Ms. Sobel, a former science reporter for The New York Times, confesses in her source notes that ''for a few months at the outset, I maintained the insane idea that I could write this book without traveling to England and seeing the timekeepers firsthand.'' Eventually she did visit the National Maritime Museum in Greenwich, where the four clocks that James Harrison constructed are exhibited.
She writes, ''Coming face with these machines at last -- after having read countless accounts of their construction and trial, after having seen every detail of their insides and outsides in still and moving pictures -- reduced me to tears.''
Such is the eloquence of this gem of a book that it makes you understand exactly how she felt.

Here's a swell little book that tells an amazing story that is largely forgotten today but that deserves to be remembered.

It is the story of the problem of navigation at sea--which plagued ocean-going mariners for centuries--and how it was finally solved.

It is the story of how an unknown, uneducated and unheralded clockmaker solved the problem that had stumped some of the greatest scientific minds. And it is the story of how the Establishment of the 18th Century tried to block his solution.

The essential problem is this: In the middle of the ocean, how can you tell where you are? That is, how can you tell how far east or west of your starting point you have gone?