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Why is the sky blue?

The next time someone asks you, don't tell them it's simply because gas molecules in the air absorb light waves with short wavelengths and then reflect them back out (or, God forbid, because "the Lord made it that way"). Instead, draw on this wonderful piece from the National Post and answer that it's not blue -- it's violet:

The violet wavelengths from the sun, having still shorter wavelengths than blue, should be scattered even more. Given this, shouldn't the sky be violet, not blue? Indeed the sky is violet, if you observe not with the naked eye but with an instrument that objectively measures the intensity of the spectrum at different wavelengths. Such a device, a spectrophotometer, shows that, in fact, the highest peak of the intensity of skylight occurs in the violet range. But why do we see blue, nonetheless? The resolution of the mystery lies in our daytime vision, which happens to be eight times less sensitive to violet than to blue light.

Read on to learn how Plato, da Vinci, Descartes, Newton, and others tried to answer the question.

photo from the spectacular Trek Earth

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History
A Very Brief History of Chamber Pots

Some of the oldest chamber pots found by archeologists have been discovered in ancient Greece, but portable toilets have come a long way since then. Whether referred to as "the Jordan" (possibly a reference to the river), "Oliver's Skull" (maybe a nod to Oliver Cromwell's perambulating cranium), or "the Looking Glass" (because doctors would examine urine for diagnosis), they were an essential fact of life in houses and on the road for centuries. In this video from the Wellcome Collection, Visitor Experience Assistant Rob Bidder discusses two 19th century chamber pots in the museum while offering a brief survey of the use of chamber pots in Britain (including why they were particularly useful in wartime).

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A Tour of the New York Academy of Medicine's Rare Book Room
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The Rare Book Room at the New York Academy of Medicine documents the evolution of our medical knowledge. Its books and artifacts are as bizarre as they are fascinating. Read more here.

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