chamber full of liquid, and containing also a membranous expansion for the distribution of the nerve of hearing. Let us next advert to the action of these different parts in producing the sensations of sound.

3. The waves of sound enter the passage of the outer ear, and strike the membrane of the tympanum. The structure of the outer ear is adapted to collect and concentrate the vibrations like an ear-trumpet. The form of the shell gives it a reflecting surface for directing the sound inwards; while the passage is believed to increase their intensity by resonance. Reaching the membrane of the tympanum, the beats communicate themselves to its surface and set it vibrating, which is done all the more easily that the membrane is very thin and light in its structure. Experiments have shown, that the only means of receiving with effect the vibrations of the air, is to provide a thin stretched membrane of this nature. The vibrations of the membrane are communicated to the chain of small bones traversing the middle ear, and connected through the oval foramen with the enclosed liquid of the inner ear. By these means a series of beats are imparted to the liquid, which diffuse themselves in waves all through the passages of the labyrinth, and operate by compressing the membranous labyrinth, and through it the imbedded fibres of the auditory nerve, which compressions are the immediate antecedent of the sensation of hearing. The character of the sensation will of course vary with the character of the waves, according as they are violent or feeble, quick or slow, simple or complex, and so forth.

There is little difference of opinion as to the general course of the action now described. The transitions have all been imitated by experiments, and it has been found that the arrangement is a good one for bringing about the ultimate effect, namely, the gentle compression of the filaments of the nerve of hearing. No other medium could serve the final contact so well as a liquid, but in order to impress the liquid itself, an intermediate apparatus between it and the air is

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requisite. This intermediate apparatus is solid, and composed of two parts, the first a light expanded membrane, susceptible to the beats of the air, the second firm and compact (the chain of bones), to produce a sufficiently powerful undulation in the liquid. The membrane once affected is able to communicate vibrations to the bones; and the last of the chain, the stapes, is able to impress the labyrinthine fluid. So far the process has been rendered sufficiently intelligible.

The separate functions of the different parts of the inner ear are not understood. In the cochlea (the most important part), the membrane wherein the nerve is spread takes on peculiar tooth-shaped forms, and also contains elastic films or laminæ. The length of each lamina is about 7 of an inch, and their thickness Too of an inch. The laminæ lie upon the ends of the tooth-shaped forms, and are arranged like the keys of a piano, and closely packed together. Wundt believes that different tones affect different parts of the nerve of hearing thus disposed, and that as elastic bodies respond each to some particular tone, and remain quiet when other tones are sounded, so these elaastic laminæ are divided into groups for separate notes, and excite the connected nerve fibres accordingly.

There are three muscles in the interior of the tympanum attached to the small bones. The largest, called tensor tympani, is inserted in the malleus, and its direction is such as to draw inwards, and tighten the membrane of the tympanum. The second, laxator tympani, also inserted in the malleus, is supposed to have the action indicated by the name, but its muscular character has been doubted: the membrane of the tympanum would relax by mere elasticity, when the action of the tensor muscle is remitted. The third muscle is the stapedius, attached to the stapes, and seeming to govern the contact of that bone with the membrane of the oval foramen: the tensor tympani concurring with it to tighten the membrane.

It has not been well ascertained on what occasions and

with what effect the tensor tympani is brought into play. The only distinct observation on the matter is that made by Wollaston, namely, that when the membrane of the tympanum is stretched, the ear is rendered less sensible to grave sounds, such as the deep notes of the organ, or the sounds of thunder and cannon. If, therefore, the ear is exposed to very intense sounds of the deep kind, such as the firing of artillery, the tensor tympani coming into play would in some measure deaden the effect. The action would make little or no difference to the hearing of acute sounds, such as the sharp notes of a call-whistle. Probably these muscles are excited by the reflex action of the sounds; possibly, also, they may be of the voluntary class, that is, they may come into play in the voluntary acts of listening and of preparing the ear to resist loud sounds. The only circumstance assignable as determining the reflex action of the tensor tympani is simply the intensity of the sound. We may suppose that every sound whatever brings on a reflex action to stretch the membrane, and the stronger the sound the greater the action. When sounds are too loud, and of the grave kind, this tension mitigates them; when too loud and acute, it either has no effect, or makes the evil worse.

