The full title of this book is “Longitude: The true story of a lone genius who solved the greatest scientific problem of his time” by Dava Sobel. A long title for a relatively short book. Ms. Sobel has written a fascinating and very readable book.
First remember that before GPS and satellite guidance sailors had to find other ways on a vast open sea without landmarks to figure out just where the heck they really were to get to their destination. Next remember that latitudes are the human designated lines that run “horizontally” on the globe as we imagine it. The equator is a latitude line, for instance. Longitude lines run from pole to pole.
When sailors ventured out they could tell pretty closely what latitude they were near because of the location of the sun in a particular season. Determining longitude was nearly impossible. If Columbus could have accurately judged longitude, he would have known he was far short of reaching the islands around India as he thought he had.
Because of lost voyages and horrific shipwrecks the need to judge longitude at sea became a great priority during the 18th century. Cash prizes were offered by several entities, including the government of England. There were two primary theories on how to practically accomplish the goal. One was voluminous star charts to decide where you were and another was clocks. If you could know for certain what time it was in the port you left (or a prime meridian) and where you were at high noon by setting a separate clock, you knew how far you were from that port or meridian and thus longitude.
With atomically accurate clocks in our age I had no idea how tough it was to keep time in those days. Temperature variations and ship movements rendered pendulum and spring fed clocks to provide too much variation from the accuracy required. Thus begins a terrific narrative by Ms. Sobel as she takes you on a fabulous journey with colorful characters and simple scientific explanations. (I have probably rendered many errors in the descriptions above but she will guide you safely to harbor.) I enjoyed the book tremendously and highly recommend it. Enjoy!