In 1743, Captain George Anson and HMS Centurion ventured into the unimaginably vast Pacific to hunt down a single Spanish ship, the Nuestra Señora de Covadonga. Better known as the Acapulco galleon, she carried silver between the Philippines and Mexico each year and was the richest treasure ship in the world. Despite all the millions of square miles of ocean, the ships met and fought each other. Anson triumphed, captured the treasure, and returned home to a hero’s welcome. Curiously, his success resulted from the primitive state of navigation at the time.
Cartographers had long divided their charts with gridlines to aid navigation. Latitude lines run parallel to the equator, perpendicularly crossing longitude lines, which intersect at the poles. Finding a ship’s latitude is a relatively straightforward task, depending mainly on measuring a noontime altitude of the sun. The equipment to make such measurements requires little more than a good eye and a steady hand.