im 
InaudibU by certain Ears > 
fer from the gryllus campestris, because I hav^ often heard the 
cry of that insect perfectly. 
From the numerous instances in which I hate 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 infclined to think, that at the limit of hearing, the 
interval of a single note between two sounds, ipay 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 a party 
in succession, as the sounds approach and pass the limits of their 
hearing. Those who enjoy a temporary triumph, are often 
compelled in their turn to acknowledge to how short a distance 
their little superiority extends. 
Though it has not yet occurred to nie 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 in- 
sensibility. I have conversed with more than one person who 
never heard ihe cricket or the bat, and it appears far more likely 
that such sounds were always beyond their powers of percep- 
tionj^ than that they never had been uttered in their presence. 
The range of human hearing comprised between the lowest 
notes of the organ and the highest known-cry of insects, includes 
more than nine octaves, the whole of which are distinctly per- 
ceptible by most ears, although the vibrations of a note at the 
higher extreme are six or seven hundred fold more frequeat 
than those which constitute the gravest audible sound. 
Since there is nothing in the constitution of the atmosphere 
to prevent the existence of vibrations incomparably more fre- 
quent than any of which we are conscious, we may imagine that 
animals like the grylli, whose powers appear to commence near- 
ly where ours terminate, may have the faculty of hearing still 
sharper sounds, which at present we do not know to exist ; and 
nS 
