Our attention has been directed to an article in Frank Leslie's Illustrated Newspaper on a " new theory of acoustics," principally relating to music, by S. B. Driggs. A person may be well acquainted with acoustics, and may understand the principles upon which the science of music is based, and yet may be no mUSlClan. On the other hand, a person may be a musician, and yet be unacquainted with the laws of acoustics. A musician is a person who can readily strike the different notes of music and produce harmonious sounds, either with the voice or an instrument. The art of music is solely a practical one. The number of musicians, as well as non-mnsicians, who are acquainted with the cause of sound and music, is but small, therefore a brief dissertation on the subject will not be devoid of interest or instruction. Mr. Driggs says, in regard to his new theory of acoustics, " I discard the belief that sound is produced by air alone, commonly called concussion, producing waves or circles of air, and shall treat sound itself as possessing a more independent existence, and attempt to show that atmospheric air acts more in the capacity of a medium to convey it to the ear, and is the telegraph wire that conveys the impression it receives, and that is not the first cause." It was at one time believed that sounds were produced by emissions from bodies, like odors from flowers, and that these affected the sense of hearing as perfumes the sense of smellingj Mr. Driggs appears to be tinged with a kindred opinion. He is evidently mistaken in supposing that any scientific man acquainted with the laws of acoustics entertains the opinion that atmospheric air is either the first or only cause of sounu, or that it is eventhesale medium for conv'eying it. Sound is caused by the simple but rapid mechanical vibrations of various elastic bodies. These when moved or struck so as to vibrate, communicate the same kind of vibrations to the auditory nerve of the ear, and are then appreciated by the mind. Sound is conducted through the air, but there are other conductors superior to air, such as iron which conducts it seventeen times fasterj some kinds of wood eleven times, and water four and a half times faster. This power of conduction depends oil the peculiar structure of the body not its densityj the atmosphere, however, is the great and general medium of s6und, although any other body which can communicate the same vibrations to the auditory nerve will answer the same purpose. By closing the ears and inserting a long strip of dry wood between the teeth, the ticking of a watch or any other sound produced at the extreme end of it will be heard more distinctly than coming through the air, and having both ears open j this is a very old and well-known fact. The instrument called the syren for counting the number of sound waves produced in a second of time, will yield the same tones in water as in air, thus proving that air is not the sole cause or medium of sounds. A strong wind moving at the rate of twenty feet per second causes no sound j a body, such as the haud, swept rapidly through the air, although it produces waves, does not cause sound. Why is this ? If sound is caused by vibrations, why do the waves of the atmosphere produced in these instances not cause sound ? It has been demonstrated by accurate experiments that the air must move with a wave velocity of 1,125 feet per second to produce sound j a lesser wave velocity is not appreciated as sound by the human ear. The wings of a bee or a musquito must therefore vibrate to produce air waves of 1,125 feet velocity, or we could not hear their humming noise. The chirp of a cricket and the booming of a cannon move with a velocity of 1,125 feet per second. Simple sounds consist of a succession of rapid waves moving irregularly; musical sounds consist of a series of simple sounds falling upon the ear at regular inter-vals. These sounds or vibrations reach the ear and agitate the air within it, communicat- ing an equal Amount of vibration to thetym-pan or membrane stretched across a cell in the head, in which are arranged a series of curious little bones, namely, the malleus (hammer), incus (anvil), os orbicularo (rounded bone and the smallest in the human body), and the stapes (stirrup). The latter is connected with a membrane, which closes three semi-circular canals filled with water j these are lined with an expansion of the auditory nerve, which take up the vibrations to the mind. The sense of sounds—both simple and harmonious—depends on the proper condition of the very delicate. and complicated organs of hearing. It is easy to conceive how a very small derangement of the ear bones, the membranes, or the fluid in the ear cells, will injure the sense of hearing in regard to both the volume and the character of sounds. If we take the string of an instrument and strike it so as to produce sixteen waves moving at the rate of 1,125 feet per second, weob-tain what ii considered the lowest musical sound, which is the note, C. If we vibrate the string, so as to produce