WASHINGTON - 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 mansion overlooking the Potomac, and paid tribute to the man who, more than anyone else, ensured that Americans would not be British subjects.

In the morning, the 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 (D., Ga.), who marched in the "Bloody Sunday" demonstrations 50 years ago.

Charles and Camilla spent about 20 minutes touring the King memorial. They also visited the Lincoln Memorial, where they were greeted by historians Michael Beschloss and Pulitzer Prize-winning author Doris Kearns Goodwin.