Of all the eponymous discoveries that emerged from 19th-century physics—Young’s fringes, the Biot–Savart law, the Fresnel lens, the Carnot cycle, the Faraday effect, Maxwell’s equations, Michelson’s interferometer, and many more—only one is heard daily on the evening news: the Doppler effect.1 The effect, which describes the change in a wave’s frequency heard by an observer moving relative to the wave source, is shown in figure 1. You experience the effect as you wait by the roadside for a train to pass by or a jet to fly overhead. Albert Einstein may have the most famous name in physics, but Christian Doppler’s is probably the most commonly used. That’s ironic because Doppler was hounded by a pompous nemesis, ridiculed for his effect, stripped of his university position, and forced to abandon Vienna in public disgrace and declining health. He finally retreated to Venice and died a few months later.
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