598 



PHYSIOLOGY 



mental tone with vibrations per second in the ratio of 1, 2, 3, 4, 5, and 6, etc. 

 Thus if the fundamental tone be c, the overtones, or harmonics, will be 

 produced as is shown below : 



2 . 



9 



10 



34567 8 



VIBRATIONS PER SECOND 



132 2x132 3x132 4x132 5x132 6x122 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 addi- 

 tion 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 overtones 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 over- 

 tones. 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 each component tone is composed are combined together to form a 

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

 vibrations of which it is made up, and to the time relationship (phase) between 

 them. 



Thus in the diagram (Fig. 303) the wave shown by the continuous line 



FIG. 303. d, a compound sound wave, which may be analysed into a, the 

 fundamental tone, and b and c, the first and second overtones. (HENSEN.) 





is compounded of the series of simple vibrations represented by the different 

 dotted lines. The component fundamental overtones and harmonics can 

 be readily identified in a tone experimentally by employing the series of 

 resonators described above. By practice it is possible to train the ear to 

 recognise strong overtones without the use of resonators. 



