223 



ON THE TRANSMISSION OF MUSICAL SOUNDS THROUGH 

 SOLID LINEAR CONDUCTORS, AND ON THEIR SUBSE- 

 QUENT RECIPROCATION. 



By CHARLES WHEATSTONE. 



I- 



HHHE 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 aeriform medium 

 was alone capable of receiving sonorous impressions ; and in 

 conformity with this opinion, Lord Bacon, when noticing 

 this experiment, assumes that the sound is -propagated by 

 spirits contained within the pores of the body*. The first 

 correct observations on this subject appear to have been made 

 by Dr. Hooke in 1667 ; who made an experiment with a 

 distended wire of sufficient length to observe that the same 

 sound was propagated far swifter through the wire than through 

 the air i. Professor Wunsch, of Berlin, made, in 1788, a 

 similar experiment, substituting 1728 feet of connected wooden 

 laths for the wire, and confirmed Dr. Hooke's results J. 



* ' If a rod of iron or brass be held with one end to the ear, and the other be 

 struck upon, it makes a much greater sound than the same stroke upon the rod, 

 when not so contiguous to the ear. By which, and other instances, it should 

 seem that sounds do not only slide upon the surface of a smooth body, but also 

 communicate with the spirits in the pores of the body.' Sylva Sylvarum, Pho- 

 nics, 3. 



' The pneumatical part, which is in all tangible bodies, and has some affinity 

 with air, performs, after a sort, the office of the air. Thus the sound of an empty 

 barrel is in part created by the air on the outside, and in part by that in the 

 inside ; for the sound will be less or greater, as the barrel is more or less empty ; 

 though it communicates also with the spirit in the wood, through which it passes 

 from the outside to the inside.' Sylva Sylvarum, Phonics, 2. 



f ' And though some famous authors have affirmed it impossible to hear 

 through the thinnest plate of Moscovy glass, yet I know a way by which 'tis easy 

 to hear one speak through a wall a yard thick. It has not yet been thoroughly 

 examined, how far otacoustics may be improved, nor what other ways there may 

 be of quickening our hearing, or conveying sounds through other bodiet than the 

 air ; for that that is not the only medium I can assure the reader, that I have, by 

 the help of a distended wire, propagated the sound to a very considerable distance 

 in an instant, or with as seemingly quick a motion as that of light ; at least, 

 incomparably swifter than that which at the same time was propagated through 

 the air ; and this not only in a straight line, or direct, but in one bended in many 

 angles.' Preface to Hooke's ' Micrographia,' 

 t Acad. fieri. Deutsch, abh. 1788, 87. 



