CHAPTER XXII. 



THE EAR. 



The ear is an apparatus constructed according to such 

 physical and physiological laws as will enable it to take 

 cognizance of sound vibrations. The adaptation of this organ 

 to physical sound vibrations is one of remarkable perfec- 

 tion, exceeding, possibly, any other instrument which has 

 to do with the manipulation of sound waves. Evidently, 

 therefore, it is necessary in order to understand the anatomy 

 and physiology of this sense organ to become somewhat ac- 

 quainted with the physical properties of sound waves. 



THE NATURE OF SOUND. 



Sound, that is, sound viewed from its physical stand- 

 point, is a vibratory motion. The body moving may be 

 either gaseous, liquid or solid. The vibration is, however, 

 a molar vibration ; the mass of the medium in question must 

 vibrate. In this sound differs fundamentally from heat and 

 light, which are also forms of motion, but these latter are 

 produced by the molecular motion of the body giving out 

 the heat or light. This distinction may be easily made 

 clear by imagining a bell struck first with a hammer. The 

 blow sets in vibration the entire mass of the bell. This vi- 

 bration may be felt with the finger, and a small object sus- 

 pended near the bell is violently thrown away from it as 

 soon as it touches it. One is able almost to see the oscil- 

 lation of the whole metal backwards and forwards. If the 

 bell be grasped and held firmly it soon ceases to vibrate and 

 the sound is gone. If, on the other hand, such a bell 

 should be placed over a fire it would gradually become 

 warmer and warmer, and if the heating process should con- 

 tinue, might even be raised to a red heat, and so produce 

 light. In this instance it is not the whole mass of the bell 

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