Prince Charles learned something new on his tour of the nation's capital Wednesday: His uncle built a better polo stick.
Charles and his wife, Camilla, got the royal tour of the U.S. capital, being ushered around Washington's monuments and memorials on the National Mall by a handful of American luminaries.
It was on a tour of the National Archives, though, where Charles was genuinely surprised and delighted. National Archivist David Ferriero presented the prince with a patent application submitted in 1931 by his uncle, Lord Louis Mountbatten, for a new kind of polo stick.
Charles, himself a polo player, laughed and said he had no idea that his uncle had designed a polo stick.
He also laughed when shown a telegram from the U.S. embassy in London to the Secretary of State, sent in 1957 seeking instructions to ensure that a toy car that had been given to Charles, then 8 years old, would be working properly when he returned home to play with it.
Earlier in the day, at George Washington's Mount Vernon estate in Virginia, Charles and Camilla toured the iconic mansion overlooking the Potomac, and paid tribute to the Founding Father who, more than anyone else, ensured that Americans would not be British subjects.
Charles also toured the working farm on the estate, viewing a demonstration of a specially designed threshing barn by Washington and patting the horn of an ox named Jed.
"You've got to watch these," Charles quipped, referring to the horns.
Kitty Morgan of Mount Vernon brought her two sons to the estate and was one of hundreds who lined up to catch a glimpse of the couple. The boys were rewarded with the chance to shake Camilla's hand.
Originally from Britain, Morgan said she "decided my boys, being British, needed to see their future sovereign."
She said they never would have been able to get so close to the royal couple in England because the crowds would have been overwhelming.
In the morning, the British royal couple was joined by two civil rights leaders for their tour of the Martin Luther King Jr. memorial — the Rev. Jesse Jackson, a protege of King; and Rep. John Lewis of Georgia, who marched in the "Bloody Sunday" demonstrations for minority voting rights 50 years ago.
Charles and Camilla spent about 20 minutes touring the King memorial. The couple paused briefly to read some of King's quotations about the civil rights movement that are engraved in stone.
"Darkness cannot drive out darkness, only light can do that. Hate cannot drive out hate, only love can do that," read one quotation where the royal couple paused to see King's words from 1963.
The royal couple also visited the Lincoln Memorial, where they were greeted by historians Michael Beschloss and the Pulitzer Prize-winning Doris Kearns Goodwin, author of "Team of Rivals: The Political Genius of Abraham Lincoln."
After a day of playing tourist, Charles delved into the nitty-gritty of environmental policy, speaking about the dangers of accumulating plastic waste in the world's oceans.
He gave a 10-minute speech to a joint meeting of the Global Ocean Commission and the International Sustainability Unit, a charitable group established by the prince to address environmental concerns.
He cited a study estimating that by 2025, there will be one ton of plastic in the oceans for every three tons of fish.
"Although the evidence surrounding the links between plastic waste and human health are not yet clear, I would tentatively suggest that they are unlikely to be beneficial," he said dryly.