288 LETTEES ON NATURAL MAGIC. 



exhaustion, liis ears were insensible to all sounds below 

 F, marked by the base clef. "If I strike the table before 

 me," says he, " 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 pro- 

 duced by quicker vibrations of parts around the point of 

 contact. When the ear is exhausted it hears only the 

 latter sound, without 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 exhausted ear ; but the 

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

 as before exhaustion." Dr. Wollaston supposes that this 

 excessive tension of the drum of the ear, when produced 

 by the compressed air in the diving-bell, will also produce 

 a corresponding deafness to low tones. This curious experi- 

 ment has been since made by Dr. Colladon, when descend- 

 ing in the diving-bell at Howth in 1820. "We de- 

 scended," says he, " so slowly that we did not notice the 

 motion of the bell ; but as soon as the bell was immersed 

 in water, we felt about the ears and the forehead a sense 

 of pressure, which continued increasing during some 

 minutes. I did not, however, experience any pain in tho 

 ears ; but my companion suffered so much that we were 

 obliged to stop our descent for a short time. To remedy 

 that inconvenience, the workmen instructed us, after 

 having closed our nostrils and mouth, to endeavour to 

 swallow, and to restrain our respiration for some moments, 

 in order that, by this exertion, the internal air might act 

 on the Eustachian tube. My companion, however, having 

 tried it, found himself very little relieved by this remedy. 

 After some minutes, we resumed our descent. My friend 

 suffered considerably ; he was pale ; his lips were totally 

 discoloured; his appearance was that of a man on tho 

 point of fainting ; he was in involuntary low spirits, 



