PAUL Dirac could conjure laws of nature from pure thought and he became one of the youngest Nobel Prize winners, but his character was dominated by a relentless application of logic, Louisa Gilder writes.

This biography is a gift. It is both wonderfully written and a thought-provoking meditation on human achievement, limitations and the relations between the two. Here we find a man with an almost miraculous apprehension of the structure of the physical world, coupled with gentle incomprehension of that less logical, messier world of other people.

At Cambridge University in 1930, Subrahmanyan Chandrasekhar took a class in quantum mechanics from the 28-year-old Paul Dirac. Three years later, Dirac would become the youngest theoretician to receive the Nobel Prize in Physics up to that time (50 years after that, Chandrasekhar would become one of the older ones). Chandrasekhar described Dirac as a "lean, meek, shy young 'Fellow' (i.e., of the Royal Society) who goes slyly along the streets. He walks quite close to the walls (like a thief!), and is not at all healthy." Dirac's class - which Chandrasekhar took in its entirety four times, even though Dirac taught it by repeating material from his recently published textbook word for word - was "just like a piece of music you want to hear over and over again."

Dirac is the main character of a thousand humorous tales told among physicists for his monosyllabic approach to conversation and his innocent, relentless application of logic to everything. Listening to a Dirac story is like slipping into an alternate universe: Dirac reads "Crime and Punishment" and reports it "nice" but notes that in one place the sun rises two times in a day; Dirac eats his dinner in silence until his companion asks, "Have you been to the theater or cinema this week?" and Dirac replies, "Why do you wish to know?"

His work was as sui generis as his social skills. "The great papers of the other quantum pioneers were more ragged, less perfectly formed than Dirac's," explained Freeman Dyson, who took Dirac's course as a precocious 19-year-old. Dirac's discoveries "were like exquisitely carved marble statues falling out of the sky, one after another. He seemed to be able to conjure laws of nature from pure thought." (Most notably, Dirac predicted the existence of anti-matter in 1928 because his just discovered relativistic electron equation required it.) "It was this purity that made him unique."

In 1990, Helge Kragh wrote "Dirac: A Scientific Biography," a useful resource comprising physics, a little history and a dessert of Dirac stories in a chapter entitled "The Purest Soul." And indeed, what else besides quantum mechanics and amusing anecdotes did this great and single-minded physicist's life hold?

"The Purest Soul" is a quotation about Dirac from Niels Bohr, as is Graham Farmelo's title. ("Dirac is the strangest man," Bohr said, "who ever visited my institute.") But purity and strangeness were not the whole story. Kragh's book offers a collage of a brilliant and peculiar man seen from the outside; Farmelo's is a tapestry, and he provides glimpses of the inside.

A senior research fellow at the Science Museum in London, Farmelo gives us the texture of Dirac's life, much of it spent outdoors - from long Sunday walks as a young man, looking like "the bridegroom in an Italian wedding photograph," "dressed in the suit he wore all week, his hands joined behind his back, both feet pointing outward as he made his way around the countryside in his metronomic stride;" to late-life canoeing trips with Leopold Halpern, a physicist even stranger than he, "through forests of sassafras and American beech trees, draped with Spanish moss.

"The alligators made scarcely a sound: the silence was broken only by the rhythmic sloshing of the paddles, the cry of a circling osprey, the occasional shuffling of wind passing through shoreline gaps in the forest." (After lunch, they swam and paddled back, "scarcely exchanging a word.")

We follow Dirac from his pinched and chilly childhood in Bristol (a few blocks away from the two-years-younger Archie Leach, aka Cary Grant); through his discovery, visiting the Bohrs in Copenhagen, of what a happy family was like; his fiercely loyal friendship with Werner Heisenberg; his joyful beach honeymoon, still in a three-piece suit; his careful fatherhood (constructing for his daughters' cat a door wider than its whiskers); to his death in Florida in 1984.

The science writing in "The Strangest Man" isn't glib, but neither does it require problem-solving on the part of the reader. In most cases, Farmelo presents the technical matter clearly and efficiently, and in all cases - one of the great joys of the book - Dirac's scientific insights are placed within the circumstances in which they were born: e.g., the "sweltering July" of 1926 when Dirac, sitting at his college desk, produced his paper on what became Fermi-Dirac statistics.

In a prologue, Farmelo describes a visit to the elderly Dirac paid by his biologist colleague Kurt Hofer. Through the eyes of Hofer, we see Dirac suddenly break out of monosyllables to talk for two hours with increasing vehemence about his monstrous father. This represents the author's careful decision to keep the tale Dirac told about his childhood separate from - even as it overshadows - the rest of the book, and it ends with Hofer's thoughts, not Dirac's: "I simply could not conceive of any childhood as dreadful as Dirac's."

The conflict between this prologue (which gives ample reason for Dirac to be bitter about his father) and the seemingly warm family life that emerges in the first chapter casts a tension over the rest of the book very similar to that felt when reading a mystery.

In a memorable episode, Dirac and his wife visited their closest friends, Peter and Anna Kapitza, in Russia. In 1937 the friends reunited at the Kapitzas' summer house in the piney woods of Bolshevo.

Farmelo handles such scenes with a refreshing, clear-eyed understanding of how complicated the world actually is. Dirac did not °?- probably could not - know what the former Soviet Union really was; he also could not know who his father really was, and his father could not really know him.

These complexities and unresolvably cubist perspectives make, paradoxically, for the most satisfying and memorable biography I have read in years.