The compass was most likely invented during the Qin dynasty of China, which lasted from 221 B.C. until 206 B.C. Lodestones, which are composed of a magnetic iron oxide, were used by Chinese fortunetellers in order to construct their fortunetelling boards.
The first compass came about when people began to realize that the lodestones were great for pointing out legitimate directions. The early compass was comprised of a lodestone spoon-shaped mechanism, which rested on a square slab marked with the constellations and other essential points. The handle of the spoon would always point toward the south.
In the eighth century, magnetized needles first appeared. While still chiefly a Chinese mechanism, the needles replaced the lodestones as the direction-informing device. Between 850 and 1050, compasses first began to be used as navigational devices on ships. Zheng He, who made seven voyages on the ocean between 1405 and 1433, is the first person on record to use a compass as a navigational aid.
Nineteenth century Scottish scientist Sir William Thomson, who eventually became Lord Kelvin, invented the compass design with needle slung on silk threads through a skeleton card. In order to reduce friction, the skeleton card was made of fine rice paper, and the pivot was comprised of agate and ruby jewels. This revolution dramatically improved both the compass and its accuracy.
While any ship can check its exact location using a satellite and navigation system, all ship captains still have a magnetic compass on board. With today's technology, we realize that the Earth's magnetic field has some curves and moves around. This is called magnetic field variation. However, the variations can be accounted for on navigation charts, limiting the problems that they present.
