Not less wonderful is the construction of the eye itself. The optic nerve is the part of the eye which conveys visions to the mind. Suppose instead of it being where you observe it, at the back part of the eye, it had been brought out to the front, and that reflections from objects had fallen directly upon it. It is obvious that it would have been exposed to injury from every floating particle of dust, and we would always have felt such a sensation as is caused by a burn or scald when the skin peels off and leaves the ends of the nerves exposed to the air. Also the tender points of the fibres of the optic nerve would soon become blunted and the eye of course useless. How then is the nerve to be protected, and yet the sight not obstructed? If it were covered with skin as the other nerves are, we could not see through it. For thousands of years after men had eyes and used them, they knew no substance at once hard and transparent, which could answer the double purpose of vision and protection. To this day man knows no substance clear enough for vision, hard enough for protection, and elastic enough to resume its form {60} after a blow. Now observe in the eye, that forward part, called the cornea, is as it were the watch-glass. It it is made of a substance at once hard, transparent and elastic; something which man has never been able to imitate. It may be asked, what is the use of so many lenses in the eye? Light when refracted through a lens, becomes separated into its component colors--red, yellow, green, blue and violet. So that if the crystalline lens of the eye alone were used, we should see every white object, bluish in the middle, and yellowish and reddish at the edges. This difficulty perplexed Sir Isaac Newton all his life, and he never discovered the mode of making a refracting telescope which would obviate it. That remained for M. Dolland, a celebrated physician, to do; and he did it by studying and imitating the formation of the eye. Now what absurdity to say that a law of nature, such as gravity, or electricity has such a knowledge of the principles of optics and mechanics as the eye proclaims its Former to have! In all this we see marks of the most admirable design. The eye is fitted both to gaze at the stars millions of miles away and minutely examine objects only a few inches distant. In the brightness of sunshine the pupil contracts in order to protect the optic nerve from injury; in twilight it expands so as to admit a greater amount of light. When we wish to regulate the admission of light to our rooms we have recourse to very clumsy contrivances. A self-acting window which shall expand in the twilight and partially close of its {61} own accord as the light increases towards noon, has never been manufactured by man. In short, anatomists have already observed more than eight hundred contrivances in the dead eye, while the greatest contrivance of all, the power of seeing, is utterly beyond their ken.