François de Rozier and the Marquis d'Arlandres made the first human flight when they lifted off from the Bois de Boulogne, Paris, in a hot-air balloon built by the Montgolfier brothers
The SI unit of frequency, in particular the number of times something occurs in one second, abbreviated Hz. Named after Heinrich Rudolph Hertz (1857-94). The unit is sometimes alternatively expressed as CPS.
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