One of the first forces of nature to be discovered by humans was magnets. The history of magnets dates back as early as the 4th century BC when the attraction between lodestone and iron was documented in Chinese literature. Lodestone creates its own magnetic force and is referred to as a natural permanent magnet. Iron is an induced magnet, in that it only becomes magnetized by the presence of a permanent magnet, like lodestone and is what creates the attraction. Ferrofluid is a liquid form induced magnet. The liquid, in the presence of a permanent magnet, will become magnetized.