Page:Elementary Text-book of Physics (Anthony, 1897).djvu/191

 CHAPTER IV.

ANALYSIS OF SOUNDS AND SOUND SENSATIONS.

151. Quality.—As has already been stated, the tones of different instruments, although of the same pitch and intensity, are distinguished by their quality. It was also stated that the quality of a tone depends upon the manner in which the vibration is executed. The meaning of this statement can best be understood by considering the curves which represent the vibrations. In Fig. 57 are given several forms of vibration curves of the same period.

Every continuous musical tone must result from a periodic vibration, that is, a vibration which, however complicated it may be, repeats itself at least as frequently as do the vibrations of the lowest audible tone. According to Fourier's theorem (§ 21), every periodic vibration is resolvable into simple harmonic vibrations having commensurable periods. It has been seon that all sounding bodies may subdivide into segments, and produce a series of tones of which the vibration periods generally bear a simple