tomb. Vain and baseless may be the whole phantasy, yet it is one on which fancy loves to dwell, and which hope would readily believe substantial. Unknown, as thou art, therefore, to whomsoever this symbol of distinguished station is devoted, peace be with thy dust; and long be that memory thine, which shall exist in the breasts of the living, when the herald's tinctures shall have faded into indistinctness, and his skilfully devised achievement mouldered to decay on the time-worn stone.

Passing over the spaces once occupied by several monumental brasses, and, among others, one, the remoteness of whose date is indicated by the hawk perched on the wrist of the figure, deeply let into the graven stone: we arrive at an inscription, over which we are tempted for a few moments to linger. "Hic jacet frater Robertus Bonner, quondam hujus monasterii monarchus, qui quadraginta sex annis continuis et ultra ministrabat in diversis officiis monasterii præscripti, videlicet in officiis coquarii refectorarii et infirmarii." Ah! perished and forgotten artist! A skilful hand we will warrant his to have been, in compounding the delicate marchpane, or spicing the sparkling hippocras. Well did he know how to make palatable the carp or tench, of goodly size, extracted from the abbey ponds, on the day of unwelcome fast, or to deck the board with confectionary of strange device on the festival of his patron saint, or to garnish the smoking boar's head at the time of merry yule, when the blazing log sent far and wide its light over the waste, from the gorgeously stained windows of the warm refectory. No ordinary talent, we may well imagine, was required for so important a post as his, and no ordinary judges were those who assayed and commended his labours. But they who prepared, and they who partook of the feast, are alike departed from the scene of their festivity for ever; and the same fate which sweeps from earth the names of the mighty, threatens soon to obliterate even this brief record of the services of nearly half a century zealously and efficiently performed. Yet pious is the wish with which the humble monk has closed the list of his duties, and, if sincerely expressed, we may hope that, though long forgotten amidst the scenes of his labours on earth, he has yet been remembered where the secret aspirations of the heart are heard, and recorded as one who, trusting in the sole refuge on which penitence can rely, has therefore been not unforgiven. Much yet remains undescribed,—the square altar tomb, long falsely considered as that of king Offa; the northern transept, with its ceiling, on which the death of the martyr is so grotesquely represented; the winding ascent within the great tower itself, giving access to the battlemented height, from which the whole neighbouring country seems like a cultivated garden spread beneath us: but it will be thought, we imagine, that our stay within the Abbey church has been already somewhat of the longest. We, therefore, pass from the beautifully-wrought western porch, and, after many a reluctant pause, bid farewell to its long-withdrawing aisles and intersecting transepts.

Nor have we allowed ourselves space or time to describe in detail those other remains which attach so irresistible an interest to St. Alban's. Above all, we must deny ourselves the pleasure, at least for the present, of following out the train of recollections which crowd on us as we visit the spot where lie the ashes of the immortal philosopher who effected the greatest intellectual revolution which mankind have ever witnessed, whose rising banished those fallacious shadows which had for ages fascinated and imposed on the whole civilized world, and poured on the human race the light of a sound and rational philosophy. We must, we say, though reluctantly, refrain from indulging those mingled feelings of admiration, astonishment, and regret, which seem in association with the name of Lord Bacon; and neither expatiate on the undying glory reflected on his name from his writings, nor examine his controverted history, and

"Draw his frailties from their dread abode."

Denying ourselves this enjoyment, we feel that we have broken the strongest tie which detains us in the scene we have been attempting to describe, and we therefore take our leave of it with all the charms which Time and Art have been emulous in bestowing on it; with its frequent reminiscences of the dead, and its solemn, but it may be hoped not unprofitable, appeals to the living.

545

ON THE STUDY OF PHYSICS.

(Concluded from p. 505.)

ALTHOUGH the human eye is not provided with so complex an apparatus as many of the lower classes of animals, yet it is impossible to examine it, without admiring the skill with which it has been formed, and acknowledging its adaptation to all the purposes contemplated in its construction. It is true that man has numerous wants, which cannot be supplied by a mere examination of nature. A too entire dependence upon his senses will mislead and deceive him, and in cases of perpetual occurrence they require assistance from his invention.

