Ropey? These old clips were held together with sticky-back plastic

ALONE figure walks at the water’s edge on a windswept Celtic beach, her hair whipped by the salty breeze as she gazes longingly out to sea. Why, this must be wild-spirited Demelza with her heart breaking for Cap’n Ross.

Sadly not. The camera swoops on Professor Danielle George of Manchester University, wondering how she’s going to cobble together an hour of old documentary clips about volcanoes and tsunamis, and somehow make it new and interesting.

Try as she might, she couldn’t. Decoding Disaster: A Timewatch Guide (BBC4) was so badly constructed, it might as well have been patched together with glue and sticky-back plastic. You’d never guess that Prof George’s PhD is in electrical engineering.

Lumps of ancient film were spliced into one long, rambling, waffly mess. We had half an hour about Atlantis and Pompeii, then some stuff on the Black Death, and finally a segment on flooding around the Bristol Channel.

The theme seemed to be that science, even when it doesn’t have the faintest idea what it’s talking about, is really wonderful.

We heard one scientist on a forgotten history show from 1984 explaining that the 14th-century plague was probably anthrax, and another in 2004 declaring it to be a strain of ebola.

Generations of Mediterranean archaeologists couldn’t work out where Atlantis was, but that didn’t stop them making vague guesses on camera.

Since each programme proved the previous one wrong, you would suspect that none of the ‘experts’ wanted to be reminded of their mistakes.

There were rare moments of interest. A young Magnus Magnusson popped up on the unspoilt Greek isle of Santorini in 1972, talking about the Minoan civilisation, with an open-necked shirt, blond hair and a golden tan. Goodness knows why he ditched that job for the gloom of the Mastermind studio.

For a demonstration of how to string together a boxload of half-fossilised bits and reinvent them as something fascinating, you need the Natural History Museum.

For the past six months the great entrance hall has been closed while the famous diplodocus skeleton was dismantled, and we had a sneak preview of the new exhibit in Horizon: Dippy And The Whale (BBC 2).

The bones of a 100-year-old blue whale have been assembled, not in a flatly rigid pose like a cod on a fishmonger’s slab, but in a dramatic dive — lunging out of the rafters and down towards the visitors as if to gobble them up. It promises to be an extraordinary artwork, never mind a museum exhibit, and David Attenborough’s narration gave a vivid sense of how much planning has gone into the display. Visitors will get their first sight of it today at 10am.

As a casual aside, the show conveyed what Timewatch had tried so hard to do and failed: how scientific attitudes change over the decades. When the whale was beached on the west coast of Ireland in 1891, no one gave a thought to its value as an exhibit... except for one astute entrepreneur, who paid £111 for the carcass as dog food, but cleverly sold it for £250 to the museum as an educational object.

Forty years later, the skeleton was reassembled by workmen who wedged the bones into place with wooden splints and wads of newspaper.

Colourful details like this made the story fascinating. What TV professors so often fail to understand is that it’s no good telling us how fabulous science is. Show us — and trust the facts to do the rest.