha. 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 under- going 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 conse- quently 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 situat- ed 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 that is remote. A person who was using an optical instrument, would manage this matter by changing, as the occasion required, his lens or his tele- scopes; or by adjusting the distance of his glasses with hig 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 effected, (for if the known
be so thrown as to pass through the aperture, and fall upon the retini without touching the iris at all, still a contraction of the iris immediately takes place. So that light upon the iris alone occasions no contraction, although it is the part which really contracts when the same light falli upon a distant part. The design here is too obvious to need being en- larged upon. I low could the iris acquire the power of contracting when light falls on another membrane, for the protection of that membrane > although it does not contract when the light falls upon itself alone ? — [Ed. * The focus of the refracted rays must fall exactly on the retina, sa ^hat the point of vision may be neither produced beyond it, nor shorten ed so as not to reach it. The latter defect exists in short-sighted per sons, from too great convexity of the cornea or lens. The former is tht defect cf long-sighted persons, in whom there is an opposite confoinuu tion of those parts.- Paxton.
APPLICATION OF THE ARGUMENT. 19
s 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 sulhcient for the purpose, is so minute as to elude ordinary observation. Some very late discove- ries, 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 tht» parts of the eye undergo. It is found, that by the action of certain muscles [PI. II. fig. 7.] 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 isdirectedtoanear object, three changes are produc- ed in it at the same time, all severally contributing to the ad - justment required. The cornea, or outermost coat of the eye, is rendered more round and prominent; the crystalline lens underneath is pushed forwards; 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 an- terior part of two pellucid globes, which, when they come to be examined, are found to be constructed upon strict op- tical principles ; the selfsame 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, deliver- ing it over to the action of another part; that to a third, and so onward; the progressive action depending ror ita success upon the nicest and minutest adjustment of the i>arts concerned; yet these parts so in fact adjusted *s t<?
20 APPLICATION OF THE ARGUMENT.
produce, not by a simple action or effect, but by a combi- nation of actions and effects, the result which is ultimately wanted. And forasmuch as this organ would have to ope- rate under different circumstances, with strong degrees ol light and with weak degrees, upon near objects, and upon remote ones, and these differences demanded, according tc 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 delinea- ted, 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 occa- sionally 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 con- trivance for making a watch regulate itself, by inserting within it a machinery, which, by the artful use of the dif- ferent 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 it is without a contriver?
But this, though much, is not the whole : by different species of animals the faculty we are describing is possess- ed, in degrees suited to the different range of vision which their mode of life, and of procuring their food, requires. Birds, for instance, 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 necessary that they should have the power of seeing very near objects distinctlv. On the other hand, from being often elevated much above the ground, living in air, and moving through it with great velocity, 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 ac- cordingly is, that two peculiarities are found in the eyes of birds, both tending to facilitate the change upon which the adjustment of the eye to different distances depends. The one is a bony, yet, ii. most species, a flexible rim of
ArFLiC_;iON OF THE ARGUMENT 2)
hoop,* [Plate III. fig. 1, 2.] surrounding the broadest part of the eye; which, confining the action of the muscles to vhat part, increases the effect of their lateral pressure upon the orb, by which pressure its axis is elongated for the pur- pose of looking at very near objects. The other is an ad- ditional muscle, called the marsupium, [Plate III. fig. 3, 4, 6.] to draw, upon 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 ex treme to another of their scale of adjustment, with more ease and readiness than the eyes of other animals.
The eyes of jishes also, compared with those of terres- trial animals, exhibit certain distinctions of structure adap- ted to their state and element. We have already ob- served upon the figure of the crystalline compensating by its roundness the density of the medium through which their light passes. To which we have to add, that the eyes of fish, in their natural and indolent state, appear to be adjusted 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 in a much higher degree convex than that of land animals, a corresponding difference attends its muscular conformation, viz. that it is throughout calculated for flattening the eye.
The iris also in the eyes of fish does not admit of con- traction. This is a great difference, of which the proba- ble reason is, that the diminished light in water is never too strong for the retina.
In the eel, [Plate III. fig. 5.] which has to work its head
* The flexible rim, or hoop, consists of bony plates, which in all birds occupy the front of the sclerotic; lying close together and overlap- ping each other. These hony 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 li^ht, passing through a lens, will be refracted to a point or focus beyond tho lens, and this focus will be less distant in proportion as the lens approach- es to a sphere in shape. This principle is very naturally applied to the explanation 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 ia immediately within the circle made by these scales, must be pressed forward* and rendered more convex, from the focus of the eye becoming altered, ox its axis being elongated. This consequent convexity of the cornea renders small objects near the animal very distinct. Without this structure a biro, would be continually liable to dash itself agaiust tree when flving in .t thick forest, and would be unable to see the murV •hjects on which it sometimes feeds. — Paxton.
22 APPLICATION OF THE ARGUMENT.
througli sand and gravel, the roughest and harshest sub< stances, there is placed before the eye, and at some dis- tance from it, a transparent, horny, convex case or cover- ing, which, without obstructing the sight, defends the or- gan. To such an animal, could anything be more wanted, or more useful?
Thus, in comparing the eyes of different kinds of ani- mals, we see, in their resemblances and distinctions, one general plan laid down, and that plan varied with the vary- ing exigencies to which it is to be applied.
There is one property, however, common, I believe, to all eyes, at least to all which have been examined,* namely, ihat 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 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 unperceived 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 re- flect without wonder upon the smallness, yet correctness, of the picture, the subtilty of the touch, the fineness of the lines. A landscape of five or six square leagues is brought into a space of half an inch diameter; y<i the multitude of objects which it contains, are all preserved; are all discrim- inated in their magnitudes, positions, figures, colors. The prospect from Hampstead-hill is compressed into the com- pass 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 distinctly per- ceived throughout its whole progress; for it is only by means of that perception that the motion of the coach it- self is made sensible to the eye. If anything can abate our admiration of the smallness of the visual tablet compar- ed with the extent of vision, it is a reflection, which the view of nature leads us, every hour, to make, viz. that in he hands of the Creator, great and little are nothing.
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 aione amounts to a manifestation of intelligence hav ing been exerted in the structure ; besides this, which forms
* The eve of the seal or sea-calf, I understand, js. an exception -^ Mem Acad Paris, 170] , p. 123.
APPLICATION OF THE ARGUMENT. 23
no doubt, the leading character of the organ, there is to be seen, in everything belonging to it and about it, an ex- traordinary degree of care, and anxiety for its preservation, due. if we may so speak, to its value and its tenderness. If is lodged in a strong, deep, bony socket, composed by the junction of seven different bones,* hoik wed out at their edges. In some few species, as that of the coatimondi,"}' 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 shows the same care. Within this socket it is embedded in fat, of all animal substances the best adapted both to its repose and motion. It is sheltered by the eyebrows; an arch of hair, which, like a thatched penthouse, prevents the sweat fend moisture of the forehead from running down into it.
But it is still better protected by its lid. Oftiie super- ficial parts of the animal frame, I know none which, in its office and structure, is more deserving of attention than the eyelid. It defends the eye; it wipes it; it closes it in sleop.J 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 intelligible, mo<e appropriate, or more mechanical ? If it be overlooked by „he observer of nature, it can only be because it is ob- vious 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 u iderstandino- we sometimes neglect the strongest observations, being taken up with others, which, though more recondite and scientific, are, as solid argu- ments, 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 con- stantly supplied by a secretion for the purpose; and tho superfluous brine is conveyed to the nose through a perfora- tion in the bone as large as a goose-quill. [Plate IV. fig. 1 .] When once the fluid has entered the nose, it spreads itself upon the inside of the nostril, and is evaporated by the cur- rent of warm air, which, in the course of respiration, is con-
* Heister, sect 89. t Mem. of the R. Ac. Paris, p. 117.
t The muscles which accomplish these actions are seen in Tab. XIV. Fig. 1, 2. The eyelids also moderate the force of a too brilliant light, ath* 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 protect the eye from the •mail particJ* of dust that float in the air. — Paxton.
24 APPLICATION OF THE ARGJMENT.
tinually passing over it. Can any pipe or outlet for cany ing off the waste liquor from a dye-house or a distillery, be more mechanical than this is? Tt is easily perceived, that the eye must want moisture : but could the want of the eye generate the gland which produces the tear, or bore the hole by which it is discharged, — a hole through a bone?
It is observable, that this provision is not found in fish; the element in which they live supplying a constant lotion to the eye.
It were, however, injustice to dismiss the eye as a piece of mechanism, without noticing that most exquisite of all contrivances, the nictitating membrane, which is found in the eyes of birds and of many quadrupeds. [Plate IV. fig. 2.] Its use is to sweep the eye, which it does in an in- stant; to spread over it the lachrymal humour; to defend it also from sudden injuries: yet not totally, when drawn upon the pupil, to shut out the light. The commodious ness with which it lies folded up in the inner corner of the eye, ready for use and action, and the quickness with which it executes its purpose, are properties known and obvious to every observer: but what is equally admirable, though not quite so obvious, is the combination of two different kinds of substance, muscular and elastic, and or two different kinds of action, by which the motion of this membrane is performed. It is not, as in ordinary cases, by the action of two antagonist muscles, one pulling for- ward and the other backward, that a reciprocal change is effected; but it is thus: The membrane itself is an elastic substance, capable of being drawn out by force like a piec« of elastic gum, and by its own elasticity returning, when the force is removed, to its former position. Such being its nature, in order to fit it up for its office, it is connected by a tendon or thread with a muscle in the back part of the eye: this tendon or thread, though strong, is so fine as not to obstruct the sight, even when it passes across it; and the muscle itself, being placed in the back part of the eye, [Plate IV. fig. 3, 4, and 5,] derives from its situation the advantage, not only of being secure, but of being out of the way; which it would hardly have been in any posi- tion that could be assigned to it in the anterior part of the orb, where its function lies. When the muscle behind tfie eye contracts, the membrane, by means of the communi- cating thread, is instantly drawn over the fore-part of it. When the muscular contraction (which is a positive, and, most probably, a voluntary effort,) ceases to be exerted the elasticity alone of the membrane brings it back again
APPLICATION OF THE ARGUMENT. 2.c,
jo its position.* Does not this, if anything can lo it, be- speak an artist, master of his work, acquainted with hig materials? " Of a thousand other things," say the French academicians, "we perceive not the contrivance, because we understand them only by the effects, of which we Know not the causes: but we here treat of a machine, all the parts whereof are visible; and which need only to be looked upon to discover the reasons of its motion and ac- tion."!
In the configuration of the muscle which, though placed behind the eye, draws the nictitating membrane over the eye, there is, what the authors just now quoted, deserved- ly call a marvellous mechanism. I suppose this structure to be found in other animals; but, in the memoirs from which this account is taken, it is anatomically demonstrat- ed only in the cassowary. The muscle is passed through a loop formed by another muscle; and is there inflected, as if it were round a pulley. This is a peculiarity; and observe the advantage of it. A single muscle with a straight tendon, which is the common muscular form, would have been sufficient, if it had had power to draw far enough. But the contraction, necessary to draw the mem- brane over the whole eye, required a longer muscle than could lie straight at the bottom of the eye. Therefore, in order to have a greater length in a less compass, the cord of the main muscle makes an angle. This, so, far, answers the end; but, still farther, it makes an angle, »iot round a fixed pivot, but round a loop formed by another muscle; which second muscle, whenever it contracts, oi course twitches the first muscle at the point of inflection and thereby assists the action designed by both.
One question may possibly have dwelt in the reader's mind during the perusal of these observations, namely, Why should not the Deity have given to the animal the faculty of vision at once'? Why this circuitous perception; the ministry of so many means; an element provided for the purpose; reflected from opaque substances, refracted throigh transparent ones; and both according to precise laws; then, a complex organ, an intricate and artificial ap- paratus, in order, by the operation of this element, and in conformity with the restrictions of these laws, to produce an image upon a membrane communicating with the brain?
* Phil. Tran. 1796.
r Memoirs for a Natural History of Anima/s ^y the Royal Academy of Sciences at Paris, done into English by order of the Royal Society 1701, p. 249.
26 APPLICATION OF THE ARGUMENT.
Wherefore all this? Why make the difficulty in o^der to surmount it? If to perceive objects by some other mode than that of touch, or objects which lay out of the reach of that sense, were the thing purposed ; coula not a simple volition of the Creator have communicated tie ca- pacity ? Why resort to contrivance, where power is omnip- otent? Contrivance, by its very definition and nature, is the refuge of imperfection. To have recourse to expedi- ents, implies difficulty, impediment, restraint, defect of power. This question belongs to the other senses, as well as to sights; to the general functions of animal life, as nu- trition, secretion, respiration; to the economy of vegeta- bles; and indeed to almost all the operations of nature. The question, therefore, is of very wide extent; and amo*ngst other answers which may be given to it, beside rea sons of which probably we are ignorant, one answer is this: It is only by the display of contrivance, that the existence, the agency, the wisdom of the Deity, could be testified to his rational creatures. This is the scale by which we as- cend to all the knowledge of our Creator which we possess, s ) far as it depends upon the phenomena, or the works of na- f are. Take away this, and you take away from us every sub- ject of observation, and ground of reasoning; I mean as ou: rational faculties are formed at present. Whatever is done God could have done without the intervention of instru- ments or means: but it is in the construction of instru- ments, in the choice and adaptation of means, that a ere a-" tive intelligence is seen. It is this which constitutes the order and beauty of the universe. God, therefore, has been pleased to prescribe limits to his own power, and to work his ends within those limits. The general laws of matter have perhaps the nature of these limits; its inertia, its reaction ; the laws which govern the communication of motion, the refraction and reflection of light, the constitu- tion of fluids non-elastic and elastic, the transmission of Bound through the latter; the laws of magnetism, of elec- tricity; and probably others, yet undiscovered. These aro general laws; and when a particular purpose is to be e£ fected, it is not by making a new law, nor by the susper* sion of the old ones, nor by making them wind, and bend, and yield to the occasion ; (for nature with great steadiness adheres to and supports them;) but it is, as we have seen n the eye, by the interposition of an apparatus, correspond- ing with these law *, and suited to the exigency which re- Bults from them, that the purpose is at length attained. As wa have said, therefore, God proscrih~r Mmits to his power,
APPLICATION OF THE ARGUMENT 21
thai he may let in the exercise, and thereby exhibit denion- Btrations of his wisdom. For then, i. c. such laws and lim- itations being laid down, it is as though one Being should have fixed certain rules; and, if we may so speak, provid- ed certain materials; and, afterwards, have committed to another Being out of these materials, and in subordination to theso rules, the task of drawing forth a creation: a sup- position which evidently leaves room, and induces indeed a necessity for contrivance. Nay, there may be many such agents, and many ranks of these. We do not advance this as a doctrine either of philosophy or of religion; but we say that the subject may safely be represented under this view, because the Deity, acting himself by general laws, will have the same consequences upon our reasoning, as if he had prescribed these laws to another. It has been said, that the problem of creation was, " attraction and matter being given, to make a world out of them:" and, as above explained, this statement perhaps does not convey a false idea.
