.370 THE SENSORIAL FUNCTIONS. 



Chapter V. 



HEARING. 



^ 1. Acoustic Principles. 



The knowledge acquired by animals of the pre- 

 sence and movements of distant objects is derived 

 almost wholly from the senses of hearino; and of 

 sight; and the apparatus, necessary for the exercise 

 of these senses, being more elaborate and refined 

 than any of the organs we have yet examined, 

 exhibits still more irrefragable evidence of those 

 profound designs, and that infinite intelligence^ 

 vrhich have guided the construction of every part 

 of the animal frame. 



Sound results from certain tremulous or vibratory 

 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 move- 

 ments of the sounding body. These sonorous vi- 

 brations are transmitted with great velocity through 

 those 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 

 filaments of a particular nerve called the acoustic, 

 or auditory nerve, of which the structure is adapted 

 to receive these peculiar impressions, and to com- 

 municate them to the brain, where they produce 

 changes, which are immediately followed by the 

 sensation of sound. Sound cannot traverse a void 



