MUSICAL AND HARMONIC SOUNDS. 



181 



vibrating it will give out a sound corresponding 



to the rapidity of its vibrations, and arising from 



the successive blows or impulses given to the air 



Fig. 40. 



by the string. This sound is called the funda- 

 mental sound of the string, and its acuteness or 

 sharpness increases with the number of vibrations 

 which the string performs in a second. 



If we now touch the vibrating string A'B 

 lightly with the finger, or with a feather at the 

 middle point C, Fig. 40, it will give out a more 

 acute but fainter sound than before, and while 

 the extent of its vibrations is diminished, their 

 frequency is doubled. In like manner, if we 

 touch the string A"B*, Fig. 40, at a point C, so 

 that A'C is one-third of A"B', the note will be 

 still more acute, and correspond to thrice the 

 number of vibrations. All this might have been 

 expected; but the wonderful part of the experi- 

 ment is, that the vibrating string A'B' divides 

 itself at C into two parts A'C, CB', the part A'C 

 vibrating round A and C as fixed points, and the 

 part C B' round C and B', but always so that the 

 part A'C is at the same distance on the one side 