We have made choice of the eye as an instance upon which to rest the argument of this chapter. Some single example was to be proposed; and the eye offered itself un- der the advantage of admitting of a strict comparison with optical instruments. The ear, it is probable, is no less artificially and mechanically adapted to its office than the eye. But we know less about it: we do not so well un- derstand the action, the use, or the mutual dependency of its internal parts. Its general form, however, both external and internal, is sufficient to show that it is an instrument adapted to the reception of sound; that is to say, already knowing that sound consists in pulses of the air, we per- ceive, in the structure of the ear, a suitableness to receive im- pressions from this species of action, and to propagate these impressions to the brain. For of what does this structure consist? [PI. V. fig. 1.] An external ear, (the concha,) calcu- lated, like an ear-trumpet, to catch and collect the pulses of which we have spoken; in large quadrupeds, turning to Lhe sound, and possessing a configuration, as well as mo- tion, evidently fitted for the office: of a tube which leads into the head, lying at the root of this outward ear, the folds and sinuses thereof tending and conducting the air towards it: of a thin membrane, like the pelt of a drum, stretched across this passage upon a bonv rim: of a chain of moveable, and infinitely curious bones, forming a com-
28 APPLICATION OF THE ARGUMENT
munication, and the only communication that can Le ob- served, between the membrane last mentioned and the in- terior channels and recesses of the skull: of cavites, sim- ilar in shape and form to wind instruments of music, being spiral or portions of circles: of the eustachian tube, like the hole in a drum, to let the air pass freely into and out of the barrel of the ear, as the covering membrane vibrates, or as the temperature may be altered: the whole labyrinth hewn out of a rock; that is, wrought into the substance of the hardest bone of the body. This assemblage of con* nected parts constitutes together an apparatus, plainly enough relative to the transmission of sound, or of the im- pulses received from sound, and only to be lamented in not being better understood.
The communication within, formed by the small bones of the ear, is, to look upon, more like what we are accustomed to call machinery, than anything I am acquainted with in animal bodies. [PI. V. fig. 2.] It seems evidently designed to continue towards the sensorium, the tremulous motions which are excited in the membrane of the tympanum, or what is better known by the name of the " drum of the ear." The compages of bones consists of four, which are so dis posed, and so hinge upon one another, as that if the mem- brane, the drum of the ear, vibrate, all the four are put in motion together; and, by the result of their action, work the base of that which is the last in the series, upon an aperture which it closes, and upon which it plays, and which aperture opens into the tortuous canals that lead to the brain. This last bone of the four is called the stapes. The office of the drum of the ear is to spread out an ex- tended surface, capable of receiving the impressions of sound, and of being put by them into a state of vibration. The office of the stapes is to repeat these vibrations. It is a repeating frigate, stationed more within the line. From which account of its action may be understood, how the sensation of sound will be excited by anything which communicates a vibratory motion to the stapes, though not, as in all ordinary cases, through the intervention of the membrana tympani. This is done by solid bodies applied to the bones of the skull, as by a metal bar held at one end between the teeth, and touching at the other end a tremulous body. It likewise appears to be done, in a con- siderable degree, by the air itself, even when this mem- brane, the drum of the ear, is greatly damaged. Either in the natural or preternatural state of the organ, the use pf the chain cf bones is to pro "agate the impulse in a di
APPLICATION OP THE ARGUMENT SJ'J
reckon towards the brain, and to propagate it with the ad- vantage of a lever; which advantage consists in increasing the force and strength of the vibration, and at the same time diminishing the space through which it oscillates; 30th of which changes may augment or facilitate the stiil deeper action of the auditory nerves.
The benefit of the eustachian tube to the organ, may be made out upon known pneumatic principles. Behind tho drum of the ear is a second cavity, or barrel, called the tympanum. The eustachian tube is a slender pipe, but sufficient for the passage of air, leading from this cavity into the back part of the mouth. Now, it would not have done to have had a vacuum in this cavity; for, in that case, the pressure of the atmosphere from without would have burst the membrane which covered it. Nor would it have done to have filled the cavity with lymph or any other secretion; which would necessarily have obstructed, both the vibration of the membrane and the play of the small bones. Nor, lastly, would it have done to have occupied the space with confined air, because the expansion of that air by heat, or its contraction by cold, would have distend- ed or relaxed the covering membrane, in a degree inconsis- tent with the purpose which it was assigned to execute. The only remaining expedient, and that for which the eustachian tube serves, is to open to this cavity a commu- nication with the external air. In one word; it exactly answers the purpose of the hole in a drum.
The membrana tympani itself, likewise, deserves all the examination which can be made of it. It is not found in the ears of fish; which furnishes an additional proof of v/hat indeed is indicated by everything about it, that it is appropriated to the action of air, or of an elastic medium. It bears an obvious resemblance to the pelt or head of 8 drum, from which it takes its name. It resembles also a drum-head in this principal property, that its use depends upon its tension. Tension is the state essential to it. Now we know that, in a drum, the pelt is carried over a hoop, and braced, as occasion requires, by the means of strings attached to its circumference In the membrane of the ear, the same purpose is provided for, more simply, but not less mechanically, nor less successfully, by a different ex pedient, viz. by the end of a bone (the handle of the mul leus) pressing upon its centre. It is only in very large animals that the texture of this membrane can be discern- ed In the Philosophical Transactions for the year 1800, ivol i.) Sir Everard Home has given some curious observa
»jf APPL CATION OF THE ARGUMENT.
(::ons upon the ear, and the drum of the ear of an elephant
[PI v. fig 4.] He discovered in it what he calls a radiated muscle, that is, straight muscular fibres, passing along the membrane from the circumference to the centre; from the bony rim which surrounds it towards the handle of the malleus to which the central part is attached. This mus cle he supposes to be designed to bring the membrane into unison with different sounds: but then he also discovered, that this muscle itself cannot act, unless the membrane be drawn to a stretch, and kept in a due state of tightness, by what miy be called a foreign force, viz. the action ol the muscles of the malleus. Our author, supposing his ex- planation of the use of the parts to be just, is well founded in the reflection which he makes upon it: "that this mode of adapting the ear to different sounds, is one of the most beautiful applications of muscles in the body; the median" ism is so simple, and the variety of effects so great." *
In another volume of the transactions above referred to, and of the same year, two most curious cases are related, of persons who retained the sense of hearing, not in a perfect, but in a very considerable degree, notwithstanding he almost total loss of the membrane we have been de- scribing In one of these cases, the use here assigned to
* A3 the ear of man and fish has been described, it may not be im- proper in this place to state, that the other classes of animals are no less admirably provided with an ear, adapted to their peculiar habits and economy.
In amphibious animals the organ of hearing has an intermediate struc- ture; in some species of this class, the ear resembling fish, in others it more resembles the formation of terrestrial animals.
There is an important addition to this organ in birds: viz. a cochlea atd proper tympanum.
In quadrupeds we find a more complicated organization; to collect the vibrations of sound, they have an external ear, and all those parts, though of a different figure, which belong to the human ear.
The capacity for enjoyment of music is mental, but all the cur'oui varieties of sound, which are the source of this enjoyment, are communi- cated by the mechanical provisions of the ear. We are astonished at the varieties of sensation; the ear is capable of perceiving four or five hundred variations of tone in sound.
** Hence we may conceive a prodigious variety in the same tone, arising from irregularities of it occasioned by constitution, figure, situation or manner of striking the sonorous body; from the constitution of the clastic medium, or its being disturbed by other motions; and from the constitution of the ear itself, upon which the impression is made. A rlute, a violin, a hautboy, a French horn, may all sound the same tone, and be easJy distinguishable. Nay, if twenty human voices ^und the same note, and with equal strength, there will be some difference." Reid's Enquiry, page 98. — Parton.
PLANTS AND ANIMALS. 3
.hat membrane, of modifying the impressions of sound b)> change of tension, was attempted to be supplied by strai ing the muscles of the outward ear. " The external ear, ' we are told, '* had acquired a distinct motion upward and backward, which was observable whenever the patient istened to anything which he did not distinctly hear; when he was addressed in a whisper, the ear was seen im mediately to move ; when the tone of voice was louder, it then remained altogether motionless."
It appears probable, from both these cases, that a collate ral, if not principal, use of the membrane, is to cover and protect the barrel of the ear which lies behind it. Both the patients suffered from cold: one, " a great increase ol deafness from catching cold;" the other, " very considera- ble pain from exposure to a stream of cold air." Bad ef- fects therefore followed from this cavity being left open to the external air; yet, had the Author of nature shut it up by any other cover, than what was capable, by its texture, o{ receiving vibrations from sound, and, by its connexion with the interior parts, of transmitting those vibrations to the brain, the use of the organ, so far as we can judgp must have been entirely obstructed.
CHAPTER IV.
OF THE SUCCESSION OF PLANTS AND ANIMALS.
The generation of the animal no more accounts for the contrivance of the eye or ear, than, upon the supposition stated in a preceding chapter, the production of a watch by the motion and mechanism of a former watch, would account for the skill and intention evidenced in the watch so produced; than it would account for the disposition of the wheels, the catching of their teeth, the relation of the several parts of the works to one another, and to their com- mon end; for the suitableness of their forms and places to their offices, for their connexion, their operation, and the useful result of that operation. I do insist most strenu- ously upon the correctness of this comparison; that it holds as to everv mode of specific propagation; and that whatever was true of the watch, under the hypothesis above mentioned, is true of plants and animals.
I. To begin with the fructification of plants. Can it be dcubted but that the seed contains a particular organize
t*2 OF THE SUCCESSION OF
tion? Whether a latent plantule with the means of tem- porary nutrition, or whatever else it be, it encloses an or ganization suited to the germination of a new plant. Has the plant which produced the seed anything more to d with that organization, than the watch would have Ijad to do with the structure of the watch which was produced in the course of its mechanical movement ? I mean, Has it any- thing at all to do with the contrivance? The maker and con- triver of one watch, when he inserted within it a mechanism suited to the production of another watch, was, in truth, the maker and contriver of that other watch. All the prop- erties of the new watch were to be referred to his agency: the design manifested in it, to his intention: the art, to him as the artist: the collocation of each part to his placing* the action, effect, and use, to his counsel, intelligence, and workmanship. In producing it by the intervention of a former watch, he was only working by one set of tools in stead of another. So it is with the plant and the seed produced by it. Can any distinction be assigned between the two cases; between the producing watch, and the pro- ducing plant; both passive, unconscious substances; both, by the organization which was given to them, producing their like, without understanding or design; both, that is, instruments?
II. From plants we may proceed to oviparous animals, from seeds to eggs. Now, I say, that the bird has the same concern in the formation of the egg which she lays, as the plant has in that of the seed which it drops; and no other, nor greater. The internal constitution of the egg is as much a secret to the hen, as if the hen were inan imate. Her will cannot alter it, or change a single feather of the chick. She can neither foresee nor determine o. which sex her brood shall be, or how many of either; yel the thing produced shall be, from the first, very different in its make, according to the sex which it bears. So far, therefore, from adapting the means, she is not beforehand apprized of the effect. If there be concealed within that Bmooth shell a provision and a preparation for the produc- tion and nourishment of a new animal, they are not of hei providing or preparing: if there be contrivance, it is none of hers. Although, therefore, there be the difference of iife and perceptivity between the animal and the plant, it ia a difference which enters not into the account. It is a for- eign circumstance. It is a difference of properties not employed. The animal function and the vegetable fimc tion are alike destitute of any design which can operate upon
PLANTS AND ANIMALS. 33
khe form of the thing produced. The plant has no de* sign in producing the seed, no comprehension of the na- ture or use of what it produces; the bird with respect to its vgg> is not above the plant with respect to its seed. Neith- er the one nor the other bears that sort of relation to what proceeds from them, which a joiner does to the chair which he makes. Now a cause, which bears this relation to the effect, is what we want, in order to account for the suita- bleness of means to an end, the fitness and fitting of one thing to another, and this cause the parent plant or ani- mal does not supply.
It is farther observable concerning the propagation of plants and animals, that the apparatus employed exhibits no resemblance to the thing produced; in this respect holding an analogy with instruments and tools of art. The filaments, antherre, and stigmata of flowers, bear no more resemblance to the young plant, or even to the seed, which is formed by their intervention, than a chisel or a plane does to a table or chair. What then are the filaments, antherse, and stigmata of plants, but instruments strictly so called? *
III. We may advance from animals which bring forth eggs, to animals which bring forth their young alive: and of this latter class, from the lowest to the highest; from irrational to rational life, from brutes to the human species;
* Nearly akin to the reproduction of plants and animals by generation, is the reproduction of parts of animal bodies which have been destroyed, and the reparation of those which have been injured. To say nothing of the reproduction of limbs in crustaceous animals, the wonderful but well attested fact, of the formation of a new eye in an animal of the "lizard kind, in the plaie of one which had been cut out of the socket, is one which no atheistical theory can approach, in the way of explanation. In the pro- cess by which a new eye is formed, the apparatus, instruments and materials, employed, bear no resemblance to the organ to be farmed. The small capillary vessels of the root of the eye, construct a new eye, out of the blood which circulates in them. To use a mode of expression like that of our author — the vessels which thus construct a new eye, bear no more resemb.ance to it, than a chisel or a plane, to a table or a chair; and the blood out of which it is m; de, no more resemblance to it when made, than the metallic ores when taken out of the mine, to a complete and perfectly constructed watch. In this case, we find a contrivance exist- ing in a whole race of animals, for the accomplishment of a purpose which it is not called upon to accomplish in one instance out of a thousand. If ths reader will examine the several atheistical modes of evading the force of tho argurrents for the existence of Clod, referred to in the next chapter, as w ill as in various other parts of this volume, he will find that they signally fail in their application to this case. — Ed.
34 PLANTS AND ANIMALS.
without perceiving, as we proceed, any alteiation «vnatcvet in the terms of the comparison. The rational animal does not produce its offspring with more certainty or success Jian the irrational animal; a man than a quadruped, a quadruped than a bird; nor (for we may follow the grada- tion through its whole scale) a bird than a plant; nor a plant than a watch, a piece of dead mechanism, would do, upon the supposition which has already so often been re- peated. Rationality therefore has nothing to do in the business. If an account must be given of the contrivance which we observe; if it be demanded, whence arose either the contrivance by which the young animal is produced, or the contrivance manifested in the young animal itself, it is not from the reason of the parent that any such account can be drawn. He is the cause of his offspring in the same sense as that in which a gardener is the cause of the tulip which grows upon his parterre, and in no other. We ad- mire the flower; we examine the plant; we perceive the conduciveness of many of its parts to their end and office; we observe a provision for its nourishment, growth, pro- tection, and fecundity; but we never think of the gardener in all this. We attribute nothing of this to his agency; yet it may still be true, that without the gardener w*» should not have had the tulip: just so it is with the suc- cession of animals even of the highest order. For the contrivance discovered in the structure of the thing pro- duced, we want a contriver. The parent is not that contri- ver. His consciousness decides that question. He is in total ignorance why that which is produced took its present form rather than any other. It is for him only to be astonished by the effect. We can no more look therefore to the intel- ligence of the parent animal for what we are in search of, a cause of relation, and of subserviency of parts to their use, which relation and subserviency we see in the procreated body, than we can refer the internal conformation of an acorn to the intelligence of the oak from which it dropped, or the structure of the watch to the intelligence of the watch which produced it; there being no difference, as fax as argument is concerned, between an intelligence which u< not exerted, and a intelligence which does not exist.
