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part 



SOUND 



CHAPTER XXXI. 



SOUND : ITS NATURE, REFLECTION, AND REFRACTION. 



THE nature of sound. Like light, sound is 

 also considered a mode of motion, as due to vibrations. 

 But, whereas the vibrations of the luminiferous ether 

 are regarded as transverse, the vibrations of the sound- 

 conducting medium are regarded as longitudinal to 

 the direction of propagation of the sound. The 

 movements are still to and fro movements, no longer 

 across, buc in the line of the advancing sound. 

 Suppose a series of particles in line with one another, 

 and at rest, and let a shock be communicated to the 

 tirst of the series. Under the influence of the 

 impulse it moves along the line, and pushes against 

 the second particle, to which it communicates the 

 pulse. After its impact with the second particle, it 

 recoils and returns to its original position, completing 

 its to and fro movement. It has, moreover, handed 

 on its motion to the second particle, and the second, 

 owing to the shock, moves towards the third particle, 

 from the impact with which it also recoils and returns 

 to its own position., having, in its turn, communicated 

 the motion to a succeeding particle. So the process 

 goes on, each particle performing only a to and fro 

 movement, the impulse nevertheless being carried 

 from one end to the other of the series. It must not, 

 however, be supposed that the medium in which 

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