VIBRATION OF BODIES IN GENERAL. -i] 



hope to give a complete solution ti.l our knowledge has advanced 

 much beyond its present condition. 



Indeed, in the science of Acoustics there is a vast body of facts to 

 which we might apply what has just been said ; but for the sake of 

 pointing out some of them, we shall consider them as the subjects of 

 one extensive and yet unsolved problem. 



CHAPTER VT. 

 PROBLEM OF DIFFERENT MODES OF VIBRATION OF 



BODIES IN GENERAL. 



"IVTOT only the objects of which we have spoken hitherto, strings and 

 IN pipes, but almost all bodies are capable of vibration. Bells, gongs, 

 tuning-forks, are examples of solid bodies ; drums and tambourines, of 

 membranes ; if we run a wet finger along the edge of a glass goblet, 

 we throw the fluid which it contains into a regular vibration ; and the 

 various character which sounds possess according to the room in which 

 they are uttered, shows that large masses of air have peculiar modes 

 of vibration. Vibrations are generally accompanied by sound, and 

 they may, therefore, be considered as acoustical phenomena, especially 

 as the sound is one of the most decisive facts in indicating the mode 

 of vibration. Moreover, every body of this kind can vibrate in many 

 different ways, the vibrating segments being divided by Nodal Lines 

 and Surfaces of various form and number. The mode of vibration, 

 selected by the body in each case, is determined by the way in which 

 it is held, the way in which it is set in vibration, and the like circum- 

 stances. 



The general problem of such vibrations includes the discovery and 

 classification of the phenomena ; the detection of their formal laws ; 

 and, finally, the explanation of these on mechanical principle?. Wo 

 must speak very briefly of what has been clone in these ways. The 

 facts which indicate Nodal Lines had been remarked by Galileo, 

 on the sounding board of a musical instrument; and Hooke had 

 proposed to observe the vibrations of a bell by strewing flour upon 

 it. But it was Chladni, a German philosopher, who enriched acous- 

 tics with the discovery of the vast variety of symmetrical figures of 

 Nodal Lines, which are exhibited on plates of regular forms, when 



