.762 'THE SENSE OF. HEARING 



by simply striking a note of the same character upon some other instru- 

 ment. The piano answers back with a note very similar to that re- 

 ceived by it from the distance. Also, if a certain note is struck in 

 the vicinity of a series of tuning forks, only that tuning fork will 

 answer which possesses the same periodicity of vibration as the primary 

 sound. These phenomena are made possible by the property of 

 sympathetic vibration or vibration of influence. As has been pointed 

 out, the transmission of the sonorous undulations may be effected in 

 two ways, namely, by direct contact, and by the transfer of the waves 

 through air without actual contact. It is to be noted, however, that 

 while elastic bodies may be set into vibration by neighboring bodies and 

 media, they cannot be activated unless their own periodicity corre- 

 sponds precisely to that of the activator. Thus, a string possess- 

 ing a vibratory quality of 125 in a second, will not be 

 affected by vibrations in air of 100 to the second. 



Helmholtz has devised an apparatus, called the 

 resonator, by means of which it is possible to analyze 

 sounds in accordance with their properties of sympa- 

 thetic vibration. It consists of a spherical capsule made 

 of copper or brass. Its two opposite sides are perfor- 

 ated. Through one of these the sound is conducted into 

 the interior of the resonator and from here through the 

 opposite opening into the external auditory meatus. 

 Konig has introduced an important modification of this 

 appliance by constructing it of two hollow cylinders. By 

 sliding these telescopically into one another, the size of 

 *^is capsule may be either increased or decreased. If 

 the rubber tube attached to its outlet is now introduced 

 into the auditory meatus of one ear while the other ear is closed, the 

 sounds entering through the opposite orifice, will appear stifled with the 

 exception of the one corresponding to this resonator. This particular 

 one sounds out clearly from among the confused monotone of the 

 others. 



If resonators of varying size are employed, it is possible in this way 

 to determine the presence or absence of the different tones or overtones 

 represented by them. Any given sound may thus be separated into its 

 components. This power of analysis is also possessed by the auditory 

 apparatus, or rather, by the constituents of the organ of Corti of the 

 internal ear. As Ohm has stated: every motion of the air which cor- 

 responds to a composite mass of musical tones, may be reduced into 

 their simple pendular vibrations, and each single vibration corre- 

 sponds to a simple tone, sensible to the ear and having a pitch deter- 

 mined by the periodic time of the corresponding motion of the air. 

 These facts suggest that the organ of Corti acts in the manner of a 

 resonator, its different cellular elements being adjusted to conform to 

 these simple vibrations. The manner in which this activation is 

 brought about will be discussed in a succeeding chapter. 



