How a Famous Renaissance Cartographer Imagined The North Pole
Gerardus Mercator is one of the most famous cartographers in history. His work is highlighted by his projection, the Mercator Projection, that is still used in map making to this day. Mercator’s 1569 map of the world was one of the best received maps of his era which was punctuated by inaccurate charts and conflicting accounts of how the world actually looked.
While the Mercator Projection is still a useful tool in maritime navigation, some of his other ideas did not stand the test of time. One such idea involved his hypothesis about why compasses pointed north. In the Age of Exploration, everyone knew that compasses pointed north at all times but no one knew exactly why. Compasses were magnetic so it must have had something to do with magnetism.
Mercator theorized that the North Pole was dominated by a phantom island made out of a black metallic rock that sat in the midst of a giant whirlpool at the top of the world. Mercator was so respected at this time that many cartographers of the era started drawing this island at the top of the world to reflect his ideas.
Today, we know that there is no land at the North Pole and that the expanse is almost entirely made of sea ice.
Mercator named his idea rupes nigra which means black rock in Latin. He suspected that the island must exist at the top of the globe and that it was precisely 33 “French miles” in circumference. The giant slab of magnetic rock would explain why all of the compasses in the world pointed north.
There is no exact reasoning given for the 33 “French miles” number that he came up with for the size of the island. Perhaps that is the number he believed a rock would need to be in order to pull compass needles from thousands of miles away.
Mercator does give reasoning for why the rock must undoubtedly sit in the middle of a giant whirlpool. Mercator describes rupes nigra in a letter written in 1577 to a…