thirty-two vibrations in the same time, we obtain the same sound exactly, but a different pitch j it is also the note, C, but an octave higher. And if we proceed to double the number of these vibrations until we attain to a fourteenth (214) power, namely, 8,192 vibrations in a second, we reach the highest note in common music, which is five octaves above the middle, C, of the piano. The extreme limits of the human voice in males varies from 384 to 1,266 vibrations per second j in females from 1,152 to 3,240. Like the seven colors of the rainbow, there are but seven notes of music, which are A, B" C, D, E, F, Gj; each represents (according to its position on the staff) a certain nUmber of vibrations in a second. All music, from the loftiest oratorio to the most simple lay of the shepherd on his reed pipe, is produced by regulur combinations of these vibrations. When they are not regular, we have discord, not music. Upon this theory the whole science of music is based. Every key in a piano is arranged so as to produce a certain number of rapid vibrations in a given time. If we take, for example, a string which will make one hundred oscilations in a second, and shorten it to half its former length, its vibrations will be doubled—it will oscilate 200 times in a second, and yield a note exactly an octave higher than the former one. It is by this arrangement of strings that the different notes are struck on the pianofore. As these strings generate a definite number of vibrations in a given time, unless the keys are struck so as to make these occur at regular intervals of time, mere noise and not music is the result. The keys of the pianoforte are arranged in multiples of 2 to produce harmony. When two keys close together are struck, there is discord, because their vibrations do not occur at regular intervals. If the interval is a third, it is harmonious, because it is regular, and is obtained by striking two keys, leaving one untouched between the two beating fingers. Of course, there is much in the combinations of sounds apart from these statements, which cannot now be enlarged upon, but we think we have conveyed a very clear idea of the causes of sound and music. A very remarkable proof of the vibratory nature of sound is heard when two notes very nearly, but not quite unisonant are sounded together. A periodical interruption of the sound called a beat occurs at intervals which are longer, the nearer the two notes approach to perfect identity, and may often be as long as half a second. To understand this, we must remember that each pulsation of air consists of two contrary motions to and fro. Now, if one sound produces the forward motion when the other tends to produce the backward motion, the two, if equal, will annihilate one another, and produce silence. This is exactly in accordance with the laws of mechanics, and proves that sounds arc produced by the motion of ponderable bodies. Another mmical phenomenon called Bym- pathy goes to establish the same fact. The waves of sound set in motion by a flute, cause the wires of a pianoforte, each according to its note, to vibrate with the same notes of the flute. A gla8s vase pitched to a certain note may be set ringing by the human voice striking the same notej and it is stated that Madame Catalani, the celebrated Italian vocalist, whose voice was of great power and compass, had on several occasions broken crystal goblets with her voice. This is explained by the well-known laws of mechanics upon tl:e same principle by which several suspension bridges have been broken down by the regular pulsations of wind storms, and the steady regular tramp of soldiers passing over them. The regular waves of the atmosphere communicated to the glass goblet set its particles vibrating, and these pulsations accumulated until the disruptive force exceeded that of the cohesion which held the particles of glass together, when as a legitimate mechanical con-sequence, the goblet was rent in pieces. There are various qualities of the human voice, as well as instruments. Seldom do we hear two voices in a choir of the same quality of tone—although all may be singing at the same pitch—they are as various in quality as the hnman face is in form., The cause of this is mostly owing to theform of the waves, which each singer imparts to the atmosphere by the construction of the throat and mouth. Some waves are of the form of elipses, such as those produced by stringsj others as circles, such as those of the flute and organj but the forms of sound waves are of endless variety, hence the different qualities of the sounds we hear from voice, harp, pianoforte, flute and organ. We cannot tell why it is that regular mechanical vibrations of the atmosphere are the source of so much pleasure to man j we only know that such is the fact. He is constituted to enjoy musicj it imparts exquisite delight, and is the chief of all ennobling and innocent amusements.
This article was originally published with the title "The Cause of Sound and Music" in Scientific American 13, 38, 302 (May 1858)