An illustration of a loadstone (or lodestone) from "De Magnete" by William Gilbert. A loadstone is a piece of magnetite that has magnetic properties and attracts iron or steel. William Gilbert (1544-1603) was an English physician, physicist and natural philosopher whose primary scientific work was De Magnete... (1600) (On the Magnet and Magnetic Bodies, and on the Great Magnet the Earth), and who is credited as one of the originators of the term "electricity." A unit of magnetomotive force, also known as magnetic potential, was named the Gilbert in his honor. In De Magnete, he describes many of his experiments with his model Earth called the terrella. From these experiments, he concluded that the Earth was itself magnetic and that this was the reason compasses point north (previously, some believed that it was the pole star (Polaris) or a large magnetic island on the north pole that attracted the compass). He was the first to argue, correctly, that the centre of the Earth was iron, and he considered an important and related property of magnets was that they can be cut, each forming a new magnet with north and south poles.