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TIL that francium has never been seen with the naked eye because a sample large enough to be viewed would generate so much heat that would vaporize itself almost instantly.

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XmXQ TIL Augustin Mouchot, a French math teacher, was a 19th-century inventor of the earliest solar-powered engine. It converted solar energy into mechanical steam power. In 1878 he showcased his solar-powered concentrator at the Exposition Universelle in Paris & took home the gold medal from the fair.
rRwAo TIL that the plagues of the Middle Ages have made around 10% of Europeans resistant to HIV. These individuals carry a genetic mutation (known as CCR5-Ä32) that prevents the virus from entering the cells of the immune system. The plagues of the Middle Ages played a part in creating these mutations.
XLYD TIL the CEO of McDonald’s makes the same pay in an hour as a worker does at $8.25 in four months
wQQ7 TIL In 1990 Muhammad Ali went to Iraq and negotiated the release 15 United States civilians being held captive by meeting personally with Saddam Hussein
OoGxR TIL that Wilhelm Röntgen didn't know what kind of rays he discovered in 1895, and called them X-Strahlen (X-rays, "unknown rays"). They were later named röntgen rays in a lot of languages, but stuck as X-rays in english