342 Dr. Weber on the Interference of Sound. 



uniform fin at vibration is, in fact, the standing vibration, it 

 may be explained why standing vibrations, and especially the 

 sounding, are most independent of the first vibration — of the 

 excitement of the tone; and also why Chladni's figures of sound 

 are likewise very independent of it. The reverberating vibra- 

 tion consists of the first intersection of the waves just excited, 

 and may in many instances coincide with the sounding vibra- 

 tion ; for which reason also the reverberating figures are often 

 represented like the figures of sound, (see Savart's former 

 treatises). One recognizes, however, the figures of reverbera- 

 tion by a great dependence on the original agitation, ex.gr. on 

 the direction in which the sounding body is moved. Finally, 

 it is evident, that vibrations without any acoustic effect may at 

 times be of the same nature as the sounding and reverberating 

 vibrations ; for all standing vibrations, for instance such as are 

 so weak as not to act upon the organs of hearing, belong to 

 this class. 



Supplement to the foregoing Paper. On the Employment of 



a resounding Membrane for the Observation of the Interference 

 of the Undulations of Sound*. 



I have stated in an Essay on Savart's Experiment with me- 

 diately agitated Membranes, (Seep. 340, 341.) that in these 

 membranes we observe neither an original sound nor a re- 

 sonance, when an organ-pipe, a bell, a swinging disk, or any 

 other longitudinally or transversely swinging body of a flat 

 surface is held before the membrane. I have however suc- 

 ceeded in making such a membrane resound by simply hold- 

 ing a tuning-fork before it, so that one prong was held close 

 to it, parallel with the diagonal line of the square frame. The 

 sound of a tuning-fork by itself is but slightly heard, or not 

 at all, at a little distance. But on bringing it in the manner 

 described towards the membrane, without touching it, the 

 sound is heard distinctly ; while it is perceived that it pro- 

 ceeds, not from the fork, but from the membrane. 



(With the help of such a resounding membrane I have been 

 enabled to observe the phenomena of the action of the undu- 

 lations of sound, the description and investigation of which has 

 appeared in the Jahrbuch, 1826. iii. p. 385 to 430.) 



The sounding of the membrane is in fact very distinct, when 

 the outside of a prong is turned towards it. It is equally di- 

 stinct when the two prongs are brought near at an equal di- 

 stance ; but on turning the tuning-fork gradually from the first 

 position into the second, we come to a point where the sounding 



* From Schweiggcr's Jakrbuch, Band xx. p. 247. 



of 



