A Timeline of Events in Electromagnetism

Human fascination with electromagnetism, the interaction of electric currents and magnetic fields, dates back to the dawn of time with the human observation of lightning and other unexplainable occurrences, such as electric fish and eels. Humans knew there was a phenomenon, but it remained shrouded in mysticism until the 1600s when scientists began digging deeper into theory.

This timeline of events about the discovery and research leading to our modern understanding of electromagnetism demonstrates how scientists, inventors, and theorists worked together to advance the science collectively.

600 BCE: Sparking Amber in Ancient Greece

The earliest writings about electromagnetism were in 600 BCE, when the ancient Greek philosopher, mathematician and scientist Thales of Miletus described his experiments rubbing animal fur on various substances such as amber. Thales discovered that amber rubbed with fur attracts bits of dust and hairs that create static electricity, and if he rubbed the amber for long enough, he could even get an electric spark to jump.

221–206 BCE: Chinese Lodestone Compass

The magnetic compass is an ancient Chinese invention, likely first made in China during the Qin dynasty, from 221 to 206 BCE. The compass used a lodestone, a magnetic oxide, to indicate true north. The underlying concept may not have been understood, but the ability of the compass to point true north was clear.

1600: Gilbert and the Lodestone

Toward the late 16th century, the "founder of electrical science" English scientist William Gilbert published "De Magnete" in Latin translated as "On the Magnet" or "On the Lodestone." Gilbert was a contemporary of Galileo, who was impressed by Gilbert's work. Gilbert undertook a number of careful electrical experiments, in the course of which he discovered that many substances were capable of manifesting electrical properties.

Gilbert also discovered that a heated body lost its electricity and that moisture prevented the electrification of all bodies. He also noticed that electrified substances attracted all other substances indiscriminately, whereas a magnet only attracted iron.

1752: Franklin's Kite Experiments

American founding father Benjamin Franklin is famous for the extremely dangerous experiment he ran, of having his son fly a kite through a storm-threatened sky. A key attached to the kite string sparked and charged a Leyden jar, thus establishing the link between lightning and electricity. Following these experiments, he invented the lightning rod.

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Franklin discovered there are two kinds of charges, positive and negative: objects with like charges repel one another, and those with unlike charges attract one another. Franklin also documented the conservation of charge, the theory that an isolated system has a constant total charge.

1785: Coulomb's Law

In 1785, French physicist Charles-Augustin de Coulomb developed Coulomb's law, the definition of the electrostatic force of attraction and repulsion. He found that the force exerted between two small electrified bodies is directly proportional to the product of the magnitude of charges and varies inversely to the square of the distance between those charges. Coulomb's discovery of the law of inverse squares virtually annexed a large part of the domain of electricity. He also produced important work on the study of friction.

1789: Galvanic Electricity

In 1780, Italian professor Luigi Galvani (1737–1790) discovered that electricity from two different metals causes frog legs to twitch. He observed that a frog's muscle, suspended on an iron balustrade by a copper hook passing through its dorsal column, underwent lively convulsions without any extraneous cause.

To account for this phenomenon, Galvani assumed that electricity of opposite kinds existed in the nerves and muscles of the frog. Galvani published the results of his discoveries in 1789, together with his hypothesis, which engrossed the attention of the physicists of that time.

1790: Voltaic Electricity

Italian physicist, chemist and inventor Alessandro Volta (1745–1827) read of Galvani's research and in his own work discovered that chemicals acting on two dissimilar metals generate electricity without the benefit of a frog. He invented the first electric battery, the voltaic pile battery in 1799. With the pile battery, Volta proved that electricity could be generated chemically and debunked the prevalent theory that electricity was generated solely by living beings. Volta's invention sparked a great deal of scientific excitement, leading others to conduct similar experiments which eventually led to the development of the field of electrochemistry.

1820: Magnetic Fields

In 1820, Danish physicist and chemist Hans Christian Oersted (1777–1851) discovered what would become known as Oersted's Law: that an electric current affects a compass needle and creates magnetic fields. He was the first scientist to find the connection between electricity and magnetism.

1821: Ampere's Electrodynamics

French physicist Andre Marie Ampere (1775–1836) found that wires carrying current produce forces on each other, announcing his theory of electrodynamics in 1821.

Ampere's theory of electrodynamics states that two parallel portions of a circuit attract one another if the currents in them are flowing in the same direction, and repel one another if the currents flow in the opposite direction. Two portions of circuits crossing one another obliquely attract one another if both the currents flow either towards or from the point of crossing and repel one another if one flows to and the other from that point. When an element of a circuit exerts a force on another element of a circuit, that force always tends to urge the second one in a direction at right angles to its own direction.

1831: Faraday and Electromagnetic Induction

English scientist Michael Faraday (1791–1867) at the Royal Society in London developed the idea of an electric field and studied the effect of currents on magnets. His research found that the magnetic field created around a conductor carried a direct current, thereby establishing the basis for the concept of the electromagnetic field in physics. Faraday also established that magnetism could affect rays of light and that there was an underlying relationship between the two phenomena. He similarly discovered the principles of electromagnetic induction and diamagnetism and the laws of electrolysis.

1873: Maxwell and the Basis of Electromagnetic Theory

James Clerk Maxwell (1831–1879), a Scottish physicist and mathematician, recognized that electromagnetism's processes could be established using mathematics. Maxwell published "Treatise on Electricity and Magnetism" in 1873 in which he summarizes and synthesizes the discoveries of Coloumb, Oersted, Ampere, Faraday into four mathematical equations. Maxwell's equations are used today as the basis of electromagnetic theory. Maxwell predicts the connections of magnetism and electricity leading directly to the prediction of electromagnetic waves.

1885: Hertz and Electric Waves

German physicist Heinrich Hertz proved Maxwell's electromagnetic wave theory was correct, and in the process, generated and detected electromagnetic waves. Hertz published his work in a book, "Electric Waves: Being Researches on the Propagation of Electric Action With Finite Velocity Through Space." The discovery of electromagnetic waves led to the development to the radio. The unit of frequency of the waves measured in cycles per second was named the "hertz" in his honor.

1895: Marconi and the Radio

In 1895, Italian inventor and electrical engineer Guglielmo Marconi put the discovery of electromagnetic waves to practical use by sending messages over long distances using radio signals, also known as the "wireless." He was known for his pioneering work on long-distance radio transmission and his development of Marconi's law and a radio telegraph system. He is often credited as the inventor of the radio, and he shared the 1909 Nobel Prize in Physics with Karl Ferdinand Braun "in recognition of their contributions to the development of wireless telegraphy."

Sources

• "André Marie Ampère." St. Andrews University. 1998. Web. June 10, 2018.
• "Benjamin Franklin and the Kite Experiment." The Franklin Institute. Web. June 10, 2018.
• "Coulomb's Law." The Physics Classroom. Web. June 10, 2018.
• "De Magnete." The William Gilbert Website. Web. June 10, 2018.
• "July 1820: Oersted and electromagnetism." This Month in Physics History, APS News. 2008. Web. June 10, 2018.
• O'Grady, Patricia. "Thales of Miletus (c. 620 B.C.E.—c. 546 B.C.E.)." Internet Encyclopedia of Philosophy. Web. June 10, 2018
• Silverman, Susan. "Compass, China, 200 BCE." Smith College. Web. June 10, 2018.