« AnteriorContinuar »
quakes shook the ground, nor rent the foundations of nature. No volcanoes vomited their rivers of lava, nor overwhelmed the plains with deluges of fire.-No barren deserts of heath and sand disfigured the rich landscape of the world—no tempests nor hurricanes tossed the ocean, nor scorching heats, nor piercing colds, nor pestilence, nor disease, annoyed the human frame.-In the paradisiacal state of the world, we may reasonably suppose, that all the elements of nature contributed directly to the pleasure and enjoyment of man, and of the other tribes of animated existence; and that they were not subjected, as they now are, to the operation of those natural agents which so frequently spread destruction and ruin among the abodes of men. To suppose the contrary to have happened, would be inconsistent with the state of pure and happy intelligences, and with the benignity of the Creator; and would imply, that God was either unwilling, or unable to remove such physical evils. But we cannot suppose it beyond the limits of Infinite Wisdom and Omnipotence, to create and arrange a world entirely free from those evils and inconveniences which now flow from the operation of certain physical agents; without, at the same time, supposing that his power and intelligence are confined within certain bounds, beyond which they cannot pass. And, therefore, if, in the existing constitution of things, the harmony of nature is occasionally disturbed, and its beauty defaced, by earthquakes, storms, and tempests-we must remember, that the inhabitants of the earth are now a depraved race of mortals, no longer adorned with primeval purity and innocence; and that the physical economy of our globe has undergone a certain derangement, corresponding to the moral state of its present occupants. But since this earth, even in its present state of degradation and derangement, presents to the view of every beholder so many objects of beauty and magnificence, and so numerous traces of Divine Beneficence-we may reasonably conclude, that scenes of Divine Wisdom and Goodness, far more glorious and transporting, must be displayed in those worlds where moral evil has never shed its malign influence, and where the
inhabitants-superior to disease and death-bask for ever in the regions of immortality. And, therefore, however admirable the displays of Divine Wisdom may appear in the sublunary scene around us, they must be considered as inferior to those which are exhibited in many other provinces of Jehovah's empire, in so far as they are blended with those physical derangements which indicate his displeasure against the sins of men.
Were we now to direct out attention to the mechanism of animated beings, and to consider the numberless contrivances and adaptations in their organical structure and functions, a thousand instances of exquisite wisdom and design, still more striking and admirable, would crowd upon our view. For, although the general fabric of the world, and the immense variety of objects it contains, are evident proofs of a Wise and Intelligent Contriver, yet it is chiefly in the minute and delicate contrivances of organical structures, their adaptation to the purposes of life, motion, and enjoyment, and their relation and correspondence to the surrounding elements, that the consummate skill of the Great Architect of nature is most strikingly perceived. But as it forms no part of my present plan to enter on so extensive a field of illustration, on which volumes might be written, I shall content myself with merely stating an example or two. My first example shall be taken from
THE STRUCTURE OF THE HUMAN EYE.
The eye is one of the nicest pieces of mechanism which the human understanding can contemplate; but as it requires a knowledge of its anatomical structure, and of the .principles of optics, to enable us to appreciate its admirable functions, I shall confine myself to a few general descriptions and remarks.
The eye is nearly of a globular form. It consists chiefly of three coats, and three humours. The first or outer coat, is termed Sclerotica; it is every where white and opaque, and is joined at its anterior edge to another which has more convexity than any other part of the globe
of the eye, and, being exceedingly transparent, is called the Cornea. These two parts are perfectly different in their structure, and are supposed, by some anatomists, to be as distinct from each other as the glass of a watch is from the case into which it is fixed.-Next within this coat is that called the Choroides, on account of its being furnished with a great number of vessels. It serves, as it were, for a lining to the other, and is joined with that part of the eye termed the iris. The iris is an opaque membrane like the choroides, but of different colours in different eyes, as grey, black, or hazel. It is composed of two sets of muscular fibres, the one of a circular form, which contracts the hole in the middle, called the pupil, when the light is too strong for the eye; and the other of radial fibres, tending every where from the circumference of the iris towards the middle of the pupil; which fibres, by their contractions, dilate and enlarge the pupil, when the light is weak, in order to let in more of its rays.-The third coat is called the retina, upon which are painted the images of all visible objects, by the rays of light which flow from them. It spreads like net-work all over the inside of the choroides, and is nothing more than a fine expansion of the optic nerve; by which nerve the impressions of visible objects are conveyed to the brain.
