A compass relies on the earth's magnetic field to define the four cardinal directions of north, south, east, and west. The invention of the magnetic compass transformed navigational practices both on land and sea, giving travelers another method of orientation besides physical landmarks and positions of stars and planets. The particular type of earth known as lodestone was known in all early societies, as soon as they began working with iron. Suspended with a simple cord, a lodestone (literally, leading stone) aligns itself with the cardinal points, one part of it always pointing North. Magnetic compasses guided travelers on land, sea, and eventually air. In the seventeenth century, Edmond Halley collated slight variations from celestial North observed by numerous travelers and began mapping the magnetic field of the earth. Magnetic navigation and surveying became much more precise, when corrected by these maps, and continues to this day. Electrical experimenter Hans Christian Oersted used this simple device to discover the magnetic properties of electrical current. Incorporated into an electrical circuit by experimenters such as Michael Faraday, they became meters and indicating devices. The dashboard of every automobile incorporates several of these magnetic indicators, driven by other components to show fuel level, temperature, speed, etc.