He's an evangelist, a preacher. For him, the world is divided into the believers and the unbelievers, only, in his book, it is the believers who are in error, condemned to the darkness of ignorance. Salvation and light lies on the straight and narrow path of rationality. Even though you are beset on all sides by the lure of psychic powers, The X Files, dowsing, homeopathy, chiropractice, let the scientific method be your one and only true guide.
For years now, he has been taunting the world of mediums, spoon-benders and all who claim paranormal powers. Currently, he is offering more than $1m to anyone who can successfully demonstrate psychic powers, according to a simple agreement of what constitutes success. Dozens have tried to claim it, but none has succeeded. Has he ever feared he might lose the money: "No one has even come close," he says.
Next week, the amazing Randi will be unleashed on the British public in a mini lecture tour, which starts on Monday at the British Association meeting in Cardiff. At least nine brave souls have declared that they will take up his mocking gauntlet. They should be under no illusion that he will treat them kindly should they fail. For instance, when a nurse wrote to him recently claiming that a form of healing known as Therapeutic Touch worked on the principles of quantum physics he replied: "Cynthia, Cynthia, Cynthia. Dipping into quantum physics may fool a few folks, but your view of it is just plain wrong, silly, unscientific, and juvenile. It's just nut stuff. I hope you're a better nurse than you are a scientist."
Is there any difference between American and British fans of the paranormal? "No, people are pretty much the same around the world, although what they go for varies. In Britain, you are very big on dowsing for some reason. They seem very honest folk, just self-deluded." Randi will team up next week with our very own bare-knuckle atheist, Richard Dawkins, Professor of the Public Understanding of Science at Oxford University, to bash the believers.
Although Randi is delighted to take on all comers, his name has been inextricably entwined with that of Uri Geller, the professional spoon- bender, for the past 20 years. Ever since he advised Johnny Carson how to make his studio magician-proof, and Geller sat for an agonising 23 minutes unable to manage a single psychic feat, the two have conducted a malevolent dance. Randi wrote a book entitled The Magic of Uri Geller, which claimed he was no more than a magician, and not a very good one at that. Geller, for his part, sued Randi in several countries around the world.
However, Geller is still performing - he used ``psychic powers'' to make seeds sprout in his hands earlier this year in the Albert Hall - and Randi is still pursuing him, although cautiously. "I do this trick by having some radish or mustard seeds poured into the hand of a spectator," explains Randi. "Then I reveal that one or two of the seeds are sprouted, and I gradually move away the other seeds so that one sprout seems to develop. It's an old trick, mentioned in a similar form by Madame Blavatsky when she visited India." Then he delivers the sly killer punch: "Mr Geller, however, does his demonstration by genuine supernatural means, he tells us. To me, that seems to be the hard way."
Another of Randi's targets was the French biochemist Jacques Benveniste, whose homeopathic claims were aggressively challenged when Randi and others investigated his lab 10 years ago for the journal Nature. Has he given up? Not at all. Earlier this year he announced that he could send homeopathic remedies over the Internet. Treatment by e-mail.
And this highlights Randi's problem: the hydra-headed nature of his adversary. However many times he lops off a paranormal head with the simple sword of scientific method, several more sprout in their place. Furthermore, and this is the really galling part, the public goes on believing in them. For years, the polls have been showing that Randi and the rationalists are in the minority: 61 per cent of people believe there are paranormal things that science cannot explain, and 71 per cent of women believe in some sort of a god, and so on.
What is needed is proper scientific education, says the American Committee for Scientific Investigation of Claims of the Paranormal (CSICOP). Randi's own contribution to this is the James Randi Educational Foundation, in Fort Lauderdale, Florida. Set up with the aid of an anonymous donation of $2m from a computer magnate, the 5,200-square-foot facility contains a library of 1,220 books on the paranormal and related subjects, 700 hours of video, and high-speed, 24-hour Internet access for researchers and students. Funds also come from lectures, television appearances and regular seminars for $199 a head.
But, ultimately, Randi's great value is not so much as an educator but as a scientific street fighter. He is a magician, a self-confessed scam artist and trickster. He knows how these things work. Scientists may be suspicious, but often they are hard put to say just where the trapdoor is. Most of us have no way of assessing miracle claims. After all, we go to David Copperfield to be shown miracles on a nightly basis.
However, show Randi a tape of a paranormal exponent, such as Joao Teixeira de Faria - the "miracle" healer of Brazil, who claims to have cured 15 million people over 35 years with psychic operations such as placing a knife inside the eye - and this is what you get: "The `eyeball' stunt he does is very old. I saw it done in carnivals when I was a kid. There are no pain nerves in the sclera [the white of the eye] that would react to a knife being placed there. That is the most common thing that this man does, regardless of the patient's complaint. Refer to my book Flim- Flam! to see me with a knife under my eyelid. Or try it yourself."
So why do people persist in these foolish beliefs, even when the cold light of reason shows them to be absurd? It is not a question Randi is particularly revealing about. "They want comfort," he suggests. Well, yes, that other great rationalist, Karl Marx, said something similar about opium of the people. Then, like everyone else, he blames the media. "TV programmes don't want to hear about reality. That Hitler died in his bunker is not a story. Say he's alive in Rio and you've got a series." But this hardly seems a good enough explanation for the sale of about 40 paranormal books for every one of his which debunk the stuff.
But, as he might say, you don't ask a molecular biologist to fix your teeth. Randi is a performer. He's brilliant at knockabout, and has lots of humour. I asked if all his targets were equally risible. Didn't homeopathy have some evidence for it? "Do you know what the theory of it is? It's complete madness," he snaps back. "However, it is one of the delusions you Brits are particularly keen on. Probably because the Windsors have been relying on it for 220 years. Maybe that's why they are in the state they are today."