tions of the particles of certain bodies. The material substances which have this quality are termed sonorous, as wood, brass, iron, &c.; but it exists in different bodies in very various degrees.

The quality of sonorousness, therefore, in any substance, is properly a susceptibility of motion among its own parts. When it is forcibly struck, this motion exists first in itself, and is afterward communicated to the circumambient air. The movement of the air which is thus caused, is again communicated, like the concentric waves of water agitated by a stone thrown into it, to other portions successively, till it reaches the ear.

The air, accordingly, is the medium of communication between the sonorous body and the tympanum of the ear. It is true that many solid bodies are good conductors of sound as well as the atmosphere; but as portions of air, through which the vibratory motion must of course pass, are in all cases interposed between that organ and the sounding body, it is not necessary to dwell upon them here. It is sufficient for our present purpose merely to understand, that there is in every sounding body, in the first place, a vibratory motion among its own particles from some cause or other; that this vibration or undulation is communicated from the sounding body to the air, and from one portion of air to another, till it reaches the organ of hearing. Why the internal sensation should at once follow the completion of this process is another inquiry, which we do not undertake to explain. We have before us the antecedent and the consequent, the affection of the organ of hearing by an outward impulse, and the new mental state within; but the reason of this invariable connexion in two things that are entirely distinct and different, is a matter beyond our limited comprehension.

65. Varieties of the sensation of sound.

The sensations which we thus become possessed of by the hearing, are far more numerous than the words and the forms of speech, having relation to them in different languages, would lead us to suppose. It will help to illustrate this subject if we recur a moment to the sense of TASTE. The remark has somewhere been made to this ef

fect, and probably with much truth, that if a person were to examine five hundred different wines, he would hardly find two of them of precisely the same flavour. The diversity is almost endless, although there is no language which distinguishes each variety of taste by a separate name. It is the same in respect to the sensations of sound. These sensations exhibit the greatest variety, although the differences are too minute to be separated and distinctly represented by language.

These views will appear the less objectionable, when it is remembered that sounds differ from each other both in the tone and in the strength of the tone. It is remarked by Dr. Reid, that five hundred variations of tone may be perceived by the ear; also an equal number of variations in the strength of the tone; making, as he expressly informs us, by a combination of the tones and of the degrees of strength, more than twenty thousand simple sounds, differing either in tone or strength.

In a perfect tone, a great many undulations of elastic air are required, which must be of equal duration and extent, and follow each other with perfect regularity. Each undulation is made up of the advance and retreat of innumerable particles, whose motions are all uniform in direction, force, and time. Accordingly, there will be varieties also and shades of difference in the same tone, arising from the position and manner of striking the sonorous body, from the constitution of the elastic medium, and from the state of the organ of hearing.

Different instruments, such as a flute, a violin, and a bass viol, may all sound the same tone, and yet be easily distinguishable. A considerable number of human voices may sound the same note, and with equal strength, and yet there will be some difference. The same voice, while it maintains the proper distinctions of sound, may yet be varied many ways by sickness or health, youth or age, and other alterations in our bodily condition to which we are incident.

§ 66. Manner in which we learn the place of sounds.

It is a fact worthy of notice in respect to sounds, that we should not know, previous to all experience on the sub

ject, whether a sound came from the right or left, from above or below, from a smaller or a greater distance. And this will appear the less surprising, when we remember, that the undulations of air are always changed from their original direction by the channels and the windings of the ear before they strike the tympanum. Abundant facts confirm this statement.

Dr. Reid mentions, that once, as he was lying in bed, having been put into a fright, he heard his own heart beat. He took it to be some one knocking at the door, and arose, and opened the door oftener than once before he discovered that the sound was in his own breast. Some trayeller has related, that when he first heard the roaring of a lion in a desert wilderness, not seeing the animal, he did not know on what side to apprehend danger, as the sound seemed to him to proceed from the ground, and to enclose a circle, of which he and his companions stood in the

centre.