APPLICATION &*? SO
CHAPTER V.
APPLICATION OF THE ARGUMENT CONTINUED.
Every observation which was made in our first chap- ter, concerning the watch, may be repeated with strict pro- priety concerning the eye; concerning animals; concern- ing plants; concerning, indeed, all the organized parts of the works of nature. As,
J. When we are inquiring simply after the existence of an intelligent Creator, imperfection, inaccuracy, liability to disorder, occasional irregularities, may subsist in a con- siderable degree, without inducing any doubt into the question: just as a watch may frequently go wrong, seldom perhaps exactly right, may be faulty in some parts, defec- tive in some, without the smallest ground of suspicion from thence arising that it was not a watch; not made; or not made for the purpose ascribed to it. When faults are pointed out, and when a question is started concerning the skill of the artist, or the dexterity with which the work is executed, then, indeed, in order to defend these qualities from accusation, we must be able, either to expose some intractableness and imperfection in the materials, or point out some invincible difficulty in the execution, into which imperfection and difficulty the matter of complaint may be resolved; or if we cannot do this, we must adduce such specimens of consummate art and contrivance, proceeding from the same hand, as may convince the inquirer of the existence, in the case before him, of impediments like those which we have mentioned, although, what from the nature of the case is very likely to happen, they be unknown an<4 unperceived by him. This we must do in order to vindi- cate the artist's skill, or, at least, the perfection of it; as we must also judge of his intention, and of the provision employed in fulfilling that intention, not from an instance in which they fail, but from the great plurality of instances in which they succeed. But, after all, these are different questions from the question of the artist's existence; or, which is the same, whether the thing before us be a work of art or not: and the question ought always to be kept sepa- rate in the mind. So likewise it is in the works of nature Irregularities and imperfections are of little or no weight in the consideration, when that consideration relates sim- ply V the existence of a Creator. When tlie argument ve»
36 APPLICATION OF THE
spects his attributes, they are of weight; but are then to be taken in conjunction (the attention is not to rest upon them, but they are to be taken in conjunction) with the unexceptionable evidences which we possess, of skill, power, and benevolence, displayed in other instances; which evidences may, in strength, number, and variety, be such, and may so overpower apparent blemishes, as to in- duce us, upon the most reasonable ground, to believe, that *hese last ought to be referred to some cause, though we be ignorant of it, other than defect of knowledge or of be- nevolence in the author.
II. There may be also parts of plants and animals, as there were supposed to be of the watch, of which, in seme instances, the operation, in ochers, the use, is unknown These form different causes; for the operation may be un- known, yet the use be certain. Thus it is with the lungs of animals. It does not, I think, appear, that we are acquainted with the action of the air upon the blood, or in what man- ner that action is communicated by the lungs; yet we find that a very short suspension of their office destroys the life of the animal. In this case, therefore, we maybe said to know the use, nay we experience the necessity, of the organ, though we be ignorant of its operation. Nearly the same thing may be observed of what is called the lympha- tic system. We suffer grievous inconveniences from its dis- order, without being informed of the office which it sus- tains in the economy of our bodies. There may possibly also be some few examples of the second class, in which not only the operation is unknown, but in which experi- ments may seem to prove that the part is not necessary; or may leave a doubt, how far it is even useful to the plant or animal in which it is found. This is said to be the case with the spleen; which has been extracted from dogs, with- out any sensible injury to their vital function. Instances i«t *he former kind, namely, in which we cannot explain the operation, may be numerous; for they will be so iii proportion to our ignorance. They will be more or fewe to different persons, and in different stages of science Every improvement of knowledge diminishes their number There is hardly, perhaps, a year passes that does not, in the works of nature, bring some operation, or some mode of operation, to light, which was before undiscovered, — pro- bably unsuspected. Instances of the second kind, namely, where the part appears to be totally useless, I believe to be extremely rare; compared with the number of those of uhich the use is evident they are beneath any assignable
ARGUMENT CONTINUED 37
proportion; and, perhaps, have never be*n submitted to a irial and examination sufficiently accurate, long enough continued, or often enough repeated. No accounts which I have seen are satisfactory. The mutilated animal may live and grow fat, (as was the case of the dog deprived of its spleen,) yet may be defective in some other of its func- tions; which, whether they can all, or in what degree of ugor and perfection, be performed, or how ong preserv- ed, without the extirpated organ, does not seem to be as- certained by experiment. But to this case, even were it fullv made out, may be applied the consideration which we suggested concerning the watch, viz. that these superfluous parts do not negative the reasoning which we instituted concerning those parts which are useful, and of which we know the use. The indication of contrivance, with re- spect to them, remains as it was before.
III. One atheistic way of replying to our observations upon the works of nature, and to the proofs of a Deity which we think that we perceive in them, is to tell us, that all which we see must n ?cessarily have had some form, and that it might as well be its present form as any other. Let us now apply this answer to the eye, as we did before to the watch. Something or other must have occupied that place in the animal's head; must have filled up, we will say, that socket: we will say also, that it must have been of that sort of substance which we call animal substance, as flesh, bone, membrane, cartilage, &c. But that it should have been an eye, knowing as we do, what an eye com- prehends,— viz. that it should have consisted, first, of a se- ries of transparent lenses (very different, by the by, even in their substanee, from the opaque materials of which the rest of the body is, in general at least, composed; and with which the whole of its surface, this single portion of it ex- cepted, is covered:) secondly, of a black cloth or canvass (the only membrane of the body which is black) spread at behind these lenses, so as to receive the image formed / pencils of light transmitted through them; and placed at the precise geometrical distance at which, and at which alone, a distinct image could be formed, namely, at the concourse of the refracted rays: thirdly, of a large nerve communicating between this membrane and the brain; without which, the action of light upon the membrane, however modified by the organ, would be lost to the pur- poses of sensation: — that this fortunate conformation of parts should have been the lot, not of one Vidividual out of many thousand mdividuals, like the great r rizo in a lot-
D
38 APPLICATION OF THE
tery, or like some singularity in nature, but the happy chance of a whole species; nor of one species out of many thousand species, with which we are acquainted, but of by far the greatest number of all that exist; and ihat uider varieties, not casual or capricious, but bearing marks of being suited to their respective exigencies: — that all this should have taken place, merely because something must have occupied those points in every animal's fore- head,— or, that all this should be thought to be accounted for, by the short answer, "that whatever was there, must have had some form or other," is too absurd to be made more so by any augmentation. We are not contented with this answer; we find no satisfaction in it, by way of accounting for appearances of organization far short of those of the eye, such as we observe in fossil shells, petri- fied bones, or other substances which bear the vestiges of animal or vegetable recrements, but which, either in re- spect of utility, or of the situation in which they are dis- covered, may seem accidental enough. It is no way of accounting even for these things, to say that the stone, for instance, which is shown to us, (supposing the question to be concerning a petrification,) must have contained some internal conformation or other. Nor does it mend the an- swer to add, with respect to the singularity of the confor- mation, that, after the event, it is no longer to be comput- ed what the chances were against it. This is always to be computed, when the question is, whether a useful or imi- tative conformation be the produce of chance, or not: I de- sire no greater certainty in reasoning, than that by which chance is excluded from the present disposition of the nat- ural world. Universal experience is against it. What does chance ever do for us? In the human body, for in- stance, chance, i. e. the operation of causes without design, may produce a wen, a wart, a mole, a pimple, but never an eye. Amongst inanimate substances, a clod, a pebble, a liquid drop might be; but never was a watch, a telescope, an organized body of any kind, answering a valuable pur- pose by a complicated mechanism, the effect of chance In no assignable instance hath such a thing existed without intention somewhere.
IV. There is another answer, which has the same ef- fect as the resolving of things into chance; which answer would persuade us to believe, that the eye, the animal to which it belongs, every other animal, every plant, indeed every organized body which we see, are only so many out oT t1-' nocsiblc varieties and combinations of being, which
ARGUMENT CONliNUED. 39
the lapse of infinite ages has brought into existence; that the present world is the relic of that variety; millions of other bodily forms and other species having perished, be- ing by the defect of their constitutions incapable of preser- vation, or of continuance by generation. Now there is no foundation whatever for this conjecture in anything which we observe in the works of nature; no such experiments are going on at present; no such energy operates, as that which is here supposed, and which should be constantly pushing into existence new varieties of beings: Nor are there any appearances to support an opinion, that every possible combination of vegetable or animal structure has formerly been tried. Multitudes of conformations, both of vegetables and animals, may be conceived capable of exist- ence and succession, which yet do not exist. Perhaps almost as many forms of plants might have been found in the fields, as figures of plants can be delineated upon paper. A countless variety of animals might have existed, which do not exist. Upon the supposition here stated, we should see unicorns and mermaids, sylphs and centaurs, the fan- cies of painters, and the fables of poets, realized by exam- ples. Or, if it be alleged that these may transgress the limits of possible life and propagation, we might, at least, have nations of human beings without nails upon their fin- gers, with more or fewer fingers and toes than ten; some with one eye, others with one ear, with one nostril, or with- out the sense of smelling at all. All these, and a thousand other imaginable varieties, might live and propagate. We may modify any one species many different ways, all con- sistent with life, and with the actions necessary to preserva- tion, although affording different degrees of conveniency and enjoyment to the animal. And if we carry these mod- ifications through the different species which are known to subsist, their number would be incalculable. No reason can be given why, if these deperdits ever existed, they have now disappeared. Yet, if all possible existences have been tried, they must have formed part of the catalogue.
But, moreover, the division of organized substances into animals and vegetables, and the distribution and sub-distri- bution of each into genera and species, which distribution is not an arbitrary act of the mind, but founded in the order which prevails in external nature, appear to me to contiadict the supposition of the present world being the remains of an indefinite variety of existences; of a variety which rejects all plan. The hypothesis teaches, that every
40 APPLICATION OF THE
possible variety of being hath, at one time or other, fouml its way into existence, (by what cause or in what manner ig not said,) and that those which were badly formed, perish- ed; but how or why those which survived should be cast, as we see that plants and animals are cast, into regular classes, the hypothesis does not explain; or rather, the hy- pothesis is inconsistent with this phenomenon.
The hypothesis, indeed, is hardly deserving of the con- sideration which we have given to it. What should wo think of a man who, because we had never ourselves seen watches, telescopes, stocking mills, steam engines, &c made, knew not how they were made, or could prove by testimony when they were made, or by whom,— would have us believe that these machines, instead of de riving their curious structures from the thought and design of their inventors and contrivers, in truth derive them from no other origin than this, viz. that a mass of metals and oth- er materials having run when melted into all possible fig- ures, and combined themselves in all possible forms and shapes, and propoitions, these things which we see, are what were left from the accident, as best worth preserving; and, as such, are become the remaining stock of a maga- zine, which, at one time or other, has, by this means, con- tained every mechanism, useful and useless, convenient and inconvenient, into which such like materials could be thrown? I cannot distinguish the hypothesis as applied to the works of nature, from this solution, which no one would accept, as applied to a collection of machines.
V. To the marks of contrivance discoverable in animal bodies, and to the argument deduced from them, in proof of design, and of a designing Creator, this turn is sometimes attempted to be given, viz. that the parts were not intended for the use, but that the use arose out of the parts. This distinction is intelligible. A cabinet maker rubs his ma- hogany with fish skin; yet it would be too much to assert that the skin of the dogfish was made rough and granulated on purpose for the polishing of wood, and the use of cabinet- makers. Therefore the distinction is intelligible. But I think that there is very little place for it in the works of nature. When roundly and generally affirmed of them, as it hath sometimes been, it amounts to such another stretch of assertion, as it would be to say, that all the implements of the cabinet-maker's workshop, as well as the fish skin, were substances accidentally configurated, which he had picked up, and converted to his use; that his adzes, saws </a.ies and gimlets, were not mads, as we suppose, to hew
ARGUMENT CONTINUED. 4«
eu\, smooth, shape out, or bore wood with; but that, these things being made, no matter with what design, or whether with any, the cabinet-maker perceivec- that they were ap- plicable to his purpose, and turned them to account.
But, again. So far as this solution is attempted to he ap- plied to those parts of animals, the action of which does not depend upon the will of the animal, it is fraught with still more evident absurdity. Is it possible to believe that the eye was formed without any regard to vision; that it W£s the animal itself which found out, that, though formed with no such intention, it would serve to see with; and that the use of the eye, as an organ of sight, resulted from this discovery, and the animal's application of it? The same question may be asked of the ear; the same of all the senses. None of the senses fundamentally depend upo~ the election of the animal; consequently, neither upon his sagacity, nor his experience. It is the impression which objects make upon them, that constitutes their use. Under that impression, he is passive. He may bring objects to the sense, or within its reach; he may select these objects: but over the impression itself he has no power, or very little; and that properly is the sense.
Secondly, There are many parts of animal bodies which seem to depend upon the will of the animal in a greater degree than the senses do, and yet, with respect to which, this solution is equally unsatisfactory. If we apply the so- lution to the human body, for instance, it forms itself into questions, upon which no reasonable mind can doubt; such as, whether the teeth were made expressly for the mastica- tion of food, the feet for walking, the hands for holding; or whether, these things being as they are, being in fact in the animal's possession, his own ingenuity taught him that they were convertible to these purposes, though no such purposes were contemplated in their formation.
All that there is of the appearance of reason in this way of considering the subject is, that, in some cases, the organization seems to determine the habits of the ani- mal, and its choice, to a particular mode of life; which; in a certain sense, may be called "the use arising out of he part." Now to all the instances, in which there is any place for this suggestion, it may be replied, that the organ- ization determines the animal to habits beneficial and salu- tary to itself; and that this effect would not be seen so regularly to follow, if the several organizations did not bear a concerted and contrived relation to the substance by which the animal was surrounded They wouH. othcr-
42 APPLICATION OF THE
wise, be capacities without objects; powers without em- ployment. The web foot determines, you say, the duck (o swim: but what would that avail, if there were no water to swim in? The strong hooked bill, and sharp talons, of one species of bird, determine it to prey upon animals, the soft straight oill, and weak claws, of another species, determine it to pick up seeds: but neither determinations could take effect in providing for the sustenance of the birds, if animal bodies and vegetable seeds did not lie with- in their reach. The peculiar conformation of the bill, and tongue, and claws of the woodpecker, [PI. XXVII. fig. 1, 2, 3] determines that bird to search for his food amongst the insects lodged behind the bark, or in the wood, of de- cayed trees: but what would this profit him, if there were no trees, no decayed trees, no insects lodged under their bark, or in their trunk? The proboscis with which the bee is furnished, determines him to seek for honey: but what would that signify, if flowers supplied none? Facul- ties thrown down upon animals at random, and without reference to the objects amidst which they are placed, would not produce to them the services and benefits which we see; and if there be that reference, then there is in tention.
Lastly^ the solution fails entirely when applied to plants The parts of plants answer their uses, without any concur rence from the will or choice of the plant.
