CHAPTER XV 



ACOUSTICS. 



THE EAR, AND HEARING PHYSIOLOGY OF HEARING AND SOUND 



SOUND AS COMPARED WITH LIGHT WHAT IS SOUND ? VELOCITY 



OF SOUND CONDUCTIBILITY THE HARMONOGRAPH. 



BEFORE entering upon the science of ACOUSTICS, a short description of 

 the ear, and the mode in which sound is conveyed to our brain, will be no. 

 doubt acceptable to our readers. The study of the organs of hearing is not 

 an easy one; although we can see the exterior portion, the interior and 

 delicate membranes are hidden from us in the very hardest bone of the body 

 the petrous bone, the temporal and rock-like bone of the head. 



Fig 170. i. Temple bone. 2. Outer surface of temple. 3. Upper wall of bony part of hearing canal. 

 4. Ligature holding "hammer" bone to roof of drum cavity. 5. Roof to drum cavity. 6 Semi- 

 circular canals. 7. Anvil bone. 8. Hammer bone. 9. Stirrup bone. 10. Cochlea, u. Drum- 

 head cut across. 12. Isthmus of Eustachian tube. 13. Mouth of tube in the throat. 14. Auditory 

 canal. 15. Lower wall of canal. 16. Lower wall of cartilaginous part of canal. 17. Wax glands. 

 1 8. Lobule. 19. Upper wall of cartilaginous portion of canal. 20. Mouth of auditory canal 

 21. Anti-tragus. 



The ear (external) is composed of the auricle, the visible ear, the 

 auditory canal, and the drum-head, or membra tympani. The tympanum, or 

 "drum," is situated between the external and the internal portions of the ear. 

 This part is the " middle ear," and is an air cavity, and through it pass two 



