SOUND

, in Geography, denotes a strait or inlet of the sea, between two capes or head-lands.

The Sound is used, by way of eminence, for that celebrated strait which connects the German sea to the Baltic. It is situated between the island of Zealand and the coast of Schonen. It is about 16 leagues in length, and in general about 5 in breadth, except near the castle of Cronenberg, where it is but one; so that there is no passage for vessels but under the cannon of the fortress.

, in Physics, a perception of the mind, communicated by means of the ear; being an effect of the collision of bodies, and their consequent tremulous motion, communicated to the ambíent fluid, and so propagated through it to the organs of hearing.

To illustrate the cause of Sound, it is to be observed, 1st, That a motion is necessary in the sonorous body for the production of sound. 2dly, That this motion exists first in the small and insensible parts of the sonorous | bodies, and is excited in them by their mutual collision against each other, which produces the tremulous motion so observable in bodies that have a clear sound, as bells, musical chords, &c. 3dly, That this motion is communicated to, or produces a like motion in the air, or such parts of it as are fit to receive and propagate it. Lastly, That this motion must be communicated to those parts that are the proper and immediate instruments of hearing.

Now that motion of a sonorous body, which is the immediate cause of Sound, may be owing to two different causes; either the percussion between it and other hard bodies, as in drums, bells, chords, &c; or the beating and dashing of the sonorous body and the air immediately against each other, as in flutes, trumpets, &c.

But in both these cases, the motion, which is the consequence of the mutual action, as well as the immediate cause of the sonorous motion which the air conveys to the ear, is supposed to be an invisible, tremulous or undulating motion, in the small and insensible parts of the body. Perrault adds, that the visible motion of the grosser parts contributes no otherwise to Sound, than as it causes the invisible motion of the smaller parts, which he calls particles, to distinguish them from the sensible ones, which he calls parts, and from the smallest of all, which are called corpuscles.

The sonorous body having made its impression on the contiguous air, that impression is propagated from one particle to another, according to the laws of pneumatics.

A few particles, for instance, driven from the surface of the body, push or press their adjacent particles into a less space; and the medium, as it is thus rarefied in one place, becomes condensed in the other; but the air thus compressed in the second place, is, by its elasticity, returned back again, both to its former place and its former state; and the air contiguous to that is compressed; and the like obtains when the air less compressed, expanding itself, a new compression is generated. Therefore from each agitation of the air there arises a motion in it, analogous to the motion of a wave on the surface of the water; which is called a wave or undulation of air.

In each wave, the particles go and return back again, through very short equal spaces; the motion of each particle being analogous to the motion of a vibrating pendulum while it performs two oscillations; and most of the laws of the pendulum, with very little alteration, being applicable to the former.

Sounds are as various as are the means that concur in producing them. The chief varieties result from the figure, constitution, quantity, &c, of the sonorous body; the manner of percussion, with the velocity &c, of the consequent vibrations; the state and constitution of the medium; the disposition, distance, &c, of the organ; the obstacles between the organ and the sonorous object and the adjacent bodies. The most notable distinction of Sounds, arising from the various degrees and combinations of the conditions above mentioned, are into loud and low (or strong and weak); into grave and acute (or sharp and flat, or high and low); and into long and short. The management of which is the office of music.

Euler is of opinion, that no Sound making fewer vibrations than 30 in a second, or more than 7520, is distinguishable by the human ear. According to this doctrine, the limit of our hearing, as to acute and grave, is an interval of 8 octaves. Tentam. Nov. Theor. Mus. cap. 1, sect. 13.

The velocity of Sound is the same with that of the aerial waves, and does not vary much, whether it go with the wind or against it. By the wind indeed a certain quantity of air is carried from one place to another; and the Sound is accelerated while its waves move through that part of the air, if their direction be the same as that of the wind. But as Sound moves vastly swifter than the wind, the acceleration it will hereby receive is but inconsiderable; and the chief effect we can perceive from the wind is, that it increases and diminishes the space of the waves, so that by help of it the Sound may be heard to a greater distance than otherwise it would.

That the air is the usual medium of Sound, appears from various experiments in rarefied and condensed air. In an unexhausted receiver, a small bell may be heard to some distance; but when exhausted, it can scarce be heard at the smallest distance. When the air is condensed, the Sound is louder in proportion to the condensation, or quantity of air crowded in; of which there are many instances in Hauksbee's experiments, in Dr. Priestley's, and others.

Besides, sounding bodies communicate tremors to distant bodies; for example, the vibrating motion of a musical string puts others in motion, whose tension and quantity of matter dispose their vibrations to keep time with the pulses of air, propagated from the string that was struck. Galileo explains this phenomenon by observing, that a heavy pendulum may be put in motion by the least breath of the mouth, provided the blasts be often repeated, and keep time exactly with the vibrations of the pendulum; and also by the like art in raising a large bell.

