218 



GENERAL SCIENCE 



ttalleus 



Stapes 



the fibers of the auditory nerve terminate and where the 

 auditory impulses originate. To the other side of the 

 vestibule the three semicircular canals are attached. 

 incus These canals seem to have 



something to do with bal- 

 ancing the body. 



How We Hear. When 

 a vibrating body produces 

 sound waves which reach 

 the ear, the sensation of 

 sound is produced. As the 

 waves reach the ear they 

 are collected by the ex- 

 ternal ear and concen- 

 trated upon the tympanic 

 membrane, which is thus 

 set into sympathetic vi- 

 bration with the object which caused the waves. This 

 vibration is communicated through the bones of the 

 middle ear to the liquids of the inner ear. These liquids 

 distribute the vibrations to all parts of the inner ear and 

 finally to the fibers of the auditory nerve (fibers of Corti) 

 which originate the proper impulses to be conveyed to 

 the brain as sound sensations. 



Tympanic flembrane 

 FIG. 193. The Ear Bones. 



QUESTIONS 



1. What is meant by wave length? 



2. If the speed of sound increases two feet for each degree 

 Centigrade, what will be the speed at 23 C. ? 



3. If the velocity of sound on a certain day is 1120 feet per 

 second and a sounding body makes 560 vibrations per second, 

 what is the wave length? 



4. Three seconds elapse between a flash of lightning and its 

 attendant thunder. How far away was the lightning? 



