'Longitude' by Dava Sobel, ISBN: 0140258795. This book was great. It was bythe same authoras 'The Planets' and Galileo's Daughter'. Sobel charts the history of longitude / navigation and the problems associated with finding it at sea with no reference points. England eventually offered a prize to anyone that could solve the problem because the navy was losing so many ships due to errors in navigation and timekeeping with respect to the prime meridian in England. It's also a great story of the politics in the science community a hundred years ago (some things never change). Excellent book, fun to read.