It is not air alone that is capable of the impressions of Sound, but water also; as is manifest by striking a bell under water, the Sound of which may plainly enough be heard, only not so loud, and also a fourth deeper, according to good judges in musical notes. And Mersenne says, a Sound made under water is of the same tone or note, as if made in air, and heard under the water.

The velocity of Sound, or the space through which it is propagated in a given time, has been very differently estimated by authors who have written concerning this subject. Roberval states it at the rate of 560 feet in a second; Gassendus at 1473; Mersenne at 1474; Duhamel, in the History of the Academy of Sciences at Paris, at 1338; Newton at 968; Derham, in whose measure Flamsteed and Halley acquiesce, at 1142.

The reason of this variety is ascribed by Derham, partly to some of those gentlemen using strings and plummets instead of regular pendulums; and partly to the too small distance between the sonorous body and the place of observation; and partly to no regard being had to the winds.

But by the accounts since published by M. Cassini de Thury, in the Memoirs of the Royal Acad. of Scien- | ces at Paris, 1738, where cannon were fired at various as well as great distances, under many varieties of weather, wind, and other circumstances, and where the measures of the different places had been settled with the utmost exactness, it was found that Sound was propagated, on a medium, at the rate of 1038 French feet in a second of time. But the French foot is in proportion to the English as 15 to 16; and consequently 1038 French feet are equal to 1107 English feet. Therefore the difference of the measures of Derham and Cassini is 35 English feet, or 33 French feet, in a second. The medium velocity of Sound therefore is nearly at the rate of a mile, or 5280 feet, in 4 2/3 seconds, or a league in 14 seconds, or 13 miles in a minute. But sea miles are to land miles nearly as 7 to 6; and therefore Sound moves over a sea mile in 5 1/3 seconds nearly, or a sea league in 16 seconds.

Farther, it is a common observation, that persons in good health have about 75 pulsations, or beats of the artery at the wrist, in a minute; consequently in 75 pulsations, Sound flies about 13 land miles, or 11 1/7 sea miles, which is about 1 land mile in 6 pulses, or one sea mile in 7 pulses, or a league in 20 pulses.

And hence the distance of objects may be found, by knowing the time employed by Sound in moving from those objects to an observer. For Ex. On seeing the flash of a gun at sea, if 54 beats of the pulse at the wrist were counted before the report was heard; the distance of the gun will easily be found by dividing 54 by 20, which gives 2.7 leagues, or about 8 miles.

Upon the nature, production, and propagation of Sound, see the article Phonics and Echo; also the Memoirs of the Acad. and the Philos. Trans. in many places; Newton, Principia; Kircher, Mesurgia Universalis; Mersenne; Borelli, Del Suono; Priestley, Exper. and Observ. vol. 5; Hales, Sonorum Doctrina rationalis et experimentalis; 4to 1778. See also an ingenious treatise published 1790, by Mr. Geo. Saunders, on Theatres; in which he relates many experiments made by himself, on the nature and propagation of Sound. In this work, he shews the great effect of water, and some other bodies, in conducting of Sound, probably by rendering the air more dense near them. Some of his conclusions and observations are as follow:

Earth may be supposed to have a twofold property with respect to Sound. Being very porous, it absorbs Sound, which is counteracted by its property of conducting Sound, and occasions it to pass on a plane, in an equal proportion to its progress in air, unencumbered by any body.

If a Sound be sufficiently intense to impress the earth in its tremulous quality, it will be carried to a considerable distance, as when the earth is struck with any thing hard, as by the motion of a carriage, horses feet, &c.

Plaster is proportionally better than loose earth for conducting Sound, as it is more compact.

Clothes of every kind, particularly woollen cloths, are very prejudicial to Sound: their absorption of Sound, may be compared to that of water, which they greedily imbibe.

A number of people seated before others, as in the pit or gallery of a theatre, do considerably prevent the voice reaching those behind; and hence it is, that we hear so much better in the front of the galleries, or of any situation, than behind others, though we may be nearer to the speaker. Our seats, rising so little above each other, occasion this defect, which would be remedied, could we have the seats to rise their whole height above each other, as in the ancient theatres.

Paint has generally been thought unfavourable to Sound, from its being so to musical instruments, whose effects it quite destroys.

Musical instruments mostly depend on the vibrative or tremulous property of the material, which a body of colour hardened in oil must very much alter; but we should distinguish that this regards the formation of Sound, which may not altogether be the case in the progress of it.

