The publication of Longitude taught me that a book can actually improve by virtue of being read. Numerous attentive readers took the trouble to write to me to point out typos or other errors in the text, which the publisher then corrected in subsequent editions. (For example, the typesetter had inexplicably swapped the word latitude for longitude—and vice versa—on several pages.)

Many more people wrote to say they’d enjoyed reading the book, and quite a few asked questions the story had raised in their minds. Almost all of that early correspondence went back and forth by ordinary mail, and I wrote my part with a fountain pen. Now that Longitude is available as an e-book, I enjoy continuing and widening the conversation via e-mail. 

People still ask me, “What’s this book about, really?” And I tell them it really is about longitude—about the race to discover a means for determining position at sea, a challenge that stumped the wisest minds of the world for the better part of two centuries. Many famous scientists, including Galileo, Isaac Newton, and Charles Darwin, appear in the story, but the solution to the “longitude problem” came from an unknown, self-educated clockmaker, John Harrison, who devoted forty years to the effort.

The book became a surprise best-seller and is still in print. For the 10th anniversary edition in 2005, astronaut Neil Armstrong wrote a foreword that speaks of his lifelong admiration for John Harrison.

Recently I received a message from someone who had read the book, seen the made-for-TV movie based on it, and then traveled to Greenwich for a first-hand look at the original longitude sea clocks. “Never mind Stratford-upon-Avon, Stonehenge, Westminster Abbey, Big Ben, the palaces and gardens, the Tower of London, even Abbey Road,” he wrote. “The Royal Observatory was the highlight of our trip to England.” 

The Illustrated Edition

Roughly one-quarter of the many letters I received after the publication of Longitude complained that the book contained no pictures, maps, or diagrams. This loudly expressed interest in illustrations led to The Illustrated Longitude, published simultaneously in England and the United States in 1998, with 180 images selected and captioned by my co-author, William J. H. Andrewes. As organizer of the original “Longitude Symposium” at Harvard in 1993, Will had edited and illustrated The Quest for Longitude, which contained the complete text of all the technical papers delivered at that three-day event, plus pictures galore. 
(The latest paperback edition of Longitude does include an eight-page color photo insert.)  

The original Longitude cover