alluring eye. I felt her syren voice enter my soul. Instantly I made an effort to rise, and follow her inviting tones: but had scarcely advanced a pace, before I felt unable to proceed; some, until then, unseen hand held me. I turned to look at my detainer, when I perceived my two invaluable friends beside me, Education and Conscience. Still I could not determine which of the two prevented my progress. I imagine, however, that both had exerted their influence on the occasion, and that the latter had been assisted by the former. I struggled a while for freedom, and at length attained it. At first, however, I advanced by slow and cautious steps towards the throne, and at times felt more than half inclined to return to the spot I had left; but, on gazing at the path by which I had travelled, I perceived so much dreariness and gloom beshrowding it, as at once appalled, and determined me to urge my way towards the rosy path which yet appeared before.

The goddess beheld my approach, and at every symptom of irresolution, she shot from her basilisk eye such an overpower. ing influence, as drew me insensibly onwards. I felt, however, as I advanced, that the road was not so delightful as it had in prospect appeared: even among the flowers which I had noticed, poisonous thorns, which I had not in the distance perceived, sprung up and pierced me. Still I pushed forward, being determined, maugre all difficulties, to reach the throne. The goddess beheld my purpose, and most condescendingly stretched forth her hand towards me. I was, as I imagined, on the point of laying hold on it, when my friend Conscience, who had followed me through the crowd, placed himself before my eyes. The mild benignity, and approving countenance, which in former times I had seen him wear, was now changed—his heavy frown startled me ; and yet I could perceive some marks of sorrow mingled with his sternness. I had, indeed, caught occasionally a faint sight of him as I advanced towards the seat of the deity, but, instantly turning my eye to the smiling goddess, I escaped the pain which his presence might otherwise have occasioned: but now, turn which ever way I might, he stood always fronting me. He expostulated, and I answered: a kind of maniacal gratification possessed me, as I found means to meet his objections to my proceeding. Again and again, however, he returned to the attack; and I was on the point of yielding to his authority, when the goddess herself kindly came to my assistance. She had now thrown aside all that could be deemed objectionable in her appearance,

and my stern Mentor even relaxed in his austerity. Pleasure embraced the opportunity, and bore me away triumphantly in her arms, almost out of sight of my morose adviser.

Hitherto I had contemplated the goddess by the light of day alone. I soon perceived, however, that her chief power of fascination was during the hours of night; at least, that then her dominion over her votaries is most entire. As we approached her palace, I beheld a thousand blazing fires, which at once outshone the pale silver moon, and the thousand thousand trembling stars which spangled the arch of heaven.

We entered, without any annoyance, through a portal, which my conductress called Innocent Amusement. Here I perceived numbers, like myself, who had been recently delivered from the threatening vociferations of Conscience, pushing on to another little apartment, yet more highly illuminated, called Little Harm. Here the forms of strict propriety, even, were dispensed with, and frequently declaimed against. The loose jest and the loud song occasionally were heard; in some parts of the spacious place, friendly gaming was entered into with an avidity and zeal which I imagined professed gamesters could scarcely have exceeded. I had not been long here, when I was again annoyed by my invincible attendant Conscience. He seemed like the shade of myself; go whichsoever way I might, he was there. I succeeded, however, in assuring him that my intentions were perfectly pure; and that the company in which I then was, would be a security for my future conduct, as I pointed to my spiritual teacher, who at that moment I perceived among the company with several old professors of religion. He was evidently suspicious, and yet he retired with a salutary caution.

For a while, I attended to the admonitions which Conscience had given me; but an invitation from a respectable person who stood high in the favour of the presiding deity, to witness at least the hilarity of the company in an interior chamber of the palace of Pleasure, induced me to proceed. Step by step I continued to advance, while each succeeding scene of enjoyment filled me with insatiable desire to visit those beyond me.

