In the tradition of Dava Sobel's Longitude comes sailing expert David Barrie's compelling and dramatic tale of invention and discovery—an eloquent elegy to one of the most important navigational instruments ever created, and the daring mariners who used it to explore, conquer, and map the world.

Since its invention in 1759, a mariner's most prized possession has been the sextant. A navigation tool that measures the angle between a celestial object and the horizon, the sextant allowed sailors to pinpoint their exact location at sea.

David Barrie chronicles the sextant's development and shows how it not only saved the lives of navigators in wild and dangerous seas, but played a pivotal role in their ability to map the globe. He synthesizes centuries of seafaring history and the daring sailors who have become legend, including James Cook, Matthew Flinders, Robert Fitz-Roy, Frank Worsley of the Endurance, and Joshua Slocum, the redoubtable old "lunarian" and first single-handed-round-the-world yachtsman. He also recounts his own maiden voyage, and insights gleaned from his experiences as a practiced seaman and navigator.

Full of heroism, danger, and excitement, told with an infectious sense of wonder, Sextant offers a new look at a masterful achievement that changed the course of history.