Water has been little noticed, with respect to its conducting Sound; but it will be found to be of the greatest consequence. I had often perceived in newly-finished houses, that while they were yet damp, they produced echoes; but that the echoing abated as they dried.

Exp. When I made the following experiment there was a gentle wind; consequently the water was proportionally agitated. I chose a quiet part of the river Thames, near Chelsea Hospital, and with two boats tried the distance the voice would reach. On the water we could distinctly hear a person read at the distance of 140 feet, on land at that of 76. It should be observed, that on land no noise intervened; but on the river some noise was occasioned by the flowing of the water against the boats; so that the difference on land and on water must be much more.

Watermen observe, that when the water is still, and the weather quite calm, if no noise intervene, a whisper may be heard across the river; and that with the current it will be carried to a much greater distance, and vice versa against the current.

Mariners well know the difference of Sound on sea and land.

When a canal of water was laid under the pit floor of the theatre of Argentino, at Rome, a surprising difference was observed; the voice has since been heard at the end very distinctly, where it was before scarce distinguishable. It is observable that, in this part, the canal is covered with a brick arch, over which there is a quantity of earth, and the timber floor over all.

The villa Simonetta near Milan, so remarkable for its echoes, is entirely over arcades of water.

Another villa near Rouen, remarkable for its echo, is built over subterraneous cavities of water.

A reservoir of water domed over, near Stanmore, has a strong echo.

I do not remember ever being under the arches of a stone bridge that did not echo; which is not always the case with similar structures on land.

A house in Lambeth Marsh, inhabited by Mr. Turtle, is very damp during winter, when it yields an echo which abates as the house becomes dry in summer.

Kircher observes, that echoes repeat more by night than during the day: he makes the difference to be double.

Dr. Plott says, the echo in Woodstock park repeated 17 times by day, and 20 by night. And Addison's | experiment at the Villa Simonetta was in a fog, when it produced 56 repetitions.

After all these instances, I think little doubt can remain of the influence water has on Sound; and I conclude that it conducts Sound more than any other body whatever.

After water, stone may be reckoned the best conductor of Sound. To what cause it may be attributed, I leave to future enquiries: I have confined myself to speak of facts only as they appear.

Stone is sonorous, but gives a harsh disagreeable tone, unfavourable to music.

Brick, in respect to Sound, has nearly the same properties as stone. Part of the garden wall of the late W. Pitt, Esq. of Kingston in Dorsetshire, conveys a whisper to the distance of near 200 feet.

Wood is sonorous, conductive, and vibrative; of all materials it produces a tone the most agreeable and melodious; and it is therefore the fittest for musical instruments, and for lining of rooms and theatres.

The common notion that whispering at one end of a long piece of timber would be heard at the other end, I found by experiment to be erroneous. A stick of timber 65 feet long being slightly struck at one end, a sound was heard at the other, and the tremor very perceptible: which is easily accounted for, when we consider the number or length of the fibres that compose it, each of which may be compared to a string of catgut.

For the Reflection, Refraction, &c, of Sound; see Echo, and Phonics.

Articulate Sound. See Articulate.

, in Music, denotes a quality in the several agitations of the air, so as to make music or harmony.

Sound is the object of music; which is nothing but the art of applying Sounds, under such circumstances of tone and time, as to raise agreeable sensations. The principal affection of Sound, by which it becomes fitted to have this end, is that by which it is distinguished into acute and grave. This difference depends on the nature of the sonorous body; the particular figure and quantity of it; and even in some cases, on the part of the body where it is struck: and it is this that constitutes what are called different tones.

The cause of this difference appears to be no other than the different velocities of the vibrations of the sounding body. Indeed the tone of a Sound is found, by numerous experiments, to depend on the nature of those vibrations, whose differences we can conceive no otherwise than as having different velocities: and since it is proved that the small vibrations of the same chord are all performed in equal times, and that the tone of a Sound, which continues for some time after the stroke, is the same from first to last, it follows, that the tone is necessarily connected with a certain quantity of time in making each vibration, or each wave; or that a certain number of vibrations or waves, made in a given time, constitute a certain and determinate tone. From this principle are all the phænomena of tune deduced.

If the vibrations be isochronous, or performed in the same time, the Sound is called musical, and is said to continue at the same pitch; and it is also accounted acuter, sharper, or higher than any other Sound, whose vibrations are slower, and therefore graver, flatter, or lower, than any other whose vibrations are quicker. See Unison.

From the same principle arise what are called concords, &c; which result from the frcquent unions and coincidences of the vibrations of two sonorous bodies, and consequently of the pulses or the waves of the air occasioned by them.