VI. Others have chosen to refer everything to a princi pie of order in nature. A principle of order is the word* but what is meant by a principle of order, as different from an intelligent Creator, has not been explained eithei by definition or example; and, without such explanation, it should seem to be a mere substitution of words for rea- sons, names for causes. Order itself is only the adaptation of means to an end: a principle of order, therefore, can only signify the mind and intention which so adapts them. Or, were it capable of being explained in any other sense, is there any experience, any analogy to sustain it? Was a watch ever produced by a principle of order ? and why might not a watch be so produced as well as an eye ?
Furthermore, a principle of order, acting blindly and without choice, is negatived by the observation, that order is not universal; which it would be, if it issued from a cOn- Btant and necessary principle; nor indiscriminate, which if would be, if it issued from an unintelligent principle. Where order is wanted, there we find it; where order is not want- ed, i e. where, if it prevailed, it would be useless, there tv«
ARGUMENT CONTINUED. 4fc
do not find it. In the structure of the eye, (for we adhere to our example,) in the figure and position of it* several parts, the most exact order is maintained. In the forms of rock and mountainj in the lines which bound the coasts of con- nents and islands, in the shape of bays and promontories, no order whatever is perceived, because it would have been superfluous. No useful purpose would have arisen from moulding rocks and mountains into regular solids, bound ing the channel of the ocean by geometrical curves, 01 from the map of the world resembling a table of diagrams in Euclid's Elements, or Simpson's Conic Sections.
VII. Lastly, the confidence which we place in our ob- servationsPupoh the works of nature, in the marks which we discover of contrivance, choice, and design, and in our reasoning upon the proofs afforded us, ought not to be shaken, as it is sometimes attempted to be done, by bring- ing forward to our view our own ignorance, or rather the general imperfection of our knowledge of nature. Nor, in many cases, ought this consideration to affect us, even when it respects some parts of the subject immediately under our notice. True fortitude of understanding consists in not suffering what we know to be disturbed by what we do not know. If we perceive a useful end, and means adapted to that end, we perceive enough for our conclusion If these things be clear, no matter what is obscure. The argument is finished. For instance; if the utility of vision to the animal which enjoys it, and the adaptation of the eye to this office, be evident and certain, (and I can mention nothing which is more so,) ought it to prejudice the infer- ence which we draw from these premises, that we cannot expla'n the use of the spleen? Nay, more; if there be parts of the eye, viz. the cornea, the crystalline, the retina, in their substance, figure, and position, manifestly suited to the formation of an image by the refraction of rays of light, at least, as manifestly as the glasses and tubes of a dioptric telescope are suited to that purpose; it concerns not the proof which these afford of design, and of a designer, tha there may perhaps be other parts, certain muscles, for in- etance, or nerves in the same eye, of the agency or effect of which we can give no account; any more than we should be inclined to doubt, or ought to doubt, about *he construction of a telescope, viz. for what purpose it was constructed, or whether it were constructed at all, because there belonged to it certain screws and pins, the use or action of which we did not comprehend. I take it to be a general way rf infusing doubts and scruples into the mind
44 THE ARGUMENT CUMULATIVE.
to recur tc its own ignorance, its own imbecility: to tell us that upon these subjects we know little; that little im- perfectly; or rather, that we know nothing properly about the matter. These suggestions so fall in with our con- sciousnesses, as sometimes to produce a general distrust of our faculties and our conclusions. But this is an unfound* 2d jealousy. The uncertainty of one thing, does not ne- cessarily affect the certainty of another thing. Our ig- norance of many ooints need not suspend our assurance of a few Before we yield, in any particular instance, to the skepticism which this sort of insinuation would induce, we ought accurately to ascertain, whether our ignorance or doubt concern those precise points upon which our conclu- sion lests. Other points are nothing. Our ignorance of other points may be of no consequence to these, though they be points, in various respects, of great importance. A just reasoner removes from his consideration, not onlv what he knows, but what he does not know, touching mat- ters not strictly connected with his argument, i. e. not forming the very steps of his deduction; beyond these, his knowledge and his ignorance are alike relative.
CHAPTER VI.
THE ARGUMENT CUMULATIVE.
Were there no example in the world of contrivance ex- cept that of the eye, it would be alone sufficient to support the conclusion which we draw from it, as to the nece&oity of an intelligent Creator. It could never be got rid of; because it could not be accounted for by any other suppo- sition, which did not contradict all the principles we pos- sess of knowledge: the principles, according to which thing9 do, as often as they can be brought to the test of experi- ence, turn out to be true or false. Its coats and humours constructed as the lenses of a telescope are constructed, for the refraction of rays of light to a point, which forms the proper office of the organ: the provision in its muscles for turning its pupil to the object, similar to that which is given to the telescope by screws, and upon which power of direction in the eye, the exercise of its office as an optical instrument depends; the farther provision for ita defence, fo» its constant lubricity and moisture, which we see in its socket ar.d its lids, in its gland for the secretion
FUNCTIONS OF ANIMALS, &C. 43
of the matter of tears, its outlet or communication with the nose for carry ng off the liquid after the eye is washed with it; these provisions compose altogether an apparatus, a system of parts, a preparation of means, so manifest in their design, so exquisite in their contrivance, so successful in Jieir issue, so precious, and so infinitely beneficial in their use, as, in my opinion, to bear down all doubt that can ba raised upon the subject. And what I wish, un ler the title of the present chapter, to observe is, that if other parts of nature were inaccessible to our inquiries, or even if other parts of nature presented nothing to our examination out disorder and confusion, the validity of this example would remain the same. If there were but one watch in the world, it would not be less certain that it had a maker If we had never in our lives seen any but one single kind of hydraulic machine, yet, if of that one kind we understood the mechanism and use, we should be as perfectly assured that it proceeded from the hand, and thought, and skill of a workman, as if we visited a museum of the arts, and caw collected there twenty different kinds of machines foi drawing water, or a thousand different kinds for othei purposes. Of this point, each machine is a proof, inde • pendently of all the rest. So it is with the evidences of & divine agency. The proof is not a conclusion which liea at the end of a chain of reasoning, of which chain each instance of contrivance is only a link, and of which, if one link fail, the whole falls; but it is an argument separately supplied by every separate example. An error in stating an example affects only that example. The argjment is cumulative, in the fullest sense of that term. The eye proves it without the ear; the ear without the eye. The proof in each example is complete; for when the design of the part, and fcAe conduciveness of its structure to that de- sign is shown, the mind may set itself at rest; no future wmsidoration can detract anything from the force of h* sample
CHAPTER VII.
I THE MECHANICAL AND IMMECHANICAL PARTS AND I UNC- TIONS OF ANIMALS AND VEGETABLES
It is not that every part of an animal or vegetable naa not proceeded from a contriving mind; or that every part U not constructed *¥**h a new to its proper end said pur-
46 MECHANICAL AND IMMECHAN.'CAL PARTS
pose, according to the laws belonging to and governing the substance or the action made use of in that part, or that each part is not so constructed as to effectuate its purpose whilft it operates according to these laws; but it is because these laws themselves are not in all cases equal- ly understood; or, what amounts to nearly the same thing, are not equally exemplified in more simple processes, and more simple machines; that we lay dowr. the distinction, here proposed, between the mechanical parts and ether parts of animals and vegetables.
For instance; the principle of muscular motion, viz. upon what cause the swelling of the belly of the muscle and consequent contraction of its tendons, either by an act of the will, or by involuntary irritation, depends, is wholly unknown to us. The substance employed, whether it be fluid, gaseous, elastic, electrical, or none of these, or nothing resembling these, is also unknown to us: of course, the laws belonging to that substance, and which regulate its action, are unknown to us. We see nothing similar to this contraction in any machine which we can make, or any process which we can execute. So far (it is con- fessed) we are in ignorance, but no farther. This power and principle, from whatever cause it proceeds, being as- sumed, the collocation of the fibres to receive the princi- ple, the disposition of the muscles for the use and applica- tion of the power, is mechanical; and is as intelligible as the adjustment of the wires and strings by which a puppet is moved. We see, therefore, as far as respects the sub- ject before us, what is not mechanical in the animal frame, and what is. The nervous influence (for we are often obliged to give names to things which we know little about) — I say the nervous influence, by which the belly, or middle, of the muscle is swelled, is not mechanical. The utility of the effect we perceive; the means, or the preparation of means, by which it is produced, we do not But obscurity as to the origin of muscular motion bring! no doubtfulness into our observations upon the sequel o( the process: Which observations relate, 1st, to the con gtitutior of the muscle; in consequence of which consti- tution, the swelling of the belly or middle part is neces- sarily and mechanically followed by a retraction of the tendons: 2dly, to the number and variety of the muscles, and the corresponding number and variety of useful powers— whicli they supply to the animal; which is astonishingly great: 3dly, to the judicious, (if we may be permitted to use that erm, ir speaking of the author or of the works
AND F7NCTI9NS OF ANIMALS, &C. 41
of nature,) to the wise and well-contrived disposition of each muscle for its specific purpose; for moving the joint this way, and that way, and the other way; for pulling and drawing the part to which it is attached, in a determi- nate and particular direction; which is a mechanical oper ation, exemplified in a multitude of instances. To mention only one: The tendon of the trochlear muscle of the eye, '.o the end that it may draw in the line required, is passed through a cartilaginous ring, at which it is reverted, exact y in the same manner as a rope in a ship is carried over q block or round a stay, in order to make it pull in the direction which is wanted. [PI. V. fig. l.J All this, as we have said, is mechanical; and is accessible to inspection, as ca- pable of being ascertained, as the mechanism of the au- tomaton in the Strand. Suppose the automaton to be put in motion by a magnet, (which is probable,) it will supply us with a comparison very apt for our present purpose. Of the magnetic effluvium, we know perhaps as little as we do of the nervous fluid. But, magnetic attraction being as- sumed, (it signifies nothing from what cause it proceeds,) we can trace, or there can be pointed out to us, with per- fect clearness and certainty, the mechanism, viz. the steel bars, the wheels, the joints, the wires, by which the motion so much admired is communicated to the fingers of the im age: and to make any obscurity, or difficulty, or contro- versy in the doctrine of magnetism, an objection to our knowledge or our certainty concerning the contrivance, or the marks of contrivance, displayed in the automaton, would be exactly the same thing, as it is to make our ig- norance (which we acknowledge) of the cause of nervous agency, or even of the substance and structure of the nerves themselves, a ground of question or suspicion as to the reasoning which we institute concerning the mechani- cal part of our frame. That an animal is a machine, is a proposition neither correctly true nor wholly false. The distinction which we have been discussing will serve to show how far the comparison, which this expression im- plies, holds; and wherein it fails. And whether the dis- tinction be thought of importance or not, it is certainly of importance to remember, that there is neither truth noi justice in endeavouring to bring a cloud over our under- standings, or a distrust into our reasonings upon this sub- ject, by suggesting that we know nothing of voluntary motion, of irritability, of the principle of life, of sensation, of animal heat, upon all which the animal functions de- pend; for, ouv ignorance of these parts of the animal frame
48 MECHANICAL AND IMMECHANICAL PARTS
concerns not at all our knowledge of the mechanical parts of the same frame. I contend, therefore, that there i3 mechanism in animals; that this mechanism is as proper- ly such, as it is in machines made by art; that this me- chanism is intelligible and certain; that it is not the less so, because it often begins or terminates with something which is not mechanical: that whenever it is intelligible and certain, it demonstrates intention and contrivance, as well in the works of nature as in those of art; and that it is the best demonstration which either can afford.
But whilst I contend for these propositions, I do not exclude myself from asserting, that there may be, and that there are, other cases, in which, although we cannot ex- hibit mechanism, or prove indeed that mechanism is em- ployed, we want not sufficient evidence t~ conduct us to the same conclusion.
There is what may be called the chem^al part of our frame; of which, by reason of the imperfection of our chemistry, we can attain to no distinct knowledge; I mean, not to a knowledge, either in degree or kind, similar to that which we possess of the mechanical part of our frame. It does not, therefore, afford the same species of argument as that which mechanism affords ; and yet it may afford an argument in a high degree satisfactory. The gas trie juice, or the liquor which digests the food in the stom achs of animals, is of this class. Of all menstrua, it is the most active, the most universal. In the human stomach, for instance, consider what a variety of strange substances, and how widely different from one another, it, in a few hours, re- duces to a uniform pulp, milk, or mucilage. It seizes upon everything, it dissolves the texture of almost everything that comes in its way. The flesh of perhaps all animals; the seeds and fruits of the greatest number of plants; the roots, and stalks, and leaves of many, hard and tough as [hey are, yield to its powerful pervasion. The change wrought by it is different from any chemical solution which we can produce, or with which we are acquainted, in this respect as well as many others, that, in our chemistry, par- ticular menstrua act only upon particular substances. Con- sider, moreover, that this fluid, stronger in its operation than a caustic alkali or mineral acid, than red precipitate, or aqua-fortis itself, is nevertheless as mild, and bland, and inoffensive to the touch or taste, as saliva or gum-water, which it much resembles. Consider, I say, these several oroperties of the digestive organ, and of the juice with *hich it is supplied, or rather with which it is made to sup-
AND FUNCTION! OF ANIMALS, &.C 4»
ply itself, and you will confess it to be entitled tc a name, which it has sometimes received, that of "tie chemical wonder of animal nature."
Still we are ignorant of the composition of this fluid, and of the mode of its action; by which is meant, that we are not capab'e, as we are in the mechanical part ofour frame, of collating it with the operations of art. And this I call Ihe imperfection ofour chemistry; for should the time ev- er arrive, which is not perhaps to be despaired of. when we can compound ingredients, so as to form a solvent which will act in the manner in which the gastric juice acts, we may be able to ascertain the chemical princip.es upon which its efficacy depends, as well as from what part, and by what concoction, in the human body, these principles arc generated and derived.
In the meantime, ought that, which is in truth the de- fect ofour chemistry, to hinder us from acquiescing in the inference, which a production of nature, by its place, its properties, its action, its surprising efficacy, its invaluable use, authorises us to draw in respect of a creative design?
