160 
Dr Wollaston on Somids 
by quicker vibrations of parts around the point of contact. 
When the ear is exhausted it hears only the latter sound, with- 
out perceiving in any degree the deeper note of the whole table. 
In the same manner, in listening to the sound of a carriage, the 
deeper rumbling noise of the body is 'no longer heard by an ex- 
hausted ear ; but the rattle of a chain or loose screw remains at 
least as audible as before exhaustion. 
Although I cannot propose such an experiment as a means of 
improving the effect of good music, yet, as a source of amuse- 
ment even from a defective performance, I have occasionally 
tried it at a concert with singular effect ; since none of the sharp- 
er 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 sensible of ex- 
ternal pressure on the tympanum ; but it is not easy at first to 
relax the effort of inspiration with sufficient suddenness to close 
the Eustachian tube, and thus maintain the exhaustion ; neither 
is it very easy to refrain long together from swallowing the sali- 
va, 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 exter- 
nal 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 Eustachian 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 ac- 
customed to descend, probably acquire the art of opening the 
Eustachian tube by swallowing, or incipient yawning, as soon as 
the divinff-bell touches the water. 
9 . 
It seems highly probable, that in the state of artificial tension 
thus produced, a corresponding deafness to low tones is occa- 
sioned ; but, as I never have been in that situation, I have not 
bad an opportunity of ascertaining this point by direct experi- 
ment. 
