ISS On Sounds inaudihh by certain Ears. 



sudden cessation of the effort, the internal passage to the ear be- 

 comes closed by the flexibility of the Eustachian tube, which acts 

 as a valve, and prevents the return of air into the tympanum. 

 As the defect thus occasioned is voluntary, so also is the remedy; 

 for the unpleasant sensation of pressure mi the drum, and the 

 partial deafness which accompanies it, may at any instant be re- 

 moved by the act of swallowing, which opens the tube, and, by 

 allowing the air to enter, restores the equilibrium of pressure ne- 

 cessary to the due performance of the functions of the ear. 



In my endeavours to ascertain the extent to which this kind 

 of deafness may be carried, some doubt has arisen, from the dif- 

 ficulty of finding sounds sufficiently pure for the purpose. The 

 sounds of stringed instruments are in this respect defective ; for 

 unless the notes produced are free from any intermixture of their 

 sharper chords, some degree of deception is very liable to occur 

 in the estimate of the lowest note really heard. I can, neverthe- 

 less, with considerable confidence, say, that my own ears may be 

 rendered insensible to all sounds below F marked by the base 

 cliff. But as I have been in the habit of making the experiment 

 frequeiitiv, it is probable that other persons who may be inclined 

 to repeat it, will not with equal facility effect so high a degree 

 of exhaustion as T have done. To a moderate extent the ex- 

 periment is not difficult, and well worth making. The effect is 

 singularly striking, and may aptly be compared to the mechanical 

 separation of larger and smaller bodies by a sieve. If I strike 

 the table before me with the end of my finger, the whole board 

 sounds with a deep dull note. If I strike it with my nail, there 

 is also at the same time a sharp sound produced by quicker vi^ 

 brations of parts around the point of contact. When the ear is 

 exhausted it hears only the latter sound, without perceiving in 

 anv degree the deeper note of the whole table. In the same 

 manner, in listening to the sound of a carriage, the deeper rum- 

 bling noise of the body is no longer heard by an exhausted ear ; 

 but the rattle of a chain or loose screw remains at least as audible 

 as before exhaustion. 



Although 1 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 

 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 sensible of ex- 

 ternal pressure on the tympanum; but it is not easy at first to 



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