328 OUR PHYSICAL WORLD 



p. 83.) When some building, or the face of a cliff, serves as a 

 reflecting surface, the sound of the voice is sent back, as an echo, 

 to a person listening. Do you recall the incident in Treasure 

 Island in which, when the pirate crew is hunting for the buried 

 treasure, Ben Gunn scares them away by imitating the call of old 

 Flint, their dead but still dreaded captain ? Silver, hearing the 

 echo of Ben's voice, reassures himself and his companions by the 

 comment that if a " spirit" does not make a shadow it stands to 

 reason it cannot make an echo. 



The violinist throws the strings of his instrument into 

 vibration by drawing over them the bow, which takes hold of 

 the strings because it is rosined. The banjo player or the harpist 

 plucks the strings to cause them to vibrate. In the piano, 



FIG. 167. Strings stretched across a table 



the string is struck by a hammer operated by pressing a key. 

 You will notice that in harp and piano there is a string for 

 every note emitted, and these strings vary in length, caliber, 

 and tension. On the violin and banjo, however, there are only 

 a few strings, but the player varies their length by pressing them 

 down with his finger tips; only the portion between finger and 

 bridge vibrates. 



Tie one end of a string or thread to the leg of a table. Hold 

 the free end in your left hand, pull on it, and pluck the string 

 with your right hand so it will give out a note. Pull harder 

 still and again pluck the string, and you will notice that the 

 pitch of the note emitted is higher, the harder you pull. Lay 

 the string across the table, and fasten to the free end a heavy 

 weight like a flatiron. Support the string by a couple of strips 

 of wood laid on edge under it near opposite sides of the table 

 (Fig. 167). Pluck the string to get a sound and note its pitch. 



