368 COORDINATION AND SENSATION 



Compare this action with the transmission of sound waves by different 

 portions of the ear. 



To show Effects of Sound Waves. I. Place two large tuning 

 forks of the same pitch, and mounte: 1 : on thin boxes for reenforcing 

 their vibrations, near each other on a table. Vibrate one of the forks 

 for a moment and then stop it by means of the hand. Observe that 

 the other fork has been set in vibration. (This experiment does not 

 work with forks of different pitch.) 2. While holding a thin piece of 

 paper against a comb with the open lips, produce musical tones with 

 the vocal cords. These will set the paper in vibration, producing the 

 so-called " comb music." 3. Examine the disk in a telephone which is 

 set in vibration by the voice. Observe that it is a thin disk and, like 

 the membrane of the ear, has air on both sides of it. 



To show the Reinforcement of Sound. I. Vibrate a tuning fork 

 in the air, noting the feebleness of the tone produced. Then hold the 

 stem against a door or the top of a table, noting the difference. 

 2. Hold a vibrating tuning fork over a tall jar, or bottle, and gradually 

 add water. If the vessel is sufficiently tall, a depth will be reached 

 where the air in the vessel reenforces the sound from the fork. 3. 

 Hold a vibrating fork over the mouth of a small fruit jar, partly covered 

 with a piece of cardboard. By varying the size of the opening, a posi- 

 tion will be found where the sound is reenforced. If not successful at 

 first, try bottles and jars of different sizes. 



To illustrate the Manner of Vibration of the Liquid in the Internal 

 Ear. Tie a piece of dental rubber over the end of a glass or wooden 

 tube about half an inch in diameter and six inches in length. Fill the 

 tube entirely full of water and, without spilling, tie a piece of thin rub- 

 ber tightly over the other end. Holding the tube horizontally, press 

 the rubber in at one end and note that it is pushed out at the other 

 end. Make an imitation of a vibration with the finger against the 

 rubber at one end of the tube and note the effect at the other end. 

 To what do the tube and the rubber on the 

 ends of the tube correspond in the internal 

 ear? 



To show the Plan of the Larynx. Cut 

 from stiff paper four pieces of different 



FIG. 156. Simple ap- shapes as indicated in Fig. 156. (The 

 paratus for demonstrating piece to the left should have a length of 

 the larynx. about six inches, the others proportionally 



