071 Sounds inaudible hj certain Ears. 191 



note to which I allude might exceed it in acuteness, as my know- 

 ledge of the existence of this sound is derived wholly from some 

 young friends who \vere present, and heard a chirping, when I 

 was not aware of any sound. I suppose it to have been the cry 

 of some species of gryllus, and I imagine it to differ from the 

 gryllus campestris, because I have often heard the cry of that 

 insect perfectly. 



From the numerous instances in which I have now witnessed 

 the limit to acuteness of hearing, and from the distinct succes- 

 sion of steps that I might enumerate in the hearing of different 

 friends, as the result of various trials that I have made among 

 them, I am inclined 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 note is 

 heard distinctly. 



The suddenness of the transition from perfect hearing to total 

 want of perception, occasions a degree of surprise, which renders 

 an experiment on this subject with a series of small pipes among 

 several persons rather amusing. It is curious to observe the 

 change of feeling manifested by various individuals of the party, 

 in succession, as the sounds approach and pass the limits of their 

 hearing. Those who enjoy a temporary triumph, are often com- 

 pelled, in their turn, to acknowledge to how short a distance their 

 little superiority extends. 



Though it has not yet occurred to me to observe a limit to the 

 hearing of sharp sound in any person under twenty years of age, 

 I am persuaded, by the account that I have received from others, 

 that the youngest ears are liable to the same kind of insensibility. 

 1 have conversed with more than one person who never heard 

 the cricket or the bat ; and it appears far more likely that such 

 soimds were ahvays beyond their powers of perception, than that 

 they never had been uttered in their presence. 



The rangeof human hearing comprised between thelowestnotes 

 of the organ and the highest known cry of insects, includes more 

 than nine octaves, the whole of which are distinctly perceptible 

 by most ears, although the vibrations of a note at the higher ex- 

 treme are six or seven hundred fold more frequent than those 

 whi'.'h constitute the gravest audible sound. 



Since there is nothing in the constitution of the atmosphere to 

 prevent the existence of vibrations incomparably more frequent 

 than any of which we are conscious, we may imagine that ani- 

 mals like the gryili, whose powers appear to commence nearly 

 where ours terminate, may have the faculty of hearing still sharper 

 .sounds, which at present we do not know to exist ; and that there 

 niay be other insects hearing nothing in common with us, but 

 endued with a power of exciting, and a sense that perceives vibra- 

 tions 



