lxii 



against the sharp edge of a hollow metalic cylinder. These vibrations 

 are at once imparted to the air just as they would be if made by a harp 

 string. If the whistle itself be moving, the sound waves will be shorter 

 in advance of it than in its rear. The more rapidly it moves the greater 

 will be the difference in their length; hence if it be approaching, more 

 waves will enter the ear in a second of time than if it be retreating. 



The tympanum is thrown into vibrations corresponding with those of 

 the air, and when these fall in regular periodic succession at a rate not less 

 than sixteen per second, nor more than thirty-eight thousand per second, 

 they create the sensation of musical sounds. When the vibrations are 

 irregular, the sense of noise is the result. Without stopping to explain 

 how these vibratory motions of the tympanum are conveyed from it, 

 by the four minute bones within the ear, to the fluid contained in the 

 complicated organ called the labyrinth, and from thence to the nerves, 

 I will simply refer to the wonderful little organ discovered in the laby- 

 rinth by Marchese Corti, and which Tyndall pronounces to all appear- 

 ances a musical instrument similar to a lute; with three thousand micro- 

 scopic fibres stretched in such a manner that some one or other is actu- 

 ated by the various vibrations within this great range of periods. These 

 vibrations are thus taken up from the labyrinthine fluid and trans- 

 mitted to the nerve filaments which traverse the labyrinth, and by these 

 the sensations are conveyed to the brain. An ordinary lute string may be 

 roused into vibration by a note from the voice, or by an organ peal, when 

 the periods of vibration of the air producing the note and the periods 

 of vibration of the string concur. If there be discord between the note 

 and the string, the latter cannot be roused. If you sing into an open 

 piano, the strings in unison with the voice are thrown into vibration, but 

 none other. A feeble note, because of its coincidence with the periods of 

 a sonorous body, may rouse it into sound, while a far more powerful note, 

 because of its non-concurrence, would produce in it no excitement what- 

 ever. 



If two tuning-forks of exactly the same pitch be placed at a considerable 

 distance from each other in the same room, and one be struck, the other 

 will immediately respond to it. If there be discord between them the one 

 at rest will remain silent. 



The ear is attuned to a wide range of sounds. The slightest musical 

 tremor which falls upon it, within the range of eleven octaves, excites 

 some delicate fibre within the ear whose periods of vibration synchronize 

 with it; and the sense of music is thus awakened in the brain. Each one 

 of the great multitude of wavelets sent forth from a grand orchestra finds 

 in the delicate lute of Corti some chord in unison with it; thus the con- 

 cord of sweet sounds is analyzed and each tremulous ripple in the air 

 faithfully reported to the brain. If vibrations strike the tympanum but 

 find no responsive chord within the ear, they are powerless to excite audi- 

 tion. Those less than sixteen and more than thirty six thousand per 

 second find no chord in this marvelous lute attuned in harmony with 

 them, and hence they fall upon the ear unheard. 



