SCIENCE OF COMMON THINGS. 119 



How sound is obstructed. Sounds more distinct by night than by day. 



of the bell ; and as soon as the bell ceases to vibrate, it 

 ceases to make sound-waves in the air. 



7*46 Why does a split bell make a hoarse, disagreeable sound f 



Because the split of the bell causes a double vibration / 

 and as the sound-waves clash and jar, they impede 

 each other's motion, and produce discordant sounds. 



7*47' Why can persons, living a mile or two from town, hear the bells 

 of the town churches sometimes and not at others f 



Because fogs, rain, and snow obstruct the passage of 

 sound ; but when the air is cold and clear, sound is 

 propagated more easily. 



7*48 Why can we not hear sounds (as those of distant church bells') in 

 rainy weather so well as in fine weather ? 



Because the falling rain interferes with the undula- 

 tions of the sound-waves, and breaks them up. 



7*49 Why can we not hear sounds (as those of distant church bells) in 

 snowy weather so well as in fine ivealher? 



Because the falling snow interferes with the undula- 

 tions of the sound-waves, and stops their progress. 



7*5O Why can we not hear sounds (such as those of distant clocks) so 

 distinctly in a thick mist or haze as in a clear night ? 



Because the air is not of uniform density when it is 

 laden with mist; in consequence of which the sound 

 waves are obstructed in their progress. 



7*51 Why do we hear sounds better by night than by day? 



1. Because night air is of more uniform density, and 

 less liable to accidental currents ; and. 



2. Night is more still, from the suspension of business 

 and hum of men. Many sounds become perceptible 

 during the night, which during the day are completely 

 stifled, before they reach the ear, by the din and dis^ 

 cordant noises of labor, business, and "pleasure. 



7*53 Why is tlie air of more uniform density by night than it is by 

 dayf 



Because it is less liable to accidental currents ; inas 

 much as the breezes (created by the action of the sun's 

 rays) generally cease during the night. 



753 How should partition walls be made, to prevent the voices in adjoin' 

 ing rooms from being heard ? 



