By Peter Ackroyd

HarperCollins. 1,195 pp. $35

PETER ACKROYD's Dickens is a creature compact of energy, nervous, elemental, demonic. At the beginning of "the Inimitable's" phenomenal youthful success, Ackroyd observes percipiently that one of his favorite words is "flare" -- "a term which he uses variously to describe an appearance in print, a party, an argument and any kind of concerted or violent activity."

From time to time the biographer gives us vivid glimpses of this flaring -- Dickens, for instance, ascending Vesuvius as a tourist, insisting on going higher than anyone else to stare into the "fire and roar." "We looked down into the flaming bowels of the mountain and came back again, alight in half-a-dozen places, and burnt from head to foot." Or Dickens on his first American journey, running through the streets of Boston, observed by an American journalist to be "quite unable to keep his fingers off the inviting knobs that protruded from the doors as he went past, and he pulled them with such vigour that one actually came off in his hand."

This flaring energy Ackroyd also observes in Dickens's compulsively animating the world, turning it into stories and characters. The novelist picks up a glass and tells his friends, "I choose to call this a character, fancy it a man . . . and soon the fine filmy webs of thoughts, almost impalpable, coming from every direction, spin and weave about it, until it assumes form and beauty, becomes instinct with life." He acted his characters out before a mirror whilst writing -- he gave terrifying readings from his books to audiences weeping and howling with laughter.

The readings perhaps killed Dickens, and Ackroyd is interested in Dickens the killer, of himself and his people. He liked to watch executions -- he observed how a Roman beheading seemed to leave both head and trunk neckless. He worked himself up to the "killing" of his characters -- "Jo?," he writes, "Yes. Kill him." He felt the death of little Nell as a murder and wrote, "I am for the time being nearly dead with work -- and grief for the loss of my child." Ackroyd sees something sinister in this hectic activity -- he sees the killer of Jo as a man "irate, irritable, savagely angry . . . who can hardly see a child without condemning him or her to death."

At one point in his discussion of Bleak House Ackroyd makes a brilliant connection between Dickens's forcefulness and the new understanding of forces in the 19th century:

"Light. Energy. Magnetism. Thermodynamics. These are the forces which exist within the very shape of Bleak House, and in the year before Dickens began to write that narrative, the second law of thermodynamics was proposed -- how energy is converted into heat rather than useful work and so moves ineluctably towards its quietus, how the entropy of closed systems lead ultimately to disorder."

He backs this up with an intelligent perception of the importance of Dickens's observation that machine-age people "mutht be amuthed," as Sleary the circus-manager says in Hard Times, by "something in motion" -- in his case by acrobats and performing animals, in Dickens's by theatrical readings and stagey plots and rhetoric.

The problem with Ackroyd's biography is that he himself is temperamentally very different from his subject, and that, for all his understanding of Dickens's drive, his own book is not "something in motion." He has tried to follow the daily eddy of Dickens's thoughts and feelings, and has tried to marry the work and the life. He has tried to write a novelist's biography, not a scholar's, in which the works are given the central place they should take. In principle all this sounds exciting and appropriate -- in practice, it is heavy, slow and incoherent.

He has written 1,195 pages. These do not include any detailed relation of Dickens's ideas to those of his contemporaries, and only the most perfunctory portraits of his family and friends. There is little to indicate that Ellen Ternan -- Dickens' "secret friend" -- was a real woman with real problems, and we do not get to know Dickens's children separately, as people with hopes, fears and problems.

What has gone wrong? This book feels as though its author is writing under duress, as though his mind is not actively engaged. It is full of the repetition of simple rhetorical devices, simple equations between the life and the art. Dickens goes to Lausanne -- "which was not at all like Genoa -- except for the fact that they were both built beside water which was such a potent imaginative force for Dickens (in his next novel the doomed little Dombey gazes out at the waves) . . ." This is sloppy writing, with too many analogues. And there are other sorts of banal authorial asides. Dickens's true understanding of George Eliot's precise and tragic characterization of Hetty Sorrel is reduced to "did he see in her some echo of Ellen Ternan?" whilst Mrs. Skewton's Arcadian fantasies of Swiss farms, cows and china are lazily taken as a dig at Wordsworth. (Much more likely Rousseau or even Marie Antoinette.)

Ackroyd's central thesis appears to be that the invention of characters infects life until the one is indistinguishable from the other. He has some interesting examples of this in Dickens -- who retires Mrs. Nickleby to a country cottage and the next week impulsively buys just such a cottage to dispose of the problem of his embarrassing parents. But the idea has also led Ackroyd the novelist to interpolate imagined scenes into his biography in which he himself talks to Dickens, or Dickens talks to Little Dorrit, or the subjects of Ackroyd's various biographical interests talk to each other -- T.S. Eliot, Dickens, Wilde and Chatterton. Ackroyd's Dickens notes, with uncharacteristic banality, that "Biographers are simply novelists without imagination!" Ackroyd's Ackroyd, interviewed by Ackroyd, observes that he "always used to say" that biographies were like fiction, "but I never really believed it. It just sounded good at the time." He wants to understand Dickens "like a character in a novel I might write" and his understanding leads him to the view that Dickens "saw reality as a reflection of his own fiction."

Ackroyd is troubled by the idea that his Dickens is his own fiction -- but not troubled enough. His fictive interviews are inert compared to his quotations from Dickens himself, which in turn would have had more force and relief in a perfectly orthodox scholarly biography of three-quarters the length. As a novelist Ackroyd can be an uncanny ventriloquist -- his recreation of the last days of Oscar Wilde is masterly and moving, and his ear for 17th-century speech and preoccupations in Hawksmoor is uncanny and powerful, but here something -- very alive in itself -- has refused to be animated or re-animated.

And so all this mass of writing does make Dickens more hidden and mysterious. Ackroyd quotes a wonderful observation of Emerson's:

"You see him quite wrong, evidently, and would persuade me that he is a genial creature, full of sweetness and amenities and superior to his talents, but I fear he is harnessed to them. He is too consummate an artist to have a thread of nature left. He daunts me. I have not the key!"

And Dickens himself, casting his own sense of his own mystery, as Ackroyd percipiently observes, in the form of story:

"The man whose vista is always stopped up by the image of Himself. Looks down a Long walk, and can't see round himself, or over himself, or beyond himself. -- Is always blocking up his own way. -- Would be such a good thing for him if he could knock himself down."

"I have created a legend in my own mind," he wrote much earlier, "and consequently I believe it with the utmost pertinacity." This biography makes a good stab at describing the construction of the legend, but leaves the human being confusingly out of focus.

A.S. Byatt's most recent novel is "Possession: A Romance."