Another most subtile and curious function of animal bod- ies is secretion. This function is semi-chemical and semi- mechanical; exceedingly important and diversified in its effects, but obscure in its process and in its apparatus. The importance of the secretory organs is but too well at- tested by the diseases, which an excessive, a deficient, or a vitiated secretion is almost sure of producing. A single secretion being wrong, is enough to make life miserable, or sometimes to destroy it. Nor is the variety less thai, vhe importance. From one and the same blood ( I speak '>f the human body) about twenty different fluids are sepa- rated; in their sensible properties, in taste, smell, color, and consistency, the most unlike one another that is possi- ble; thick, thin, salt, bitter, sweet: and, if from our own we pass to other species of animals, we find amongst Iheir secretions not only the most various, but the most opposite properties; the most nutritious aliment, the deadliest poi- L'on; the sweetest perfumes, the most fetid odors. Of thene the greater part, as the gastric juice, the saliva, the bile, the slippery mucilage which lubricates the joints, the tears which moisten the eye, the wax which defends the ear, are, after they are secreted, made use of in the animal economy; are evidently subservient, and are actually con- tributing to the utilites of the animal itself. Other fluids seem to be separated only to be rejected. That this also ,s necessary (though why it was originally necessarv wo
E
60 MECHANICAL ANI> [MMECHANICAL PARTS
cannot tell) is shown by the consequence of the separation ueing long suspended; 'which consequence is disease and death. Akin to secretion, if not the same thing, is assim- ilation, by which one and the same blood is converted into bone, muscular flesh, nerves, membranes, tendons; things as different as the wood and 'iron, canvass and cordage, of which a ship with its furniture is composed. We have no operation of art wherewith exactly to compare all this, for no other reason perhaps than that all operations of art are ex- ceeded by it. No chemical election, no chemical analysis cr resolution of a substance into its constituent parts, no me- chanical sifting or divison, that we are acquainted with, in perfection or variety, come up to animal secretion. Never- theless, the apparatus and process are obscure; not to say absolutely concealed from our inquiries. In a few, and only a few instances, we can discern a little of the constitution of a gland. In the kidneys of large animals, we can trace the emulgent artery dividing itself into an infinite number of branches; their extremities everywhere communicating with little round bodies, in the substance of which bodies the secret of the machinery seems to reside, for there the change is made. We can discern pipes laid from these round bodies towards the pelvis, which is a basin within the solid of the kidney. (PI. VI. fig. 2.) We can discern these pipes joining and collecting together into larger pipes; and when so collected, ending in innumerable papillae, through which the secreted fluid is continually oozing into its receptacle. This is all we know of the mechanism of a gland, even in the case in which it seems most capable of being investigated. Yet to pronounce that we know nothing of animal secretion, or nothing satisfactorily, and with that concise remark to dismiss the article from our argument, would be to dispose of the subject very hastily and very irrationally. For the purpose which we want, that of evincing intention, we know a great deal. And what we know is this. We see the blood carried by a pipe, conduit, or duct, to the gland. We see an organized apparatus, bo its construction or action what it may, which we call that gland Ve see the blood, or part of the blood, after it has passed through and undergone the action of the gland, coming from it by an emulgent vein or artery, i. e. by an- other pipe or conduit. And we see also at the same time a new and specific fluid issuing from the same gland by its excretory duct, i. e. by a third pipe or conduit; which new fluid is in some cases discharged out of the body, m more iases retained within it, and there executing some impoi-
AND FUNCTIONS OF ANIMALS. 5*
tant and intelligent office. Now supposing, or admitting, thai we know nothing of the proper internal constitution of a gland, or of the mode of its acting upon the blood; then our s'iuaticn is precisely like that of an unmechanical look- er-on, who stands by a stocking-loom, a coin-mill, a earri- ng-machine, or a threshing-machine, at work, the fabric irA mecbinism of which, as well as all that passes within, cs hidden from his sight by the outside case; or, if seen, would hi too complicated for his uninformed, uninstructed Understanding '„o comprehend. And what is that situation? This epecta*jr, ignorant as he is, sees at one end a mate rial enter Ine machine, as unground grain the mill, raw cot- ton the carding-machine, sheaves of unthreshed corn the threshing-machine; and, when he casts his eye to the other e;;d of the apparatus, he sees the material issuing from it in anew state; and, what is more, in a state manifestly adapted to future uses ; the grain in meal fit for the making of bread, the wool in rovings ready for spinning into threads, the sheaf in corn dressed for the mill. Is it ne- cessary that this man, in order to be convinced that design, that intention, that contrivance has been employed about the machine, should be allowed to pull it to pieces; should be enabled to examine the parts separately; explore their action upon one another, or their operation, whether simul- taneous or successive, upon the material which is presented to them? He may long to do this, to gratify his curiosity; he may desire to do it to improve his theoretic know- ledge ; or he may have a more substantial reason for re- questing it, if he happen, instead of a common visiter, to be a mill wnght by profession, or a person sometimes call- ed in to repair such-like machines when out of order; but, for the purpose of ascertaining the existence of counsel and design in the formation of the machine, he wants no such intromission or privity. What he sees is sufficient. The effect upon the material, the change produced in it, the utility of that change for future applications, abundantly testify, be the concealed part of the machine or of its con- struction what it may, the hand and agency of a contriver. If any confirmation were wanting to the evidence which the animal secretions afford of design, it may be derived, as has been already hinted, from their variety, and from their appropriation to their place and use. They all come from the same blood: they are all drawn off by glands: yet the produce is very different, and the difference exactly adapted to the work which is to be done, or the end to be answei ed. No account can be given of this, without re-
52 OF MECHANICAL ARRANGEMENT
sorting to appointment. Why, for instance, is the saliva which is diffused over the seat of taste, insipid, whilst so many others of the secretions, the urine, the tears, and the sweat, are salt? Why does the gland within the ear sepa- rate a viscid substance, which defends that passage; the gland in the upper angle of the eye, a thin brine, which washes the ball? Why is the synovia of the joints mu- cilaginous; the bile bitter, stimulating, and soapy? Why does the juice which flows into the stomach, contain pow- ers, which make that organ the great laboratory, as it is by ti3 situation the recipient, of the materials of future nutii- tion? These are all fair questions; and no answer can bo given to them, but what calls in intelligence and intention. My object in the present chapter has been to teach three things: first, that it is a mistake to suppose that, in reason- ing from the appearances of nature, the imperfection of our knowledge proportionably affects the certainty of our conclusion; for in many cases it does not affect it at all: secondly, that the different parts of the animal frame may be classed and distributed, according to the degree of ex- actness with which we can compare them with works of art: thirdly, that the mechanical parts of our frame, or those in which this comparison is most complete, although constituting, probably, the coarsest portions of nature's workmanship, are the most proper to be alleged as proofs and specimens of design.
CHAPTER VI1J.
OF MECHANICAL ARRANGEMENT IN THE HUMAN FRAME
We proceed, therefore, to propose certain examples ta* ken out of this class: making choice of such as, amor.gst those which have come to our knowledge, appear to be the most striking, and the best understood; but obliged, per- haps, to postpone both these recommendations to a third » that of the example being capable of explanation without pla*es, or figures, or technical language.
OF THE BONES.
1 challenge any man to produce, in the joints and pivots of the most complicated or the most flexible ma •thine hat was ever oontrved, a construction more artifi
IN THE HUMAN FRAME. 55
cial, or more evidently artificial, than that whfch is seen in the vertebrae of the human neck. [PL VII. fig. 1.] Two things were to be done. The head was to have the power of bending forward and backward, as in the act of nodding, stooping, looking upward or downward; and, at the same time, of turning itself round upon the body to a certain extent, the quadrant we will say, or rather, perhaps, a hun- dred a'ld twenty degrees of a circle. For these two pur- poses, two distinct contrivances are employed: [PI. VII. fig. 2, 3, 4.] First, the head rests immediately upon the uppermost of the vertebrae, and is united to it by a hinge* joint; upon which joint the head plays freely forward and backward, as far either way as is necessary, or as the liga- ments allow; which was the first thing required. — But then the rotatory motion is unprovided for. Therefore, secondly, to make the head capable of this, a farther me- chanism is introduced; not between the head and the up- permost bone of the neck, where the hinge is, but between that bone, and the bone next underneath it. It is a me- chanism resembling a tenon and mortice. This second, or uppermost bone but one, has what anatomists call a pro- cess, viz. a projection, somewhat similar, in size and shape, to a tooth; which tooth, entering a corresponding hole or socket in the bone above it, forms a pivot or axle, upon which that upper bone, together with the head which it oupports, turns freely in a circle; and as far in the circle as the attached muscles permit the head to turn. Thus 'ire both motions perfect, without interfering with each other. When we nod the head, we use the hinge-joint, which lies between the head and the first bone of the neck When we turn 'he head round, we use the tenon and mor tice. which runs between the first bone of the neck and the second. We see the same contrivance, and the same prin- ciple, employed in the frame or mounting of a telescope, It is occasionally requisite, that the object-end of the in dtrument be moved up and down, as well as horizontally, or equatoripJly. For the vertical motion, there is a hinge, upon which the telescope plays; for the horizontal oi equatorial motion, an axis upon which the telescope and the hinge turn round together. And this is exactly the mechanism which is applied to the motion of the head, nor wi'l any one here doubt of the existence of counsel and design, except it be by that debility of mind, which can trust to its own reasonings in nothing.
We may add, that it was on another account also, ex- pedient, tha the motion of the head backward md for-
K*
54 OF MECHANICAL ARRANGEMENT
ward should be performed upon the upper surface of the first vertebra: for, if the first vertebrae itself had bent for- ward, it would have brought the spinal marrow, s.t the verj beginning of its course, upon the point of the tooth.
II. Another mechanical contrivance, not unlil e the last in its object, but different and original in its meai s, is seen in what anatomists call the fore-arm; that is, in the arm from the elbow to the wrist. [PI. VIII fig. 1, 2.] Here, for the perfect use of the limb, two motions are wanted; a motion at the elbow backward and forward, which is called a reciprocal motion; and a rotatory motion, by which the palm of the hand, as occasion requires, maybe turned up- ward. How is this managed? The fore-arm, it is well known, consists of two bones lying alongside each other, but touching only towards the ends. One, and only one of these bones, is joined to the cubit, or upper part of the arm, at the elbow; the other alone, to the hand at the wrist. The first by means, at the elbow, of a hinge-joint, (which allows only of motion in the same plane,) swing j backward and forward, carrying along with it the other btae, and the whole fore-arm. In the meantime, as often a.j there is occasion to turn the palm upward, that oth'.T bone, to which the hand is attached, rolls upon the first, by the help of a groove or hollow near each end of one bone, to which is fitted a corresponding prominence in the other If both bones had been joined to the cubit, or upper arm, at the elbow, or both to the hand at the wrist, the thing could not have been done. The first was to be at liberty at one end, and the second at the other: by which means the two actions may be performed together. The great bone, which carries the fore-arm, may be swinging upon its hinge at the elbow, at the very time that the les ser bone, which carries the hand, may be turning round it in the grooves. The management also of these grooves, or rather of the tubercles and grooves, is very observable The two bones are called the radius and the ulna. Above, e. e. towards the elbow, a tubercle of the radius plays into a socket of the ulna; whilst below, i. e. towards the wrist, ♦he radius finds the socket, and the ulna the tubercle. A single bone in the fore-arm, with a ball and socket joint at the elbow, which admits of motion in all directions, might, in some degree, have answered the purpose of both moving the arm and turning the hand. But how much better it is accomplished bv the present mechanism, any person mav convince himself, who puts the ease and quickness, with nrhi"*,1'. he can shake his hand at the wrist circularly, (inov
IN THE HUMAN FRAME. 55
mg likewise, if he pleases, his arm at the elbc;v at the same time,) in competition with the comparatively slow and laborious motion with which his arm can be made to turn round at the shoulder, by the aid of a ball and socket joint.
Ill The spine, or back bone, is a chain of joints of very wonderful construction. [PI. IX. fig. 1, 2.] Various, dif- ficult, and almost inconsistent offices were to be. executed by the same instrument. It was to be firm, yet flexible, (now I know no chain made by art, which is both these; for bv firmness I mean, not onlv strength, but stability:) Jinn, to support the erect position of the body; flexible, to allow of the bending of the trunk in all degrees of curva- ture. It was farther also (which is another, and quite a distinct purpose from the rest) to become a pipe or conduit for the safe conveyance from the brain, of the most important fluid* of the animal frame, that, namely, upon which all voluntary motion depends, the spinal marrow ; a substance not only of the first necessity to action, if not to life, but of a nature so delicate and tender, so susceptible, and so impatient of injury, as that any unusual pressure upon it, or any considerable obstruction of its course, is followed by paralysis or death. Now the spine was not only to furnish the main trunk for the passage of the medullary substance from the brain, but to give out, in the course of its progress, small pipes therefrom, which, being afterwards indefinitely subdivided, might, under the name of nerves, distribute this exquisite supply to every part of the body. The same spine was also to serve another use not less want- ed than the preceding, viz. to afford a fulcrum, stay, or basis, (or, more properly speaking, a series of these) foi the insertion of the muscles which are spread over ihf trunk of the body; in which trunk there are not. as in the limbs, cylindrical bones, to which they can be fastened and, likewise, which is a similar use, to furnish a suppoi for the ends of the ribs to rest upon
Bespeak of a workman a piece of mechanism whicL shall comprise all these purposes, and let him set about to contrive it; let him try his skill upon it; let him feel the
* It seems proper to remark here, that the form of expression made use of in this case implies what is not strictly true. The spinal marrow, 01 more properly the spinal nerve, is not a fluid but a solid cord extending from the brain down through the canal of the spine, from which branehei are distribute 1 to ail parts of the body. Dr. I'aley in this instance prob- ably had in view the animal spiri s, a subtile fluid, which was formerly Delie\ed to be seated in the >rain, And carried through the nerves to tin* differ* nt par's. — Ed.
56 OF MECHANICAL ARRANGEMENT
difficulty of accomplishing the task, before he be *ioid how the same thing is effected in the animal frame. Nothing* will enable him to judge so well of the wisdom which hag been employed; nothing will dispose him to think of it so truly. First, for the firmness, yet flexibility, of the spine, it is composed of a great number of bones (in the human subject, of twenty-four) joined to one another, and compact- ed by broad bases. Tbe breadth of the bases upon which the parts severally rest, and the closeness of the junction, give to the chain its firmness and stability; the number of parts, and consequent frequency of joints, its flexibility. Which flexibility, we may also observe, varies in different parts of the chain: is least in the back, where strength more than flexure, is wanted; greater in the loins, which it was necessary should be more supple than the back, and greatest of all in the neck, for the free motion of the head. Then, secondly, in order to afford a passage for the descent of the medullary substance, each of these bones is bored through the middle in such a manner, as that, when put togettier, the hole in one bone falls into a line, and corresponds with the holes in the two bones con- tiguous to it. By which means the perforated pieces, when joined, form an entire, close, uninterrupted channel; at least, whilst the spine is upright, and at rest. But, as a settled posture is inconsistent with its use, a great diffi- culty still remained, which was to prevent the vertebra; shifting upon one another, so as to break the line of the canal as often as the body moves or twists; or the joints gaping externally, whenever the body is bent forward, and the spine thereupon made to take the form of a bow. These dangers, which are mechanical, are mechanically provided against. The vertebrre, by means of their processes and projections, and of the articulations which some of these form with one another at their extremities, are so locked in and confined, as to maintain, in what are called the bodies or broad surfaces of the bones, the relative position nearly un- altered; and to throw the change and the pressure, produced by flexion, almost entirely upon the intervening cartilages, the springiness and yielding nature of whose substance ad- mi's of all the motion which is necessary to be performed upon them, without any chasm being produced by a separa- .ion of the pa>-ts. I say, of all the motion which is necessa- ry; for although we bend our backs to every degree almost of inclination, the motion of each vertebrae is very small: Buch is the advantage we receive from the chain beinp f mposed of so many links, the spine of so many bone*
18 THE HUMAN FRAME. 57
Had it consisted of three or four bones only, in bonding the body the spinal marrow must have been bruised at every angle. The reader need not be told, that these inter- vening cartilages are gristles; and he may see them in perfection in a loin of veal. Their form also favors the same intention. They are thicker before than behind; so that, when we stoop forward, the compressible substance of the cartilage, yielding in its thicker and anterior oart to the force which squeezes iU, brings the surfaces of the adjoining vertebra nearer to the being parallel with one; another than they were before, instead of increasing the inclination of their planes, which must have occasioned a fissure or open- ing between them. Thirdly, for the medullary canal giv- ing out in its course, and in a convenient order, a supply of nerves to different parts of the body, notches are made in the upper and lower edge of every vertebra, two on each edge, equi-distant on each side from the middle line of the back. When the vertebrae are put together, these notches, exactly fitting, form small holes, through which the nerves, at each articulation, issue out in pairs, in order to send their branches to every part of the body, and with an equal bounty to both sides of the body. The fourth purpose assigned to the same instrument is the insertion of the bases of the muscles, and the support of the ends of the ribs; and for this fourth purpose, especially the for merpartofit, a figure, specifically suited to the design, and unnecessary for the other purposes, is given to the constituent bones. Whilst they are plain, and round, and smooth, towards the front, where any roughness or projec tion might have wounded the adjacent viscera, they run out behind, and on each side, into long processes, to which processes the muscles necessary to the motions of the trunk are fixed; and fixed with such art, that, whilst the verte- brae supply a basis for the muscles, the muscles help to keep these bones in their position, or by their tendons to tie them together.
