Ancient Greeks observed that magnetite, or lodestone, attracts iron. Some time before 200 a.d., the Chinese sculpted magnetite into spoon-shaped compasses. They called these stones “south pointers.” By 1150 a.d., Chinese navigators used compasses with magnetized iron needles. But properties of magnets were not well explained until 1600. In that year, the English physician William Gilbert published De Magnete.