untouched. In this chapter our author is laying the foundation for a course of reasoning on the mechanism displayed in the animal body. The argument in favour of a creating and presiding Intelligence may be drawn from the study of the laws of physical agency :—such as the properties of heat, light, and sound; of gravitation, and chemical combination; the structure of the globe, the divisions of land and sea, the distribution of temperature; nay, the mind may rise to the contemplation of the sun and planets, their mutual dependence, and their revolutions; but, as affording proofs obvious not only to cultivated reason but to plain sense, almost to ignorance, there is nothing to be compared with that for which our author is preparing the reader in this chapter, the mechanism of the animal body, and the adaptations which affect the well-being of living creatures.

CHAPTER III.

APPLICATION OF THE ARGUMENT."

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

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• The arguments adduced in this chapter being drawn from the laws according to which light is refracted by the humours of the eye, the reader may be inclined to peruse the few observations on the elements of this part of physics in the Appendix, No. 16.

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

mathematical instrument maker have done more to show his knowledge of his principle, his application of that knowledge, his suiting of his means to his end; I will not say to display the compass or excellence of his skill and art, for in these all comparison is indecorous, but to testify counsel, choice, consideration, purpose? 7

The reader will find a comparison, more in detail, between the eye and optical instruments, in the Appendix, No. 17.

In illustration of the instance adduced here, of the adaptation of the fish's eye to the medium in which it lives, we may observe that the powers in the human eye, for example, of drawing the pencil of rays to a focus, and producing an accurate image upon the expanded optic nerve (called the retina, from its net-work structure) in the bottom of the eye, depends principally upon two circumstances,—the form of the cornea and the convexity of the lens. That the cornea may produce this effect, it is not only necessary that it should be convex, (as in the left-hand figure on page 22,) but that the rays should enter it from a rarer medium. As this cannot be effected in the water, the lens or crystalline humour, which is much denser than water, is brought into operation. In the eye of an animal living in the atmosphere, the lens is removed backwards, and resembles the optician's double convex lens; but in the fish it is a sphere, and being brought in contact with the

To some it may appear a difference sufficient to destroy all similitude between the eye and the telescope, that the one is a perceiving organ, the other an unperceiving instrument. The fact is that they are both instruments. And, as to the mechanism, at least as to mechanism being employed, and even as to the kind of it, this circumstance varies not the analogy at all. For observe what the constitution of the eye is. It is necessary, in order to produce distinct vision, that an image or picture of the object be formed at the bottom of the eye. Whence this necessity arises, or how the picture is connected with the sensation, or contributes to it, it may be difficult, nay, we will confess, if you please, impossible for us to

transparent cornea, it not only has the power to concentrate the rays of light coming through the water, but by its altered position it increases greatly the sphere of vision. (See the right-hand figure, page 22.) To be critically correct, we may add that it is not exactly the cornea which is deficient in the fish, but the aqueous humour behind it. An aqueous fluid being thus both behind and before the cornea, and that membrane being in a very slight degree thicker in the centre than in the margin, this part of the organ which is so efficient in the atmosphere is rendered useless in water. A man diving, for example, sees imperfectly, being in something worse than the condition of an old man who requires spectacles.