Last Night's Television - The Royal Institution Christmas Lectures, Five; Tony Robinson and the Blitz Witch, Channel 4

When everything clicks

Back in the mists of time, The Royal Institution Christmas Lectures were a staple item in the BBC's seasonal package. More recently, these venerable public talks, which were launched by Michael Faraday in 1825, migrated to Channel 4. Of late, they have found a home on Five, which says quite a lot about contemporary public-service broadcasting, none of it nice.

The lectures serve the same purpose that they always did. The aim is to present complex scientific matters to children, in a way that will grip, entertain and engage them. This year, it was the turn of Professor Christopher Bishop, who works for Microsoft in Cambridge. He lectured on "The Quest for the Ultimate Computer", and explained the process of assembling one so clearly that I for one began to feel certain that I could knock a computer together in the potting shed, if only I could be bothered.

Professor Bishop worked hard at explaining why it was that computers had become so sophisticated, so quickly, while becoming cheaper all the time as well. He trotted though the discovery of semiconductors (the first, silver sulphide, in a suitable nod to history, was happened upon by Faraday), the invention of transistors, the happy birth of the integrated circuit, and the joyous news that the more transistors you could get onto a microprocessor, the faster and the cheaper they got.

Exponential growth, he explained, with the help of some mousetraps and some ping-pong balls, had got us from black-and-white Space Invaders to interactive Star Wars: the Force Unleashed in 30 years. And, of course, he gently added, it had got us a whole lot more, including a giant leap in health care. But all that endeavour was being defeated by the intense heat that the microprocessors were beginning to generate. In another couple of years, computers would have to stop getting faster, or they'll be generating the same heat density as the surface of the sun. This seemed like a familiar and depressing story, albeit in microcosm.

But the ebullient professor was undaunted. Wouldn't the rapt audience like to be involved in making computers out of carbon monotubes? Such a thing might soon be possible, and they could process 1,000 times faster than contemporary computers. Or out of DNA? The DNA in our own bodies, he confessed, held 10,000 times more data than that contained by all the computers in the world. Wouldn't it be great to have computers that powerful? Wouldn't it be fabulous if humans became so clever that they could invent themselves?

That would depend, of course, on what humans used the very clever computers to find out. Would it, for example, rescue us from the spectacle of watching Becky McCall, who was billed as a science journalist, completely failing to debunk the idea that ectoplasm existed, smelled a bit like semen, was excreted from the orifices of mediums, and arranged itself into spirits who chatted soothingly about how lovely the other side was?

McCall was playing the sceptic to Tony Robinson's "open-minded explorer of the unexplained", in Tony Robinson and the Blitz Witch. The Blitz Witch was Helen Duncan, a "celebrated" wartime medium who made her living from promising the families of dead servicemen that she could put them in touch, one last time. Such antics are deeply unpleasant, but it is still astonishing that the woman was tried at the Old Bailey in 1944, and became the last person (so far) to be jailed under the Witchcraft Act of 1735.

Duncan attracted the attention of MI5 when she conducted a seance in Portsmouth in December 1941, at which a sailor called Sid "appeared", announcing that he had died when the HMS Barham had been bombed by a German U-boat. Naturally, the news of the ship's loss, with more than 800 of its hands, went round like wildfire, even though the Admiralty had told the relatives of the dead that for reasons of national security, the loss of the Barham should be kept to themselves.

It took a long time before Becky the sceptic got around to revealing that letters had been sent to the bereaved on 6 December, before the seance. For quite a bit of the show, she flailed around, pretending that no member of the public could possibly have known about the sinking until it was announced in The Times in February, and elaborately discussing cheesecloth and suggestibility with other so-called scientists who really ought to know better.

Clearly, the authorities had charged Duncan with witchcraft because they couldn't afford to let her carry on paying people for information, in order that she could exploit other people's grief. No doubt they couldn't afford the bother of putting together a treason case against her either. I believe it's called rough justice.

My 11-year-old son was enthralled by the show, far more so than he had been by the revelatory lecture on computers. The latter may run on logic, but logic, bizarrely, has never been a match for human credulity. It's easy to make entertaining fiction. But it's entertaining fact that provides the public service of building people with a half-decent processing speed.