632 On.the Method of judging by the Ear 
imperfections in one instance, by means of ins 
formation derived from the other senses, it will 
not fail to make use of the same aids as often 
as it can do so with advantage; it will therefore 
have recourse to this secondary species of know- 
ledge, provided the ‘pulses of air, proceeding 
from a sounding body placed not directly be- 
fore or behind the hearer, can be proved to fall 
with a greater force on one of his ears than on 
the other. 1 am apprized that this supposition 
is not countenanced by the prevailing theory 
of the propagation of sounds: according to 
which, the pulses of air diverge from every point 
in the circumference of an obstacle towards all 
parts beyond that impediment. But this theory 
appears to be a mathematical conception rather 
than a fact; it is therefore better fitted to ex- 
plain the outlines of hydrostatics, than to assist 
in the minuter parts of a physical enquiry. The’ 
laws and properties of a perfectly elastic fluid 
do not apply to the atmosphere without excep- 
tion; ‘and an occurrence, which is not unfre- 
quent, seems to prove decisively, that the’ pulses 
of air which move parallel to the axis of hear 
ing strike only one ear with effect, I mean that 
which opposes itself to their progress. If you 
happen to address yourself in an open area to a 
person who has the misfortune of being deaf on 
one side, having your mouth directed to his 
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