Hidden Depths: The Story of Hypnosis
Robin Waterfield
464pp, Macmillan, £20

"All sciences alike have descended alike from magic and superstition," says a 1930s writer quoted in Hidden Depths , "but none has been so slow as hypnosis in shaking off the evil associations of its origin." There is nothing very evil in Robin Waterfield's monumental study but there is a good deal that is distinctly uncanny, tempered by Waterfield's notably sane and enthusiastic approach to a subject he argues has immense potential for good.

For a phenomenon that might or might not exist (the jury are still out, as we shall see), hypnotism has an enormous literature. Hidden Depths is one those hefty book-as-syllabus overviews, ranging as far back as the ancients' possible use of hypnosis and giving a thorough account of its growth in the modern era, chopping off dud paradigms as it goes.

It was Anton Mesmer who got "mesmerism" off the ground in the 18th century, leading his patients into convulsions caused - or so he believed - by magnetism. He combined the pseudo-scientific paraphernalia of "magnetised water" with wizard's robes, and provided ethereal music on the glass harmonica - perhaps like a sort of early Theremin - for further spooky effect. It was nonsense, but it worked.

Then the Marquis de Puysegur discovered that Mesmer's all-important "magnetic crises" could be done away with, because the trance leading up to them was effective on its own. But Puysegur still believed in magnetism, and magnetised a tree for his grateful peasants to have trances around. It was left to a Scottish physician, James Braid, to dispose of magnetic theory altogether when he found that fixation of attention on a small bright object would do the trick on its own. He coined the word "hypnotism". When a French doctor named Liebeault subsequently showed that even Braidian fixation was not the essential thing - suggestion being the key - then hypnosis as we know it had come into practice.

Meanwhile the subject enjoyed a luxuriant and fabulous growth in all directions, most of them spurious. "Phreno-mesmerism" combined hypnotism and phrenology, playing the head like an emotional piano. In France, it was discovered that hypnotised subjects showed an uncanny ability to detect illness in others, so it became a medical practice to take a group of patients, find out which one was most susceptible to hypnosis and get him or her to diagnose the rest.

In England, mesmeric phenomena were associated with working class radicalism. Lady Eastlake complained that it was "advocated by women without principle, and lectured upon by men who drop their h's". A comic ballad of the 1840s noted: "Upon the rich it comes not o'er / They're not to it susceptible. / They only Mesmerise the poor / To please the more respectable."

Dickens was a great enthusiast, and befriended the hypnotic pioneer John Elliotson, a founder of the London Mesmeric Infirmary. The author was a keen amateur hypnotist himself, giving a long course of mesmeric treatment to the wife of a Genoese banker, Augusta de la Rue. Waterfield's book is packed with this kind of interesting and often offbeat material, reminding us that Rebel Without a Cause , the book of the James Dean film, was written by a therapist about the "hypnoanalysis" of a delinquent, and telling us that the somnambulistic experiments of a certain Charles Lafontaine ushered in "the golden age of mesmerism in Belgium" - a phrase with a surreal charm all its own.

Aside from picturesque cultural history, there are extraordinary details of hypnotic feats and cures. Predictably, many of these involve the skin, with blistering, recovery from burns, stigmata and the like. Others are more surprising, such as the subjective stretching of time that allowed a woman to count 862 objects in three seconds. There are some striking details of hypnosis in conjunction with surgery, like the work of James Esdaile in 1840s India. Esdaile found that the post-operative death rate dropped from around 50% to 5%, and gives the case history of shopkeeper Gooroochuan Shah. Shah had a monster scrotal growth which prevented him from moving, and he used it as a writing desk (which, said his case notes, "has pressed it into its present shape"). After four days of mesmeric preparation, Esdaile removed an 80lb tumour. Shah said he felt nothing, and proceeded to recover.

For all that, experts still debate whether there is any such thing as a hypnotic state, in the sense of a real trance akin to sleepwalking. Its opponents maintain that everything hypnosis does is produced not by an altered state of consciousness but by normal processes such as motivation, belief, role-playing, and social compliance between experimenter and subject. (Sceptics could argue that Shah might have been cured by his faith in the Raj, or simply conniving; an objection to which Esdaile gave common-sensical short shrift back in 1846.) Despite the spectacular feats routinely achieved by hypnotists, an American stage magician has offered $100,000 to anyone who can prove that a special state is involved, and has so far defeated two claims in court.

Waterfield believes in the special-state theory, and cites various arguments in its favour. One of them, only possible recently, involves following radioactive blood around the brain. When hypnotised and unhypnotised subjects are asked to visualise a non-existent chair, both groups describe it in vivid detail, but the hypnotised group show an increased flow of blood to the part of the brain involved with sight, while those who are just role-playing remain normal.

This is only one of the things Waterfield believes. He is also very sympathetic to telepathy and clairvoyance, citing the oddly pleasing fact that people hypnotised to believe they were looking into a crystal ball achieved far better results than people looking into a real crystal ball. The discourse this book most resembles at certain points is, unquestionably, the discourse of occultism. Following an experimenter called Hilgard, for example, he is sympathetic to the idea that we have what Hilgard terms a "hidden observer" active within us, somewhere between a guardian angel and a true self.

Alan Gauld's standard History of Hypnotism concluded, after more than 600 pages, that hypnotism was "less than real, but more than illusion". In terms of hard logic and science, Waterfield offers little advance on this, but he does make the elegant point that this ambiguous status reflects the ambiguous sensation experienced under hypnosis itself: a "parallel awareness", like the I-know-I'm-dreaming sensation of lucid dreaming, or the sensation WB Yeats experienced at a seance, when he felt his hands moving automatically: he thought he could stop them if he wanted, but let them continue anyway.

So hypnosis remains mysterious, but Waterstone is very convincing on the powers of the mind - the immense powers of imagination and belief - and he ends with a plea for the greater use of hypnosis in modern medicine. The first great age of hypnosis came to an end with ether anaesthetic on the one hand and Freudian psychoanalysis on the other. Now, however, it seems to be undergoing a revival: between 1988 and 1996, according to Waterfield, the number of psychologists with the US Olympic team rose from one to about 100. This is an important, timely and appropriately fascinating book.