Sound 173 



thrown into it. They start at the point where the stone strikes 

 the water and radiate outward in ever-widening circles. Sound 

 waves travel in the same way, except that the waves are spherical, 

 or ball-shaped. Just as the circles enlarge in the water, so the 

 spheres enlarge in the air as the. waves move outward from the 

 sound-making body. 



In a whistle, the air is set in motion by blowing a current 

 from the lips across a thin metal edge, causing it to vibrate. The 

 sound is transmitted through the air in the form of waves. 



When the drum is struck ^ c ^ 



the diaphragm vibrates, start- ,'''''- ^"_~JJ~- | 7r_Vrr~^^> N 

 ing sound waves in the air. a^'J'J'J, ,1 ~ -\tj b 



When a wire is snapped, ' x \^ -III" f IIIII -''-*''' 



its vibrations set the air in 7" d 



motion. The sound produced 



by a string of a musical instrument is the result of this motion. 

 Let a line a b represent such a string. If the string be drawn 

 up to c and released, its elasticity will not only carry it back but 

 will give it force enough to carry it to d. From thence it will 

 successively return to e, f, g, h, and so on, until the resistance 

 of the air stops its motion. 



The action of the bell illustrates how music is produced by 

 a carillon, a chime of bells upon which tunes may be played. The 

 action of the whistle illustrates the principle involved in the pro- 

 duction of music by the flute, the organ and other wind instru- 

 ments. The action of the wire or the string illustrates how this 

 principle is involved in the production of music on the harp, the 

 violin, and other stringed instruments. 



The Tuning Fork. A device called a tuning fork is used 

 in tuning musical instruments. It consists of a forked piece of 

 steel, which vibrates at a given rate when struck, and so pro- 

 duces a certain fixed tone or note. When the pitch of the cor- 

 responding note on the instrument being tuned is the same as 

 that of the tuning fork, this note is used as the basis for tuning 

 the instrument. 



The Piano Player. A piano player is an instrument which 

 operates by air pressure, to reproduce music. There is a 



