826 NATURAL THEOLOGY. 



It suffices with some to say that the undulation 

 of sound is received upon the membrane of the 

 tympanum, and by it is communicated to the at- 

 mosphere within. But how is the infinite variety 

 of sounds, all, in fact, that we hear, communicated 

 simultaneously through the same membrane ? , 

 In the first place, the membrane is not simple, 

 nor is it muscular, but contains within it cords or 

 fibres which run from its outer margin, converging 

 towards the malleus. It is now that we look with 

 great interest upon the experiments of Chladni 

 and others on metallic plates. He strews dust 

 upon one of these plates, and then brings out a 

 note by drawing the bow of the violin upon the 

 edge ; when the sand, or powder, or dust, will ar- 

 range itself in regular figures. These figures are 

 remarkable for their symmetry, dividing the cir- 

 cumference of the plate into equal parts, from 

 six to forty ; or the sand divides itself into circles 

 having the same centre with the plate, and the 

 diametrical and circular lines combine to produce 

 an astonishing variety in the configuration of the 

 particles. Here, then, we have a proof that, 

 instead of there being a general undulation or 

 vibration of the whole membrane of the tympa- 

 num, it may be subdivided, a motion taking place 

 in its minute parts, and these having many nodes 

 or centres which remain motionless ; in short, we 

 perceive a capability of motion in the membrane 

 corresponding with the variety of sounds which 

 we know to be propagated through it. And if we 



