SOUND IS CARRIED BY MATTER 267 



surface of water, small sprays of water will be thrown out, 

 showing that the prongs of the fork are in rapid motion. (A 

 rubber hammer is made by putting a piece of glass tubing 

 through a rubber cork.) 



If a light cork ball on the end of a thread is brought in 

 contact with a sounding fork, the ball does not remain at rest, 

 but vibrates back and forth, being 

 driven by the moving prongs. 



These simple facts lead us to con- 

 clude that all sound is due to the 

 motion of matter, and that a sounding 

 body of any kind is in rapid motion. 



251. Sound is carried by Matter. FlG - 165. -The bail does not 



J remain at rest. 



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 will startle fish, and 

 cause them to dart away, so we conclude that the sound must 

 have reached them through the water. An Indian puts his 

 ear to the ground in order to detect distant footsteps, because 

 sounds too faint to be heard through the air are comparatively 

 clear when transmitted through the earth. A gentle tapping 

 at one end of a long table can be distinctly heard at the 

 opposite end if the ear is pressed against the table ; if the 

 ear is removed from the wood, the sound of tapping is much 

 fainter, showing that wood transmits sound more readily than 

 air. We see therefore that sound can be transmitted to the 

 ear by solids, liquids, or gases. 



Matter of any kind can transmit sound to the ear. The 

 following experiments will show that matter is necessary for 

 transmission. Attach a small toy bell to a glass rod (Fig. 

 1 66) by means of a rubber tube and pass the rod through one 

 of two openings in a rubber cork. Insert the cork in a strong 

 flask containing a small quantity of water and shake the bell, 



