of sounds, depending apparently upon an impression communicated to their organs of touch or simple sensation. They could tell, for instance, the approach of a carriage in the street, without seeing it, before it was taken notice of by persons who had the use of all their senses. An analogous fact is observed in the habit acquired by the deaf and dumb, of understanding what is said to them by watching the motion of the lips of the speaker. Examples still more wonderful are on record, but certainly require confirmation. A story, for instance, has lately been mentioned in some of the medical journals, of a gentleman in France who lost every sense, except the feeling of one side of his face; yet it is said that his family acquired a method of holding communication with him, by tracing characters upon the part which retained its sensation.

Much ingenuity has been bestowed upon attempts to explain how, with two eyes, we see only one object; and why that object is seen erect, when we know that the image on the retina is inverted. All that need be said upon the subject, and all that can properly be said, appears to be, that such is the constitution of our nervous system. It is on the same principle, that by the sense of touch, in which may be concerned a thousand or ten thousand distinct points of contact, we receive the impression of only one body; or, what perhaps may appear a more strictly analogous case, we receive the impression of but one body, though we grasp the substance with two hands, or with ten distinct fingers. For the healthy perception in both these cases, however, a certain arrangement is required, which we may call the natural harmony of the nervous system; and when this harmony is disturbed, the result is remarkably altered. Thus, squinting produces the vision of a double image,* because the images fall upon what we may call unharmonizing points of the retina; and the same principle may be illustrated in à very curious manner by a simple experiment with the

This effect may easily be produced by pressing one of the eyes a little out of its natural position by means of the finger at the corner of it, while looking at a single object. It will be made to appear double.

Extraordinary case of a gentleman in France. object appears single and direct. Analogous case.

Difficulty of explaining why the
Effect of squinting, what?

sense of touch. If a small round body, such as a pea, be laid upon the palm of the one hand, and rolled about between the first and second fingers of the other, in their natural position, one pea only is felt; but, if the fingers are crossed, so that the pea is rolled between the opposite surfaces of the two fingers, a most distinct impression of two peas is conveyed.

Of the whole of the remarkable process of sensation and perception, we know nothing but the facts, that certain impressions made upon the organs of sense are followed by certain perceptions in the mind; and that this takes place, in some way, through the medium of the brain and nervous system. We are in the habit of saying, that the impressions are conveyed to the brain; but, even in this, we probably advance a step beyond what is warranted. We know that the nerves derive their influence from their connection with the brain, or as forming along with it one great medium of sensation; but we do not know whether impressions made upon the nervous fabric connected with the of sense organs are conveyed to the brain; or whether the mind perceives them directly, as they are made upon the organs of sense. The whole subject is one of those mysteries which are placed above our reach, and in which we cannot advance a single step beyond the knowledge of the facts. Any attempt to speculate upon it is therefore to be considered as contrary to the first principles of philosophical inquiry. We must simply receive the facts as of that class which we cannot account for in the smallest degree; and the evidence which we derive from our senses, of the existence and properties of the things of the material world, is to be recognised as one of those fundamental laws of belief which admit of no other proof than that which is found in the universal conviction of mankind.

Before concluding the subject of perception, it remains to be noticed that a certain voluntary effort is required for the full exercise of it; or, at least, for that degree of perception which leaves an impression capable of being retained. It is familiar to every one, that when the mind is closely occupied, numerous objects may pass before our eyes, and cir

Experiment with the touch. Extent of our knowledge of sensation. The brain. Difficulty of the subject. Voluntary effort necessary. Evidence of it.

sumstances may be talked of in our hearing, of which we do not retain the slightest recollection; and this is often in such a degree as implies, not a want of memory only, but an actual want of the perception of the objects. We cannot doubt, however, that there was the sensation of them; that is, the usual impression made upon the eye in the one case, and the ear in the other. What is wanting, is a certain effort of the mind itself, without which sensation is not necessarily followed by perception;-this is what we call Attention. It is a state or act of the mind which is exercised by different individuals in very different degrees. It is much influenced by habit; and though it may not often be wanting in such a degree as to prevent the perception of objects, it is often deficient in a manner which prevents the recollection of them, and consequently has an extensive influence upon the intellectual character.

