CHAPTER XII 



HELMHOLTZ IN BONN AND HEIDELBERG SENSATIONS 



OF TONE CONTINUED 



HELMHOLTZ showed next how a compound 

 wave of sound might be analysed by the 

 application of the principle of resonance. The air in 

 any cavity or vessel, such as a bottle with a narrow 

 neck, or the familiar shell held to the ear, which, 

 in the days of childhood, we thought gave us the 

 sound of the sea, is thrown into sympathetic vibration 

 by the vibrations of any sounding body in its vicinity, if 

 the vibration periods of the body and of the cavity are 

 approximately the same. In the first instance Helm- 

 holtz used, as had previously been done by Ohm, two 

 bottles, with fairly wide mouths ; and then the size of 

 the cavity could be altered by filling the bottle more 

 or less full of water. Streams of air were directed 

 across the mouths through flattened gutta-percha 

 tubes. The bottles were tuned to b and ', an 

 interval of an octave. The sound of the first bottle 

 was like the vowel U, but when the sound of the 

 K 



