« PreviousContinue »
serena, so as to press, without and behind the ball upon the silken cord, all correspondence between the soul and the world by means of the eye is suspended or destroyed. It is very evident that even when the eye has the most complete soundness, it is still nothing more than an organ or an instrument. When a man is lost in thought, rays of light from many objects in his neighbourhood may fall upon his eye, and form the appropriate images, and yet the mind may have no consciousness of them. A friend may enter the room or retire from it; he may have stood before us, and yet we may not be at all conscious of his presence or his departure. And there is such a thing as merely bodily vision—a man walking on a road is so taken up with some subject of reflection as to be unconscious of his progress or his fatigue, and yet may be so far alive and awake to the world about him as to step aside from a stone in his path. Science can tell us nothing more, and perhaps it would be difficult, if not impossible, to give a satisfactory reason why we do not see with the tip of the finger, with the nostril, or with the tongue. No image, it is true, is or can be formed on these by the rays of light; but we cannot form a conjecture how the immaterial mind is benefited or assisted in its apprehension of visibles by means of the images.
THE ANATOMY OF THE EAR.
We propose to follow a different course in this part of our subject from that which we adopted in the former. We shall preface a few remarks on the construction of this organ, by touching on the theory of hearing, and thus shall clear our way to the great argument of our theme. Sound is nothing more than air in motion; and in order to conceive aright on the
subject, we must call to mind that we are moving in an ocean of fluid matter, whose tides are the winds, and whose waves are the media of all oral communication. The manner in which the air is proved to be the medium of sound is as follows: A bell which rings by clock-work is put into the glass receiver of an air-pump, and just as the air is withdrawn, (although the stroke of the tongue or clapper be observably given with equal force,) the sound decays till it dies away upon the ear. It may be proper to mention here the properties of a wave, or, as it is called, a pulse, of air :
1. It is spherical. A wave upon the water (as a stone thrown into a lake will show) is of a circular shape; on the contrary, a wave of air is of a spherical form, like the longitudinal section of an egg: hence a place of worship should always have its longest diameter from the pulpit to the front wall: and hence the most remote seats in the side galleries of a chapel that is nearly square are altogether unfit for hearing with ease and distinctness.
2. The pulses of air decrease in condensation, and enlarge in volume, as they proceed from the vibrating body; and hence they are less and less distinct; i. e., as they retire from the spot whence they originate, the waves become shallower. This will be perfectly understood by calling to recollection what we have observed in the waves enlarging from the centre on a sheet of water.
3. They have all equal velocity, whether strong or faint; and the reason is, that the velocity depends upon the elasticity of the air, which cannot be altered by the character of the vibration, whether powerful or weak; that is, the wave rolls on with the same speed whether it be deep or shallow.
4. All the pulses of the same sonorous body are equal in breadth, and given in equal times.
5. Sounds may be propagated from several different bodies, and be all of them distinctly heard; the one not interrupting the other: thus, for example, a concert of music is a compound of many sounds, blended and yet distinct. Concords in music occur when two waves of different volume strike the ear together; discords, when two or more waves strike irregularly. A grave sound, called a flat in music, is a broad wave with an intermission of equal breadth; an acute sound, or sharp, is a narrow wave, with a narrow interstice.
6. Pulses of air, like waves of water, are capable of reverberation, or of being floated back from the obstruction that they first meet; whence the mystery of echo is explainable. Sound travels at the rate of 1142 feet in a second; and by counting with care the interval between the report and echo of a pistol, you may calculate the breadth of a river; if the man who discharges it be on one side, and there be a wall or rocky bank on the other. Divide the number of seconds by two, and multiply the result by 1142. Woodstock Park has an echo of such compass as that a whole line of poetry may be reverberated.
It is by conventional use and habit that sound is the medium of distinct communication, and the vehicle of thought. The eye receives images of the objects contemplated; but the sounds received by the ear have no natural or necessary connection with the idea, or otherwise all languages would be alike.
Proceed we now to the organ of hearing.
It is seated at each side of the head; and thus there is a double organ; probably for the reason that there were two consuls at Rome, namely, that if one died, or
became otherwise incapable, the other should sustain the duties of the office. The situation of the external ear is one which man, had the choice been left to him, might not have selected; and yet it is one, now that the matter has been determined by the highest wisdom, which appears the best, and the only one.
The shape and material of the outer ear are matters worthy of attention. The figure is that of a sphere, in this respect corresponding to the form of the pulses of air. The inner part of the sphere has scooped cavities, which doubtless, in a way not well understood, tend to condense the air, and to deepen the sound. The outer ear is composed of cartilage, a substance half way between bone and skin, and of all others the most elastic were it of skin, it would hang down, and thus greatly weaken the faculty of hearing; were it of bone, it would not only be liable to accident, and especially to fracture; but would also yield less, if at all, to the pulses of air and thus more delicate sounds would entirely be lost to us, and one high source of gratification would have been altogether forfeited. The outer ear is capable, from its material, of light tremulous motion from the air; too minute to be seen, and yet very important for the use of the organ. Some have ima, gined that we should have had as much power by the muscles to move the ear as brutes are possessed of, were it not for the foolish custom of bandaging the heads of children; but this is idle conjecture; for we have not, in consequence of our erect posture, and greater facilities for turning the head, and of moving round the body, the same occasion for a ready faculty of turning the ear which brutes have.
The more difficult task now comes to be attempted, that of describing the inner ear.
Across the bottom of the canal, leading inward from the outer ear, (and into which we can introduce the finger,) lies a fine membrane, called, very appropriately, "the head of the drum ;" for such it is in fact. Within this membrane there is a cavity, supposed to be about half the size of the last joint of the little finger,the air floating up against the drum-head sets it into a tremulous motion,-stronger or weaker, quicker or slower, just as the case may be. On the inside of the drum-head are four small bones, so small that you can only see them distinctly when they are taken out, and placed upon coloured paper. One of these, fancifully called the hammer, is fastened at the handle to the drum-head; its motion bends down the hammer upon the pellicle of bone, called the anvil; the anvil communicates the shock to the minute globe, and that transmits it to the stirrup. The edge of the stirrup stretches out of the body of the drum into a little arched cavity farther into the bone: (namely, the temporal bone, in which the whole apparatus of hearing is lodged, and which in order to serve that purpose, is, perhaps, the hardest in the whole body:) in this inner cavity there is a small quantity of water spread over the thread-like nerve of hearing: the nerve receives its impression from the motion communicated to the water; and to amplify and diversify the impression, as it would seem, the drum, the bones, the two cavities already mentioned, and another of a spiral form, are all designed. In some way, which human wisdom hath never discovered, this impression made on the nerve is carried along its course into the brain; the soul there hears the tidings from its messenger, and meditates in its inner council-chamber on the things of which it is advised by its servants without.