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1827 __ « On the transmission of Musical sounds through solid liner conductors and on their subsequent reciprocation »
Charles Wheatstone (1802-1875)
French comment : En 1827, Charles Wheatstone publia un rapport sur des . expériences d’acoustique et une description du kaleïdophone. Cet appareil contenait des principes que son inventeur devait développer plus tard dans l’invention d’un photomètre. En 1828, Wheatstone publia le résultat de ses expériences sur la vibration des colonnes d’air et, en 1831, une étude sur la transmission des sons à travers les solides dans laquelle il indiqua un moyen de transmettre les sons musicaux à des distances très-éloignées. (J. AYLMER, Nécrologie publiée dans la revue scientifique illustrée de L’électricité N°2 du 15 Février 1876)
Original excerpt : « The fact of the transmission of sound through solid bodies, as when a stick or a metal rod is placed at one extremity to the ear, and is struck or scratched at the other end, did not escape the observation of the ancient philosophers : but it was for a long time erroneously supposed, that an aëriform medium was alone capable of receiveing sonorous impressions; and in conformity with this opinion, Lord Bacon, when noticing this experiment, assumes that the sound is propagated by spirits within the pores of the body (Cf. “Sylva Sylvarum.Phonics”, Paragr. 3, 1627). [...] Chadlni had, in an ingenious manner, inferred the velocity of sound in different solid substances; and his results are fully confirmed by calculations from other grounds. His method was founded on Newton’s demonstration, that sound travels through a space of a given length, contained in a tube open at both ends, makes a single vibration. His own discovery of the longitudinal vibrations of solid bodies, which are exactly analogous to the ordinary vibrations of columns of air, enabled hom to apply this proposition to solid bodies, and to establish the general law, that sound is propagated through any elastic substance in the same time in which this substance makes one longitudinal vibration. [...] In all the experiments (above alluded to), the sounds transmitted were either more noises, such as the blow of a hammer, or [...] a single musical sound, produced by striking a silver spoon attached to one end of the conducting wire; and in no case were any means employed for the subsequent augmentation of the transmitted sound. I believe that, previous to the experiments which I commenced in 1820, none had been made on the transmission of the modulated sounds of musical instruments; nor had it been shown that sonorous undulations, propagated through solid linear conductors of considerable lenght, were capable of exciting, in surfaces with which they were in connexion, a quantity of vibratory motion, sufficient to be powerfully audible when communicated through the air. [...] It will be necessary to make few observations on the augmentation of sound which results from the connexion of a vibrating body with other bodies capable of entering into simultaneous vibration on it. This participation of the vibrations of an original sounding body is called ‘resonance’, or reciprocation of sound. Sonorous bodies are audible (the extent of their excursions being supposing equal) in proportion to the quantity of their vibrating surfaces. [...] It will be obvious in what manner two square piano-fortes of two harps may be so connected as mutually to reciprocate each other’s sounds; by such an arrangement, two performers in different rooms may play a duet together to two distinct audiences, or one may eacho the performance of the other. If the transmission is required to be horizontal, ie. between two rooms on the same floor, cabinet piano-fortes must be employed [For instance in the case of a vertical apparatus, the wire between the instruments, consisted of four portions : the first part touched the sounding-board of the piano-forte, and reached half-way to the floor; the second passed through the insulating-tube in the floor, and terminated when it reached the ceiling of the room below in a hook; a third part was suspended from this hook by a loop; and the fourth, after identifying itself with one of the apparent wires of another instrument]. The sounds of an instrument may be at the same time transmitted to more than one place; for instance, communications may be made from a square piano-forte to a resounding instrument above, and to another below: and the communications may be even continued through a series of reciprocating instruments. If the instruments be not in adjacent rooms, but be further removed from each other, a person in the intermediate room, through the conductor passes, will hear no sound but what is communicated by the ordinary means. Hence it would be possible to extend a horizontal conductor through a series of rooms belonging to different houses, and (provided the instrument connected with one of its extremities be constantly played upon) to hear at pleasure the performance in any of these rooms, by merely attaching a reciprocating instrument to the conductor; on removing this instrument, the sonorous undulations would pass inaudibly to the next apartment. These observations will equally apply to the transmission of other musical sounds, which will be hereafter noticed. [...] In a similar manner, the sounds of an entire orchestra may be transmitted, viz. by connecting the end of the conductor with a properly sounding-board, so placed as to resound all the instruments. [...] Compared with an ordinary band, heard at a distance through the air, the effect is as a landscape seen in a miniature beauty through a concave lens, as compared with the same scene viewed by the ordinary vision through a murky atmosphere. [...] Could any conductiong substance be rendered perfectly equal in density and elasticity, so as to allow the undulations to proceed with a uniform velocity without any reflections or interferences, it would be easy to transmit sounds through suc conductors from Aberdeen to London, as it is now to establish a communication from one chamber to another. Whether any substance can be rendered thus homogeneous and uniform remains for future philosophers to determine. The transmission to distant places, and the multiplication of musical performances, are objects of far less importance than the conveyance of the articulations of speech. » (Charles Wheatstone)
Source : Wheatstone, Charles (1827), “On the transmission of Musical sounds through solid liner conductors and on their subsequent reciprocation”, In the Quarterly Journal of Science, Literature and the arts. First published in 1827 in the Journal of the Royal Institution, N°. IV, London : John Murray, Albemarle Street, August, 1831, pp. 223-238.
Urls : http://www.gloubik.info/sciences/spip.php?article18 (last visited )

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