The sky isn’t blue. It’s actually violet, but a quirk of human vision makes us less sensitive to those wavelengths.

Seeing a red apple should increase your confidence that all ravens are black.

Why? Because the statement “All ravens are black” is logically equivalent to “All non-black things are non-ravens.” And seeing a red apple (or green grass) confirms this belief.

This is logically inescapable, even if it’s counterintuitive. It’s known as Hempel’s paradox.

Math prodigy George Bidder was born to a Devonshire stonemason in 1806. In a public appearance at age 11, he answered each of these questions in less than a minute:

• What is the cube root of 673,373,097,125? “Answer, 8,765.”
• If a mouse can draw one ounce and a half, how many mice can draw 50,000 tons? “Answer, 1,194,666,666, and one ounce over.”
• If a coach travels from Exeter to Plymouth, 44 miles, every day in a year, how often does a wheel turn round that is 2 feet 9 inches? “Answer, 30,835,200.”
• If a fan of a windmill goes round 15 times in a minute, how many times will it go round in 7 years, 4 months, 1 week, 2 hours, 3 minutes — 365 days 6 hours to the year, and 28 days to the month? “Answer, 57,897,245.”
• If the ministers have taken of the income tax 12 millions of money in 1-pound notes, how many miles would they cover a road 30 feet wide, each note being 8 inches by 4 and a half? “He directly answered, 18 miles, 1,653 yards, and one foot.”
• Suppose the earth to consist of 971 million of inhabitants, and suppose they die in 33 years and four months, how many have returned to dust since the time of Adam, computing it to be 5,850 years? “Answer, 170,410,500,000.” Multiply it again by 99. “Answer, 16,870,639,500,000.”

(Reported in Kirby’s Wonderful and Scientific Museum, 1820)

In September 2002, astronomers noticed something odd: An object about 60 feet long was orbiting Earth. It must have arrived recently, but it didn’t resemble any recently launched spacecraft. It might have been an asteroid … but it appeared, spookily, to bear titanium dioxide paint. Was it an alien ship?

The object disappeared again in June 2003, so officially we’re still baffled. But the best guess is that it’s an old stage of Apollo 12 that somehow wandered away from Earth in 1971, circled the sun about 30 times, and came home to visit. If that’s true then it might come back again in 2032—we can visit it on our rocket scooters.

In 1864, the Inuit gave the skin and skull of an “enormous” yellow-furred bear to naturalist Robert MacFarlane. He packed them up and shipped them to the Smithsonian Institution, where they were placed in storage and forgotten.

Fifty-four years later, zoologist Clinton Hart Merriam unpacked the remains and realized they represented an entirely new species, and MacFarlane’s specimen was apparently the last of its kind. No one has ever seen a living “MacFarlane’s bear,” except for those Inuit — and now their story is lost.