Pumice is the only rock that floats on water.

It will eventually become waterlogged and sink though!

The umbrella was invented to block the sun, not the rain.

In fact, ancient umbrellas would be pretty worthless in the rain, since they were made out of paper. The Chinese were the first ones to figure out how to waterproof their umbrellas with wax and lacquer. 

The "umbra" in umbrella is actually Latin for "shadow", which gives you an idea of what they were originally intended for. Umbrellas became popular in the 1500s in Europe, but only for women. Men's umbrellas didn't come out until the 1700s. 

Gandhi once wrote a personal letter to Hitler.

This letter was the first of two attempts by Gandhi to preempt the onset of World War II. Sadly, the British government did not allow the letter to be delivered. Just over a month later, Germany invaded Poland, an event that many consider the beginning of the war. 
The following is a transcript of Gandhi’s letter:

“Dear friend, 

Friends have been urging me to write to you for the sake of humanity. But I have resisted their request, because of the feeling that any letter from me would be an impertinence. Something tells me that I must not calculate and that I must make my appeal for whatever it may be worth. 

It is quite clear that you are today the one person in the world who can prevent a war which may reduce humanity to a savage state. Must you pay that price for an object however worthy it may appear to you to be? Will you listen to the appeal of one who has deliberately shunned the method of war not without considerable success? Any way I anticipate your forgiveness, if I have erred in writing to you. 

I remain, 
Your sincere friend 

M. K. Gandhi”

The main voice actors on The Simpsons are paid $400,000 per episode.

In comparison, Charlie Sheen (the highest-paid sitcom star) only earns $350,000 an episode! The deal includes all the lead actors: Dan Castellaneta (Homer), Julie Kavner (Marge), Nancy Cartwright (Bart), Yeardley Smith (Lisa), Hank Azaria (Moe), and Harry Shearer (Ned Flanders). Now in its 22nd season, The Simpsons is the longest running prime time entertainment series in U.S. history – 484 episodes and counting! 

SpongeBob SquarePants has worked at the Krusty Krab for over 31 years.

This is indicated in The SpongeBob Squarepants Movie by our hero's 374 consecutive Employee of the Month awards. That may seem like a long time, but the funny thing is, for SpongeBob it isn't. Sponges can live to be 500 years old! 

George Washington has a pair of library books that are 221 years overdue.

George checked out a couple volumes from the New York Society Library on October 5th, 1789. This was about five months into Washington’s presidency, back when New York was still USA's capital. The ledger showed no return date, and they were borrowed by a patron who signed his name simply as “President.” 

Alas, ALL libraries DO have due dates, and George’s should have been returned by November 2nd of that year. Being that the books were not returned by that date (or on any day since, for that matter), if you factor in inflation, the first president has accumulated a late fee of $300,000! Fortunately for all you descendants of Washington out there, the library is not actively pursuing the overdue fine - but they would appreciate the books being returned! 

A Spanish woman has claimed ownership of the Sun.

Angeles Duran was inspired when she heard about an American man who had claimed ownership over the moon and many of the planets in the solar system. Her justification is that, while no country is allowed to claim any planet or star, there's no such rule against an individual doing so. 

She's already filed the necessary paperwork to claim ownership of the sun. Next, she's going to try to implement a fee for people who want to use the sun. But don't worry, she says most of the money will go to charity.