TABLE OF CONTENTS Two natural substances, amber and lodestone, have awakened curiosity since ancient times. Amber is sap that oozed long ago from certain softwood trees, such as pine. Over many centuries, it hardened into a semitransparent solid akin to model plastics and ranging in color from yellow to brown. It is a handsome ornamental stone when polished, and sometimes contains the remains of insects that were caught in the sticky sap. Ancient Greeks recognized a strange property of amber. If rubbed vigorously against cloth, it can attract nearby objects, such as bits of straw or grain seeds.
Lodestone is a metallic mineral that also has unusual properties. It attracts iron. Also, when suspended or floated, a piece of lodestone always turns to one particular position, a north-south direction. The first known written description of the navigational use of lodestone as a compass in Western countries dates from the late twelfth century, but its properties were known even earlier in China. Today, lodestone would be called magnetized iron ore.
The histories of lodestone and amber are the early histories of magnetism and electricity. The modern developments in these subject areas began in 1600 with the publication in London of William Gilbert's book De Magnete (On Magnets). Gilbert (1544 1603) was an influential physician, who served as Queen Elizabeth's chief physician. During the last 20 years of his life, he studied what was already known of lodestone and amber. Gilbert made his own experiments to check the reports of other writers...
