Holmes always gets his man

The Art of Biography/ Is different from Geography/ Geography is about Maps/ Biography is about Chaps." So concluded Edmund Clerihew Bentley, managing in just 16 words to irritate geographers, women and, presumably, biographers. Richard Holmes is best known for his biographies of chaps, notably his two-volume life of Coleridge. He has also written at length on Shelley, Dr Johnson, and the French poet Gerard de Nerval, whose caprices included walking a lobster on a pink ribbon leash in the Jardin des Tuileries. Indeed, over the course of three decades Holmes has produced a book every three or four years, a "languid, circadian" writing rhythm that has pushed continuously at the envelope of biographical form.

Sidetracks assembles the shorter pieces that Holmes has penned while "snuffling" along the trails of his main biographical quarries. As might be expected from a 30-year retrospective, it is a mixed bag both in terms of subject and quality. Holmes is at his most convincing when discussing the Romantics: the best pieces here include a revisionist monograph on the hoaxster and poet Thomas Chatterton, a "Philosophical love story" about William Godwin and Mary Wollstonecraft, and fine shorter "impressions" of John Stuart Mill and the Gothic eccentric Charles Maturin, who pasted a red patch on his forehead as a Do Not Disturb sign when in the throes of literary creation. Far less successful are a sheaf of rather smug "Letters from Paris" and two radio plays about de Nerval and Shelley. The book is also riddled with typographical errors, the most unfortunate of which turns Felix Nadar, the 19th-century French photographer, into "Felix Nadir".

The finest of Holmes's Romantic "impressions" is of the Reverend Richard Barham (1788-1845), author of the ghoulish and enormously popular Ingoldsby's Legends . Like Holmes, Barham loved clambering around in family trees and managed to trace his own ancestry back to William FitzUrse, one of the knights who murdered Thomas a Becket. FitzUrse was a suitably macabre antecedent for the reverend who, as Holmes recounts, preferred to write his stories after midnight with a bat perched on his shoulder "like some familiar gargoyle" and who, when asked if he liked children (six of his own had died), replied: "Yes Ma'am, boiled with greens."

These are the sorts of detail that bring a biographical subject immediately to life, and which Holmes excels at discovering and deploying. W. H. Auden several times pointed out the affinities between the detective and the literary critic: like his famous pipe-smoking namesake, Holmes has an intuitive knack for untangling the past, and getting his man.

Slipped in between the longer pieces are sketches of Holmes's own life, reflecting on how he was led down these "sidetracks", and on the nature of biography. During these interludes, the purpose behind Sidetracks is made clear, namely Holmes's desire to argue biography into the pantheon of the art forms. Holmes rightly sensed early in his career that the "naturalistic novel" - a form with so many practitioners and so few successes - was becoming devalued, at least in Britain. He turned instead to the creative biography, a genre that demands the skills of the novelist and the literary sleuth and that, he claims, "at its best seems to fulfil Dr Johnson's own epitome of fine literature, balancing entertainment with instruction, and helping us the better to enjoy life or to endure it". But one feels uneasy about agreeing with Holmes's manifesto. A biography, however good, just is not equal to a great novel, play or poem; it occupies a mid-ground located somewhere between research and art.

And yet, and yet. Boswell's Life of Samuel Johnson has certainly become part of the canon. Holmes pays homage to Boswell, the "godfather of English biography", with a wonderful essay on his sojourn in Utrecht. Boswell went to Holland to escape his rakehell instincts and immerse himself in an atmosphere of sombre Protestant diligence. For a while it worked. He boasted to his diary how he would "bounce up" daily at 6.30am "with as much viv-acity as if a pretty girl, amorous and willing, were waiting for me". He drafted a resolution about his future life entitled "The Inviolable Plan" in which "he determined to... mould himself into a 'Christian gentleman'". (The "plan" showed Boswell's powerful impulse to give himself biographical form, an impulse that would later be deflected into his life of Johnson, much to the profit of posterity.) But, as Holmes drolly narrates, Boswell's natural libertinism began to corrode his simulated puritanism, and by the time he left he had spent a vice-ridden weekend in Amsterdam and "fallen in love with a Dutch girl more intelligent than he".

All that is best in Holmes comes out in this essay; his pungent sense of delight in both the strangeness and the familiarity of the literary past, and his great ability to communicate that delight.

Robert Macfarlane is a writer and reviewer based in Cambridge.