. of the Position of Sonorous Bodies, 624 
which constitutes the topic of the present essay. 
But it will be proper to say something, in the 
first place, respecting the accuracy of this organ 
in distinguishing the difference of two sounds 
that are known to be nearly equal in force; 
because the truth of my opinion rests on this 
fundamental fact.—The want of a sure method 
of measuring the momentum of the air when 
agitated by a vibrating body, with the same 
certainty that the angles between rays of light 
are measured, appears to be the reason why 
the accuracy in question is so generally over- 
looked. But though it seems very difficult to 
give a general rule for measuring magnitudes 
of this description, the following experiment 
proves, in a very satisfactory manner, what a 
delicate faculty the sense of hearing is.—A bolt, 
driven by a spring against a fixed piece of metal, 
may be made to produce a succession of strokes 
of equal force; consequently the concussions 
given to the air, by any two of these strokes, 
will also be equal; and will therefore occasion 
like effects on the same ear, placed at equal 
distances from the spring, the state of the wind. 
and weather being the same in both cases.— 
I caused an instrument of the preceding de- 
scription to be struck repeatedly at the dis 
tance of 40 feet from my ear, care being taken , 
to place it in the axis of hearing produced ; after 
