THE HUMAN EAR. 167 



nerves, one to the face, and the other to the tongue. The internal ear is 

 called the " labyrinth," from its intricate structure. We give an illustration 

 of the auditory apparatus of man (fig. 1 70). 



The auricle, or exterior ear, is also represented, but we need not go into 

 any minute description of the parts. We will just name them (fig. 171). 



Sound is the motion imparted to the auditory nerve, and we shall see 

 in a moment how sound is produced. The undulations enter the auditory 

 canal, having been taken up by the auricle ; the waves or vibrations move at 

 the rate of 1,100 feet a second, and reach the drum-head, which has motion 

 imparted to it. This motion or oscillation is imparted to other portions, and 

 through the liquid in the labyrinth. The impressions of the sound wave are 

 conveyed to the nerve, and this perception of the movement in the water of 

 the labyrinth by the nerve threads and the brain causes what we term 

 " hearing." 



10 



Fig. 171. i. Pit of anti-helix. 2,6, 10. Curved edge of the auricle. 3. Mouth of auditory canal. 

 4. Tragus. 5. Lobe. 7. Anti-helix. 8. Concha. 9. Anti-tragus. 



Let us now endeavour to explain what sound is, and how it arises. 

 There are some curious parallels between sound and light. When speaking 

 of light we mentioned some of the analogies between sound and light, and 

 as we proceed to consider sound, we will not lose sight of the light we have 

 just passed by. 



Sound is the influence of air in motion upon the hearing or auditory 

 nerves. Light, as we have seen, is the ether in motion, the vibrations strik- 

 ing the nerves of the eye. 



There are musical and unmusical sounds. The former are audible 

 when the vibrations of the air reach our nerves at regular intervals. 

 Unmusical sounds, or irregular vibrations, create noise. Now, musical tones 

 bear the same relation to the ear as colours do to the eye. We must have 

 a certain number of vibrations of ether to give us a certain colour (vide 

 table). " About four hundred and fifty billion impulses in a second " give 

 red light. The violet rays require nearly double. So we obtain colours by 



