CHAPTER XXXI 



SOUND 



How sounds are caused and carried to us. All the informa- 

 tion which we possess of the world around us comes to us 

 through the use of the senses of sight, hearing taste, touch, 

 and smell. Of the five senses, sight and hearing are generally 

 considered the most valuable. The 

 sounds we hear are due to motion of 

 some kind, a sudden noise is traced to 

 the fall of an object, to an explosion, 

 or to a collision ; in fact, is due to the 

 motion of matter. A pianb gives out 

 sound whenever a player strikes the 

 keys and sets in motion the various 

 wires within the piano ; speech and song 

 are caused by the motion of chest, 

 vocal cords, and lips. 



If a large dinner bell is rung, its mo- 

 tion or vibration may be felt on touching 

 it with the finger. When a tuning fork 

 is made to give forth sound by striking FIG. 145. 

 it against the knee, and is then touched 

 to the surface of water, small sprays of 

 water are thrown out, showing that the prongs of the fork are in 

 rapid motion. In most cases sound reaches the ear through 

 the air; but air is not the only medium through which sound is 

 carried. A loud noise startles fish and causes them to dart 

 away, so we conclude that the sound reaches them through the 



sdi 



Sprays of water 

 show that the fork is in 

 motion. 



