October 21 in history — On This Day
1983
The Metre Is Defined Through the Speed of Light
At the 1983 General Conference on Weights and Measures, concluding October 21, delegates adopted a definition of the metre tied to the speed of light.
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Chicago After the Fire: From Burned Blocks to a New Skyline
A photograph taken after the 1871 fire can make Chicago look as though its future had been decided by a wall of flame. A view from around 1905 tells a different story: tall offices, busy transport routes and commercial streets crowded again.
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