If scientists' ears were keen enough to distinguish the different sound-waves in the noise caused by a street car, they might be able to cause other sound-waves to neutralize the din. Last week Dr. J. P. Foltz, engineer, invited scientists to the Westinghouse Research Laboratories, East Pittsburgh, Pa. to show them a small contraption which could analyze the street car's rattle-bang-clank-screech. The machine consists of a microphone, an amplifier, a filter circuit which allows only one wavelength at a time to pass to the meter for measuring. Since the machine weighs only...
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