Introduction From the time of Columbus, the American continent was seen by Europeans as a barrier between Europe and the Orient. A passage through it was the prime object of many voyages of exploration. Magellan had sailed around South America in 1520, but the icy northern shores were mysterious and seemed unassailable. The search for a sea route across the top of North America began in the 16th century as a commercial venture sponsored by London merchants. By the 19th century it was obvious that a Northwest Passage would not be a useful seaway, but finding it became an obsession, as did the attainment of the North Pole late in the century.