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

INTENSITY OF SOUNDS.

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stimulation. The effect, at a given point, takes the character of pungency, like the action of ammonia on the nose, or a smart stroke on the skin. A loud speaker is exciting. The rattle of carriages, the jingle of an iron work, the noise of a cotton mill, the ringing of bells close to the ear, the discharge of musketry and ordnance, are all exciting from their intensity; to fresh and vigorous nerves plunged into them after quietness, these noises give pleasure. They may be described, however, as a coarse excitement; there is a great cost of tear and wear of nerve for the actual satisfaction.

The intensity, rising beyond a certain pitch, turns to pain. The screeching of a parrot-house, the shrill barking of the smaller species of dogs, the whistling in the fingers practised by boys in the streets, the screaming of infants, are instances of painful pungency. The sharping of a saw, and the scratching of a piece of glass, yield an intense shrill note. In most of these cases, we must suppose an element of dissonance as well as a great and smarting intensity. The only criterion of marked dissonance, as opposed to mere pungency, is the offence given to the ear under all conditions, and not merely under fatigue or exhaustion.

The suddenness of sounds, by the abrupt transition, aggravates their intensity on the general principle of Relativity. If unexpected, they produce the discomposure usually attending a breach of expectation.

7. Volume or Quantity.-This means the sound coming from a sounding mass of great surface or extent. The waves of the many sounding sea,' the thundery discharge, the howling winds, are voluminous sounds. A sound echoed from many sides is voluminous. The shout of a great multitude is impressive from the volume. Grave sounds, inasmuch as they require a larger instrument, are comparatively voluminous.

Whether sounds be sweet or indifferent, their multiplication has an agreeable effect on the ear. The sensation is extended in volume or amount without the waste of nervous power accompanying great pungency. Both physically and

mentally, these sounds conform to the laws of massive sensation.

If a sound is intrinsically harsh or grating, or if painful from intensity, the increase in volume will be an increase of pain; as in machinery. The braying of the ass combines the harsh and the voluminous.

8. Pitch or Tune.-By pitch is meant the acuteness or graveness of a sound, as determined by the ear, and resolvable into the rate of vibration of the sounding body, or the number of vibrations in a given time. The gravest sound audible to the human ear is (according to Helmholtz) 16 vibrations a second; the highest audible sound corresponds to 38,000 vibrations a second; being a compass of eleven octaves. One of the deepest tones in use on orchestra instruments is the E of the double bass, giving 411 vibrations a second. The highest note of the orchestra (D) of the piccolo flute) is 4752 vibrations. (Helmholtz: Tyndall's Lectures on Sound, p. 72). The practical range is thus about seven octaves. At the upper limit of hearing, persons differ as much as two octaves; the squeak of the bat and the sound of a cricket are unheard by some ears.

A sound of uniform pitch is a musical note. In the fact of uniform continuance, there is a pleasure of the nature of harmony. It is only such sounds that can be farther combined into musical harmonies.

Although, in music, less intervals than a semitone are not. admitted, the ear can distinguish still smaller differences. A quarter of a tone makes a marked difference to an ordinary ear. A good musician can distinguish two tones whose vibrations are as 1149 to 1145, sounded after each other, and even a smaller difference if they are sounded together. Two pitchforks whose number of vibrations per second are 1209 and 1210, sounded simultaneously, can be distinguished by a first-rate ear.

9. The waxing and waning of sound. The gradual increase or diminution of the loudness of a sound, is one of the effects introduced into musical composition, owing to the