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Chapter V. 



HEARING. 



§ 1 . Acoustic Principles. 



The knowledge acquired by animals of the pre- 

 sence and movements of distant objects is de- 

 rived almost wholly from the senses of hearing 

 and of sight ; and the apparatus, necessary for 

 the exercise of these senses, being more ela- 

 borate and refined than any of the organs we 

 have yet examined, exhibit still more irre- 

 fragable evidence of those profound designs, and 

 that infinite intelligence, which have guided the 

 construction of every part of the animal frame. 



Sound results from certain tremulous or vi- 

 bratory motions of the particles of an elastic 

 medium, such as air or water, excited by any 

 sudden impulse or concussion given to those 

 particles by the movements of the sounding 

 body. These sonorous vibrations are trans- 

 mitted with great velocity through these fluids, 

 till they strike upon the external ear ; and, then, 

 after being concentrated in the internal passages 

 of the organ, they are made to act on the fila- 



