every moment, to the provident care and goodness of our Beneficent Creator, for thousands of enjoyments which we seldom think of, and for which we are never sufficiently grateful." With much compassion, as well as astonishment, at the goodness of our loving Creator," says Dr. Nieuwentyt, "have I considered the sad state of a certain gentleman, who, as to the rest, was in pretty good health, but only wanted the use of those two little muscles that serve to lift up the eyelid, and so had almost lost the use of his sight-being forced, as long as this defect lasted, to shove up his eyelids every moment, with his own hands.”*

How admirable, then, is the formation of the eye, and how grateful ought we to feel at the consideration, that we are allowed to enjoy all the transporting pleasures of vision, without the least perplexity or effort on our part! If the loss of action in a single muscle produces so many distressing sensations and efforts, what would be the consequence if all the muscles of the eye were wanting or deranged? And, is it man that governs these nice and intricate movements? Or is it the eye itself, as a selfdirecting machine, that thus turns around, seasonably and significantly, towards every visible object? Man knows neither the organs of vision, nor the functions they ought to perform. The eye is only an unconscious machine, in the hands of a Superior Intelligence, as a watch, or a steam engine, is in the hands of a mechanic. It is God alone who constantly performs its movements, according to certain laws, which he has submitted to our inclinations and desires; "for in him we live and move."—We are desirous to see certain objects around us :-This is all the share we have in the operations of our eyes; and, without perplexing our understanding, without the least care or management, in regard to any of the functions, we can, in a few moments, take a survey of the beauties and sublimities of an extensive landscape, and of the glories of the vault of heaven. Thus, the Divine Being operates not only in this, but in a thousand different ways, in the various senses and contrivances which belong to our animal sys

* Nieuwentyt's Religious Philosopher, vol. I. p. 232.

tem; and yet, thoughtless and ungrateful man often inquires, in the language of doubt and hesitation, "Where is God my Maker ?"—He is in us, and around us, directing every movement in our animal frame to act in harmony with the surrounding elements, and to minister to our enjoyment; and it is only when his exquisite operations are deranged by external violence, that we feel inconvenience or pain.

Such are only a few general outlines of the structure of the eye; for no notice has been taken of the numerous minute veins, arteries, nerves, lymphatics, glands, and many other particulars which are connected with this organ. But, all this delicate and complicated apparatus, in the structure of the eye, would have been of no use whatever for the purpose of vision, had not a distinct substance been created to act upon it, exactly adapted to its nature and functions. In order that the eye might serve as the medium of our preceptions of visible objects, light was formed, and made to travel from its source at the rate of 195,000 miles in a second of time. This prodigious velocity of light is, doubtless, essential to the nature of vision; since it actually exists, and since we find that it radiates with the same swiftness from the most distant visible star, as from the sun which enlightens our system. To abate the force of this amazing velocity, its particles have been formed almost infinitely small- -a circumstance which alone prevents this delightful visitant from becoming the most tremendous and destructive element in nature. Dr. Nieuwentyt has computed, that, in one second of time, there flows 418,660,000,000,000,000,000,000,000,000, 000,000,000,000,000 particles of light out of the burning candle, which number contains at least 6,337,242,000,000 times the number of grains of sand in the whole earth, supposing every cubic inch of the earth to contain a million of grains. It has been justly remarked, by Mr. Ferguson, and other authors, that "if the particles of light were so large, that a million of them were equal in bulk to an ordinary grain of sand, we durst no more open our eyes to the light, than suffer sand to be shot point blank against them, from the mouth of a cannon. It may also be re

marked, that the property which all bodies possess, of reflecting light, is essential to the purpose of vision, without which, the splendid and variegated scene of nature would be changed into a dreadful gloom; and were the rays of light of one uniform colour, and not compounded of various hues, one object could not be distinguished from another, and the beautiful aspect of our globe would instantly disappear.