Pleasure now assumed a more than half

commanding aspect. Nothing terrified, for even her authority was fascinating, I replied with Shakespeare's Hamlet to the ghost of his father:-"Lead on, I'll follow." There was even a frantic recklessness in my feelings and in my proceedings. I had

now gained the grand banqueting hall of this superb palace. At the time of my entry, it was crowded with votaries, from every walk of life. I could easily describe a host of characters who were then figuring away in all the luxury of sense--but I forbear; it would be a blot upon my country, and

66

England, with all thy faults, I love thee still."

To draw aside the vail, would be to expose scenes which would shock an infidel; or to arm the opposers of truth and righteousness with weapons of the most destructive order, and make the sons of Belial, with satanic exultation, cry-"Ah! ah! so would we have it."

The high-raised throne of the goddess of Pleasure was composed of every kind of alluring material, of which the imagination can have any notion. Upon it sat the deity, distributing her favours most lavishly, as her votaries made application; and yet I could not perceive one who was satisfied, although all could enjoy the possessed. Such a scene of discord and confusion never before was seen as in this apartment. Every species of infamy, even of the most disgusting order, was allowed and exercised. Each party, and almost each individual, had their particular object in view, and, without scarcely noticing others, they pressed after their own gratification. Aged matrons and delicate females here lost their temper and their beauty, sacrificed their place even in the temple of Pleasure, and offered up their reputation at the shrine of their fascinating goddess.

I had not been long within this spacious saloon, before an intoxicating giddiness seized me; and while I drank largely of the nectareous streams which flowed round the place, and courted the taste, I felt a dissatisfaction, for which I had no means of accounting. I had already advanced to the very throne of Pleasure, and no enjoyments which the goddess had to impart were withheld from me: still I wanted something I did not possess, and could not define. I imagined I perceived, floating in empty space, and encircling the whole of the revellers, "Vanity of vanity, all is vanity, and vexation of spirit." I was endeavour. ing to divert my attention from the sight, and from the thoughts the sight produced, by diving into a fount of ambrosial felicity, the nature of which is to cause an entire forgetfulness of the past, and contempt of the future, when, suddenly, I was smitten by one of the scythe-bearer's emissaries, called Disease, who lay concealed in the fount of felicity. Scarcely had the blow been given, before Conscience, with a voice

of deadful accusation, and a frown terrifically threatening, stood before me. I strove again to soften his brow, but in vain ; my sophistry had failed me, and I now felt the correctness of the statement— "No weapon can such deadly wounds impart,

As Conscience, rous'd, inflicts upon the heart." The goddess, who had before smiled so graciously, deserted me. As she retreated, the mask which she had assumed, and by which I had been deceived, fell off; and her face, distorted with every fell passion, and wrinkled and deformed by disease, was presented. With a cruel mockery, more bitter than I imagined rage itself could have displayed, she taunted and jeered me. The obsequious crowds too, who had lately vowed eternal and unchanging regards, as if fearing a similar stroke with myself by continuing with me, fled with precipitantness, and I was left alone, wounded and wretched.

During my attendance upon Pleasure, I had neglected all business, and incurred a variety of expenses, which I now had no means of meeting. Without pity or concern for my miserable condition, I was dragged to the bar of Justice. The charges preferred against me were proved most clearly, and orders were issued for my immediate execution: not only for obligations which I could not discharge, but for rebellion against the sovereign to whom I owed implicit obedience, but whose service I had deserted, when I joined with the partisans of Pleasure; Conscience continued to frown upon me, pitiless as the bosom of "Milton's Lucifer," when

"the wary fiend
Stood on the brink of hell, and look'd awhile,
Pondering his voyage."

The messenger of death advanced to perform his office upon me. A shriek of misery escaped my lips, and a cry of agony rose from my heart, when suddenly an unseen figure arrested his upraised arm; and a form, lovelier than the sons of men, bending over me as I lay prostrate and bound, snapped asunder my bonds, and raising me upon my feet, smiled soothingly upon me, and exclaimed-"I am thy salvation; another year is granted thee; be watchful and be wise."

The high, unutterable rapture, which flowed through my bosom, raised me from my slumbers, and, awaking, I exclaimed"Prayer has prevailed-my reprieve is signed—the first ray of this morning which greeted my gladdened eyes, confirms the fact-I am spared to see the commemoration of another year."

