564 PHYSIOLOGY 



When the same note is sounded on different instruments, i.e. 

 tuning-fork, violin, piano, trumpet, human voice, every person, 

 whether he has an educated musical ear or not, can say at once what 

 kind of instrument is being used. This fact shows that the sound 

 wave produced by these instruments must differ, altogether apart 

 from any differences in amplitude or in number of vibrations per 

 second, and if the sound waves produced by these instruments be 

 recorded an actual difference is found in the shape of the curve. 



If a stretched wire be plucked so as to set it into transverse vibra- 

 tions it will give out a certain note, dependent on its length, its thick- 

 ness, and the tension to which it is subjected. If its length be halved 

 it will give out a note which is of double the number of vibrations 

 per second. If only one-third of the wire be set "into vibrations the 

 sound wave produced will have three times the number of vibra- 

 tions of that of the whole string. When the string is free to vibrate as 

 a whole the segments of it tend to vibrate even while the whole string 

 is vibrating. If therefore we take the note given out by the whole 

 string, the ' fundamental tone,' as corresponding to 132 vibrations per 

 second, there will also be a series of notes superadded to the funda- 

 mental tone with vibrations per second in the ratio of 1 , 2, 3, 4, 5, and 

 6, &c. Thus if the fundamental tone be c, the overtones, or harmonics, 

 will be produced as is shown below : 



122: 



VIBRATIONS PER SECOND 



132 2x132 3x132 4x132 5x132 6x132 7x132 8x132 9x132 10x132 



Nearly all musical instruments, as well as the apparatus for 

 producing the human voice, resemble a stretched wire in giving out 

 overtones in addition to the fundamental tones, and the difference in 

 the quality of various instruments is chiefly determined by the varying 

 predominance of the different overtones. In some the higher over- 

 tones may be most marked, in others only the lower overtones. The 

 tuning-fork is practically the only instrument the note of which is 

 pure, i.e. free from harmonics or overtones. It must be remembered 

 that these different tones arrive at the external ear simultaneously. 

 We do not have some particles of air vibrating at one rate and other 

 particles at another rate, but all the simple vibrations of which the 

 component tone is composed are combined together to form a com- 

 pound wave, the shape of which differs according to the constituent 

 vibrations of which it is made up. 



