MUSIC AND SOUND INSTRUMENTS 435 



stones, such as diamonds and sapphires. The needle or stone 

 runs in the groove which was produced by a recorder. Large needles 

 are sometimes used to produce great volume of tone. Needles 

 of this type soon ruin a record, as the weight and resistance of 

 the needle passing over the tiny undulations on the record wear 

 them down quickly. The needle or stone is attached to a diaphragm 

 which is caused to vibrate by the impressions made on the record. 



EIG. 329. A section of a record produced by a tenor voice singing the letters 

 a, e, i, o, u. Magnified. 



This diaphragm causes sound waves which imitate the human 

 voice, or other sounds which were recorded on the original record. 

 The record is turned under the needle by a spring which must be 

 wound up from time to time. 



Telephone. Sound waves striking a thin membrane or disc cause 

 the membrane or disc to vibrate. This principle is used in the human 

 ear. The ear drum is a thin membrane which vibrates when sound 

 waves strike it, sending vibrations through the auditory nerve. 



Alexander Graham Bell got his idea of the telephone from the 

 vibrating membrane in the ear. He thought it would be possible 