'Dr. Wollaston performed many experiments upon the effects of tension of the membrana tympani, and he found that deafness to grave notes was always induced, which, as most ordinary sounds are of a low pitch, is tantamount to a general deafness. Shrill sounds, however, are best heard when the tympanic membrane is tense. Müller remarks, and we have frequently made the same observation, that the dull rumbling sound of carriages passing over a bridge, or of the firing of cannon, or of the beating of drums at a distance, ceases to be heard immediately on the membrana tympani becoming tense; while the treading of horses upon stone pavement, the more shrill creaking of carriages, and the rattling of paper, may be distinctly heard.'-TODD and BOWMAN, vol. II., p. 95.

4. Passing now to Sounds considered as sensations, we

may distinguish these into three classes; the first comprises the general effects of sound as determined by Quality, Intensity, and Volume or Quantity, to which all ears are sensitive. The second class includes Musical sounds, for which a susceptibility to Pitch is requisite. Lastly, there is the sensibility to the Articulateness, Distance, and Direction of sounds, which are the more intellectual properties.

5. Sweetness. Under the head of Quality, the terms sweet, rich, mellow, are applied to the pleasing effects of simple sounds. Instruments and voices are distinguished by the sweetness of their individual tones; there is something in the material and mechanism of an instrument that gives a sweet and rich effect, apart altogether from the music of the airs performed upon it. Other instruments and sounds have a grating, harsh, unpleasant tone, like bitterness in taste, or a stink in the nostrils. Some substances, by their texture, have a greater sweetness of note than others. Thus silver is distinguished among the metals; and glass is also remarkable for rich, mellow tones.

The researches of Helmholtz and others seem to establish the fact that the differences of sounds as regards Sweetness (with its opposites), Timbre, and Vowel Quality, are owing to the combination of the principal tone of each with a number of over-tones; which combinations are susceptible of great variety. So strong is the tendency of sounding bodies to yield these over-tones-a vibrating string nearly always vibrates in fractions as well as in its whole length-that pure tones, although experimentally producible, are scarcely known to us at all. Tones very nearly pure arise from wide-stopped organ pipes. The effect of these on the ear is mellow, but insipid; they are intermediate between the sweet and the harsh.

According to this view, the sweetness, even of an individual sound, is a harmony; the ground tone is combined with overtones in a pleasing concord. A harsh grating sound is a combination of dissonant tones. Noise, as opposed to the sweet or the melodious, is dissonance.

On this theoretical basis, the primary division of sounds would

be into Simple sounds, Sweet combinations or concords, and Harsh combinations or discords. But as simple sounds are practically non-existent, we may still abide by the three-fold classification in the text, namely, (1.) Sweetness and Harshness, (2.) Intensity, and (3.) Volume. The second and third properties, Intensity and Volume, are important modifications of sound whatever be the degree of sweetness or of harshness; and they give a character to such as belong to neither extreme.

The sensation of the sweet in sound I have characterized as the simple, pure, and proper pleasure of hearing; a pleasure of great acuteness but of little massiveness. The acuteness of it is proportioned to the rank of the ear as a sensitive organ, or to the susceptibility of the mind to be stirred and moved through the channel of hearing. There is a great superiority in the endurableness of sweet sounds over the sweets of the inferior senses. In Touch the distinction exists in the comparison with Taste and Smell; in Hearing there is a farther progress, and we shall have to note the crowning pitch of this important property when we come to the sense of Sight. By virtue of this fact we can obtain from sight and hearing a larger amount of enjoyment within the same degree of fatigue or exhaustion, or before reaching the point of satiety. Hence one reason for terming these the 'higher senses.'

The persistence in the intellect, which governs the ideal continuance and reproduction of the pleasures and pains of sound, is of the same high order, and probably grows out of the same fundamental superiority of the sense.

The opposite of sweetness is described by the epithets harsh and grating, and is the characteristic pain of hearing. But in accounting for the extremely painful sounds, we must not confine ourselves to the fact of dissonance.

6. Intensity, Loudness.-Sounds are more or less faint or loud. A gentle or moderate sound, neither sweet nor harsh, is agreeable in stillness, simply as a sensation, and under the conditions wherein stimulation, as such, is pleasurable. According as the loudness of a sound increases, so does the

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