That most important, however, and general property, viz the strength of the compages, and the security againt lux- ation, was to be still more specially consulted: for where so many joints were concerned, and where, in every one, derangement would have been fatal, it became a subject ol studious precaution. For this purpose, the vertebrae are articulated, that is, the moveable joints between them are formed by means of those projections of their substance, which we have mentioned under the name of processes; and these so lock in with, and overwrap one another, a
^8 OF MECHANICAL ARRANGEMENT
o secure the body of the vertebne, not only from i cc ldent ally slipping, but even from being pushed out of its place Dy any violence short of that which would break the bone. I have often remarked and admired this structure in the chine of a hare. In this, as in many instances, a plain ob- server of the animal economy may spare himself the disgust of bein<j present at human dissections, and yet learn enough for his information and satisfaction, by even examining thr bones of tk e animals which come upon his table. Let him take, for example, into his hands, apiece of the clean-pick- ed bone of a hare's back; consisting, we will suppose, of three vertebrae. He will find the middle bone of the three so implicated by means of its projections or processes, with the bone on each side of it, that no pressure which he can use, will force it out of it",s place between them. It will give way neither forward, nor backward, nor on ei'her side. In whichever direction he pushes, he perceives, in the form, or junction, or overlapping of the bones, an impedi- ment opposed to his attempt ; a check and guard against dislocation. In one part of the spine, he will find a still farther fortifying expedient, in the mode according to which the ribs are annexed to the spine. Each rib rests ipon two vertebrae. That is the thing to be remarked, md any one may remark it in carving a neck of mutton The manner of it is this: the end of the rib is divided by a middle ridge into two surfaces; which surfaces are join- ed to the bodies of two contiguous vertebrae, the ridge ap- plying itself to the intervening cartilage. Now this is the very contrivance which is employed in the famous iron bridge at my door at Bishop-Wearmouth ; and for the same purpose of stability; viz. the cheeks of the bars, which pass between the arches, ride across the joints, by which the pieces composing" each arch are united. Each cross- bar rests upon two of these pieces at their place of junction; and by that position resists, at least in one direction, any tendency in either piece to slip out of its place. Thus perfectly, by one means or the other, is the danger of slip- ping laterally, or of being drawn aside out of the line of the back, provided against: and to withstand the bones being pulled asunder longitudinally, or in the direction of that line, a strong membrane runs from one end of the chain tc the other, sulhcient to resist any force which is ever likeh to act in the direction of the back, or parallel to it, ana consequently to secure the whole combination in their ©laces. The general result is, that not only the motions of rhe h unan body necessary for the ordinary offices of life
IN THE HUMAN FRAME. 59
are performed with safety, but that it is an accident hari- ly ever heard of, that even the gesticulations of a harlequin distort his spine.
Upon the whole, and as a guide to those who may be in- clined to carry the consideration of this subject farther, there are three views under which the spine ought to be regarded, and in all which it cannot fail to excite our ad- miration. These views relate to its articulations, its liga- ments, and its perforation, and to the corresponding advan- tages which the body derives from it, for action, for strength, and for that which is essential to every part, a secure com munication with the brain.*
* It will be useful to append to the remarks of Dr. Paley upon the mechanism of the spine and of other parts of the body, some observations by a very eminent anatomist and surgeon now living, who has lately considered the subject of Animal Mechanism in its connexion with Natu ral Theology, and has presented some striking and original views. These observations have been published as one of the treatises of the Society for the Diffusion of Useful Knowledge, which forms the ninth number of the series. These extracts will be the more instructive asgiv ing views of a professional observer in confirmation of those of our au- thor ; and they will also serve as additional illustrations of the same great truths which he has endeavoured to enforce. — Ed.
" The spinal column, as it is called, serves three purposes : .t is the great bond of union between all the parts of the skeleton; it forms a tube for the lodgement of the spinal marrow, a part of the nervous system as important to life as the brain itself ; and lastly, it is a column to sustain the head.
We now see the importance of the spine, and we shall next explain how the various offices are provided for.
If the protection of the spinal marrow had been the only object of this structure, it is natural to infer that it would have been a strong and unyielding tube of bone; but, as it must yield to the inflexion of the body, it cannot be constituted in so strict an analogy with the skull. It must, therefore, bend; but it must have no abrupt or considerable bending at one part; for the spinal marrow within would in this way suffer.
By this consideration we perceive why there are twenty-four bones in the spine, each bending a little; each articulated or making a joint with ts fellow; all yielding in a slight degree, and, consequently, permitting .11 the whole spine that flexibility necessary to the motions of the body. It is next to be observed that, whilst the spine by this provision moves in every direction, it gains a property which it belongs more to our present purpose to understand. The bones of the spine are called vertebra; at each interstice between these bones, there is a peculiar gristly substance, which is squeezed out from between the bones, and, therefore, permit* them to approach and play a little in the motions of the body. This gristly substance is enclosed in an elastic binding, or membrane of grea. strength, which passes from the edge or border of one vertebra, to the bor- der of the one next it. When a weight is upon the body, the sort giisUo w presged out, and the membrane yields: the moment the weight *s ntmo^
60 ON MECHANICAL ARRAN DEMENT
The structure of the spine is not in general djfferetit hi different animals. In the serpent tribe, however, it is con- ed, the membranes recoil by their elasticity, the gristle is pressed into la place, and the bones resume their position.
We can readily understand how great the influence of these twenty four joinings must be in giving elasticity to the whole column ; and how much this must tend to the protection of the brain. Were it not for this interposition of elastic r.iateiial, every motion of the body would j. rodi co ajar to the delicate texture of the brain, and we should suffer almost as much in alighting on our feet, as in falling on our head. It is, as we have already remarked, necessary to interpose thin plates of lead or slate be- tween the different pieces of a column to prevent the edges (technically called arrises) of the cylinders from coming in contact, as they would, ia that case, chip or split off.
But there is another very curious provision, for the protection of the brain; we mean the curved form of the spine. If a steel spring, perfectly straight, be pressed between the hands from its extremities, it will resist, notwithstanding its elasticity, and when it does give way, it will be with a jerk.
Such would be the effect on the spine if it stood upright, one bone perpendicular to another; for then the weight would bear equally; the spine would yield neither to one side nor to the other; and, consequently, there would be a resistance from the pressure on all sides being balanced. We, therefore, see the great advantage resulting from the human spine being in the form of an italic f. It is prepared to yield in the direction of its curves; the pressure is of necessity more upon one side of the col- umn than on the other; and its elasticity is immediately in operation without a jerk. It yields, recoils, and so forms the most perfect spring; admirably calculated tocarrythe head without jar, or injury of any kind.
The most unhappy illustration of all this is the condition of old age. The tables o^the skull are then consolidated, and the spine is rigid: if an old man should fall with his head upon the carpet, the blow, which would be of no consequence to the elastic frame of a child, may to him prove fatal; and the rigidity of the spine makes every step which he takes, vi- brate to the interior of the head, and jar on the brain.
We have hinted at a comparison between the attachment of the spine to the pelvis and the insertion of the mast of a ship nto the hull. The mast goes directly through the decks without touching them, and the 1 ee] of the mast goes into the step, which is formed of large solid pieces of oak timber laid across the keelson. The keelson is an inner keel resting upon the floor-timbers of the ship and directly over the proper keel. These are contrivances for enlarging the base on which the mast /eetfl as a column; for as, in proportion to the height and weight of a column. Its base must be enlarged, or it would sink into the earth; so, if the matt were to bear upon a point, it would break through the bot'om of tho ship.
The mast is supported upright by the shrouds and stays. The shrouds secure it against the lateral or rolling motion, and the stavs and backstays ogainst the pitching of the ship. These form what is termed the standing -igging.
The mast does not bear upon the deck or on the beams of the ship; in- deed f.bere is a spa^e covered with canvass between the deck and the mas*
IN THE HI MA I FllAME I \
giderably varied; but with a strict reference to the convent* ency of the animal. [PI. IX. fig. 3, 4, 5] For, whereas in
We often hear of a new ship going to sea lo stretch her rigging; that is, to permit the shrouds and stays to be stretched by the motion of the ship, after which they are again braced tight; for if she were overtaken by a storm before this operation, and when the stays and shrouds wore relaxed, the mast would lean against the upper deck, by which it would be sprung or carried away. Indeed, the greater proportion of masts that are lost are lost in this manner. There are no boats which keep the sea tn ouch storms as those which navigate the gulf of Finland. Their masta ire not attached at all to the hull of the ship, but simply rest upon the utep.
Although the spine has not a strict resemblance to the mast, the con • tiwances of the ship-builder, however different from the provisions of na- ture, show what object is to be attained; and when we are thus made aware of what is necessary to the security of a column on a moveable base, we are prepared to appreciate the superior provisions of nature for giving security to the human spine.
The human spine rests on what is called the pelvis, or basin; — a circle of bones, of which the haunches are the extreme lateral parts; and the sa- crum (which is the keystone of the arch) may be felt at the lower part of the back. To this central bone of the arch of the pelvis the spine is connected; and, taking the similitude of the mast, the sacrum is as the step on which the base of the pillar, like the heel of the mast, is socket- ed or morticed. The spine is tied to the lateral parts of the pelvis by powerful ligaments, which may be compared to the shrouds. They se- cure the lower part of the spine against the shock of lateral motion or rolling; but, instead of the stays to limit the play of the spine forwards and backwards in pitching, or to adjust the rake of the mast, there is a very beautiful contrivance in thelower part of the column.
The spine forms here a semicircle which has this effect; that whether by the exertion of the lower extremities, the spine is to be carried forward upon the pelvis, or whether the body stops suddenly in funning, the jar which would necessarily take place at the lower part of the spine, if it stood upright like a mast, is distributed over several of the bones of the spine; and, therefore, the chance of injury at any particular part is di- minished.
For example, the sacrum, or centre bone of the pelvis, being carried forward, as when one is about to run, the force is communicated to the lowest bone of the spine. Rut, then, the surfaces of these bones stand with a very si'ght degree of obliquity to the line of motion; the shock communicated from the lower to the second bone of the vertebrae is still in a direction very nearly perpendicular to its surface of contact. The same takes place in the communication of force from the second to the thin', and from the third to the fourth; so that before the shock of the horizontal motion acts upon the perpendicular spine, it is distributed over four bones of that column, instead of the whole force being concentrated upon the joining of any two.
If the column stood upright, it would be jarred at the lowest point of contact with its base. But by forming a semicircle, the motion would produce ajar en the very lowest part of the column, and which is distrib- uted over a considerable portion of the column; and in point rf fact, (hia part of the spine never gives way. Indeed, we should be inclined to of-
F
B2 OF MECHANICAL ARRANGEMENT
quadrupeds tne number of vertebrae is from thirty o forty . in the serpent it is nearly one hundred and fifty where- as in men and quadrupeds the surfaces of the bones are fiat, and these flat surfaces laid one against the other, and bound tight by sinews; in the serpent the bones play one within another like a ball and socket,* so that they have a free motion upon one another in every direction; that is to say, in men and quadrupeds, firmness is more consulted; "*n seipents, pliancy. Yet even pliancy is not obtained at the expense of safety. The backbone of a serpent, for coherence and flexibility, is one of the most curious pieces of animal mechanism with which we are acquainted. The chain of a watch, (I mean the chain which passes between .he spring-barrel and the fusee,) which aims at the same properties, is but a bungling piece of workmanship in com- parison with that of which we speak. "j*
IV. The reciprocal enlargement and contraction of the chest to allow for the play of the lungs, depends upon a simple yet beautiful mechanical contrivance, referrible to the structure of the bones which enclose it. [PI. X. fig. 1 The ribs are articulated to the backbone, or rather to its side
fer this model to the consideration of nautical men, as fruitful in hints for improving naval architecture.
Every one who has seen a ship pitching in a heavy sea, must have asked himself why the masts are not upright, or rather, why the fore mast stands upright, whilst the main and mizzen masts stand oblique to the deck or, as the phrase is, rake aft or towards the stern of the ship.
The main and mizzen masts incline backwards, because the strain is greatest in the^brward pitch of the vessel; for the mast having received an impulse forwards, it is suddenly checked as the head of the ship rises; but the mast being set with an inclination backwards, the motion falls more in a perpendicular line from the head to the heel. This advantage s lost in the upright position of the foremast, but it is sacrificed to a supe- rior advantage gained in working the ship; the sails upon this mast act more powerfully in swaying the vessel round, and the perpendicular posi- tion causes the ship to tack or stay better; but the perpendicular position, as we have seen, causes the strain in pitching to come at right angles t« the mast, and is, therefore, ir^re apt to spring.
These considerations give aa interest to the fact, that the human spine, from its utmost convexity near its base, inclines backwards." — BelP& Treatise on Animal Mechanics.
*l)er. I'liys. Theol. p. 396.
