HEARING 



651 



of the large wave; the quality is determined by that of the large 

 wave and the wavelets. 



The simplest musical tone is produced by a body like a tuning- 

 fork vibrating in simple harmonic motion that is to say, in such a 

 manner that the waves are all of equal size. This can be seen by 

 the tracing made, by a vibrating tuning-fork (time-marker) upon a 

 revolving kymograph. Such a sound is uniform, weak, and dull, 

 and quickly becomes monotonous. If two tuning-forks be sounded, 

 one of which vibrates twice as fast as the other, there can be heard 

 the tones of the two forks and a combination of the tones. The 



B e 



V 



FlG. 380. TO ILLUSTRATE THE FORMATION OF A COMPOUND WAVE FROM TWO 



PENDULAR WAVES. (Helmholtz.) 



A and B, Pendular vibrations, B being the octave of A. If superposed so that e, 

 coincides with d and the ordinates are added algebraically, the non-pendular 

 curve is produced. If superposed so that e coincides with d' the non-pendular 

 curve D is produced. 



form of vibration will vary according as the forks produce at the same 

 time rarefaction or condensation, or one is producing rarefaction while 

 the other is producing condensation of the air (curves G and D, Fig. 380). 

 From an indefinite series of such vibrations, of which the period of 

 vibration of the fundamental is always a multiple of the least 

 frequent of the series, an infinite variety of curves may be obtained, 

 yielding musical tones having the same fundamental pitch, but 

 differing in quality according to the character of the wavelets. 



The character of the musical notes of different instruments may 

 be analyzed by means of resonators. A note resonates in a cylinder 

 having the same wave-length of vibrations that constitutes the original 

 note, or an exact divisor of the wave-length of that note. If different 



