COMPOSITION OF SOUND WAVES. 299 



if touched at one-fourth its length, the tone will be the 

 second octave above. Of course, any other aliquot part of 

 the length of the string may be used. In any case, the 

 experiment with riders may be repeated to indicate the 

 position of the segments and nodes. 



464. Quality or Timbre. As a sounding body 

 vibrates as a whole and in segments at the same time, the 

 fundamental and the harmonics blend. The resultant 

 effect of this blending of fundamentals and harmonics con- 

 stitutes what we call the quality or timbre of the sound. 

 We recognize the voice of a friend not by its loudness nor 

 by its pitch, but by its quality. When a piano and violin 

 sound the same tone, we easily distinguish the sound of 

 one from that of the other, because, while the fundamentals 

 are alike, the harmonics are different. Hence, the total 

 effects of the fundamentals and the harmonics, or the 

 qualities, are different. The possible combinations of fun- 

 damentals and harmonics, or forms of vibratory motion, 

 are innumerable. 



. The pupil is advised to read the section on Harmonics in 

 the third of Tyndall's Lectures On Sound, Chap. Ill, 9. Become 

 the owner of the book, if you can. 



465. Classes of Musical Instruments. Mu- 



sical instruments may be divided into two classes, stringed 

 instruments and wind instruments. The sounds sent forth 

 by stringed instruments are due to the regular vibrations of 

 solids ; those sent forth by wind instruments, to the regular 

 vibrations of columns of air confined in sonorous tubes. 



466. Sonorous T vibes. The material of which a 

 sonorous tube is made does not affect the pitch or loud- 

 ness of the sound, but does determine its timbre or quality. 