+ In fish, which have more elastic, but less flexibfe. bodies, the structure of the spine diri'ers. The end of each vertebra is a cup containing a viscid fluid, which keeps the bones from approaching nearer to each other than he mean state of the elasticity of the lateral ligaments ; the fluid is in- compressible, therefore forms a ball round which the bony cups mov ; the ball having no cohesion, the centre of motion is always adapted t .as *han^e which the joint undergoes without produring friction.-— Fa.' ,/i
IN THE HUMAN FRAME. b?
projections obliquely : * that is, in their natural position, thev bend or slope from the place of articulation downwards But the basis upon which they rest at this end being fixed the consequence of the obliquity, or the inclination down- wards, is, that when they come to move, whatever pulls the ribs upwards, necessarily, at the same time, draws them out; and that, whilst the ribs are brought to a right angle with the spine behind, the sternum, or part of the chest to which they are attached in front, is thrust forward. The simple action, the afore, of the elevating muscles does the business; whereas, if the ribs had been articulated with the bodies of the vertebra? at right angles, the cavity of the thorax could never have been farther enlarged by a change of their position. If each rib had been a rigid bone, ar- ticulated at both ends to fixed bases, the whole chest had been immoveable. Keill has observed, that the breastbone in an easy inspiration, is thrust out one-tenth of an inch and he calculates that this, added to what is gained to the space within the chest by the flattening or descent of the diaphragm, leaves room for forty-two cubic inches of air to enter at every drawing-in of the breath. When there is a necessity for a deeper and more laborious inspiration, the enlargement of the capacity of the chest may be so increas- ed by effort, as that the lungs may be distended with seventy or a hundred such cubic inches. | The thorax, says Schel- hammer, forms a kind of bellows, such as never have been, nor probably will be, made by any artificer. J
* For the mode of articulation of the ribs with the vertebrae, see Plate IX. Fig. 1 and 2.
t Anat. p. 229.
$ The thorax, or chest, is composed of bones and cartilages, so dis- posed as to sustain and protect the most vital parts, the heart and lungs, and to turn and twist with perfect facility in every motion of the body; and to be in incessant motion in the act of respiration, without a moment's interval during a whole life. In anatomical description, the thorax is formed of the vertebral column, or spine, on the back part, the ribs on either side, and the breastbone, or sternum, on the fore part. But th© thing most to be admired is the manner in which these bones are united, and especially the manner in which the ribs are joined to the breastbone, by the interposition of cartilages, or gristle, of a substance softer than bone, and more elastic and yielding. By this quality they are fitted for protecting the chest against the effects of violence, and even for sustaining life after the muscular power of respiratioi has become too feeble to con- tinue without this support.
If the ribs were complete circles, formed of bone, and extending from t'le spine to the breastbone, life would be endangered by any accident;J f-'icture; and even the rubs and jolts to which the human frame is con j-iually erposed, '^ould be toe much far their delicate and brittle textura
61 01 MECHANICAL ARRANGEMENT
V The patella, or kneepan is a c irious little b ne , in •ts form and office, unlike any other hone of the body. [PI X. fig. 2, 3.] It is circular: the size of a crown piece; pretty thick; a little convex on both sides, and covered with a smooth cartilage. It lies upon the front of the knee: and the powerful tendons, by which the leg is brought forward, jass into it, (or rather it makes a part of their continu- ation,) from their origin in the thigh to their insertion in
f>iif these evils are avoided by the interposition of the elastic cartilage. On their fore part the ribs are eked out, and joined to the breastbone by
neans of cartilages, of a form corresponding to that of the ribs, being, as it were, a completion of the arch of the rib, by a substance more adapted to yield in every shock or motion of the body. '\ he elasticity of this portion subdues those shocks which would occasion the breaking of the ribs. We lean forward, or to one side, arid the ribs accommodate themselves, not by a change of form in the bones, but by the bending or filasticity of the cartilages. A severe blow upon the ribs does not break them, because their extremities recoil and yield to the violence. It is only in youth, however, when the human frame is in perfection, that this pli- ancy and elasticity have full effect. When old age approaches, the car- tilages of the ribs become bony. They attach themselves firm I v to the breastbone, and the extremities of the ribs are fixed, as if the whole arch were formed of bone unyielding and inelastic. Then every violent blow upon the side is attended with fracture of the rib, an accident seldom oc- curring in childhood, or in youth.
But there is a purpose still more important to be accomplished by means of the elastic structure of the ribs, as partly formed of cartilage. This is in the action of breathing, or respiration; especially in the more
lighly-raised respiration which is necessary in great exertions of bodily
strength, and in violent exercise. There are two acts of breathing — ex~
... ~
viratwn, or the sending forth of the breath ; and inspiration, or the
drawing in of the breath. When the chest is at rest, it is neit ter in a state of expiration nor in that of inspiration ; it is in an intermediate con- dition between these two acts. And the muscular effort by which either inspiration or expiration is produced, is an act in opposition to the elastic property of the ribs. The property of the ribs is to preserve the breast in the intermediate state between expiration and inspiration. The musclea of respiration are excited alternately, to dilate or to contract the cav'ty ok the chest, and, in doing so, to raise or to depress the ribs. Hence it is, that both in inspiration and in expiration the elasticity of the ribs ia Cal.ed into play; and, were it within our province, it would be easy to ghow, that the dead power of the cartilages of the ribs preserve life by respiration, after the vital muscular power would, without such assistance, be too weak to continue life.
It will at once be understood, from what has now been explained, how, •n age, violent exercise or exertion, is under restraint, in so far as it de- pends on respiration. The elasticity of the cartilages is gone, the circle of the ribs is now unyielding, and will not allow that high breathing, that Budden and great dilating and contracting of the cavity of the chest, which is required for circulating the blood through the lungs, and relieving the heart amidst the more tumultuous flowing of the blood which exercisa «ud e*ertioi )roduce. — Bell's Treatise on Animal Mechanics.
UN HIE HUxMAlN FRAME. O-^
vht tibia. It protects both the tendon and the joint from any injury which either might suffer by the rubbing ni'one •against the other, or by the pressure of unequal surfaces. It also gives to the tendons a very considerable mechan- ical advantage, by altering the line of their direction, and by advancing it farther out from the centre of motion; and this upon the principles of the resolution of force, upon which principles all machinery is founded. These are its uses. But what is most observable in it is, that it appears to be supplemental, as it were, to the frame; added, as it anould almost seem, afterward; not quite necessary, but very convenient. It is separate from the other bones; that is, it is not connected with any other bones by the com- mon mode of union. It is soft, or hardly formed, in infan- cy; and produced by an ossification, of the inception or progress of which no account can be given from the struct- ure or exercise of the part.
VI. The shoulder-blade is, in some material respects, a very singular bone: appearing to be made so expressly for its own purpose, and so independently of every other reason. [PI. X. fig. 4.] In such quadrupeds as have no collar-bones, which are by far the greater number, the shoulder-blade has no bony communication with the trunk, either by a joint, or process, or in any other way. It does not grow to, or out of, any other bone of the trunk. It does not apply to any other bone of the trunk; (I know not whether this be true of any second bone in the body, ex- cept perhaps the os hyoVdes.) [PI. X. fig. 5.] In strict- ness, it forms no part of the skeleton. It is bedded in the flesh; attached only to the muscles. It is no other than a foundation bone for the arm, laid in separate, as it were, and distinct, from the general ossification. The lower limbs connect themselves at the hip with bones which form a part of the skeleton; but this connexion, in the upper limbs, being wanted, a basis, whereupon the arm might be articulated, was to be supplied by a detached ossifica- tion for the purpose.
I. The above are a few examples of bones made re- markable by their configuration: but to almost all the bones belong joints; and in these, still more clearly than in the form or shape of the bones themselves, are seen both contrivance and contriving wisdom. Every joint is a curiosity, and is also strictly mechanical. There is the hinge-joint, and the mortice and tenon joint; each as manifestly sucn, and as accurately defined, as any which can be produced out of a cabinet-makei's sho ; and one
66 OF MECHANICAL ARRANGEMENT
c the oilier prevails, as either is adapted to the motion winch is wanted: e. g. a mortice and tenon, or ball and socket joint, is no* squired at the knee, the leg standing in need only of a motion backward and forward in the same plane, for which a hinge-joint is sufficient; a mortice and tenon, o ball and socket joint, is wanted at the hip, that not only the progressive step may be provided for, but the interval between the limbs may be enlarged or contract- ed at pleasure. Now, observe, what would have been the inconvemency, i. e. both the superfluity and the defect of articulation, if the case had been inverted: if the ball and socket joint had been at the knee, and the hinge-joint at the hip. The thighs must have been kept constantly to- gether, and the legs have been loose and straddling. There would have been no use, that we know of, in being able to turn the calves of the legs before ; and there would have been great confinement by restraining the motion of the thighs to one plane. The disadvantage would not have been less, if the joints at the hip and the knee had been both of the same sort; both balls and sockets, or both hin- ges: yet why, independently of utility, and of a Creator who consulted that utility, should the same bone (the thigh-bone) be rounded at one end, and channelled at the other?
The hinge-joint is not formed by a bolt passing through the two parts of the hinge, and thus keeping them in their places; but by a different expedient. A strong, tough, parchment-like membrane, rising from the receiving bones, and inserted all round the received bones a little below their heads, encloses the joint on every side. This mem- brane ties, confines, and holds the ends of the bones to- gether; keeping the corresponding parts of the joint, i. e. the relative convexities and concavities, in close application o each other.*
For the ball and socket joint, beside the membrane al ready described, there is in one important joint, as an additional security, a short, strong, yet flexible ligament, 'nserted by one end into the head of the ball, by the other
* This membrane is the capsular, or bursal ligament, common ft every movable joint. It certainly connects the bones together, but doe? not possess much strength: its chief use is to produce and preserve the synovia in .be part where it is required. The security and strength of the hinge -jcint depends on certain ligaments called lateral ligaments, and the endons of those muscles which pass over it. In the particular in stance of the knee, from its being the largest joint in ihe body, there is a* we shall presently find, an additiona contrivance to prevent dislocation
PaxtoiU
IN THE HUH AN FRAME 61
w
into hi bottom of the cup; which ligament keeps tho two parts of the joint so firmly in their place, that none of the motions which the limb naturally performs, none of the jerks and twists to which it is ordinarily liable, nothing less indeed than the utmost and the most unnatural vio- lence, can pull them asunder [PI. XI. fig. 1.] It is hardly imaginable, how great a force is necessary, even to stretch, still more to break, this ligament; yet so flexible s it, as to oppose no impediment to the suppleness of the joint * By its situation also, it is inaccessible to injury from sharp edges. As it cannot be ruptured, (such is its strength,) so it cannot be cut, except by an accident which would sever the limb. If I had been permitted to frame a proof of contrivance, such as might satisfy the most dis- trustful inquirer, I know not whether I could have chosen an example of mechanism more unequivocal, or more free from objection, than this ligament. Nothing can be more mechanical; nothing, however subservient to the safety, less capable of being generated by the action of the joint I would particularly solicit the reader's attention to this provision, as it is found in the head of the thigh-bone ; to its strength, its structure, and its use. It is an instance upon which I lay my hand. One single fact, weighed by a mind in earnest, leaves oftentimes the deepest impres- sion. For the purpose of addressing different understand- ings and different apprehensions — for the purpose of senti- ment, for the purpose of exciting admiration of the Crea- tor's works, we diversify our views, we multiply examples; but for the purpose of strict argument, one clear instance is sufficient; and not only sufficient, but capable, perhaps, of generating a firmer assurance than what can arise from a divided attention.
The ginglymiiSj or hinge-joint, does i ot, it is manifest, admit of a ligament of the same kind with that of the ball and socket joint, but it is always fortified by the species ot agament of which it does admit. The strong, firm, invest- ing membrane, above described, accompanies it in every part; and in particular joints, this membrane, which is properly a ligament, is considerably stronger on the sides than either before or behind, in order that the convexities may play true in their concavities, and not be subject to slip sideways, which is the chief danger; foi the muscular
* This ligament is also common to all quadrupeds, even in the more large and unwieldy, as the Hippopotamus and Rhinoceros — it is wanting in the elephant only, whose limbs, ill qualified for active increments, do uol seem to require this security to the joint. — Paxton.
68 OF MECHANICAL ARRANGEMENT
tendons generally restrain the part 3 from going farther than they ought to go in the plane oi their motion. In the knee, which is a joint of this form, J.nd of great importance, there are superadded to the corr.non provisions hi the stability of the joint, two strong ligaments which cross each other; and cross each other in such a manner, as to secure the joint from being displ& zed in any assignable di- rection. [PI. XI. fig. c2.] "I think," says Cheselden, "that the knee cannot be completely dislocated withou* breaking the cross ligaments."* We can hardly help com- paring this with the binding up of a fracture, where the fil- 'et is almost always strapped across, for the sake of giving firmness and strength to the bandage.
Another no less important joint, and that also of the gin- glymus sort, is the ankle; yet, though important, (in order, perhaps, to preserve the symmetry and lightness of the .imb,) small, and, on that account, more liable to injury. [PI. XI fig 4.] Now this joint is strengthened, i. e. is defended fro»n dislocation, by two remarkable processes or prolongations of the bones of the leg: which processes form the protuberances that we call the inner and outer ankle. It is part of each bone going down lower than the other part, and thereby overlapping the joint: so that, if the joint be in danger of slipping outward, it is curbed by the inner projcct'on, i. e. that of the tibia; if inward, by the outer projection, i. e. that of the fibula. Between both, it is looked in its position. I know no account that can be given of this structure, except its utility. Why should the tibia terminate, at its lower extremity, with a double end, and the fibula the same, but to barricade the joint on both sides by a continuation of part of the thickest of the bone over it ? f
* Ches. Anat. ed. 7th, p. 45.
t The most obvious proof of contrivance is the junction of the fcot to the bones of the leg at the ankle-joint. The two bones of the leg, called the tibia and the fibula, receive the great articulating bone of the foot (the astragalus) between them. And the extremities of these bones of the leg project so as to fcrm the outer and inner ankle. Now, when we gtep forward, and whilst the foot is raised, it rolls easily upon the enda of these bones, so that the tve may be directed according to the inequali- ties of the ground wear^t tread upon; but when the foot is planted, and the body is carried O^vard perpendicularly over the foot, the joint of the leg and Toot oec'jtn* , fixed, and we have a steady base to rest upon. We next observe, 'Iiat, in talking', the heel first touches the ground. If the bones of the ie^ ,ve- ^ i erpendicular over the part which first touches the ground, we /no>'',*i c .ne down with a sudden jolt, instead of which M 1 descend in a Sdinioirc' j, the centre of which is the point of the heel.
And when the toes Lave come to the ground we are far from losing \h«
IN THE HUMAN FRAME. 69
The joint at the shoulder compared with the joint at the hip, though both ball and socket joints, discovers a differ- ence in their form and proportions, well suited to the dif- ferent offices which the limbs have to execute. The cup or socket at the shoulder is much shallowor and flatter than it is at the hip, and is also in part formed of caitilago set round the rim of the cup. The socket, into which the head of the thigh-bone is inserted, is deeper, and made of more solid materials.* This agrees with the duties as-
advantages of the structure of the foot, since we stand upon an e'astie arch, the hinder extremity of which is the heel, and the anterior the halls cf the toes. A finely formed foot should he high in the instep. The walk of opera dancers is neither natural nor heautiful; hut the surprising exercises which they perform give to the joints of the foot a freedom of motion almost like that of the hand. We have seen the dancers, in their morning exercises, stand for twenty minutes on the extremities of their toes, after which the effort is to hend the inner ankle down to the floor, in preparation for the Bolero step. By such unnatural postures and ex- ercises the foot is made unfit for walking, as may he ohserved in any of the retired dancers and old figurantes. By standing so much upon the toes, the human foot is converted to something more resembling that of a quadruped, where the heel never reaches the ground, and where the paw is nothing more than the phalanges of the toes.
