1 88 THE HUMAN BODY. 



classes musical sound and noise. They both have the same 

 origin, the vibrations of a body transmitted to the air. The 

 short duration of a noise, and the lack of isochronism in its 

 vibrations, do not permit us to appreciate its musical value, 

 and this distinguishes it from musical sound. Thus the ex- 

 plosion of gas or powder, the crack of a whip, or the 

 breaking of a branch make a noise, but give no musical 

 sound. The limit between sound and noise is otherwise in- 

 sensible, and varies according to the individual. A noise as 

 well as a sound may be grave or acute, feeble or intense. 

 The difference in the duration of the sensation does not 

 permit us to compare noise to sound, but yet the ear seizes 

 the relation between two noises as well as between two 

 musical sounds. 



A sound is called musical when its pitch can be estimated 

 absolutely and relatively to other sounds grave or acute; or, 

 in other words, when the number of vibrations follows a 

 constant law and can be determined. 



Whatever may be the difference, however, between a noise 

 and a musical sound, the one is only a variety or degree of 

 the other, and both, proceeding from the same source, may 

 be studied under the generic denomination of sound. 



Sound has four fundamental properties duration, pitch, 

 intensity, and timbre or distinctive quality. The three first 

 named are defined by the words which express them: as 

 for the timbre, it is the resonance peculiar to each instru- 

 ment, to each voice, which enables us to distinguish without 

 difficulty the notes of a violin, a clarionette, or a flute, and 

 to recognize individuals by hearing them speak or sing. 



The duration of a sound is measured by the time that the 

 body vibrates from which it proceeds ; it is high and acute 

 according to the number of vibrations, and its intensity is 

 measured by the amplitude or range of the vibrations which 

 cause it, and this amplitude is in proportion to the force 

 acting on the sonorous body. 



The "timbre" of sounds was long an insoluble enigma to 

 the physicist. and the physiologist. |. Miiller had suspected 

 its origin in attributing it either to the isochronism of 

 sonorous waves of different velocity, or to waves' of different 



