Long before Captain Cook started charting the Pacific, the Polynesians were navigating the ocean without the use of instruments or charts. They had learned to 'read' the elements. The waves built up by the prevailing winds could be relied on to 'set' in the same direction. A build-up of clouds usually meant there was land beneath, and even at night a slight glow on the horizon suggested there must be an island thereabouts. Perhaps most impressively, without ever resorting to a sextant, they navigated by the stars. By memorising the position of the constellations, they crossed vast tracts of oceans with a confidence that can only be envied by most modern sailors. Likewise, the sailors of northern Europe studied the habits of birds to show them the direction of land. If an auk flew past a Viking boat with a beak full of fish, they knew it was heading back to its nest. If its beak was empty, then it would be heading out to sea to fill it.