SAN DIEGO — Alan Houston, a political science professor at UC San Diego, had come to the end of a trip to London to research a book about Benjamin Franklin.
He thought he might spend the day having fun with friends, but decided to make one more visit to the British Library.
In his last request for documents, he stumbled on something unexpected: a letter written by Franklin and copied by a British literary figure named Thomas Birch.
Houston had never seen it. Not believing his eyes, he looked for more.
In all, Houston found 47 letters Birch had reproduced that were written by Franklin, to him or about him in 1755, when the French and Indian War was starting to bloody the American continent.
"I couldn't sit still; I couldn't work," Houston said Thursday. "On the last day, on the last document, and I had this incredible discovery. I ran out of the library and called my wife in San Diego."
Once back in the U.S., Houston consulted the definitive collection of Franklin writings. The letters were not in it.
Since discovering the letters in November 2007, Houston has keep the secret to himself and a small coterie of Franklin experts. Now, he has written an article based on the letters for the April edition of the William and Mary Quarterly.
Although the letters will not trigger a reevaluation of Franklin, Houston said, they add nuance to the understanding of his skill as a negotiator and his role as a military strategist.
Claude-Anne Lopez, consulting editor to the Benjamin Franklin papers project at Yale University and author of "My Life With Benjamin Franklin," said Houston's discovery "will help round out our understanding of Franklin.
"It's very exciting," she said. "They're new documents, and Franklin scholars love documents."
Houston was in London to work on his book, "Benjamin Franklin and the Politics of Improvement," which was published last year. He said he has found undiscovered documents in the past but never a collection of this size.
Birch was a member of the Society of Antiquaries of London and secretary of the Royal Society from 1752 to 1765. His papers fill 400 volumes at the library. Until Houston's discovery, it was unknown that he copied letters from Franklin.
Houston submitted copies to other scholars for authentication but kept their location to himself, lest another professor scoop him on his discovery.
The letters, Houston said, show Franklin's skill at finding provisions for British Gen. Edward Braddock for his assault on a French fort at what is now Pittsburgh. Braddock had been promised 2,500 horses and 250 wagons.
When he received only 200 horses and 20 wagons, the temperamental Braddock was enraged. Franklin, who was prominent in business and political circles in Philadelphia, interceded and negotiated with Pennsylvania farmers.
In a letter to the state's governor, Franklin gently chided him for letting politics keep him from honoring a promise:
"Being occasionally at the Camp at Frederic a few days since, I found the General and officers of the Army occasionally exasperated on account of their not being supplied with Horses and Carriages, which had been expected from this province; but, thro' the dissensions between our Governor and Assembly, Money hath not been provided nor any taken for that purpose."
Braddock was killed soon after, and his forces lost that battle but continued the war.
To Houston, 51, the letters show that Franklin was grappling with issues that confront American leaders today: how to forge alliances and rally public support during times of war.
"He was on the early side of the world we still live in," said Houston, who has taught at UC San Diego for 20 years.
Some modern researchers have wondered whether Franklin's eye wandered while he was in England, far from his wife, Deborah. Although it does not settle the issue, in one of the letters Franklin pleads with his wife: "Write to me, by every opportunity. I long to be with you, as ever. Your loving husband."
To the scholar's chagrin, the popular perception of Franklin is still largely drawn from the image of the kite-flying, almanac-writing fellow with the funny haircut.
Do today's students of American history have a fuller sense of Franklin and his role in shaping the nation?
"They do when they come to my class," said Houston, joy embedded in his voice.