Brigg.

THE STRUCTURE OF THE EYE, AND THE THEORY OF VISION.

THE eyes of all animals consist of an assemblage of lenses, which concentrate the rays emanating from each point of external objects on a delicate tissue of nerves, called the retina; there forming an image, or exact representation, of every object which is the thing immediately perceived or felt by the retina. Anatomists divide the eye into two parts, i. e. the internal, which is the globe or ball of the eye; and the external, which comprehends all those parts surrounding the ball, and subservient to it. The eye-lids, which immediately cover the ball of the eye, are composed of muscular fibres, covered by the common integuments, and lined by a very fine and smooth membrane, which is from thence extended over every part of the ball of the eye. This membrane is called the tunica conjunctiva, and being thus returned from the eye to the inside of the lids, it effec. tually hinders any extraneous bodies from getting behind the eye, into the orbit; its chief use is to smooth the parts it covers, and render the friction less between the eye and the eye-lids.

Each eye-lid is cartilaginous at its edge; and this border, which is called tarsus, is furnished with a row of hairs, named cilia, or eye-lashes. The cilia serve to protect the eyes from insects, and minute bodies floating in the air, and likewise to moderate the action of the rays of light, in their passage to the retina. The supercilia, or eyebrows, are placed on the upper border of the socket of the eye, and have been considered as serving to protect the eyes, from the perspiration which would otherwise occasionally flow into them from the forehead. It is remarkable that the eye-brows are peculiar to the human species.

The inner angle of each orbit, or that part of it which is near the nose, is called canthus major, or the greater angle; and the outer angle, which is on the opposite side of the eye, is the canthus minor, or little angle. In the upper and outer part of the orbit, is seated a small gland, called the lachrymal gland. Its use is to furnish a watery secretion, called the tears, which answer the purpose of washing out dust, and keeping the outer surface of the eye moist, without which, the transparent cornea would be less pellucid, and the rays of light be disturbed in their passage to the retina; and that this liquor may be rightly disposed of, we are continually, though unconsciously, closing the eye-lids, to distribute it equally.

At the inner corner of the eye, between the eye-lids, is a little reddish body, called caruncula lachrymalis, which seems placed there, to keep that corner of the eye-lids from being so totally closed, as to hinder the discharge of tears from the eye-lids during sleep. Close to this caruncule, are situated the puncta lachrymalia, which are small holes, one in each eye-lid, designed to carry off the superfluous tears into the ductus ad nasum.

The internal eye, or ball of the eye, is, generally speaking, of a spherical figure, but considerably more prominent in front. It consists of three principal chambers, filled with media of perfect transparency, and of refractive powers differing sensibly inter se, but none of them greatly different from that of pure water.

The first of these media, occupying the anterior chamber, is called the aqueous humour, and consists, in fact, chiefly of pure water, holding a little muriate of soda and gelatine in solution, with a trace of albumen; the whole not exceeding eight per cent. Its refractive index, according to the experiments of M. Chossat, and those of Dr. Brewster and Dr. Gordon, is almost precisely that of water, viz. 1.337; that of water being 1.336. The cell in which the aqueous humour is contained, is bounded, on its anterior side, by a strong, horny, and delicately transparent coat, called the cornea, the figure of which, according to the delicate experiments and measures of M. Chossat, is an ellipsoid of revolution about the major axis; this axis, of course, determines the axis of the eye: but it is remarkable, that in the eyes of oxen, measured by M. Chossat, its vertex was never found to be coincident with the central point of the aperture of the cornea, but to lie always about 10° (reckoned on the surface) inwardly, or towards the nose, in a horizontal plane. The ratio of the semi-axis of this ellipse to the excentricity, he determines at 1.3; and this being nearly the same with 1.337, the index of refraction, it is evident that parallel rays incident on the cornea in the direction of its axis, will be made to converge to a focus situated behind it, almost with mathematical exactness; the aberration which would have subsisted, had the external surface a spherical figure, being nearly destroyed.

