114: SCIENCE OF COMMON THINGS. 



Production of sound. Drum of the ear. 



PART IV. 



SOUND. 



CHAPTEK I. 



ORIGIN AND TRANSMISSION OF SOUND. 



How is sound produced f 



Sound is heard when any sudden shock or impulse, 

 causing vibrations, is given to the air, or any other 

 body, which is in contact directly or indirectly with the 

 drum of the ear. 



T22 What is the drum or tympanum of the ear ? 



A thin membrane which closes the aperture of the 

 ear. 



7*23 How do the vibrations of the air, striking upon the drum of the ear, 

 give us the sensation of sound ? 



Behind the drum of the ear are various cavities and 

 tubes in the bone which form the side of the head, in 

 which the minute fibres of the auditory nerve are dis- 

 tributed. When the drum of the ear is made to vibrate 

 freely .by the action of the sonorous undulations of the 

 external air, the vibrations are communicated by the 

 action of minute bones, nmscles, and fluids contained in 

 the cavities of the ear, to the nerve, and from thence the 

 impressions are conveyed to the brain. 



Fig. 29 is a perspective magnified view of the interior of the ear. The 

 several parts of the ear, and the progress of sound towards the nerve 

 which communicates the sensation to the brain, may, however, be best 

 illustrated by reference to Fig. 30 : 



1. There is external to the head a wide-mouthed tube, or ear-trumpet, 

 <$, for catching and concentrating the waves of sound. It is movable in 



