Page images
PDF
EPUB

and do not point out the defects of the text in almost any material instance. Thus, there are very good figures in Plate IV., and a fit description for explaining the curious mechanism of the nictitating membrane; but the great omission of the text is not supplied, namely, that the contrivance is mathematically exact for giving a great augmentation of velocity, according to the most ordinary principles of dynamics. This could easily have been shown by a few lines, and a single diagram on the plate now referred to. So in Chapter VIII., the text having omitted to note the reason for the different bones of the skull being placed and joined in the way we find them; a very scanty addition is made to this by the single remark, that the vitreous tablet being so brittle is not joined by dovetailing. In discoursing of the eye, Paley falls, we apprehend, into an error in supposing that Dolland was led to his discovery of the different dispersive, which he calls refractive, powers of glasses, by considering the composite structure of the eye. The ingenious papers of that great optician, in the Philosophical Transactions, give the history of his discovery, and they make no mention of this fact-and, indeed, give a quite different history of the discovery, vol. iv. p. 733. At all events, he certainly was not the person who first reasoned to the improvement of glasses, from the construction of the eye, as Paley represents, in vol. i. p. 20, when he says; at last it came into the mind of a sagacious optician to • inquire how this matter was managed in the eye,' &c. For David Gregory's Treatise (Catoptrice et Dioptricæ Sphærice Elementa) published in 1713, concludes thus : Quod si ob dif

ficultates physicas, in speculis idoneis torno elaborandis, et po• liendis etiamnum lentibus, uti oporteat, fortassis media diversæ • densitatis ad lentem objectivam componendam adhibere utile • foret, ut a Natura factum observemus in Oculi fabricâ ubi

christallinus humor (fere ejusdem cum vitro virtutis ad radios • lucis refringendos) aqueo et vitreo (aquæ, quoad refractionem,

haud absimilibus) compingitur, ad imaginem, quam distincte fieri potuit, a naturâ nihil frustra molienti, in oculi fundo de

pingendam. Neither Paley nor his commentator have remarked that the eye is not, in fact, an achromatic instrument, without an adjustment; and that if that be altered, or if objects be viewed by one-half of its lenses, the different refrangibility is not correct, and colours are produced—as any one may see, by viewing an object, as a candle or the bar of a window, and covering part of his eye. As he draws the obstacle near the bar, the sides of it will be, one blue, and the other red or orange. Nothing is said too of the singular artifice, on the purest principles of optics, by which the crystalline humour is made more dense in the centre, its substance actually varying. We may note another plain omission under the head of the Bee. Neither under the head of instinct, nor when he is describing the convenience of the comb under that of insects, does Paley give by far the most extraordinary of all instincts and of all the accommodations of the comb; the size of the angles, and their being discovered by mathematicians (through the resource of the Auxional calculus) to be the precise size, which makes the greatest possible saving of room and of materials. This omission, the present edition does not supply.

We have noted these in passing, as a few instances of defects. We should certainly hold it none, that any one branch of the immense subject under discussion was wholly left out; for its vastness, coextensive with all creation, makes a selection the very essence of such a work. But where any subject is introduced, and a very important consideration belonging to it is left out, nay, as in the case of nictitation and of the honey-comb, by much the most striking illustration, it becomes proper to request the learned author's

attention to the matter, for a future edition. When we first gave an account of Paley's work, in 1803, we observed that Natural Theology was a subject which admitted of no originality, and on which we never expected discoveries to be made. We doubt if we should have said so, had we then known that the work which stands next to Mr Paxton's was, after so considerable a lapse of time, to make its appearance. The Treatise on Animal Mechanics possesses very great originality; and may be regarded, not in principle, perhaps, but in applying principles to facts, as having made discoveries.

This is one of those admirable works for which we are indebted to that very important Institution, among the best fruits of the enlightened times we live in, the Society for Diffusing Useful Knowledge, whose proceedings formed the subject of an article in our last Number. The Treatise before us has appeared as a kind of appendix, or practical application of the doctrines of Dynamicks, unfolded in some previous works of the Society, composing portions of the Library now published by them periodically;-and none of these publications has, we believe, given greater satisfaction. By an extraordinary union of profound anatomical and physiological knowledge, with the power of striking illustration, and plain, perspicuous writing, the learned and ingenious author of this work has lent a much more scientific aspect to the doctrines of Natural Theology, than they before had possessed. Indeed, with the exception of Mr Ray, a great naturalist, and Dr Derham, a respectable one, most of the writers who treated on final causes, were divines or moralists, and not natural philosophers. Hence they were often found ignorant of details; and frequently were misled by imaginary relations, not the result of scientific inquiries, but of speculative theology. The consequence was, that real philosophers got a prejudice against a topic, which, to be treated safely, requires to be managed very delicately; errors of no little absurdity were committed; and it is hard to say if scoffers did not, upon the whole, gain more than worshippers, by many of those wellmeaning, but ill-qualified authors. Mr Stewart (Outlines, $ 283,) justly remarks, upon the abuse, as well as the use of the speculation concerning Final Causes; and regards an explanation of both, as still being a desideratum in science. But he observes, that it is no longer so necessary as formerly to banish this inquiry from Physics, because the true method of philosophizing is generally understood, and the danger of confounding Final with Physical Causes, is far less imminent. He remarks, most properly, that in Anatomical inquiry, every one proceeds upon the maxim, that nothing in any animal's body was made in vain, and refuses to rest satisfied, as long as the use of any part or function remains unexplained; thus admitting, that Final Causes may not only be sound inferences from the known truths of philosophy, but may be guides in discovering new ones. The anecdote which Mr Boyle gives respecting Harvey's grand discovery, is a striking illustration of this doctrine; and might far better have served the purpose of Paley's argument, than the remark which he makes on Dolland's discovery, which we have above commented upon. • I remember,' says Mr Boyle, * that when I asked our famous Harvey what were the things • that induced him to think of the circulation of the blood ? he 6 answered me, that when he took notice that the valves in the • veins of so many parts of the body were so placed that they 'gave a free passage to the blood towards the heart, but oppo

