Richard Feynman was a particularly American sort of genius. He was born in 1918 into a middle-class Jewish family and grew up in, of all places, Far Rockaway, Queens, an outer borough of New York City. His father was uneducated but would walk with his son on the beach, pointing out shells and birds, even though he often couldn't identify them. Feynman grew up with a distaste for formality and pretense and with an iconoclasm that went beyond wearing open-collared shirts and playing practical jokes (he liked to pick locks) to the way he approached physics. He liked to derive things from first principles, reinventing theories merely to understand them better. To describe the dynamics of fundamental particles, his rival, physicist Julian Schwinger, spun a masterful web of mathematics; Feynman drew pictures. The two shared the Nobel Prize for this work in 1965, but by then a new generation of physicists preferred the "Feynman diagrams" because they yielded more intuitive insight than all that math.

James Gleick's superb biography, "Genius," is still the best work on Feynman's life. "Perfectly Reasonable Deviations From the Beaten Track" (465 pages. Basic Books), a collection of letters edited by Feynman's daughter, Michelle, is for those who want to rummage around in the recesses of this irrepressible personality. There are heart-rending letters to his first wife, Arline Greenbaum, who was dying of tuberculosis while Feynman was sequestered in Los Alamos, New Mexico, helping to build the A-bomb. Years later, after Arline's death, Feynman prevailed upon Gweneth Howarth, a Welsh woman he met in Europe, to live with him as his housekeeper. "I'm looking forward to being much happier," he wrote. She came, and the two eventually married.

Science in the American century had become a big enterprise, and genius wasn't so rare as it was in Einstein's day. "When you describe what went on in your head as the truth haltingly staggers upon you... you are describing how science is done," he writes to James Watson, codiscoverer of DNA. "I know, for I have had the same beautiful and frightening experience." Feynman also wrote to students and the public. A woman who had heard him speak wrote asking why physicists preferred equations to yield zeroes, rather than infinity, even though symbols for both contain "circles." "I am very happy to see so much really understood," responds the polite Feynman. However, "it is not philosophy we are after, but the behavior of real things." No one had his particular talent for seeing them as they were.