Marx's latest book about the sea, its mysteries and exploration shows almost no personal interest in his material, and has none of the lift of Still More Adventures (1976). What it does have, extracted from his files, is a survey of man's millenial efforts to move about underwater. Marx begins with the earliest accounts of diving in the Old World and in the New World, the Polynesian invention of underwater goggles, the first diving bells and Leonardo's designs for remaining underwater for hours (both practical and impractical), and the earliest snorkels. The first diving bells are fascinating, especially that built by John Day in 1774: Day descended in a 50-ton sloop he'd made watertight, and after 24 hours the people waiting for him around Plymouth Harbor began to be alarmed. They never saw him, or his boat, again. Today's highly sophisticated equipment, submarines, deep-sea research capsules, and underwater habitats are described interestingly enough but without enthusiasm. The net result: serviceable.