Science writing has thrown up some unlikely runaway best-sellers, and somewhere on the lighter, storybook end of the scale is Dava Sobel's Longitude. More a 176-page potted history than a hard-science book, it's a neatly condensed tale of how the greatest navigational problem of the 18th century was solved not by the bigwigs at Greenwich, but by a much-maligned Yorkshire clockmaker, John Harrison, who produced a series of extraordinarily accurate time-pieces.
At first enormous, esoteric, whirring devices, over the course of his life Harrison refined his clocks almost to the size of pocket-watches.
Harrison was a true Enlightenment creature: a self-educated master horologist, who also developed theories of the musical scale. His early, ingenious wooden clocks, with intricate parts made of lignum-vitae (which exudes its own lubricating oil), include the 1722 tower clock in Brocklesby Park in Barrow in Yorkshire - which has run continuously, apart from a cleaning job in 1884, for 270 years.
Time defines longitude, and an accurate clock is crucial to determining one's position at sea. With 3,000 English ships a year sailing to the Caribbean slave colonies by the 1700s, the need was pressing. Harrison's accurate, friction-free clocks were the first to prove themselves impervious to the heaving of the waves and the extreme changes in temperature.
A "king's ransom" of £20,000 was set aside by the Longitude Act of 1714 for a reliable method of determining longitude to within half a degree, and with his first 85lb nautical clock in 1737, Harrison had it cracked. Yet even after his fourth in 1759 - which lost only five seconds in 81 days at sea - the Board of Longitude denied him the full honour.
Headed by the Astronomer Royal, Nevil Maskelyne, who was working on his own lunar charts, the Board was baldly set on the solar-lunar angular-distance method, which did not stand up to either scrutiny or navigational experience. Eventually, it grudgingly gave Harrison the prize, but he was largely written out of history.
Sobel's little book is a ripping historical yarn of a good man vindicated, with a clear villain in Maskelyne. Since it emerged in 1995, it has lingered in bestseller lists on both sides of the Atlantic, and been translated into 22 languages. Its author, a former science writer for the New York Times, is a thin, friendly, well-mannered 51-year-old lady. Originally from the Bronx, she now lives in Long Island with her two teenage children. In the Westbury hotel last week, promoting the new paperback edition, she was calm and good-humoured, sitting stiffly in her chair; a peculiar, spiralling scarf, like a DNA molecular model, spilling over the neck of a neat, navy suit. Her second husband, Alfonso, a fit-looking middle-aged man with blazing blue eyes, scampered out of the seat to let me sit in for the interview.
The origins of the book lie in a 1993 seminar given at Harvard by Will Andrewes, curator of historical scientific instruments. After Sobel had written up the background to Harrison's discoveries for Harvard magazine, a small New York publisher asked her for a book on the subject, specifying that it should be short.
Longitude had already taken off before Andrewes published his own hard-science megatome, The Quest For Longitude, but according to Sobel there were no hard feelings: "On the contrary, he was delighted, because he said, `all my life, I've been trying to make John Harrison a household name, and now you've done it'." Needless to say, sales of The Quest have since been picking up nicely. She Sobel has put an elegant stamp and spin on the tale but, I remark, having read Longitude one comes away with little understanding of the clocks themselves. "I myself don't understand the clocks the way a trained horologist does, but I understand the basic principles," she replies. "I'm more interested in the story, because clock science is extremely complicated, especially as the book had to be without diagrams.
"When I wrote it, I thought nobody would want to read it. Even the title seemed off-putting, a kind of a strike-dread-in-the-heart title. So I told it in a spirit that showed that when you have a great, unsolved problem, the lore that grows up around it is thick and wonderful. All that is part of the fun of the puzzle, just like the `longitude lunatic' in Hogart's engraving of Bedlam in A Rake's Progress."
Now, she and Andrewes are working on an illustrated edition, due out in October. "I get many letters about the book, most of them positive, but even they bemoan the fact that there are no diagrams, so finally I was able to bring Will in as co-author, to chose illustrations and write long captions. I think he was very happy we had a chance to do this together."
Even in her own life, the book represented some vindication, as her husband left her just before she began it. She now says she couldn't have done it if she had still been married. "It was a huge risk, getting into serious debt to credit card companies, the mortgage on my house, the necessary repairs which just weren't done. My ex-husband was also a writer and we always shared expenses. So if one of us took an assignment that paid nothing, the other had to work two or three times as hard, and we just didn't do that."
Together, Sobel and her ex-husband had co-authored a number of books, including one on back-pain relief (Sobel suffers from scoliosis, a curvature of the spine, while her husband had a debilitating muscular condition) and another on arthritis. "That did well, it was a useful book, and had a very long life in mail order."
So has Longitude made her a fortune? "Well, it got me out of debt, and what I'm doing now is such a luxury because I'm working on only one thing, and I've never done that before. I tell you, it's nice."
Her current book project stems from something she stumbled on while researching Longitude - letters Galileo wrote to his daughter, a nun. "It's a very different book, because with her as a nun having such a close relationship with him, it throws a different cast over his science and context. Everybody has some association with Galileo - usually, it's as the great genius and scientific mind opposed to the medieval mentality of the church, but the real story is much more interesting."
Longitude is published in paper- back by Fourth Estate, price £5.99 in the UK