NATURE OF SOUND. 



the articulation is complete and confusedly blend with it. If the 

 reflector be 224 feet distant, there will be time to pronounce two 

 syllables before the reflected wave returns. The echo of both 

 syllables may then be heard ; and so on. The echo may be heard 

 sometimes when the direct sound cannot be heard. 



(&.) Suppose the speaker to stand 1120 feet from the reflecting 

 substance. If then he speak ten syllables in two seconds, the echo 

 of the first will return just as the last is spoken ; the echo of each 

 syllable will be distinct. But if he continues to speak, the direct 

 and the reflected sounds will become blended and confused. The 

 reflecting surface should be a large, vertical wall, or similar object, 

 as a huge rock. 



(c.) When two opposite surfaces, as parallel walls, successively 

 reflect the sound, multiple echoes are heard. Sometimes an echo is 

 thus repeated 20 or 30 times. 



EXERCISES. 



1. If 18 seconds intervene between the flash and report of a gun, 

 what is its distance, the temperature being 82 F.? 



2. What will be the length of the sound waves propagated through 

 air at a temperature of 15 C. by a tuning-fork that vibrates 224 

 times per second ? 



3. State clearly the difference between a transverse and a longi- 

 tudinal wave. 



4. Determine the temperature of the air when the velocity of 

 sound is 1150 feet per second. 



5. If A is 50 m. from a bell, and B is 70 m. from it, how will the 

 loudness of the sound as heard by B compare with the loudness as 

 heard by A ? 



6. A shot is fired before a cliff, and the echo heard in six seconds. 

 The temperature being 15 C. find the distance of the cliff. 



7. A certain musical instrument makes 1100 vibrations per 

 second. Under what conditions will the sound waves be each a foot 

 long? 



8. How many vibrations per second are necessary for the forma- 

 tion of sound waves four feet long, the velocity of sound being 

 1120 feet ? What will be the temperature at the time of the experi- 

 ment? 



9. Taking the velocity of sound as 332 m., find the length of a 

 wave if there are 830 vibrations per second. 



10. The waves produced by a man's voice in common conversation 

 are from eight to twelve feet long. If the velocity of sound be 