This arch of the foot, from the heel to the toe, has the astragalus, re- sembling the keystone of an arch; but, instead of being fixed, as in ma sonry, it plays freely between two bones, and from these two bones, a strong elastic ligament is extended, on which the bone rests, sinking 01 rising as the weight of the body bears upon it, or is taken off, and this it is enabled to do by the action of the ligament which runs under it.
This is the same elastic ligament which runs extensively along the back of the horse's hind leg and foot, and gives the fine spring to it, but whicr .s sometimes ruptured by the exertion of the animal in a leap, producing irrecoverable lameness.
Having understood that the arch of the foot is perfect from the heel tf the toe, we have next to observe, that there is an arch from side to side for when a transverse section is made of the bones of the foot, the ex posed suffice presents a perfect arch of wedges, regularly formed like thf stones of an arch in masonry. If we look down upon the bones of the foot, we shall see that they form a complete circle horizontally, leaving a space in their centre. These bones thus form three different arches — forward; across; and horizontallv: they are wedged together, and bound by ligaments, and this is what we alluded to when we said that the fonn dations of the Eddystone were not laid on a better principle; but our id niratioii is more excited in observing, that the bones of the foot are not only wedged together, like the courses of stone for resistance, but that sihiity is combined with elasticity and lightness.
Notwithstanding the mobility of the foot in some positions, yet when the weight of the body bears directly over it, it becomes immovable, and the bones of the leg must be fractured before the foot yields.
BelVs Treatise on .inimal Mechanics.
* The socket for the head of the thigh-bone is indetd deeper than that it the shoulder, bu *he " n.iterials " which form the concavities are the
70 0F MECHAaMCIL ARRANGEMENT
signed to each part. The arm is an instrument of motion piincipally, if not solely. Accordingly the shallowness of the socket at the shoulder, and yieldingness of the car- tilaginous substance with which its edge is set round, and which in fact composes a considerable part of its concavi- ty, are excellently adapted for the al.owance of a free mo- tion and a wide range; both which the arm wants. Whereas, the lower limb, forming a part of the column of the body; having to support the body, as well as to be the means of its locomotion; firmness was to be consulted, as well as action. With a capacity for motion, in all direc- tions indeed, as at the shoulder, but not in any direction to the same extent as in the arm, was to be united stabili- ty, or resistance to dislocation. Hence the deeper excava- .ion of the socket; and the presence of a less proportion of cartilage upon the edge.
The suppleness and pliability of the joints we every moment experience; and the firmness of animal articu- lation, the property we have hitherto been considering, may be judged of from this single observation, that, at any given moment of time, there are millions of animal joints in complete repair and use, for one that is disloca- ted; and this, notwithstanding the contortions and wrench- es to which the limbs of animals are continually subject.
II. The joints, or rather the ends of the bones which form them, display also, in their configuration, another use. The nerves, blood-vessels, and tendons, which are neces- sary to the life, or for the motion of the limbs, must, it is evident, in their way from the trunk of the body to the place of their destination, travel over the movable joints; and it is no less evident, that, in this part of their course, they will have, from sudden motions, and from abrupt changes of curvature, to encounter the danger of compres- sion, attrition, or laceration. To guard fibres so tender against consequences so injurious, their path is in those parts protected with peculiar care; and that by a provision in the figure of the bones themselves. The nerves which supply the fore-arm, especially the inferior cubital nerves, are at the elbow conducted, by a kind of covered way, be- tween the condyles, or rather under the inner extuberances of the bone, which composes the upper part of the arm.*
»arna; both are solid bone covered by cartilage, and both have a rim of a strong fibro-cartihginous texture, not only for the purpose of rendering the socket deeper, but for preventing frnctures of the rim in robust txer tises, to which, were it bonv, it would be very liable — Paxton. f.'haa. An T) 255, ed. 7th
IN THE HU31AN FRAME. 1 \
At the hue, the extremity of the thigh-bone is divided by a sinus or cleft into two heads or protuberances: and these heads on the back part stand out beyond the cylinder of the bone. Through the hollow, which lies between the hind parts of these two heads, that is to say . under the ham, between the hamstrings, and within the concave re- cess of the bone formed by the extuberances on each side; in a word, along a defile, between rocks, pass the greal vessels and nerves which go to the leg.* Who led these vessels by a road so defended and so secured? In the joint at the shoulder, in the edge of the cup which receives the head of the bone, is a notch which is joined or covered at the top with a ligament. Through this hole, thus guarded, the blood-vessels steal to their destination in the arm, in- stead of mounting over the edge of the concavity ."[
III. In all joints, the ends of the bones, which work against each other, are tipped with gristle. In tne uall and socket joint, the cup is lined, and the ball capped with it. The smooth surface, the elastic and unfriable nature of cartilage, render it of all substances the most proper for the place and purpose. I should, therefore, have pointed this out amongst the foremost of the provisions which have been made in the joints for the facilitating of their action, had it not been alleged, that cartilage in truth is only nascent or imperfect bone ; and that the bone in these places is kept soft and imperfect, in consequence of a more complete and rigid ossification being prevented from taking place by the continual motion and rubbing of the surfaces; which being so, what we represent as a designed advan tage, is an unavoidable effect. I am far from being con- vinced that this is a true account of the fact; or that, if it were so, it answers the argument. To me, the surmount- ing of the ends of the bones with gristle, looks more like a plating with a different metal, than like the same metal kept in a different state by the action to which it is exposed At all events, we have a great particular benefit, though arising from a general constitute n: but this last not being quite what my argument requires, lest I should seem by applying the instance to overrate its value, I have though* it fair to state the question which attends it.
IV. In some joints, very particularly in the knees, there are loose cartilages or gristles between the bones, and with- in the joint, so that the ends of the bones, instead of work- ing upon one another, work upon the intermediate cartila ges. [PI. XL fig. 3.] Cheselden has observed J that the
• Ches. An. p. 35. t lb. 30. t lb. p. 13.
72 OF MECHANICAL ARRANGEMENT
contrivance of a loose ring is practised by mechanics, where the friction of the joints of any of their machines is great, as between the parts of crooked-hinges of large gates, or under the head of the male screw of large vices. The cartilages of which we speak, have very much of the form of these rings. The comparison moreover shows the rea- son why we find them in the knees rather than in other joints. It is an expedient, we have seen, which a mechan- ic resorts to, only when some strong and heavy work is to be done. So here the thigh bone has to achieve its motion at. the knee, with the whole weight of the body pressing upon it, and often, as in rising from our seat, with the whole weight of the body to lift. It should seem also, from Ches- elden's account, that the slipping and sliding of the loose cartilages, though it be probably a small and obscure, change, humored the motion of the end of the thigh-bone, under the particular configuration which was necessary to be given to it for the commodious action of the tendons; (and which configuration requires what he calls a variable socket, that is, a concavity, the lines of which assume a different curvature in different inclinations of the bones.) V. We have now done with the configuration: but there is also in the joints, and that common to them all, another exquisite provision, manifestly adapted to their use, and concerning which there can, I think, be no dispute, namely, the regular supply of a mucilage, more emollient and slippery than oil itself, which is constantly softening and lubricating the parts that rub upon each other, and thereby diminishing the effect-of attrition in the highest possible degree.* For the continual secretion of this im- portant liniment, and for the feeding of the cavities of the joint with it, glands are fixed near each joint; the excre- tory ducts of which glands dripping with their balsamic contents, hang loose like fringes within the cavity of the joints. A late improvement in what are called friction wheels, which consists of a mechanism so ordered, as to be regularly dropping oil into a box, which encloses the axis, the nave, and certain balls upon which the nave revolves, may be said, in some sort, to represent the contrivance' in the animal joint; with this superiority, however, on the
* This mucilage is termed synovia ; vulgarly called joint oil, but it has no property of oil. It is very viscid, and at the same time smooth and shppery to the touch; and therefore better adapted than any oil to lubricate the interior of the joints and prevent ill effects from friction.
Paa ton
IN THE HUMAN FRAME. 7i
part of the joint, viz. that here, the oil is not only drojped, but made*
In considering the joints, there is nothing, perm.ps, which ought to move our gratitude more than the reflection, how well they wear. A limb shall swing upon its hinge, 01 play in its socket, many hundred times in an hour, for six- ty years together, without diminution of its agility: which is a long time for anything to last; for anything so much worked and exercised as the joints are. This durability 1 should attribute, in part, to the provision which is made for the preventing of wear and tear, first by the polish of the cartilaginous surfaces, secondly, by the healing lubrication of the mucilage; and, in part, to that astonishing property of animal constitutions, assimilation; by which, in every portion of the body, let it consist of what it will, substance is restored, and waste repaired. f
* A joint then consists of the union of two bones, of such a form as to permit the necessary motion; but they are not in contact; each articulat- ing surface is covered with cartilage, to prevent the jar which would re- sult from the contact of the bones. This cartilage is elastic, and the celebrated Dr. Hunter discovered that the elasticity was in consequence of a number of filaments closely compacted, and extending from the sur- face of the bone, so that each filament is perpendicular to the pressure m?de upon it. The surface of the articulating cartilage is perfectly smooth, and is lubricated by a fluid called synovia, sygnifying a muci- lage, a viscous or thick liqv.or. This is vulgarly called joint oil, but it has 10 property of oil, although it is better calculated than any oil to lu- bricate the interior of the joint.
Wl en inflammation comes upon ajoint, this fluid is not supplied, and the joint is stiff, and the surfaces creak upon one another like a hing"1 without oil. A delicate membrane extends from bone to bone, confining this lubricating fluid, and forming the boundary of what is termed the cavity of the joint, although, in fact, there is no unoccupied space. Ex- ternal to vhis capsule of the joint, there are strong ligaments going from point to point of the bones, and so ordered as to bind them together without preventing their proper motions. From this description of a single joint, we can easily conceive what a spring or elasticity is given to the foot, where thirty-six bones are joined together. — HeWs Treatise on Animal Mechanics.
+ If the ingenious author's mind had been professionally called to con- template this subject, he would have found another explanation. There Li no resemblance between the provisions against the wear and tear of machinery and those for the preservation of a living part. As the struc ture of the parts is originally perfected by the action of the vessels, the function 3r operation of the part is made the stimulus to those vessels. The cuticle on the hands wears away like a glove; but the pressure stim nlates the living surface to force successive layers of skin under that vrhich is wearing, or, as the anatomists call it, desquamating; by which they mean, that the cuticle does not change at once, but comes oft' in squamae, or scales. The teeth are subject to pressure in chewing or masticating, and they would, by this action, have been driven deeper in the jaw, and
74 OF THE MUSCLES.
Movable joints, I think, compose the curiosity . f bcnes* but their union, even where no motion is intendea or want- ed, carries marks of mechanism and of mechanical wis- dom. The teeth, especially the front teeth, are one bone fixed in another, like a peg driven into a board. The sutures of the skull are like the edges of two saws clap- ped together, in such a manner as that the teeth of one enter the intervals of the other.* We have sometimes one bone lapping over another, and planed down at the edges; sometimes also the thin lamella of one bone received into a narrow furrow of another. In all which varieties, wo seem to discover the same design, viz. firmness of juncture, without clumsiness in the seam.
CHAPTER IX.
OF THE MUSCLES.
(Muscles, with their tendons, are the instruments hy which animal motion is performed. It will be our business
rendered useless, had there not been a provision against this mechanicaf effect. This provision is a disposition to grow, or rather to shoot out of their sockets; and this disposition to project, balances the pressure whicl they sustain* and when one tooth is lost, its opposite rises, and is in dan- ger of being lost also, for want of that very opposition. — Bell's Treatisi on Animal Mechanics.
* Most of the bones of the skull are composed of two plates or tablets, with an intermediate spongy, vascular substance; the outer tablet is^&- rnis, having the edges curiously indented and united by a dove-tailed
tare; the inner from its brittleness is called vitreous, and therefore
erely joined together in a straight line ; this mode of union is not acci- dental— not the result of chance, but design. The author of the treatise on " Animal Mechanics " gives the following admirable illustration of the structure: —
" Suppose a carpenter employed upon his own material — he would join a box with regular indentations by dove-tailing, because he knows that the material on which he works, from its softness and toughness, admits of sucb adjustment of its edges. The processes of bone shoot in- to the opposite cavities with an exact resemblance to the fox-tail wedge of the carpenter.
" But if a workman in glass or marble were to join these materials, he would smooth the edges and unite them by cement; for if he could suc- ceed in indenting the line of union, he knows that his material would chip off on the slightest vibration.
" Now apply this principle to the skull, the outer table, which resem- bles wood, is indented and dove-tailed; the inner glassy ta^le has it* edoee simply laid in contact." — Paxton.
OF THE MUSCLES. 7i
t*> jv int out instances in which, and properties with respect fo »vhich, the disposition of these muscles is as strictly mechanical, as that of the wires and strings of a puppet.*
I. We may observe, what I believe is universal, an ex- act relation between the joint and the muscles which move it. Whatever motion the joint, by its mechanical construc- tion, is capable of performing, that motion, the annexed muscles, by their position, are capable of producing. For example; if there be, as at the knee and elbow, a hinge- joint, capable of motion only in the same plane, the lead- ers, as they are called, i. e. the muscular tendons, are placed in oirections parallel to the bone, so as, by the con- traction or relaxation of the muscles to which they belong to produce that motion and no other. If these joints were c°pable of a freer motion, there are no muscles to produce it. Whereas at the shoulder and the hip, where the bal1 and socket joint allows by its construction of a rotatory 01 sweeping motion, tendons are placed in such a position, and pull in such a direction, as to produce the motion of which the joint admits. For instance, the sartorius or tailor's muscle, rising from the spine, running diagonally across the thigh, and taking hold of the inside of the main bone of the leg, a little below the knee, enables us, by its contraction, to throw one leg and thigh over the other; giving effect, at the same time, to the ball and socket join?, at the hip, and the hinge-joint at the knee. [PI. XII. fig. 1.]
There is, as we have seen, a specific mechanism in the bones, for the rotatory motions of the head and hands; there is, also, in the oblique direction of the muscles belonging to them, a specific provision for the putting of this mechanism of the bones into action. [PL XII. fig. 2.] And mark the consent of uses. The oblique muscles would have been inefficient without that particular articulation; that particular articulation would have been lost, without the oblique muscles. It may be proper, however, to observe with respect to the head, although I think it does not vary !he case, that its oblique motions and inclinations are »flen motions in a diagonal, produced by the joint action of mus-
* Muscles are the fleshy parts of the body which surround the bone9, having a fibrous texture; a muscle being composed of a number of mus- cular faciculi, which are composed of fibres still smaller; thene result from fibres of a less volume, until by successive division we arrive at very small fibres no longer divisible. These muscular fibres are longer O' shorter according to the muscles to which they belong; and every fi- bre is fixed by its two extremities to tendon or aponeurosis, which are the " wires and strings which conduct the muscular power wher the* •ontrict. — Paxton.
16 OF THE MUSCLES.
cles tying in straight direction. But whether the puU be sm« gle or combined, the articulation is always such, as „o be capable of obeying the action of the muscles. The oblique muscles attached to the head, are likewise so disposed, as to be capable of