On the contrary, the result of less frequent coincidences of those vibrations, is what is called discord.

Another considerable distinction of musical Sounds, is that by which they are called long and short, owing to the continuation of the impulse of the efficient cause on the sonorous body for a longer or shorter time, as in the notes of a violin &c, which are made longer or shorter by strokes of different length or quickness. This continuity is properly a succession of several Sounds, or the effect of several distinct strokes, or repeated impulses, on the sonorous body, so quick, that we judge it one continued Sound, especially where it is continued in the same degree of strength; and hence arises the doctrine of measure and time.

Musical Sounds are also divided into simple and compound; and that in two different ways. In the first, a Sound is said to be compound, when a number of successive vibrations of the sonorous body, and the air, come so fast upon the ear, that we judge them the same continued Sound; like as in the phenomenon of the circle of fire, caused by putting the fired end of a stick in a quick circular motion; where supposing the end of the stick in any point of the circle, the idea we receive of it there continues till the impression is renewed by a sudden return.

A Simple Sound then, with regard to this composition, should be the effect of a single vibration, or of as many vibrations as are necessary to raise in us the idea of Sound.

In the second sense of composition, a simple Sound is the product of one voice, or one instrument, &c.

A Compound Sound consists of the Sounds of several distinct voices or instruments all united in the same individual time, and measure of duration, that is, all striking the ear together, whatever their other differences may be. But in this sense again, there is a twofold composition; a natural and an artificial one.

The natural composition is that proceeding from the manifold reflections of the first Sound from adjacent bodies, where the reflections are not so sudden as to occasion echoes, but are all in the same tune with the first note.

The artificial composition, which alone comes under the musician's province, is that mixture of several Sounds, which being made by art, the ingredient Sounds are separable, and distinguishable from one another. In this sense the distinct Sounds of several voices or instruments, or several notes of the same instrument, are called simple Sounds, in contradistinction to the compound ones, in which, to answer the end | of music, the simples must have such an agreement in all relations, chiefly as to acuteness and gravity, as that the ear may receive the mixture with pleasure.

Another distinction of Sounds, with regard to music, is that by which they are said to be smooth or even, and rough or harsh, also clear and hoarse: the cause of which difference depends on the disposition and state of the sonorous body, or the circumstances of the place; but the ideas of the differences must be sought from observation.

Smooth and Rough Sounds depend chiefly on the sounding body; of which we have a notable instance in strings that are uneven, and not of the same dimension and constitution throughout.

As to clear and hoarse Sounds, they depend on circumstances that are accidental to the sonorous body. Thus, a voice or instrument will be hollow and hoarse if sounded within an empty hogshead, that yet is clear and bright out of it: the effect is owing to the mixture of different Sounds, raised by reflections, which corrupt and change the species of the primitive Sound.

For Sounds to be fit to obtain the end of music, they ought to be smooth and clear, especially the first; since, without this, they cannot have one certain and discernible tone, capable of being compared to others, in a certain relation of acuteness, which the ear may judge of. So that, with Malcolm, we call that an harmonic or musical Sound which, being clear and even, is agreeable to the ear, and gives a certain and discernible tune (hence called tunable Sound), which is the subject of the whole theory of harmony.

Wood has a particular vibrating quality, owing to its elasticity; and all musical instruments made of this matter, are of a thickness proportioned to the superficies of the wood, and the tone they are to produce.

Metals are sonorous and vibrative, producing a harsh tone, very serviceable to some parts of music. Most wind instruments are made of metal, which is acted upon in its elastic and tremulous quality, being capable of being reduced very thin for that purpose. Instruments of this kind are such as horns, trumpets, &c. Some instruments however depend more on the form than the material; as flutes, for instance, which, if their lengths and bore be the same, have very little difference in their Sounds, whatever the matter of them may be. See Harmonical.

SOUND-Board, the principal part of an organ, and that which makes the whole machine play. This Sound-board, or summer, is a reservoir into which the wind, drawn in by the bellows, is conducted by a portvent, and thence distributed into the pipes placed over the holes of its upper part. This wind enters them by valves, which open by pressing upon the stops or keys, after drawing the registers, which prevent the air from going into any of the other pipes beside those it is required in.

Sound-board denotes also a thin broad board placed over the head of a public speaker, to enlarge and extend or strengthen his voice.

Sound-boards, in theatres, are found by experience to be of no service; their distance from the speaker being too great, to be impressed with sufficient force. But Sound-boards immediately over a pulpit have often a good effect, when the case is made of a just thickness, and according to certain principles.

Sound-Post, is a post placed withinside of a violin, &c, as a prop between the back and the belly of the instrument, and nearly under the bridge.