[graphic]

sed the passage of the venal blood the contrary way; he was • incited to imagine, that so provident a cause as Nature had not

placed so many valves without design; and no design seemed ' more probable, than that, since the blood could not well, because

of the interposing valves, be sent by the veins to the limbs, it • should be sent through the arteries, and return through the • veins, whose valves did not oppose its course that way. It is not, indeed, to be wondered at, that the structure of the body should turn men's thoughts towards these speculations, in modern times, when even the ancient philosophers, averse as they were to the inductive methods, were led by it to philosophize far more soundly than on almost any other subject. Faciliusque intelligetur, a diis immortalibus hominibus esse provisum,' says Cicero, arguing against the Epicurean doctrines, “si tota hominis fabricatio perspecta, omnisque humanæ naturæ figura atque perfectio.' (De Nat. Deorum. Lib. ii.)

That the subject, then, is as strictly scientific, as it is noble and delightful, there can be no doubt; and it is truly gratifying to find it treated according to its high deserts. The treatise before us is not the work of a declamatory moralist, or a sentimental enthusiast, or a narrow-minded bigot; but of a man of profound science, who does homage to the truths of religion, because they cross the path of his philosophic inquiries; who bears the testimony of facts to the doctrines of a sublime theology, which those facts inculcate, along with the other lessons he had gone in quest of. It is not the priest who leaves the temple to gather Rowers for its adornment; but the sage who brings to the altar his offering, from the fruits he has so richly collected, of an all-pervading and supreme intelligence.

It is inconsistent with our present purpose to offer any analysis of this admirable Paper. It is divided into six chapters, after the Introduction. In these are successively treated, the Architecture of the Skull; the Mechanism of the Spine ; the structure of the Bones, and Joints of the Extremities ; the Cordage of the Tendons ; the Muscles and Muscular Motion ; and the works upon such subjects which have before appeared. We shall do no more than give a specimen or two, rather to exhibit the manner in which the discourse is conducted, than to show even a sample of its contents.

The following passage is the beginning of the Chapter upon the Skull:

• It requires no disquisition to prove that the brain is the most essential organ of the animal system, and being so, we may presume that it must be especially protected. We are now to inquire how this main object is attained ?

• We must first understand that the brain may be hurt, not only by sharp bodies touching and entering it, but by a blow upon the head which shall vibrate through it, without the instrument piercing the skull. Indeed, a blow upon a man's head, by a body which shall cause a vibration through the substance of the brain, may more effectually deprive him of sense and motion than if an axe or a sword penetrated into the substance of the brain itself.

Supposing that a man's ingenuity were to be exercised in contriving a protection to the brain, he must perceive that if the case were soft, it would be too easily pierced; that if it were of a glassy nature, it would be chipped and cracked ; that if it were of a substance like metal, it would ring and vibrate, and communicate the concussion to the brain.

Further thoughts might suggest, that whilst the case should be made firm to resist a point, the vibrations of that circular case might be prevented by lining it with a softer material; no bell would vibrate with such an incumbrance; the sound would be stopped like the ringing of a glass by the touch of a finger.

. If a soldier's head be covered with a steel cap, the blow of a sword which does not penetrate will yet bring him to the ground by the percussion which extends to the brain; therefore, the helmet is lined with leather, and covered with hair; for, although the hair is made an ornament, it is an essential part of the protection: we may see it in the head-piece of the Roman soldier, where all useless ornament being despised as frivolous, was avoided as cumbrous.

We now perceive why the skull consists of two plates of bone, one external, which is fibrous and tough, and one internal, dense to such a degree that the anatomist calls it tabula vitrea (the glassy table.)

• Nobody can suppose this to be accidental. It has just been stated, that the brain may be injured in two ways; a stone or a hammer may break the skull, and the depressed part of the bone injure the brain ; whilst, on the other hand, a mallet struck upon the head will, without penetrating effectually, deprive the brain of its functions, by causing a vibration which runs round the skull and extends to every portion of its contents.

• Were the skull, in its perfect or mature state, softer than it is, it would be like the skull of a child; were it harder than we find it is, it would be like that of an old man. In other words, as in the former it would be too easily pierced; so, in the latter, it would vibrate too sharply and produce concussion. The skull of an infant is a single layer of elastic bone; on the approach to manhood it separates into two tables ; and in old age it again becomes consolidated. During the active years of man's life the skull is perfect; it then consists of two layers, united by a softer substance ; the inner layer is brittle as glass, and calculated to resist anything penetrating ; the outer table is tough, to give consistence, and to stifle the vibration which there would be if the whole texture were uniform and like the inner table.

• The alteration in the substance of the bones, and more particularly in the skull, is marvellously ordered to follow the changes in the mind of the creature, from the heedlessness of childhood to the caution of age, and even the helplessness of superannuation.

• The skull is soft and yielding at birth ; during childhood it is elastic, and little liable to injury from concussion ; and during infancy, and up to the period of maturity, the parts coming in contact with the ground, are thicker, whilst the shock is dispersed towards the sutures (the seams or joinings of the pieces), which are still loose ; but when, with advancing years, something tells us to give up feats of activity, and falls are less frequent, the bones lose that nature which would render concussion harmless, and at length the timidity of age teaches man that his structure is no longer adapted to active life.'

He thus, in the second chapter, describes another provision for the protection of the brain, namely, the curved form of the spine

• A steel spring being perfectly straight, if pressed betwixt the hands

« PreviousContinue »