The Fly in the Cathedral by Brian Cathcart

If there really was a race to split the atom, says John Morrish, then it had more in common with a primary school sports day

Recently, Jeremy Clarkson had a lot of fun on BBC2 at the expense of John Logie Baird, who was shown inventing television in his attic room with the help of knitting needles, bicycle lamps and the lid of a coffin. What Clarkson didn't know was that, at almost exactly the same time, a group of serious young scientists at the University of Cambridge was attempting to take apart the fundamental particles of matter - with the help of several lumps of plasticine. Mr Harbutt's best modelling clay was used to seal joints in the glass vacuum tubes of the Cavendish Laboratory's high-voltage rectifiers. These created a direct current powerful enough to direct a stream of protons at a sliver of lithium, not to break up its atoms - that had happened years before - but to split its nucleus.

It was a bit of improvisation, typical of the way things worked during this last great adventure of what we might call "small science": amateurish, hands-on, conducted on workbenches by men in labcoats. This book tells a great story: how a group of cautious, essentially modest men achieved something that made the world sit up. Products of a practical culture, they built their own equipment, then took it apart, cleaned it and started again. When they weren't doing that, they were mending watches, building amateur radios and going to church.

Plasticine's part in the story is short-lived. Just as it had replaced sealing wax from the Bank of England, it was in turn superseded because it kept getting sucked inside the equipment. It was replaced, symbolically, by a new, high-technology putty, developed by Metropolitan-Vickers, the giant engineering company which supplied much of the project's equipment and some key personnel. As Baird found with his knitting needles, make do and mend could take you only so far.

Nonetheless, there is much to envy about the pre-war life of science. True, money was desperately short. One experimenter complained that if they asked for six brass screws, they'd be given four steel ones. And yet, a good informal system of liaison with industry was in operation, and the lab benefited enormously from benign ignorance and neglect on the part of university authorities, government and society at large. And rather than losing talent, Oxford and Cambridge were attracting the best from all over the world, though the material rewards were small.

One of the most touching byways in Brian Cathcart's gently compelling book is the story of the Irish researcher Ernest Walton and his slow-motion, long-distance courtship of a fellow Methodist named Winifred Wilson. It took two years of near-daily letters - and the successful smashing of the nucleus - before he was emboldened to change his signature from "Ernest W" to the more intimate "Ernest". Even then, marriage had to wait until he'd returned in triumph to take up a post in Ireland. His older colleague John Cockroft, meanwhile, had waited nine years, including service in the trenches, before he felt it prudent to marry his fiancée, Elizabeth Crabtree. "Cambridge has a way of running off with money," he cautioned. "I don't think you would enjoy life in mediocre rooms with an insufficient income, in a place like this." And he didn't even have a student loan to repay.

Cathcart gives us a straightforward, unfussy account of the experiments and the experimenters, led by the veteran Ernest Rutherford, of whom it was said, "His mind was like the bow of a battleship. There was so much weight behind it, it had no need to be as sharp as a razor." A force of nature, he ran his lab by monopolising the best young scientists and chivvying them to one end: to find out what was inside the atomic nucleus.

One idea came from George Gamow, a Soviet citizen with a keen interest in table tennis and parlour games, as well as applying quantum theory to the nucleus. His visit to Cambridge provided the theoretical basis for Cockroft and Walton's experiments, although Rutherford always valued experiment above speculation. "That stuff!" he once scoffed, talking about Einstein's theories. "We never bother with that in our work."

Truly, this was an age of innocence. Scientists travel freely from Russia to Denmark to Germany to the US, usually passing through Cambridge on the way. Everyone knows everyone else and what they are up to. If there was a race to split the atom, it resembled one of those primary school events in which the winner triumphs because everyone else has fallen over. The Cavendish's feat came as a surprise, and the celebrations seem to have involved little more than a firm handshake, a vote of thanks, and a round of tea and cakes in the canteen. C P Snow's famous story of Cockroft walking around Cambridge in a daze, announcing to strangers that "We've split the atom! We've split the atom!" was an invention.

Even so, the event captivated press and public. Reynold's Illustrated News had the scoop. "Science's Greatest Discovery," it declared, promising "Energy Without Limit". The Daily Express, not quite sure, noted "The Atom Split, But World Still Safe."

That turned out to be an optimistic view, but the scientists concerned had little time or inclination to speculate on the possible consequences of their work. Shut in a wooden box, they counted microscopic flashes and clicks as atoms of lithium split and turned into atoms of helium, a process pursued since the days of the alchemists and now attained. They were, says Cathcart, preoccupied with practicalities. The more they studied the atom, the less likely it seemed that its energy could ever be used. In fairness, the key to that was the chain reaction, which would need another 10 years and the impetus of a world war.

And yet they must have thought about it all; the newspapers certainly did. This book disappoints on that score: we learn little of the scientists' speculations, fears and possible regrets. Obsessively focused, they didn't even think about radiation hazards until one of the team developed lesions on his hands that would not heal.

Cathcart's title, referring to the relative size of the nucleus within the atom, is a borrowed metaphor. In the best popular science tradition, he comes up with more himself, turning the arcana of sub-atomic physics into images most readers will be able to imagine. The theorists, of course, insist that the concepts involved are not only beyond visualisation, but beyond conception. Cathcart has ignored that, providing an admirably concise account of the science behind a very human story.