3°9 
inaudible by certain ears. 
Although I cannot propose such an experiment as a means 
of improving the effect of good music, yet, as a source of 
amusement even from a defective performance, I have occa- 
sionally tried it at a concert with singular effect ; since none 
of the sharper sounds are lost, but by the suppression of a 
great mass of louder sounds, the shriller ones are so much 
the more distinctly perceived, even to the rattling of the 
keys of a bad instrument, or scraping of catgut unskilfully 
touched. 
Those who attempt exhaustion of the ear for the first 
time, rarely have any difficulty in making themselves sensi- 
ble of external pressure on the tympanum ; but it is not easy 
at first to relax the effort of inspiration with sufficient sudden- 
ness to close the Eustachian tube, and thus maintain the ex- 
haustion ; neither is it very easy to refrain long together 
from swallowing the saliva, which instantly puts an end to 
the experiment. 
I may here remark, that this state of excessive tension, of 
the tympanum is sometimes produced by sudden increase of 
external pressure, as well as by decrease of that within, as 
is often felt in the diving-bell as soon as it touches the water ; 
the pressure of which upon the included air closes the Eus- 
tachian tube, and, in proportion to the descent, occasions a 
degree of tension on the tympanum, that becomes distressing 
to persons who have not learned to obviate this inconvenience. 
Those who are accustomed to descend, probably acquire the 
art of opening the Eustachian tube by swallowing, or in- 
cipient yawning, as soon as the diving-bell touches the 
water. 
It seems highly probable that, in the state of artificial 
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