The inside of the globe of the eye, within these tunics or coats, is filled with three humours, called the aqueous, the crystalline, and the vitreous. The aqueous humour lies at the fore-part of the eye, and occupies all the space between the crystalline and the prominent cornea. It has the same specific gravity and refractive power as water, and seems chiefly of use to prevent the crystalline from being easily bruised by rubbing, or by a blow-and perhaps it serves for the crystalline humour to move forward in, while we view near objects; and backward, for remoter objects; without which, or some other mechanism, effecting the same purpose, we could not, according to the laws of optics, perceive objects distinctly, when placed at different distances.-Behind the aqueous lies the crystalline humour, which is shaped like a double convex glass, and is a little more convex on the back than on the
fore-part. This humour is transparent like crystal, is nearly of the consistence of hard jelly, and converges the rays which pass through it, from visible objects, to its focus at the bottom, or back-part of the eye.-The vitreous humour lies behind the crystalline, and fills up the greatest part of the orb of the eye, giving it a globular shape. It is nearly of the consistence of the white of an egg, and very transparent; its fore-part is concave, for the crystalline humour to lodge in, and its bark-part, being convex, the retina is spread over it. It serves as a medium to keep the crystalline humour and the retina at a due distance. From what has been now stated, it is obvious, that the images of external objects are depicted on the retina, in an inverted position, in the same manner as the images formed by a common covex lens; but how the mind, in this case, perceives objects erect, is a question, about which the learned have been divided in their opi nions.*
The ball of the eye, as now described, is situated in a bony cavity, called its orbit, composed by the junction of 7 different bones, hollowed out at their edges. This cavity is, in all the vacant spaces, filled with a loose fat, which serves as a proper medium for the eye to rest in, and as a socket in which it may move. It is sheltered by the eyebrows, which are provided with hair, to prevent the descending sweat of the forehead from running down into it. As a still farther protection to this delicate organ, it is furnished with the eye-lid, which, like a curtain, is drawn over it with inconceivable swiftness, for its security, on the approach of danger. It also serves to wipe it from superfluous moisture, and to cover it during sleep. In the upper part of its orbit, it is furnished with a gland, to supply it with water sufficient to wash off dust, and to keep its outer surface moist, without which the cornea would be less transparent, and the rays of light would be disturbed in their passage; and the superfluous water is conveyed to the nose through a perforation in the bone.
An idea of the relative positions of the coats and humours described above, may be obtained by a simple inspection of the Plate, Fig. 6.
For the purpose of enabling the eye to move in its socket, six muscles are provided. These are admirably contrived to move in every direction, upwards or downwards, to the right, or to the left, or in whatever direction the occasion may require; and thus we are spared the trouble of turning our heads continually towards the objects we wish to inspect. If we want to look upward, one of these muscles lifts up the orb of the eye; if we would cast our eyes to the ground, another muscle pulls them down. A third muscle moves the globe outwards towards the temples, and a fourth draws it towards the nose. A fifth, which slides within a cartilaginous ring, like a cord over a pulley, and is fastened to the globe of the eye in two points, makes it roll about at pleasure. A sixth lies under the eye, and is designed to temper and restrain, within proper bounds, the action of the rest, to keep it steadily fixed on the object it beholds, and to prevent those frightful contortions which otherwise might take place. By these, and a multitude of other mechanical contrivances, all acting in harmonious combination, the eye, as a natural telescope and microscope, is made to advance, to recede, to move to the right, and to the left, and in every other direction; and to view near and distant objects, with equal distinctness; so that a single eye, by the variety of positions it may assume, performs the office of a thousand.
The utility of these several movements, and the pain and inconvenience which would be suffered, were any of them wanting, can scarcely be conceived, by any one whose eyes have always remained in a sound state. We are so much accustomed to the regular exercise of our visual organs, that we seldom reflect on the numerous delicate springs which must be set in action, before the functions of vision can, with ease, be performed. But were any one of the muscular organs, now described, to fail in its functions, we should soon experience so many inconveniences, as would throw a gloom on all the other comforts of life; and convince us, how much we are indebted,
* Flies and other insects, whose eyes are immoveable, have several thousands of distinct globes in each eye. See note page 91.