It is by custom or experience that we learn to distinguish the place of things, and, in some measure also, their nature, by means of their sound. It is thus that we learn that one noise is in a contiguous room, that another is above our heads, and another is in the street. And what seems to be an evidence of this is, that when we are in a strange place, after all our experience, we very frequently find ourselves mistaken in these respects.

If a man born deaf were suddenly made to hear, he would probably consider his first sensations of sound as originating wholly within himself. But, in process of time, we learn not only to refer the origin of sounds to a position above or below, to the right or left, but to connect each particular sound with a particular external cause, referring one to a bell as its appropriate external cause, another to a flute, another to a trumpet.

§ 67. Application of these views to the art of ventriloquism. We are naturally led to make a few remarks here in explanation of VENTRILOQUISM, a well-known art, by which persons can so modify their voice as to make it appear to their audience to proceed from different objects, distances, and directions. There is no peculiarity of structure

in ventriloquists, as is often supposed; except that the capacity of the chest and the lungs is sometimes found to be greater than usual. It is also true, that the power and activity of the muscles, connected with the organs of speech and with the chest and lungs, is considerably increased by frequent exercise. Nevertheless, the great natural requisite on the part of the ventriloquist is to be able to mimic sounds; and he will be likely to succeed nearly in proportion to his skill in this particular. The secret, then, of his acoustic deceptions, supposing him to be capable of exact imitation, will be sufficiently understood by referring to the statement maintained in the preceding section, viz., That, previous to experience, we are unable to refer sounds to any particular external cause.

The sound itself never gives us any direct and immediate indication of the place, or distance, or direction of the sonorous body. It is only by experience, it is only by the association of place with sound, that the latter becomes an indication of the former. Now supposing the ventriloquist to possess a delicate ear, which is implied in his ability to mimic sounds, he soon learns, by careful observation, the difference which change of place causes in the same sound. Having in this way ascertained the particular modulations of sound, which, in accordance with the experience of men and the associations they have formed, are appropriate to any particular distances, direction, or object, it is evident, whenever he exactly or very nearly imitates such modulations, that the sounds must appear to his audience to come from such distance, object, or direction.

One part of the art, however, consists in controlling the attention of persons present, and in directing that attention to some particular place by a remark, motion, or some other method. If, for instance, the sound is to come from under a tumbler or hat, the performer finds it important to have their attention directed to that particular object, which affords him an opportunity for the exercise of all those associations which they have formed with any sound coming from a very confined place. All, then, that remains for him to do, is to give his voice a dull modulation and on a low key, which we know from our experience

to be the character of confined sounds. Then there seems to be a voice speaking under a tumbler or hat; and if any person should, either intentionally or unintentionally, lift these articles up, the ventriloquist immediately utters himself more distinctly and freely, like a person who has been very much confined on being readmitted into the free and open air. It is also necessary, when his face is towards his auditors, that he should make use chiefly of the muscles of the throat; an outward and visible moving of the lips would much weaken the deception.

68. Uses of hearing and its connexion with oral language. Although, as in the cases just mentioned, the artifices of men may sometimes impose upon this organ and lead its decisions astray, it is one, in the ordinary calls for its exercise, of exceeding value. One of the distinguished benefits of the sense of hearing is, that, in consequence of it, we are enabled to hold intercourse with each other by means of spoken language, without which the advancement of the human mind must have inevitably been very limited. It is by means of speech that we express our feelings to the little company of our neighbours and our own family; and without it this pleasant and cheering intercourse must be almost entirely suspended. Not limited in its beneficial results to families and neighbourhoods, it has been the medium of the transmission of thought from age to age, from generation to generation. So that in one age has been concentrated the result of all the researches, the combination of the wisdom of all the preceding.

"There is, without all doubt," it has been observed, "a chain of the thoughts of human kind, from the origin of the world down to the moment at which we exist, a chain not less universal than that of the generation of every being that lives. Ages have exerted their influence on ages; nations on nations; truths on errors; errors on truths."

Whether oral language was an original invention of man, or whether, in the first instance, it was a power bestowed upon him by his Creator and coeval with the human race, the ear must, in either case, have been the pri