Motions of mediately agitated Membranes. 341 



Such a paper will sound even on any one pushing against the 

 frame or gently blowing upon it. If one strewed upon this 

 paper held horizontally some grains of coarse sand, and held 

 a bell of a watch or a small disk of glass over the paper, ex. gr. 

 near a corner, making it sound by means of a violin-bow, the 

 sand began to move, and collected in those lines described by 

 Savart. 



In these experiments I found : — 



1. That here also in the mediately agitated membranes an 

 actual intersection of the reposing lines nowhere takes place, 

 as Oerstedt and Strehlke have observed in sounding plates. 



2. That the deepening or heightening of the tone of the 

 organ-pipe, and the change of elasticity by the wetting of 

 the membrane, are not the only means whereby the nodes in 

 mediately agitated membranes became curved ; but that this 

 curving of the nodes might also be produced by trifling cir- 

 cumstances ; by bringing, for instance, a sounding bell some- 

 times near a corner and sometimes near the centre of the square 

 membrane. 



3. That, as I have stated before, no trace of self-sounding 

 or reverberation of the paper is to be observed. At the meeting 

 of the Society for the Investigation of Nature, at Halle, on the 

 14-th of July in the present year (1827), I repeated these ex- 

 periments, and convinced the assembled members of it, espe- 

 cially the editors of this Journal. 



I consider therefore the careful separation of the sounding 

 reverberating vibrations from those slight motions of the bodies 

 that do not sound or reverberate (which may certainly be very 

 similar to the former), and which I have indicated in this arti- 

 cle, as necessary ; since great confusion is introduced by the 

 interference of the latter with the laws of motion of sounding 

 disks and reverberating bodies. 



It has been shown in the Doctrine of Undulation, published 

 by my brother and myself, how sounding and reverberating 

 vibrations, figures of sound and figures of vibration, should be 

 distinguished ; and how it results from this, that Savart's and 

 Chladni's experiments do not contradict each other*: but we 

 must also distinguish between these vibrations and vibrations 

 without any acoustic effect, which latter may also unite the scat- 

 tered sand into nodes. We have further shown, in the work 

 just quoted, that the sounding vibration is always of the class 

 of the standing vibrations, with which all small motions of all 

 bodies seem to terminate. From the circumstance that in all 

 these small motions of bodies left to themselves, at last a cer- 

 tain balance and uniformity manifest themselves ; and that this 

 * Vide Jahrbuch, 18%. 



uniform 