Moreover, it is not a little remarkable, that the human eye is much more subject to disease than the eyes of other animals. But man is in possession of a power by which the majority of these may be removed, and instruments may be supplied to correct the errors which arise from them. Near and long sights are common among us, but, by the use of differently shaped lenses, the inconvenience arising from these diseases may be avoided.

The limits of our vision are small, but we have extended them to an indefinite extent, by the invention of the microscope and the telescope. With the one we investigate organized structure so small, that its very existence had been before unknown. With the other we examine the constitution of worlds, which appear, without its assistance, only as points in the immensity of space. These are the results of our inquiry; but it must be remarked, that they only tend to the advancement of our improvable reason, and are in no degree connected with the improvement of the mere animal life of the human species.

We may now direct our attention to the sources of some of those errors to which the eye, as an example of the senses, is subject; first of all, briefly alluding to two or three circumstances, which would have produced important errors, and have deranged human vision, had not the Creator provided means by which they are corrected.

It is generally known, that the image of any object is painted on the retina, and that in an inverted position. But still we see, or think that we see, every thing in an erect attitude. This has been denied by some authors, who imagine that we perceive all things inverted, and that the sense of touch corrects the error of sight. In proof of this, it is stated, that if a stick with a gilded knob to one end be presented to an infant, it will stretch its hand towards the opposite end. But this is not true; and in proof of the perception of objects in their upright position, it may be stated, that in all cases where persons born blind have received sight, objects have been seen in their right position, although there has been an indistinctness of vision. This was the case with Cheselden's patient, and in numerous other more recent instances.

It must, then, be admitted that we perceive objects in their upright position, though the image is inverted when painted on the retina. There is, therefore, some effect produced between the retina and the brain, by which this error of vision is corrected, and in this circumstance we have a still further demonstration of the perfect adaptation of the organ to our convenience.

But, as we have two eyes, and as consequently two images are formed, one on the retina of each eye, it may be asked, why do we not perceive all things double? Sir Isaac Newton thought that the single vision was attributable to the union of the optic nerves before they reach the brain; but cases have occurred, in which there has been no such union, and yet the objects have been perceived singly. It is now usually explained as the result of a mere habit. It may be asked, upon the same principle, why we, having ten fingers, do not receive the impression of ten objects instead of one. When we look upon an object, we are led by experience to direct the eyes upon it in such a position, as to bring its images upon those parts of the retina where most distinct vision is produced. But, while looking stedfastly on any body, press one of the eyes upwards or 2D. SERIES, No. 36.-VOL. III.

3 z

180.-VOL. X"

downwards, so as to throw the image on some other part of the retina, and a double vision is immediately produced. The influence of habit in causing us to rightly direct our eyes upon an object is sufficient to account for single vision; but, in addition to this, we might mention the nervous sympathy which probably exists between the two eyes. Dr. Wollaston is of opinion, that a semi-decussation of each nerve takes place upon its quitting the brain; half of each nerve going to each eye, the right half of each retina being formed by one nerve, the left half by the other. By this means a powerful sympathy is established between the nerves, which, independent of habit, would be sufficient to produce single vision. But whether we imagine the effect to be produced by one of these causes or by both, it is most evident that the Creator has provided against the physical disadvantages which must have resulted from a different arrangement.

There is another instance of the same kind, in the insensibility of the punctum cæcum, The spot at which the optic nerve enters the eye is called the punctum cæcum, and is totally insensible to light, which is supposed to be occasioned by the nerve not being there divided into fibres sufficiently delicate to be acted upon by the rays of light. There is, therefore, a point in every scene of view, to which we are absolutely blind; when the right eye is used, that point is situated about 15° to the right of the object at which we look directly; when the left eye is used, about 15° to the left. This may be proved by an interesting experiment. Place two black wafers on a white ground, about three inches apart, and, standing at the distance of eleven or twelve inches, look at the right hand wafer with the left eye in such a position, that an imaginary line joining the wafers, shall be exactly parallel to a line which may be supposed to join the eyes. If the right eye be now closed, the left-hand wafer will be invisible. The success of this experiment depends upon the image of the wafer falling upon the part of the retina where the optic nerve comes in contact with it.

