Little Brown-bat 1151 



"There is an odd superstition in Sussex that persons over 

 40 years of age are unable to hear the cry of a Bat." 



According to Tyndall/ "the human ear is hmited in its 

 range of hearing musical sounds. If the vibrations number 

 less than 16 a second, we are conscious only of the separate 

 shocks. If they exceed 38,000 a second, the consciousness of 

 sound ceases altogether. 



"The range of the best ear covers about 1 1 octaves, but an 

 auditory range limited to 6 or 7 octaves is not uncommon. 



"The sounds available in music are produced by vibra- 

 tions comprised between the limits of 40 and 4,000 a second. 

 They embrace 7 octaves.' 



"While endeavouring to estimate the pitch of certain sharp 

 sounds. Dr. Wollaston remarked in a friend a total insensi- 

 bility to the sound of a small organ-pipe, which, in respect to 

 acuteness, was far within the ordinary limits of hearing. The 

 sense of hearing of this person terminated at a note 4 octaves 

 above the middle E of the pianoforte. The squeak of the Bat, 

 the sound of a cricket, even the chirrup of the common house- 

 sparrow, are unheard by some people who for lower sounds 

 possess a sensitive ear. A difference of a single note is some- 

 times sufficient to produce the change from sound to silence. 



"'Nothing can be more surprising,' writes Sir John 

 Herschel, 'than to see two persons, neither of them deaf, the 

 one complaining of the penetrating shrillness of a sound, while 

 the other maintains there is no sound at all.' Thus, while 

 one person mentioned by Dr. Wollaston could but just hear a 

 note 4 octaves above the middle E of the pianoforte, others 

 have a distinct perception of sounds full 2 octaves higher. The 

 chirrup of the sparrow is about the former limit; the cry of the 

 Bat, about an octave above it; and that of some insects, prob- 

 ably, another octave. In 'The Glaciers of the Alps' I have 

 referred to a case of short auditory range noticed by myself, 

 in crossing the Wengern Alps in company with a friend. The 

 grass at each side of the path swarmed with insects, which to 



* Sound, p. 81. 



° Each note has double the vibrations of its octave below. 



