230 LETTERS ON NATURAL MAGIC. 



the hearing or not hearing of musical notes at 

 both extremities of the scale seems to depend 

 wholly on the pitch or frequency of vibration 

 constituting the note, and not upon the intensity 

 or loudness of the noise. This affection of the 

 ear sometimes appears in cases of common deaf- 

 ness, where a shrill tone of voice, such as that 

 of women and children, is often better heard than 

 the loud and deeper tone of men. 



Dr. Wollaston remarked, that when the mouth 

 and nose are shut, the tympanum or drum of the 

 ear may be so exhausted by a forcible attempt to 

 take breath by the expansion of the chest, the 

 pressure of the external air upon the membrane 

 gives it such a tension, that the ear becomes 

 insensible to grave tones, without losing in any 

 degree the perception of sharper sounds. Dr. 

 Wollaston found, that after he had got into the 

 habit of making the experiment, so as to be able 

 to produce a great degree of exhaustion, his ears 

 were insensible to all sounds below F, marked 

 by the bass 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 produced by quicker vibra- 

 tions 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 



