SONOROUS WAVES. 



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Let a series of observers, A, B, c, D, &c., be placed in a line, at 

 distances of about 1000 feet asunder, and let a pistol be discharged 

 at P, about 1000 feet from the first observer. 



This observer will see the flash of the pistol about one second 

 before he hears the report. The observer B will hear the report 

 one second after it has been heard by A, and about two seconds 

 after he sees the flash. In the same manner, the third observer 

 at c will hear the report one second after it has been heard by the 

 observer at B, and two seconds after it has been heard by the ob- 

 server at A, and three seconds after he perceives the flash. In 

 the same way, the fourth observer at D will hear the report one 

 second later than it was heard by the third observer at c, and 

 three seconds later than it was heard by the observer at A, and 

 four seconds after he perceives the flash. 



Now it must be observed, that at the moment the report is 

 heard by the second observer at B, it has ceased to be audible 

 to the first observer at A; and when it is heard by the third 

 observer at c, it has ceased to be heard by the second observer at 

 B, and so forth. It follows, therefore, from this, that sound 

 passes through the air, not instantaneously, but progressively, and 

 at a uniform rate. 



4. As the sensation of sound is produced by the wave of air 

 impinging on the tympanum of the ear, exactly as the momentum 

 of a wave of the sea would strike the shore, it follows that the 

 interval between the production of sound and its sensation, is the 

 time which such a wave would take to pass through the air from 

 the sounding body to the ear ; and since these waves are propa- 

 gated through the air in regular succession, one following another 

 without overlaying each other, the breadth of a wave may always 

 be determined if we take the number of vibrations which the 

 sounding body makes in a second, and the velocity with which 

 the sound passes through the air. If, for example, it be known 

 that in a second a musical string makes 500 vibrations, and that 

 the sound of this string takes a second to reach the ear of a person 

 at a distance of 1000 feet, there are 500 waves in the distance of 

 1000 feet, and consequently each wave measures two feet. 



The velocity of the sound, therefore, and the rate of vibration, 

 are always sufficient data by which the length of a sonorous wave 

 can be computed. 



5. It has not been ascertained, with any clearness or certainty, 

 by what physical distinctions vibrations which produce common 

 sounds or noises are distinguished from such as produce musical 



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