The effect of attention is illustrated by various mental phenomena of daily occurrence. If we are placed in such a situation that the eye commands an extensive landscape, presenting a great variety of objects, or the wall of an apartment covered with pictures, we have the power of fixing the mind upon one object in such a manner that all the rest become to us nearly as if they did not exist. Yet we know that they are actually seen, as far as the mere sense of vision is concerned; that is, images of all of them are formed upon the retina; but they are not objects of attention, or of that peculiar voluntary effort of mind which is necessary for the full perception of them. In the same manner, a practised musician can, in the midst of a musical performance, direct his attention to one part, such as the bass,-can continue this for such a time as he pleases, and then again enjoy the general harmony of the whole. On the same principle, the mind may be so intensely fixed upon something within itself, as an object of conception or memory, or a process of reasoning, as to have no full perception of present external impressions. We shall afterward have occasion to refer to a state of mind in which this exists in such a degree, that objects of conception or memory are believed to have a real and present existence; and in which this erro

Name of this? Effect of attention illustrated. In the sense of sight. Of hearing.

neous impression is not corrected by impressions from external things-this occurs in insanity.

Attention is very much influenced by habit; and connected with this subject there are some facts of great inte rest. There is a remarkable law of the system, by which actions at first requiring much attention are after frequent repetition performed with a much less degree of it, or without the mind being conscious of any effort. This is exemplified in various processes of daily occurrence, as reading and writing, but most remarkably in music. Musical performance at first requires the closest attention, but the ef fort becomes constantly less, until it is often not perceived at all; and a lady may be seen running over a piece of music on a piano, and at the same time talking on another subject. A young lady, mentioned by Dr. Darwin, executed a long and very difficult piece of music with the utmost precision, under the eye of her master; but seemed agitated during the execution of it, and when she had concluded, burst into tears. It turned out that her attention had, during the whole time, been intensely occupied with the agonies of a favorite canary-bird, which at last dropped dead in its cage. We see the same principle exemplified in the rapidity with which an expert arithmetician can run up a long column of figures, without being conscious of the individual combinations. It is illustrated in another manner by the feats of jugglers, the deception produced by which depends upon their performing a certain number of motions with such rapidity that the attention of the spectators does not follow all the combinations.

In teaching such arts as music or arithmetic, this principle is also illustrated; for the most expert arithmetician or musical performer is not necessarily, and perhaps not generally, the best teacher of the art; but he who, with a competent knowledge of it, directs his attention to the individual minute combinations through which it is necessary for the learner to advance.

In processes more purely intellectual, we find the influence of habit brought under our view in a similar manner,

Influence of habits of attention. Illustrations. Anecdote of the young lady. Other illustrations. Illustration of this principle from the art of teaching. Influence of habit in facilitating intellectual processes.

particularly in following the steps of a process of reason. ing. A person little accustomed to such a process advances step by step, with minute attention to each as he proceeds; while another perceives at once the result, with little consciousness of the steps by which he arrived at it. For this reason, also, it frequently happens that in certain departments of science the profound philosopher makes a bad teacher. He proceeds too rapidly for his audience, and without sufficient attention to the intermediate steps by which it is necessary for them to advance; and they may derive much more instruction from an inferior man, whose mental process on the subject approaches more nearly to that which, in the first instance, must be theirs. We remark the same difference in public speaking and in writing; and we talk of a speaker or a writer who is easily followed, and another who is followed with difficulty. The former retards the series of his thoughts, so as to bring distinctly before his hearers or his readers every step in the mental process. The latter advances without sufficient attention to this, and consequently can be followed by those only who are sufficiently acquainted with the subject to fill up the intermediate steps, or not to require them.

There is a class of intellectual habits directly the reverse of those now referred to; namely, habits of inattention, by which the mind, long unaccustomed to have the attention. steadily directed to any important object, becomes frivolous and absent, or lost amid its own waking dreams. A mind in this condition becomes incapable of following a train of reasoning, and even of observing facts with accuracy and tracing their relations. Hence nothing is more opposed to the cultivation of intellectual character; and when such a person attempts to reason, or to follow out a course of investigation, he falls into slight and partial views, unsound deductions, and frivolous arguments. This state of mind, therefore, ought to be carefully guarded against in the young; as, when it is once established, it can be removed only by a long and laborious effort, and after a certain period of life is probably irremediable.

In rude and savage life remarkable examples occur of

Bad teaching. Public speaking. Habits of inattention. Consequences? Habits of attention in savage life.