the effect of habits of minute attention to those circumstances to which the mind is intensely directed by their relation to the safety or advantage of the observer. The American hunter finds his way in the trackless forests by attention to minute appearances in the trees, which indicate to him the points of the compass. He traces the progress of his enemies or his friends by the marks of their footsteps; and judges of their numbers, their haltings, their employments, by circumstances which would entirely escape the observation of persons unaccustomed to, a mode of life requiring such exercises of attention. Numerous examples of this kind are mentioned by travellers, particularly among the aboriginal natives of America.

OF FALSE PERCEPTIONS.

BEFORE leaving this subject, it is necessary to refer to some remarkable facts respecting perceptions taking place, without the presence of any external body corresponding with them. These are called false perceptions, and they are usually referred to two classes; namely, those arising in the organs of sense, in which the mind does not participate; and those which are connected with hallucination of mind, or a belief of the real existence of the object. The former only belong to this part of the subject. The latter. will be referred to in another part of our inquiry, as they do not consist of false impressions on the senses, but depend upon the mind mistaking its own conceptions for real and present existences.

Of false perceptions, properly so called, the most familiar are the musca volitantes floating before the eyes, and sounds in the ears resembling the ringing of bells, or the noise of a waterfall. Changes are also met with in the organs of sense giving rise to remarkable varieties of perception. Dr. Falconer mentions a gentleman who had such a morbid state of sensation that cold bodies felt to him as if they were intensely hot. A gentleman mentioned by Dr. Conolly, when recovering from measles, saw objects dimi

Examples? False perceptions-what? How classified? Common examples.

nished to the smallest imiginable size; and a patient mentioned by Baron Darry, on recovering from amaurosis, saw men as giants, and all objects magnified in a most remarkable manner it is not mentioned how long these peculiarities continued. This last peculiarity of perception occurred also to a particular friend of mine in recovering from typhus fever. His own body appeared to him to be about ten feet high. His bed seemed to be seven or eight feet from the floor, so that he felt the greatest dread in attempting to get out of it; and the opening of the chimney of his apartment appeared as large as the arch of a bridge. A singular peculiarity of this case however was, that the persons about him with whom he was familiar did not appear above their natural size. But the most interesting pheno mena connected with affections of this kind are furnished by the various modifications of spectral illusions These are referable to three classes.

I. Impressions of visible objects remaining for sede time after the eye is shut, or has been withdrawn from them; generally accompanied by some remarkable change in the color of the objects. Various interesting experiments of this kind are related by Dr. Darwin; one of the most striking is the following:- "I covered a paper about four inches square with yellow, and with a pen filled with a blue color wrote upon the middle of it the word BANKS in capitals; and sitting with my back to the sun, fixed my eyes for a minute exactly on the centre of the letter N in the word. After shutting my eyes, and shading them somewhat with, my hand, the word was distinctly seen in the spectrum, in yellow colors on a blue ground; and then on opening my eyes on a yellowish wall at twenty feet distance, the magnified name of BANKS appeared on the wall written in golden characters."

With a very little ingenuity, this kind of spectral illusions can be easily produced in great variety. Take a common red wafer, and lay it upon a sheet of white paper. Bring the eye down to within six or eight inches of it, and gaze very steadily and intently upon it for the space of twenty or thirty seconds. On moving the eyes away, a beau

False perception of magnitude. Examples of this. Spectral illusions; how many classes? First class? Darwin's experiments? Easy mode of producing these illusions.

tiful light blue spot, of the size and shape of the wafer, will be seen on the sheet, and will follow the eyes as they move from side to side. By cutting the wafer in two, or notching its surface, or varying its form in any way, a corresponding variety in the form of the blue spot will be produced. The effect may be varied also by using wafers of a different color, or even by bright pictures of various colors combined. The stronger the light, the more striking will be the effect. It ought to be added, that persons of weak eyes should be very cautious in trying these experiments.

