175 



On the Resonances f or Reciprocated Vibrations of Columns 



of Air. 



[By Mr. C. Wheatstonb.] 



An elastic body may be made to assume a vibratory state in two 

 ways; either, immediately, by any momentary impulse, which, 

 altering the natural positions of its particles, allows them after- 

 wards to return by a succession of isochropous oscillations to 

 their former state ; or, secondarily, by means of an immediately 

 sounding body, which causes it to reciprocate to the latter, 

 when certain conditions, on which depends its susceptibility of 

 vibrating in such a manner, are fulfilled. This reciprocation, to 

 which, when the effect is referred to, the term resonance is applied, 

 is effected by means of the undulations which are produced in the 

 air, or in any fluid or solid medium, by the periodical pulses of the 

 original vibrating body ; these undulations being capable of putting 

 in motion all bodies whose pulses are coincident with their own, 

 and, consequently, with those of the primitive sounding body. — 

 Galileo observed that a heavy pendulum might 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 

 this remark affords a correct explanation of the phenomenon. 



Some of the most obvious cases of resonance are, — the vibrations 

 of a string when another tuned in unison with it is made to vibrate ; 

 the resounding of a drinking-glass to the sound of the voice, or of 

 a musical instrument ; the reciprocated vibrations of a sounding- 

 board, communicating immediately with a vibrating string or tuning- 

 fork, &c. In the last mentioned instance, though the string and 

 the fork are the original vibrating bodies, the audible sound is 

 dependent on the resonance of the sounding-board. 



As all these effects are well known*, it is unnecessary to dilate 

 upon them here, and I may uninterruptedly proceed to the imme- 

 diate object of the present paper, viz., the investigation of the laws 

 of the resonance or phonic reciprocation of columns of air. 



§ 1. If one of the branches of a vibrating tuning-fork be brought 

 near the embouchure of a flute, the lateral apertures of which are 

 stopped so as to render it capable of producing the same sound as 

 the fork, then the feeble and scarcely audible sound of the fork will 

 be augmented by the rich resonance of the column of air within the 



♦ Biot.Traite de Physique: torn, ii, p. 183. Chladni, Traits d'Acousticjue, 

 222,223. 



