If you have an interest in navigation, I highly recommend for your reading pleasure and historical information, "The Riddle of the Compass." by Amir D. Aczel. It is a great companion to "Longitude," by Dava Sobel. The book delves into the history of the development of the magnetic compass and the significant role it played in maritime commerce in the first century AD. Oddly enough, the compass did not facilitate blue water seafaring, per se. The early sailors were decidedly blue water; it was coastal navigation that was [and still is] scary - it's the grounding thing. As an aside, the book also describes the origin of the "seven seas." Anyway, check it out.