When we look with both eyes, the spot that is insensible to one eye will be seen by the other; but it will only be half as distinct as if seen by both eyes. Two comparatively dark spots should, therefore, appear in every scene; but this error of vision is beautifully compensated for by a susceptibility, in this insensible base, to be influenced by the light of the retina. It appropriates the light of the retina by absorption, and thus conveys the same impression of colour as the adjoining parts of the retina. This error of vision is, therefore, rendered neutral; and the insensibility of the base of the optic nerve would have remained unknown, but for the experiment we have just described.

But the eye is exposed, by its very construction, to impressions which are the causes of deception. Every one has observed that certain luminous appearances are produced by pressing the eye-ball outward by a force applied between the eye and the nose. A sudden blow upon the eye, or even upon the head, will sometimes be sufficient to produce this phosphorescent appearance. Sir David Brewster has been led, by experiments made upon this appearance, to the conclusion, that when the retina is compressed in total darkness, it gives out light: when exposed to the light, and compressed, its insensibility to light is increased; and when dilated, it is insensible to all luminous impressions.

But this appearance may be produced by internal as well as external causes. If dur. ing a state of indisposition the blood-vessels exert a pressure upon the retina, luminous appearances will be produced, to which the fancy of the patient will frequently give a variety of distinct forms. The eye, under all circumstances, when intently fixed upon any confused mass, is apt to imagine that it resembles some shape with which it is acquainted. Every one, probably, has sat by the fire-side in a winter's evening, and, intently fixing his eyes upon the burning coals, has imagined a variety of figures, as volcanoes, animals, &c. to be represented by the various colourings of the fire. How often, too, have we realized, remembered, or imagined scenes in the passing clouds, or in their reflected images upon the bosom of some peaceful lake. And how much more, then, will this faculty of creating form from confused masses, be exercised by the mind, when under the influence of a deranged organization. To these two causes, perhaps, we may

chiefly attribute the phantasms which haunt the couch of the patient, even when he is in the perfect possession of his reason; the production of luminous appearances by the pressure of the blood-vessels on the retina, and the facility with which the eye gives form to any confused mass that may be presented to it. Nor will it now appear strange that the patient is not, in any degree, relieved from such delusions by closing

his eyes.

Another illusion, which must have been frequently noticed by all who have paid any attention to the operation of the organs of sense, is the indistinctness of indirect vision. If we fix the eye steadily upon any object, while the mind is intently engaged upon any subject, it loses sight, by fits, of the objects which surround it; that is, all those which are seen indirectly. Fix a round piece of white paper upon a coloured ground, and near it place a strip of white paper-then fix the eye steadily upon one, and the other will be lost sight of. The eye is, in fact, only able to see distinctly those objects on which it is directly fixed; but this defect is, in some degree, compensated for by its extreme sensi. bility to colour.

This is, no doubt, under certain circumstances, the cause of many of those apparitions which are so often declared to have been seen. In the broad glare of day, when objects are fully illuminated, the slightest motion of the eye will restore any object, seen obliquely, to its perfect form. But, in an apartment where there is only a single gleam of indistinct light, or elsewhere at the time of twilight, a very small amount of light is reflected by bodies, and in consequence of this the indistinct oblique vision is not easily corrected by direct sight.

Another illusion worthy of notice is, the capability of the eye to retain a luminous impression after the object has been withdrawn. According to the experiments of M. D'Arcet, a luminous impression is retained on the retina about the eighth part of a second after the body itself has been removed. The Thaumatrope, or wonder-turner, is constructed on this principle. It consists of a card, with different objects, or parts of an object, on opposite sides; which are so placed, that when a whirling motion is given to it, the objects are united. Thus, a part of a scene may be painted on one side, and the remaining part on the other. When the card is caused to revolve, the objects painted on the reverse sides will be united, and a continuous landscape will be seen, as though it were painted only on one side, which results from the duration of the impression upon the retina after the body has been removed.

In connexion with this subject, we may mention the phenomenon of ocular spectra, or accidental colours. If the eye has been steadfastly fixed upon a coloured light, and be then moved to a white surface, the eye will not convey the impression of either the white or the coloured surface, but a colour differing from both; and that colour, whatever it may be, is called the ocular spectrum. Thus, if we paint an object red upon a white ground, and fix the eye steadily upon it for a few seconds, a blueish-green figure will be seen, when the eye is turned upon a white surface; a blueish-green, therefore, is the accidental colour of red. Different colours have different ocular spectra: that of orange, is blue; of violet, yellow; and of black, white. The law of accidental colour is most remarkable. The accidental colour, or ocular spectrum of any colour in the spectrum, is that colour which is distant from it one half of the spectrum. Thus, if we take half the length of the spectrum by a pair of compasses, and fix one leg of the compasses in the colour, the other leg will be in the accidental

colour.

