From the day the first sailing ship left sight of land to venture to distant shores, sailors looked forward anxiously to sighting land again. Lookouts, posted high in the rigging, scanned the horizon for signs that they were approaching the shore, such as flocks of birds or cloud banks. They also watched the water, noticing changes in color that indicated that the sea was getting shallower—which meant that land might be nearby. And when they thought that what they were seeing did indeed indicate land, they cried out, "Land ho!" for all to hear.

Both mariners and passengers understood that such sightings were often misleading. Cloud banks often formed with no land beneath them; birds could be blown out to sea by storms. But at the cry of "Land ho!" the crew sprang into action to confirm the sighting. The captain and officers scanned...