As the sense of hearing, as well as that of seeing, gives us perceptions of remote objects, so it is subject to similar errors, and may deceive us, when we cannot rectify by the touch, the ideas which it excites. It communicates no distinct intelligence of the distance from whence a sounding body is heard: a great noise far off, and a small one near, produce the same sensation, and, unless we receive aid from some other sense, we can never distinctly tell whether the sound be a great or a small one. It is not till we have, by experience, become acquainted with any particular sound that we can judge of the distance from whence we hear it; but if, for example, we hear the sound of a bell, we are at no great loss to determine its distance, any more than we are of that of a cannon from the report, judging in both cases from similar sounds, which we have been previously acquainted with.
Every body that strikes against another produces a sound which is simple in bodies non-elastic, but is often repeated in such as are elastic. If we strike a bell, a single blow produces a sound, which is repeated while the sonorous body continues to vibrate. These undulations succeed each other so fast, that the ear supposes them one continued sound; whereas, in reality, they form many. A circumstance of this kind happened to myself, for lying on the bed half asleep, I distinctly counted five strokes of the hammer upon the bell of the clock, and rising immediately found it was but the hour of one, and was convinced by examining the machinery that it had struck no more. A person, therefore, who should for the first time, hear the toll of a bell, would very probably be able to distinguish these breaks of sound; and, in fact, we can readily ourselves perceive remission in sounds.
Sounding bodies are of two kinds; those unelastic ones, which being struck, return but a single sound; and those more elastic returning a succession of sounds, which uniting together form a tone. This tone may be considered as a number of sounds produced one after the other by the same body, as we find in a bell, which continues to sound for some time after it is struck. A continuing tone may be also produced from a non-elastic body, by repeating the blow quick and often, as when we beat a drum, or draw a bow along the string of a fiddle.