We are frequently subject to illusions from this phenomenon, of which we are quite unconscious; for, in every instance in which the eye is intently fixed upon any coloured surface, the accidental colour is produced when it is removed. If the objects be highly illuminated, and the eye be fixed upon it for any length of time, the spectra will be in some degree permanent, and may become dangerous to vision. Sir Isaac Newton's experiments are applicable to this point; but as they are very generally known, as detailed in Sir David Brewster's Natural Magic, it will only be necessary to recall them to the

reader's memory. After looking at a reflected image of the sun several times, the spectra became so permanent, that a picture of the sun was apparently painted on every bright object at which he looked. So seriously was his vision affected by his experiments, that he found it necessary to shut himself in a dark chamber for three days, before he could recover the use of his eyes: and, when writing to Locke on the subject, many years after, he says, "I am apt to think, if I durst venture my eye, I could still make the phantasm return by the power of my fancy."

In all the cases we have mentioned, the eye deceives us without being at all influenced by an indisposition of body, though the deception will be sometimes increased by a particular state of ill health. But spectral apparitions, whether occasional or permanent, are chiefly, if not entirely, produced by a morbid state of action in some of the vital funetions, which has a direct, though unaccountable action upon the imagination. The real cause of this phenomenon is the recalling of images, which have been before painted on the retina, by the united action of memory and imagination :

It will be hardly necessary to mention instances of spectral appearances, for but few persons are unacquainted with the works of Hibbert and of Scott. One of the most interesting cases that I remember, is that mentioned by Sir Walter, as having passed under the notice of one of his medical friends. A gentleman standing high in the legal profession, had been many years afflicted by an apparition, which had constantly attended him, and produced a state of irritation that had brought him into a weak and debilitated condition of body. In this stage of the disease, Sir Walter's friend was called in, for advice, and, after some time, extorted a confession of the source of all the debility and dejection under which the patient was labouring. When this apparition first presented itself to him, it was in the form of a cat. This apparition, however, was not a source of much annoyance; but, after a few months, the cat left him, and a gentleman-usher suddenly made his appearance, who, in his court-dress, became his constant attendant, bowing to him from place to place, and waiting near him in his own apartments. In a few months this phantasm likewise disappeared, and was followed by one of a far less amusing character, by that form which a healthy imagination can hardly paint with steadiness a skeleton. Conscious of the unreality of the appearance, he endeavoured to divest his imagination of the form, but the gloomy apparition never left him, alone or in company, and he died from the depression of spirit and debilitation of body which it occasioned.

These are a few instances in which the eye itself deceives; nor are the other senses, in proportion to the number of sensations conveyed by them, more worthy of our entire dependence. Do we not, then, live in vain show? and is it not necessary that some effort should be made, by which we may be able to correct the errors to which we are exposed on every hand? But man is not satisfied with being deceived through and by his sensations, but in every age of the world has sought, by an application of the know ledge he has acquired, to deceive others.

There can be little doubt that the mysteries of the oracles among the Greeks and Romans were philosophical impostures. At the cave of Trophonius, and the oracle of Delphi, these practices were probably conducted with more skill than at any other places. The man who is unacquainted with the facilities of deception in the hands of the philo sopher, can hardly divine the methods by which the wonders of the temple were accomplished. To such an individual, the records of the philosophical historians of the period must be enigmas. It is difficult to imagine that Plutarch, and Herodotus, and Pliny, and Cæsar, and Tacitus, were deceived as to the scenes which transpired in the sacred houses of the Greeks and Romans; and if he admit, for one moment, the veracity of the historians, he will be tempted to account for the appearance presented to the worshipper in the Grecian and Roman temples, as a direct interference of demoniacal influence. Philosophy, when misapplied, is as capable of deceiving mankind, as it is suited to its improvement when directed by a spirit of philanthropy and universal freedom. What a mighty engine is at present in the power of the natural philosopher, were he

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