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Doppler effect.

The coming of the locomotive made a particular phenomenon much more noticeable than it had been earlier. The combination of speed and a warning whistle did the trick. People noticed that the whistle was high in pitch as the locomotive approached, and that the pitch dropped suddenly as the locomotive passed and began to recede.

An Austrian physicist, Christian Johann Doppler (1803-1853), explained the phenomenon correctly by pointing out that the sound waves partake of the motion of the source and so reach the ear at shorter intervals when the source is approaching-hence higher pitch. When the source recedes, the waves reach the ear at longer intervals-hence lower pitch.

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Having done this in 1842, Doppler proceeded to check the matter experimentally a couple of years later. For two days, a locomotive pulled a flat car back and forth at different speeds. On the car were trumpeters sounding this note or that, while on the ground, musicians with a sense of absolute pitch recorded what they heard. Doppler verified his explanation in this way.

The Doppler effect turned out, in a few years, to have enormous importance in connection with astronomy.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
Words:192
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