After working for seven years to discover a relation between current electricity and magnetism, he made a discovery which proved to be the first step in the invention of the dynamo. He was using a magnetic compass, which is a small magnetic needle balanced on a steel point. The needle points nearly north and south unless disturbed by a magnet brought near it. He had tried to find if a wire through which a current is flowing would disturb the compass as a magnet does. He had tried placing the wire east and west, thinking the compass-needle would follow the wire as it does a magnet. One day, while lecturing to his students, it occurred to him for the first time to place the wire north and south over the compass-needle. He was surprised and perplexed as he did so to see the needle swing round and point nearly east and west (Fig. 21). On reversing the current the needle swung in the opposite direction. He had discovered the magnetic action of an electric current. It was learned soon afterward that a coil of wire with an electric current flowing through it acts like a magnet, and that a current flowing around a bar of soft iron makes the iron a magnet (Figs. 22 and 23). [Illustration: FIG. 21--OERSTED'S EXPERIMENT An electric current flowing over the compass-needle toward the north causes the needle to turn until it points nearly west. By permission of Joseph G. Branch.] [Illustration: FIG. 22.--A COIL WITH A CURRENT FLOWING THROUGH IT ACTS LIKE A MAGNET The coil is picking up iron filings.] [Illustration: FIG. 23--A BAR OF SOFT IRON WITH A CURRENT FLOWING AROUND IT BECOMES A MAGNET] Ampère The news of Oersted's discovery aroused great interest throughout Europe. Soon after its announcement in France, André Marie Ampère made a discovery of equal importance. Oersted had discovered electromagnetism. Ampère discovered electrical power or motion produced by an electrical current. The youth of Ampère was passed amid the stormy scenes of the French Revolution. His father had moved from his country home to Lyons and become a justice of the peace. In the destruction of the city of Lyons during the Reign of Terror he lost his head under the guillotine. The blow was too great for Ampère, then a youth of eighteen. He had been a precocious child, advanced beyond his years in all the studies of the schools. But now his strong mind failed. For a year he wandered about mechanically piling up heaps of sand or gazing upon the sky. Then his mental power returned, and he took up with eagerness the study of botany and poetry.