NOISE AND MUSIC 283 



By observation it has been found that the ear cannot dis- 

 tinguish sounds which are less than one tenth of a second apart ; 

 that is, if two sounds follow each other at an interval less than 

 one tenth of a second, the ear recognizes not two sounds, but 

 one. This explains why a speaker can be heard better indoors 

 than in the open air. In the average building, the walls are so 

 close that the reflected waves have but a short distance to travel, 

 and hence reach the ear at practically the same time as those 

 which come directly from the speaker. In the open, there are 

 no reflecting walls or surfaces, and the original sound has no 

 reinforcement from reflection. 



If the reflected waves reach the ear too late to blend with the 

 original sound, that is, come later than one tenth of a second 

 after the first impression, an echo is heard. What we $all the 

 rolling of thunder is really the reflection and re-reflection of the 

 original thunder from cloud and cliff. 



Some halls are so large that the reflected sounds cause a 

 confusion of echoes, but this difficulty can be lessened by hang- 

 ing draperies, which break the reflection. 



Noise and music. When the rapid motions which produce 

 sound are irregular, we hear noise ; when the motions are regu- 

 lar and definite, we have a musical tone. The rattling of car- 

 riage wheels on stones, the roar of waves, the rustling of leaves 

 are noise, not music. 



To produce music a body must impart short, quick shocks to 

 the air, and must impart these shocks with unerring regularity 

 and strength. A flickering light irritates the eye; a flickering 

 sound or noise irritates the ear; both are painful because of 

 the sudden and abrupt changes which they cause, the former 

 on the eye, the latter on the ear. 



The only thing essential for the production of a musical 

 sound is that the pulses which reach the ear shall be rapid and 

 regular; it is immaterial how they are produced. If a toothed 



