He tucks into wild pigeon, he dictates notes to his secretary by clinging to a wall and speaking through a window instead of simply walking round to her office, he lies in a bath like Archimedes in order to chance upon good research ideas, and he plans to establish a happiness research institute.

Who could doubt that David Weeks is an eccentric? No one, you would have thought. Yet Weeks, a 49-year-old clinical neuropsychologist at the Royal Edinburgh Hospital who once navigated nuclear submarines round the Scottish coast, does not make it into his own book, Eccentrics, which was published last week. Why not? The explanation is simple. The eccentrics in the book are even more weird.

For the past ten years (and this is another reason for labelling him "eccentric"), Weeks has spent all his spare time studying British and American eccentricity while holding down a National Health Service day job treating elderly people suffering anything from mild anxiety to senile dementia. And without funding, he has also spent all his spare cash - hence a popular science book to follow publication of the detailed findings in an obscure academic journal.

England, he says, is the haven for eccentrics. As if to prove this, he points out that "most Americans think that if you are from Great Britain, you are automatically eccentric". The United States, his home country, also has more than its fair share of odd characters, but that is partly because of "the English connection". Dating the modern history of eccentricity back to the 1550s, he has unearthed over 150 weird and wonderful people from past ages.

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Nearly all the first eccentrics were British rather than American because, according to Weeks, "frontier life in America was hard, and there was little place in it for eccentricity until the end of the 18th century". It is one of his key findings that eccentricity is "essentially a leisure activity" and that the eccentric pauper is the needle in the haystack.

The earliest eccentric listed by Weeks is one Hon. Henry Hastings. He delighted in hunting, fishing and chasing women until his death aged 99, and liked to attribute his twice-nightly virility to his twice-daily diet of oysters. Another eccentric was the royalist Sir Thomas Urquhart, who claimed to be 153rd in descent from Adam on his father's side, who developed a universal language called Logopandescteision and who died of laughter when he learned that the monarchy had been restored.

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According to Weeks, the 1700s witnessed "a great outburst of eccentricity" and by the 1800s eccentrics had started to appear across the United States. One was Joshua Abraham Norton, who claimed to be the emperor of the United States. Local people indulged him in his fancy, and when he died in 1880, the San Francisco Chronicle ran the headline "le roi est mort" and 30,000 turned up at his funeral. Another was crazily-named Oofty Goofty, otherwise known as the Wild Man of Borneo, who dressed up in furs, gave out strange animal cries, and paid his way by letting people punish him for money: a kick for ten cents, a whack with a baseball bat for 50 cents.

In this century, Weeks found a Chippewa Indian who has walked everywhere backwards since seeing the film Little Big Man in which a warrior shamed by having his life saved by a white man walks backwards until he regains his honour in battle, a woman who believes it is immoral to throw anything away and who purchased an abandoned opera house to store all her possessions, and a crackpot inventor who has constructed everything from a catamaran of bathtubs to a bra warmer by using bits of rubbish.

Down the centuries, Weeks found eccentrics from all walks of life, and especially from academia. It seems that the myth or the stereotype of the absent-minded professor is well-founded in fact, not least because, as he puts it, "in order to get a sufficient number of students, you had to be fairly colourful, and so many slightly eccentric professors actually magnified their own personal traits." He points to such past examples as John Barrett (1753-1821) whose appalling English contrasted with his fluency in the ancient tongues of Latin and Greek, and Thomas Spooner (1876-1930) the Oxford don who transposed the initial sounds of words with such silly consequences as "the Lord is a shoving leopard".

All this makes for amusing coffee table reading during those more idle moments. Yet Weeks's work has a serious point to it: that is, to reach the first scientific definition of eccentricity. At times, this may be hard to credit. After all, there does not appear to be anything earth shatteringly new in the observation that the English absent-minded professor is the archetypal eccentric.

What is more, throughout the study, the definition of the eccentric wobbles wildly. At one point, Weeks calculates that the eccentric is a one in 10,000 rarity and then comes out with the really useful comment that "eccentricity is a trait that everyone partakes of to a lesser or greater extent". At another point, he explains that eccentricity is a social construct which changes according to time and place and then proceeds to identify Isaac Newton as eccentric not because of his mathematical formulae (which were unusual) but because of his alchemical experiments (which were commonplace).

But Weeks's contribution to the science of eccentricity comes in the shape of his analysis not of historical eccentrics but of 1,000 modern eccentrics. His large sample was accumulated first by advertising in libraries, supermarkets, pubs and universities. "Eccentric? If you feel that you might be, contact . . . " read the advert. This was spotted by a journalist in Edinburgh's University Staff Club, and before long hundreds of people were claiming, nay boasting, about being eccentrics.

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There were the hoaxers and the practical jokers, but eventually Weeks was left with a working group of 309 men and 480 women (later added to) who were predominantly middle class, middle aged (although ranging from 16 to 92), and better educated than the general population. He submitted them to a series of assessments: a 90- minute interview, a standard personality evaluation and an IQ test. He also gave them the Present State Examination used by psychiatrists for the diagnosis of mental illness, especially schizophrenia.

From the results, Weeks concluded that the eccentric is non-conforming, creative, strongly motivated by curiosity, idealistic and happily obsessed with one (but usually five or six) hobbyhorses. Eccentrics are also characterised by their intelligence (the top 15 per cent), their non-competitive spirit, their unusual eating habits, their solitude, their mischievous sense of humour, and their bad spelling.

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Much of this, the solitude and the unusual eating habits, is hardly startling. What is, perhaps, is the word "happy". Weeks points to the perceived fine line between madness and eccentricity, revealing that study after study has identified the healthy sibling of a schizophrenic as eccentric. But he argues that "eccentrics are supernormal rather than abnormal" and observes that schizophrenic symptoms such as hallucinating and hearing voices are present in 15 per cent of "normal" people and only 8 per cent of eccentric people.

For this reason, he rejects the idea that eccentricity should be a diagnostic category like any other mental illness simply because "it does not specify illness". He adds that eccentrics "appear to be happier than the rest of us" partly because they "know they are different and glory in it" and partly because they are physiologically immune to stress since they are not concerned about how the world views them.

The worry, for Weeks, is that eccentricity might be waning. This not a new concern. Back in the 1850s, John Stuart Mill remarked that the fact "that so few now dare to be eccentric marks the chief danger of our time". It is not simply the passing of such characters as Peter Cook and Sir Nicholas Fairbairn that causes concern. Weeks says that "the process of wanting to 'normalise' does seem to be very strong nowadays". He wonders whether the 19th-century Californians who played along with Emperor Norton's fantasy, "even though they knew nothing about brain-cell synapses or neuro transmitters, delusional grandiose mania or borderline syndromes, in humanitarian terms got it much more right than we do now".

Saying goodbye to eccentricity would be a sad day, not least because the health benefits would seem to be huge. Fortunately, Weeks thinks that eccentricity can be learned, at least to some degree. "I don't think there would be very many people who would want to take on the entire eccentric lifestyle," he suggests. But eccentricity in moderation - if that is not a contradiction in terms - is something to be hankered after.

Weeks has already started hankering. He has developed what he calls "eccentric thinking therapy", and encourages his real patients to view the world more lightheartedly, just like an eccentric. He has also used the eccentric thinking process to become more creative, and has come up with his first patent for a natural substance to treat his neurotic patients, to make them happy. No doubt the quest for the eccentric's elixir of life will soon begin. As he notes: "We were always telling ourselves that if we could extract that happy essence and bottle it, we would be millionaires."

Eccentrics by David Weeks and Jamie James, is published by Weidenfeld and Nicolson, price Pounds 17.99.

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