VIBRATION OF SOLID BODIES. 187 



with regard to vibrating strings. By opening 

 other holes we may subdivide a' vibrating column 

 into any number of smaller vibrating columns. 

 The holes in flutes, clarionets, &c. are made for 

 this purpose. When they are all closed up, the 

 air vibrates in one column ; and by opening and 

 shutting the different holes in succession, the 

 number of vibrating columns is increased or dimi- 

 nished at pleasure, and consequently the harmonic 

 sounds will vary in a similar manner. 



Curious as these phenomena are, they are still 

 surpassed by those which are exhibited during 

 the vibration of solid bodies. A rod or bar of 

 metal or glass may be made to vibrate either 

 longitudinally or laterally. 



An iron rod will vibrate longitudinally, like a 

 column of air, if we strike it at one end in the 

 direction of its length ; or rub it in the same 

 direction with a wetted finger, and it will admit 

 the same fundamental note as a column of air ten 

 or eleven times as long, because sound moves so 

 much faster in iron than in air. When the iron 

 rod is thus vibrating along its length, the very 

 same changes which we have shown in Fig. 41, 

 as produced in a spiral spring, or in a column of 

 air, take place in the solid metal. All its par- 

 ticles move alternately towards A and towards B, 

 the metal being in the one case condensed at the 

 end to which the particles move, and expanded 

 at the end from which they move, and retaining 

 its natural density in the middle of the rod. If 

 we now hold this rod in the middle, by the finger 

 and thumb lightly applied, and rub it in the mid- 

 dle either of AB or BC with a piece of cloth 

 sprinkled with powdered rosin, or with a well- 



