Alex Marengo's programme began with the first boom in spiritualism, for which the seed was the shenanigans of two young sisters in New England, who persuaded their parents that they were the locus of spirit messages by cracking their toe joints against the footboard of their bed and bobbling apples on the end of a string. The will to believe must exist in society in a kind of supersaturated solution, because more than once such trivial specks of evidence have precipitated a sudden crystallisation of conviction. There followed a rising tide of manifestations, and though the spirits chose to demonstrate their powers in bizarrely limited ways - ringing bells, throwing trumpets, regurgitating ectoplasm - even some reputable scientists were persuaded that a new force had revealed itself. Our ancestors, before we get too condescending about this, had rather better excuses for giving such matters the benefit of the doubt - X-rays and radiation had recently been discovered, legitimising effects that would previously have been thought beyond nature. What's more, the large body of evidence about medium-trickery had not yet been amassed.
That it ever was recorded was as much down to conjurors as to men of science (who proved rather more trusting of the mediums' good intentions). Houdini, a genius of suggestion himself, repeatedly exposed fake mediums, on one occasion saving the Scientific American $5,000 which it had pledged to anyone who could perform psychic acts under stringent conditions. Houdini showed how it could be done - a sort of negative version of the principle of replication on which proper scientific method depends. Given that it's impossible to prove a negative (you can only prove that it didn't work this time, at which point there's a lot of talk of "inauspicious conditions"), this remains the most powerful tool for demystification, as the second half of the programme proved. "If they are using genuine psychic powers, then they are doing it the hard way," said one magician drily, after pointing out how simple it was to perform some of Uri Geller's tricks. Even more damningly, they were able to show you him in action from an unsuspected angle, filmed by hidden cameras during a Noel's House Party stunt. The evidence of cheating was not incontrovertible (sleight of hand is designed to defeat the eye after all), but combined with the demonstrations by self-confessed conjurors, it made a formidable case against him.
This won't perturb the truly gullible one bit. Geller's record on television outside of the field of music-hall telepathy and legerdemain has involved a number of memorably enjoyable fiascos, but people obligingly blank the failures from their minds so as not to occlude those apparently dazzling successes. Some viewers, though, those with minds open enough to accept the mundane reality over the delusory glitter of the inexplicable, will have felt the atrophied muscle of scepticism stretch a little. The film ended with the fact that James Randi (a worthy successor to Houdini in the debunking vocation) has $1.1m on offer to anyone who can prove a psychic phenomenon under controlled conditions. He's had no takers because the illusionists know, just like those television companies which actively enlarge the stupidity of their audiences, that it's much easier to take money off fools.