Although the ancient Greeks and probably earlier peoples knew about magnetism and static electricity, not much was accomplished with these interesting phenomena until the Chinese began to use the magnetic compass for navigation around 1000 ce. Some of the basic laws of magnets were written down in 1269 and William Gilbert studied both static electricity and magnetism at the end of the 16th century. Then the subject was ignored by most scientists for a long time.
In the 18th century, Stephen Grey and Charles François Du Fay revived the study of static electricity, but it was not until Pieter van Musschenbroek received the first powerful electric shock (apart from those caused by lightning) in 1745 that the subject gained attention. Van Musschenbroek was one of the inventors of the Leiden jar, a device for storing static electricity. A Leiden jar releases all of its electricity at once, causing a shock if it passes through a grounded person. Van Musschenbroek reported, "In a word, I thought it was all up with me" after his shocking experience. The discovery that electricity could cause powerful shocks prompted Benjamin Franklin's famous kite experiment, in which he showed that lightning is electricity. It could have been "all up with" Franklin during that experiment too. Other scientists who repeated the experiment were killed.
Charles Augustin Coulomb made careful studies of the forces exerted by both static electricity and magnetism in the 1780s. As early as 1733, Du Fay had discovered that there are two types of charge and that like charges repel while unlike charges attract. Coulomb showed that both magnets and electric charges obey the same rule, an inverse-square law. This implied a connection between electricity and magnetism. In 1807 Hans Christian Oersted announced that he would search for that connection.
Somewhat before this, there had been a major development in electricity that would facilitate Oersted's search. In 1771, while studying the reactions of muscle to electricity, Luigi Galvani accidentally discovered that the muscles of dead organisms twitch when placed in contact with brass and iron at the same time (published in 1791). Although Galvani thought the muscles were the sources of an electric charge, when Alessandro Volta learned of this phenomenon, Volta found that a simple chemical solution could be substituted for the muscles. With this knowledge, he cleverly constructed the first electric battery at the end of the 18th century. The battery was the first source of current electricity, electricity that moves steadily through a conductor as opposed to being quickly released from a Leiden jar.
The history of science is replete with stories of someone finding something by luck or accident. What is often overlooked in these tales is that the scientist in question had already been looking for something like the phenomenon he or she "accidentally" discovered. If Galvani had not been studying electric actions on muscle, he would not have been prepared to notice the reaction of the muscle with the metals. Similarly, Oersted discovered the connection he sought by accident while he was performing a classroom demonstration. He placed a compass over a wire carrying a current. As he did, the needle suddenly moved to become perpendicular to the current. Electricity and magnetism really are connected.
As soon as Oersted's discovery became known in 1820, there was a burst of creative activity. In 1820 alone, André-Marie Ampère and Dominique François Arago discovered that wires carrying currents attract or repel each other and that an electric current in a wire will attract iron, just as a magnet does. In 1821 the thermoelectric effect was discovered by Thomas Seebeck. Two years later, William Sturgeon built the first electromagnet.
A notable series of investigations of the relationship between electricity and magnetism was conducted almost in parallel in England by Michael Faraday and in America by Joseph Henry. Both Faraday and Henry discovered the principle of the dynamo in 1830-31, for example. Although they independently discovered many of the same connections and devices, Faraday's work was to have the greater theoretical impact while Henry's had more immediate practical application.
Faraday had observed how iron filings form patterns of lines under the influence of a magnet. He concluded that space is filled with these invisible lines, forming what we now call a field. He used his idea to explain in 1845 why some substances are diamagnetic (developing a magnetic field opposite to the one surrounding them) and others paramagnetic (developing a magnetic field parallel to the one surrounding them). When Faraday discovered that a magnetic field can affect the polarization of light, he proposed in 1845 that light may be waves in the lines of force of electromagnetism.
There were other clues to a relationship between light and electromagnetism. In 1857, for example, Gustav Robert Kirchhoff calculated the relationship between the forces of static electricity and magnetism, finding that the speed of light in a vacuum is a constant in his formula. In 1864 James Clerk Maxwell followed up Faraday's ideas with mathematical formulas that described light as waves of electromagnetism and that implied other forms of electromagnetic waves. Maxwell's work was experimentally verified in 1888 when Heinrich Hertz, following a suggestion from George Francis Fitzgerald, discovered radio waves by directly applying Maxwell's formulas.
In America, Henry developed the first practical electric motor and powerful electromagnets in 1831. In the 1830s he also developed the electrical relay that made the first practical telegraph possible. Samuel Finley Breese Morse, usually given credit for the telegraph, worked directly with Henry and incorporated his ideas into the new device.
In 1879 Edison and Joseph Swan independently invented practical lights that use electricity. With this invention, electricity moved into the home, where the many discoveries of the 19th century soon found application.