The posterior surface of the chamber containing the aqueous humour is limited by a kind of circular opaque screen, or diaphragm, called, from its variety of hues, the iris; this opaque screen consists of muscular fibres, by whose contraction or expansion, an aperture in its centre, called

the pupil, is diminished or dilated, according to the intensity of the light.

In the human eye, the pupil is round, which enables us to see in every direction alike; it is also round in those of animals, which are naturally the prey of other animals, both birds and beasts. But quadrupeds of the graminivorous kind have it horizontally oblong, by which they are fitted to view a large space over the earth: while animals of the cat kind, which climb trees, or prey indifferently on birds, or animals that hide in the earth, have their pupils perpendicularly oblong, by which means they can look upwards or downwards at the same time.

The contraction and dilation of the pupil is involuntary, and takes place by the effect of the stimulus of the light itself; and it is evidently designed to moderate and equalize the illumination of the image on the retina, which might otherwise injure its sensibility. When the iris contracts, it dilates the pupil; and by that means, suffers more rays of light to enter into the eye; whilst the contrary is effected by the circular fibres of the iris acting from the circumference towards the centre. These changes are not made with great quickness, as appears from the eyes retaining the painful effects of a strong light for some time after we come out of a dark place, and from our being unable at first to distinguish objects, on going suddenly from a light place to a dark one.

Immediately behind the opening of the iris, lies another fluid, called the crystalline lens, enclosed in its capsule, which forms the posterior boundary to the first chamber, or that containing the aqueous humour. The figure of the crystalline lens is a solid of revolution, having its anterior surface much less curved than the posterior. Both surfaces, according to M. Chossat, are ellipsoids of revolution about their lesser axes; but it would seem from his measures, that the axes of the two surfaces are neither exactly coincident in direction with each other, nor with that of the cornea. This deviation would be fatal to distinct vision, were the crystalline lens very much denser than the others, or were the whole refraction performed by it. This, however, is not the case; for the mean refractive index of this lens is only 1.384, while that of the aqueous humour is 1.337; and that of the vitreous humour, which occupies the third chamber, is 1.339; so that the whole amount of bending which the rays undergo at the surface of the crystalline, is small in comparison with the inclination of the surface

at the point where the bending takes place; and since, near the vertex, a material deviation in the direction of the axis can produce but a very minute change in the inclination of the ray to the surface, this cause of error is so weakened in its effect, as probably to produce no appreciable aberration.

The crystalline lens is composed of a much larger proportion of albumen and gelatine than the other humours of the eye; so much so, as to be entirely coagulable by the heat of boiling water. It is somewhat denser towards the centre than at the outside. According to Dr. Brewster and Dr. Gordon, the refractive indices of its centre, middle of its thickness from the centre to the outside, and the outside itself, are respectively 1.3999, 1.3786, 1.3767, that of pure water being 1.3358. This increase of density is obviously useful in correcting the aberration, by shortening the focus of rays near the centre.

The posterior chamber of the eye is filled with the vitreous humour, a fluid differing (according to Chenevix) neither in specific gravity, nor in chemical composition, in any sensible respect from the aqueous ; and having, as has been mentioned before, a refractive index but very little superior.

The refractive density of the crystalline being superior to that of either the aqueous or vitreous humour, the rays which are incident on it in a state of convergence from the cornea, are made to converge more; and exactly in their final focus is the posterior surface of the cell of the vitreous humour covered by the retina, a net-work (as its name imports) of inconceivably delicate nerves, all branching from one great nerve, called the optic nerve, which enters the eye obliquely at the inner side of the orbit, next the nose.

The retina lines the whole of the chamber containing the vitreous humour up to where the capsule of the crystalline commences. Its nerves are in contact with, or immersed in, the pigmentum nigrum, a very black velvety matter, which covers the choroid membrane, and whose office it is to absorb and stifle all the light which enters the eye, as soon as it has done its office of exciting the retina; thus preventing internal reflexions, and consequent confusion of vision. The whole of these humours and membranes are contained in a thick tough coat, called the sclerotica, which unites with the cornea, and forms what is commonly called the white of the eye.