Thus we see, that the eye is adapted to light, and light to the eye; and in this admirable adaptation the wisdom of the Creator is strikingly displayed. For light has no effect upon the ear, or upon any other organ of sensation, so as to produce a perception of visible objects; as, on the other hand, the undulations of the air have no effect upon the eye, so as to produce the sensations of sound. The eye did not produce the light, nor did the light form the eye; they are perfectly distinct from each other, yet so nicely adapted in every particular, that had any one quality or circumstance been wanting in either, the functions of vision could not have been performed in the manner in which they now operate; which strikingly demonstrates, that one and the same Intelligent Being, possessed of a wisdom beyond our comprehension, formed the curi ous structure of the eye, and endued the rays of light with those properties of colour, motion, and minuteness, which are calculated, through the medium of this organ, to produce, in sentient beings, the ideas of visible objects. And, surely, he never intended that such exquisite skill and contrivance should be altogether overlooked by rational beings, for whose pleasure and enjoyment all this benevolent care is exercised.

MANNER IN WHICH VISION IS PERFORMED.

Let us now attend a little to the manner in which vision is performed, by the medium of light acting on the organs of sight. If we take a common convex glass-a reading glass for example—and hold it at some distance from a candle or a window sash, placing a piece of white paper behind the glass, at the distance of its focus, the image of the candle or sash will be painted on the paper, in an in

verted position. This experiment may be performed, with a better effect, by darkening a room, and placing the convex glass in a hole cut out of the window shutter, when the rays of light flowing from the objects without, and passing through the glass, will form a picture of the objects opposite the window, on the white paper, adorned with the most beautiful colours. In a manner similar to this, are the images of external objects depicted on the back part of the inner coat or membrane of the eye. The rays of light, proceeding in all directions, from surrounding objects, and falling on the eye, are transmitted through the pupil; and being refracted by the different humours (particularly by the crystalline humour, which acts the part of a convex lens,) they converge to a focus on the retina, where the images of visible objects are painted in an inverted position; and, by means of the optic nerve, these images are conveyed to the mind.

The following figure will perhaps more distinctly illustrate this point. Let a, b, c, x, y, represent the globe of the eye, and A, B, C, an object at a certain distance from it. Now, it is well known that every point of a visible object sends out rays of light in all directions; and therefore, a certain portion of the rays which flow from the

object A, B, C, will fall upon the cornea, between x and y, and, passing through the aqueous humour, mn, and the crystalline humour, o p, and the vitreous humour, D E, will be converged to a focus on the retina, and paint a distinct picture, a b c, of the object A B C, in an inverted position. The rays from the point A, of the object, after being refracted by the different humours, will be brought to a point at a; those from B will be converged at b; and

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those from C at c; and, of course, the intermediate rays between A B, and B C, will be formed between a b, and bc, and the object will become visible by means of its image or representation being painted on the retina, in all the colours and proportions which belong to it. If we take a bullock's eye, and cut off the three coats from the back part, and put a piece of thin white paper over that part, and hold the eye towards the window, or any bright object, we shall see the image of the object depicted upon paper, and in an inverted position, as stated above.

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In order that we may more distinctly perceive the wonders of vision, and the numerous circumstances on which it depends, let us suppose ourselves placed on an eminence, which commands a view of a variegated and extensive landscape. Let us suppose ourselves stationed on Arthur's seat, or on the top of Salisbury Crags, in the vicinity of Edinburgh. Turning our face to the northwest, the city, with its castle, spires, and stately edifices, presents itself to our view. Beyond it, on the north and west, a beautiful country, adorned with villas, plantations, and fertile fields, stretches as far as the eye can reach, till the view is bounded by the castle of Sterling, at the distance of more than 30 miles. On the right hand, we behold the port of Leith, the shipping in the roads, the coast of Fife, the isle of Inchkeith and of May, and the Frith of Fourth, gradually losing itself in the German ocean. If we suppose the length of this landscape to be 40 miles, and its breadth 25, it will, of course, comprehend an area of a thousand square miles.

The first circumstance which strikes the mind, is the immense multitude of rays of reflected light which flow, in all directions, from the myriads of objects which compose the surrounding scene. In order to form a rude idea of this infinity of radiations, I fix my attention on a single object. I direct my eye to Nelson's monument, on the Calton hill. From the parapet at the top, a thousand different points send forth a thousand different cones of rays, which, entering my eye, render the different parts of it distinctly visible, besides myriads of rays from the same points, which flow in every other direction through the