164 THE EEASON WHY. 



"And even things without life giving sound, whether pipe or harp, except they 

 give a distinction in the sounds, how shall it be known what is 

 piped or harped." COEINTH. xiv. 



Because if a tuning fork were to be struck in a vacuum (as under 

 the receiver of an air pump) -no sound would be heard, although 

 the vibrations of the fork could be distinctly seen. 



720. How are the vibrations of sonorous bodies imparted to 

 the air ? 



When a bell is struck, the force of the blow gives an instant 

 agitation to all its particles. The air around the bell is driven back 

 by the impulse of the force, and thus a vibration of compression is 

 imparted to the air ; but the air returns to the bell, by its own 

 natural elasticity, thus producing a vibration of expansion when it 

 is again struck, and thus successive vibrations of compression and 

 expansion are transmitted through the air. 



721. How rapidly are these vibrations transmitted through 

 the air ? 



They travel at a rate of rather more than a quarter of a mile in 

 a second, or twelve miles and three-fourths in a minute. 



722. Do all sounds travel at the same rate ? 



All sounds, whether strong or weak, high or low, musical or 

 discordant, travel with the same velocity. 



723. WTiy are bells and glasses stopped from ringing by 

 touching them with the finger ? 



Because the contact of the finger stops the vibration of the atoms 

 of the metal and glass, which therefore cease to impart vibrations 

 to the air. 



724. Why does a cracked bell give discordant sounds ? 



Because the connection between the atoms of the bell being 

 broken, their vibrations are not uniform : some of the atoms vibrate 

 more intensely than the others ; the vibrations imparted to the air 

 are therefore jarring and discordant. 



725. WTiy, when we see a gun fired at a distance, do we see 

 the flash and smoke, before we hear the report ? 



Because light, which enables us to see, travels at the velocity of 



