CHAPTER III

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WAVES AND RIPPLES IN THE AIR.

Air necessary for the production of sound—A sounding body is in vibration—Harmonic motion—The difference between noise and music—The nature of an air wave—The physical qualities of air—Longitudinal or compressional waves—Wave-models to illustrate the nature of sound waves—Quality of a sound—Velocity of an air wave—An illustration on a gigantic scale—The voice of a volcano heard round the world—The effect of temperature on air-wave velocity—Comparison of theory and experiment—Circumstances affecting distance at which sounds can be heard—Funeral guns—Fog-signals and sirens—Effect of wind and density—Sensitive flames as sound-detectors—Inaudible sounds—The reflection and refraction of sound waves—A sound-lens and sound-prism—The interference of sounds—Two sounds producing silence—The phonograph—A soap-bubble film set in vibration by air waves 103

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