It's a book about navigation techniques of Pacific Islanders. I'd thought this was a lost art, only written about by westerners recently, carefully-hidden mysteries of guild-like navigator clans. But this book is from 1972 and points out its sources from various reports dating back to Captain Cook, so not all of these techniques were that secret. Just kinda secret… and how many researchers are going to travel all the way out to the Gilbert Islands or whatever when Utah is 15 hours closer, right? This book gets into details: folks from this island chain do this; folks from that island chain do that. I didn't really retain those details, but I figured out that some of the things I "knew" were overly-gross generalizations. Marshall Islanders aren't the only folks who use ocean swells for navigation; but they're more enthusiastic about the technique, and maybe the only folks who use refracted-around-bulgy-islands ocean swells to refine things. Anyhow, with all the detail-y bits, I'm glad this wasn't the first book I read on the topic, but it was a good follow-up so I could clear some he-knows-just-enough-to-be-obnoxious half-truths out of my neurons.