A friend of mine had been one day looking intensely at a small print of the Virgin and Child, and had sat bending over it for some time. On raising his head he was startled by perceiving, at the farther end of the apartment, a female figure, the size of life, with a child in her arms. The first feeling of surprise having subsided, he instantly traced the source of the illusion, and remarked that the figure corresponded exactly with that which he had contemplated in the print, being what painters call a kit-cat figure, in which the lower parts of the body are not represented. The illusion continued distinct for about two minutes. Similar illusions of hearing are met with, though less frequently than those of vision. A gentleman recently recovered from an affection of the head, in which he had been much reduced by bleeding, had occasion to go into a large town a few miles from his residence. His attention was there, attracted by the bugle of a regiment of horse, sounding a particular measure which is used at changing guard in the evening. He assured me that this sound was from that time never out of his ears for about nine months. During all this period he continued in a very precarious state of health; and it was only as his health became more confirmed that the sound of the bugle gradually left him. In regard to ocular spectra, another fact of a very singular nature appears to have been first observed by Sir Isaac Newton,—namely, that when he produced a spectrum of the sun by looking at it with the right eye, the left being covered, upon uncovering the left, and looking upon a white ground, a spectrum of the sun was seen with it also. He likewise acquired the power of recalling the spectra, after they had ceased, when he went into the dark, and directed his mind intensely,

Modes of varying the experiments. Caution. Illusion produced by looking at a print? Illusions of hearing. Newton's experiments?

as when a man looks earnestly to see a thing which is difficult to be seen." By repeating these experiments frequently, such an effect was produced upon his eyes, "that for some months after," he says, "the spectrum of the sun began to return as often as I began to meditate upon the phenomena, even though I lay in bed at midnight with my curtains drawn."

II. Impressions of objects recently seen returning after a considerable interval. Various interesting examples of this kind are on record. Dr. Ferriar mentions of himself, that when about the age of fourteen, if he had been viewing any interesting object in the course of the day, as a romantic ruin, a fine seat, or a review of troops, so soon as evening came, if he had occasion to go into a dark room, the whole scene was brought before him with a brilliancy equal to what it possessed in daylight, and remained visible for some minutes.

III. False perceptions arising in the course of some bodily disorder, generally fever. A lady whom I attended some years ago, in a slight feverish disorder, saw distinctly a party of ladies and gentlemen sitting round her bedchamber, and a servant handing, something to them on a tray. The scene continued in a greater or less degree for several days, and was varied by spectacles of castles and churches of a very brilliant appearance, as if they had been built of finely cut crystal. The whole was in this case entirely a visual phantasm, for there was no hallucination of mind. On the contrary, the patient had from the first a full impression that it was a morbid affection of vision, connected with the fever, and amused herself and her attendants by watching and describing the changes in the scenery. Α gentleman who was also a patient of mine, of an irritable habit, and liable to a variety of uneasy sensations in his head, was sitting alone in his dining-room in the twilight, the door of the room being a little open. He saw distinctly a female figure enter, wrapped in a mantle, and the face concealed by a large black bonnet. She seemed to advance

Second class? Examples. Third class? Example; the sick lady. The mind, in what state, in this case? Second example ? *

a few steps towards him and then stop. He had a full conviction that the figure was an illusion of vision, and amused himself for some time by watching it; at the same time observing that he could see through the figure, so as to perceive the lock of the door and other objects behind it. At length, when he moved his body a little forward, it disappeared. The appearances in these two cases were entirely visual illusions, and probably consisted of the renewal of real scenes or figures, in a manner somewhat analogous to those in Dr. Ferriar's case, though the renewal took place after a longer interval. When there is any degree of hallucination of mind, so that the phantasm is believed to have a real existence, the affection is entirely of a different nature, as will be more particularly mentioned under another part of our subject.

False perceptions may be corrected by one of three methods; by the exercise of other senses by a comparison with the perceptions of other persons and by an exercise of judgment. If I suspect that my eye deceives me, I apply the hand, with the perfect conviction of the improbability that the two senses should be deceived at once. If this cannot be done, I appeal to the impressions of some other persons, with an equally strong.conviction that the same sense will not be deceived in the same manner in several persons at once. Or I may do it in another way, by a reference to some known and fixed object. Suppose, for example, I see two objects where I imagine there should be but one, and suspect a visual deception; I turn my eyes to some object which I know to be single- such as the sun. If I see the sun double, I know that there is a delusion of vision; if I see the sun single, I conclude the original perception to be correct. These processes imply a certain exercise of judgment; and there are other cases in which the same conviction may arise from an exercise of judgment, without any process of this kind. In one of the cases now referred to, for example, the correction took place instantly, from observing that the lock of the door was seen as if through the figure.

Explanations. Correcting false impressions, in what ways? First method? Second

method?