296 GENERAL SCIENCE 



the prongs, as shown in the illustration, and see if the fork 

 throws the water. From these tests we can conclude 

 that: Sound is caused by a vibrating body. If the strings 

 of a violin, guitar, or piano are struck, a sound is made. 

 If an explosion of gas or powder occurs, the air is made to 

 vibrate and we hear the sound. If a book or pencil falls 

 on the floor, the floor is made to vibrate and a sound is 

 produced. If some one taps on the door, desk, table, or 

 even the brick wall, these objects will be made to vibrate 

 and a sound may be heard. 



203. Transmission of Sound. Every part of our body 

 is sensitive to the vibratory motion of a solid body which 



SHOWING SOUND WAVES IN THE AIR 



touches us; but our ears are the special organs for de- 

 tecting sound, and they are sensitive to very slight 

 vibratory motions. No sensation of sound can be re- 

 ceived unless the inner parts of the ears are disturbed by 

 a vibrating substance. Since air touches our ears all the 

 time, it is the most common substance which carries 

 the vibrations of a distant object to us. But air is not 

 the only substance that will carry sound. The Indians 

 put their ears to the ground to hear a distant noise. 

 An approaching train can easily be -heard by placing the 

 ear or teeth on the steel rail of the track. The sound of 

 the electric car is carried by the trolley wire. If two 

 stones are struck together under water, the sound can 