Such is the structure by which parallel rays, or those emanating from very distant objects, are brought to a focus on the retina.

But as we need to see objects near, as well as at a distance, and as the focus of a lens or system of lenses for near objects is longer than for distant ones, it is evident that a power of adjustment must reside somewhere in the eye; by which either the retina can be removed further from the cornea, and the eye lengthened in the direction of its axis, or the curvature of the lenses themselves altered, so as to give greater convergency to the rays. We know that such a power exists, and can be called into action by a voluntary effort; and evidently, by a muscular action, producing fatigue if long continued, and not capable of being strained beyond a certain point.

Anatomists, however, as well as theoretical opticians, differ as to the mechanism by which this is effected. Some assert, that the action of the muscles which move the eye in its orbit, called the recti, or straight muscles, when all contracted at once, producing a pressure on the fluids within, forces out the cornea, rendering it at once more convex, and more distant from the retina. This opinion, however, which has been advocated by Dr. Olbers, and even attempted to be made a matter of ocular demonstration by Ramsden and Sir. E. Home, has been combated by Dr. Young, by experiments, which shew, at least, very decisively, that the increase of convexity in the cornea has little, if any, share in producing the effect.

An elongation of the whole eye, spherical as it is, and full of fluid, to the considerable extent required, is difficult to conceive, as the result of any pressure which could be safely applied; since, to give distinct vision at the distance of three inches from the eye, (the nearest at which ordinary eyes can see well,) the sphere must be reduced to an ellipsoid, having its axis nearly one-seventh longer than in its natural state; and the extension of the sclerotica, thus produced, would hardly seem compatible with its great strength and toughness.

Another opinion which has been defended with considerable success by Dr. Young, is, that the crystalline itself is susceptible of a change of figure, and becomes more convex when the eye adapts itself to near distances. His experiments on persons deprived of this lens, go far to prove the total want of a power to change the focus of the eye in such cases, though a certain degree of adaptation is obtained by the contraction of the iris, which, limiting the diameter of the pencil, diminishes the space on the retina, over which imperfectly converged rays are diffused,

and thus, in some measure, obviates the effect of their insufficient convergence.

When we consider that the crystalline lens has actually a regular fibrous structure, (as may be seen familiarly, on tearing to pieces the lens of a boiled fish's eye,) being composed of layers laid over each other like the coats of an onion, and each layer consisting of an assemblage of fibres proceeding from two poles, like the meridians of a globe, the axis being that of the eye itself; we have, so far at least, satisfactory evidence of a muscular structure; and were it not so, the analogy of pellucid animals, in which no muscular fibres can be discerned, and which yet possess the power of motion and obedience to the nervous stimulus, though nerves no more than muscles can be seen in them, would render the idea of a muscular power resident in the crystalline easily admissible, though nerves have not as yet been traced into it. On the whole, it must be allowed, that the presumption is strongly in favour of this mechanism, though the other causes, already mentioned, may, perhaps, conspire to a certain extent in producing the effect, and though the subject must be regarded as still open to fuller demonstration.

It is evident from the preceding description of the eye, that the images of external objects must be formed inverted on the retina, and this may be seen by taking the eye of a newly killed animal, and by dissecting off the posterior coats, and exposing the retina and choroid membrane from behind, when the images will be seen like those on the rough glass screen of a small camera obscura. It is this image, and this only, which is felt by the nerves of the retina, on which the rays of light act as a stimulus; and the impressions therein produced are thence conveyed along the optic nerves to the sensorium, in a manner which we must rank at present among the profounder mysteries of physiology, but which appears to differ in no respect from that in which the impressions of the other senses are transmitted. Thus, a paralysis of the optic nerve produces, while it lasts, total blindness, though the eye remains open, and the lenses retain their transparency; and some very curious cases of half blindness have been successfully referred to an affection of one of the nerves without the other. On the other hand, while the nerves retain their sensibility, the degree of perfection of vision is exactly commensurate to that of the image formed on the retina.

In cases of a cataract, where the crystalline lens loses its transparency, the light