Columbus's Compass: Slightly Misguided

          The discovery and human history of magnetism is, of course, closely tied to the discovery and use of the compass. The first recorded use of a compass was in 206 BCE in China, during the Han Dynasty, but the observation of magnetism was nearly two hundred years earlier when Wang Xu noted that a mineral "lodestone" attracted iron utensils. However, this mysterious phenomenon was used to orient buildings according to Feng Shui rather than navigation of any sort. Then, in the middle of the 12th century, Chinese magicians used a magnetized, suspended needle to help organize troops the battlefield, and finally as a maritime navigational instrument.

Ancient Chinese Divination "Compass" c. 220 BCE

          Once the Chinese had developed this invaluable maritime technology, it could spread through trade to Europe, which it (most likely) did about the turn of the 14th century. It is speculated that the navigational compass was independently invented in Italy, but neither theory has been proven. The Europeans seemed to have a stronger spirit of exploration than the East, so the development of the compass was encouraged to a much greater degree.

Left; Astrolabe, which would have pointed Columbus to Geographic North
Right; Box-style compass, pointing to Magnetic North

          The dry box-style compass (as opposed to a magnetic needle suspended by a string or in water) began to take shape soon before Columbus set sail in 1492, and through his voyage, he noticed a very peculiar phenomenon. Earth's "Magnetic North" does not quite line up with Earth's "True North," or the geographical north pole. Therefore, as Columbus sailed across the Atlantic, he noticed his compass readings actually gaining accuracy when compared to astronomical calculations. Interestingly, he kept this (certainly terrifying) observation from his crew, fearing it would spook them.

Notice how, along Columbus's path marked in orange, the difference between each north would become less significant.
Look at the prime meridian (through true north) to help illustrate this effect..
Magnetic North in Red
Geographic North in Blue

         Unfortunately, this deviation in measurement didn't lead Columbus far enough astray to save an entire continent's culture and heritage, but nonetheless, the magnetic compass helped fan the flames of European exploration.

                                                                               

http://www.magnet.fsu.edu/education/tutorials/museum/chinesecompass.html

http://www.smith.edu/hsc/museum/ancient_inventions/compass2.html

http://theinstitute.ieee.org/technology-focus/technology-history/a-history-of-the-magnetic-compass

http://www.ngdc.noaa.gov/geomag/declination.shtml