133 



On Sounds Inaudible by certain Ears. By William Hyde Wollaston, 

 M.D. P.R.S. Read June 29, 1820. [PAi7. Trans. 1820, p. 306.] 



In this communication the author describes a peculiar insensibility 

 to certain sounds in the ears of persons not otherwise deaf, which 

 he was led to observe by trying different modes of lessening the 

 sense of hearing in himself; when he found, that by closing the 

 nose and mouth, and expanding the chest, the membrana tympani, 

 thrown into a state of tension by external pressure, made the ear 

 insensible to grave tones, without affecting the perception of sharper 

 sounds. In this case the ear was insensible to all sounds below F 

 marked by the bass cliff. 



In the natural healthy state of the ear, there seems to be no limit 

 to the power of discerning low sounds ; but if we attend to the 

 opposite extremity of the scale of audible sounds, and with a series 

 of pipes, exceeding each other in sharpness, examine their effects 

 successively upon the ears of different persons, we shall find con- 

 siderable difference in their powers of hearing them, and see reason 

 to infer that human hearing is more confined than has been supposed. 

 Dr. Wollaston's attention was called to this circumstance by finding 

 a person insensible to the sound of a small organ pipe, which, with 

 respect to acuteness, was far within the limits of his own hearing. 

 By subsequent examination, this person's hearing was found to ter- 

 minate at a note four octaves above the middle E of the pianoforte. 

 Other cases of the insensibility of the ear of certain persons to high 

 sounds are next adverted to ; such as to the chirping of the grass- 

 hopper, the cricket, the sparrow, and the bat ; the latter being 

 about five octaves above the middle E of the piano. The limit of 

 the author's own sense of hearing is at about six octaves above the 

 middle E ; and, from numerous trials, he is induced to think that, 

 at the limit of hearing, the interval of a single note between two 

 sounds may be sufficient to render the higher note inaudible, although 

 the lower one is heard distinctly. 



The range of human hearing includes more than nine octaves, the 

 whole of which are distinct to most ears, though the vibrations of a 

 note at the higher extreme are 600 or 700 times more frequent than 

 those which constitute the gravest audible sound ; and as vibrations 

 incomparably more frequent may exist, we may imagine, says the 

 author, that animals like the Grylli, whose powers appear to com- 

 mence nearly where ours terminate, may hear still sharper sounds, 

 which we do not know to exist ; and that there may be insects hear- 

 ing nothing in common with us, but endued with a power of exciting, 

 and a sense that perceives the same vibrations which constitute our 

 ordinary sounds, but so remote that the animal who perceives them 

 may be said to possess another sense, agreeing with our own, solely 

 in the medium by which it is excited, and possibly wholly unaffected 

 by those slower vibrations of which we arc sensible. 



