Nearly all books on navigation have a chapter headed Practice at Sea, A Navigator's Day at Sea, A Day's Run, etc. According to these the navigator is on deck by dawn, spends his day, without eating, in a maze of observations, entries, calculations, precalculations, correc tions and chart work; takes morning, noon, afternoon, sun set and moon readings, star readings and pole star readings, and if he gets any time for sleep it does not show on the log. He has the author's sympathy, and if this little book really helps him the author will feel fully repaid for his time and trouble.