The fact that the current passing through a wire conductor produces a magnetic field around the wire, and that two current-carrying wires could attract or repel each other depending on the direction of the current, was emphasized in 1820 by the independent writings of Hans Oersted and Andre-Marie Ampere (after whom the Sl unit of measurement of electric current, the ampere, is named). It was, however, William Sturgeon (1783-1850), a physicist working at the Royal Academy, Woolwich, London, who recognized the significance of the phenomenon. He converted electromagnetic devices from toys into practical weightlifting machines.
A horseshoe of iron around which is wound a loose current-carrying coil becomes a strong metal-lifting device when the current is switched on and, just as important, the force disappears when the current is switched off. The action of the device can be speedily controlled by electricity. Electricity can flow down miles of wire, so throwing a switch in one place can activate a distant magnet to ring a bell or move a lever. Joseph Henry (1797-1878), while a professor of mathematics and physics at the Albany Academy in the United States, improved Sturgeon's electromagnet by insulating the wire and increasing the number of turns. His electromagnet lifted 2,300 pounds (1,040 kg), a world record at the time. When Henry moved to Princeton, in 1832, he used an electromagnet as an electrical relay device to link his lab to his home. This was the first practical telegraph system. Henry, S. F. B. Morse, and Charles Wheatstone all insisted that they should be credited as the telegraph pioneer.
