Center For Integrating Research and Learning

Arrow1820 - 1829


Unknowingly following in the footsteps of Italian philosopher Gian Domenico Romagnosi, Hans Christian Ørsted became the second scientist to discover the interrelationship of magnetism and electricity. In April 1820, the Danish physicist and chemist was reportedly giving a lecture on electricity when he noticed that the needle of a nearby compass aligned itself perpendicularly to a current-carrying wire. His subsequent research didn’t get to the bottom of what he had seen, but he soon published his discovery to a world that, this time, grasped its significance. In fact, Ørsted’s news sent a shock wave through the scientific community, launching the field of electromagnetism and paving the way for the historic breakthroughs of Michael Faraday and James Clerk Maxwell later in the century.

Ørsted Compass

Immediately following Ørsted’s report, scientists set to work to explore its implications. Members of the French Academy of Science – including André-Marie Ampère, François Arago, Siméon-Denis Poisson and Jean-Baptiste Biot – were particularly productive. Ampère swiftly produced a theory demonstrating that parallel wires carrying current in the same direction attract, while those same wires repel if their currents flow in opposite directions. Ampère’s insight gave rise to the field of electrodynamics; it is after him, of course, that the amp is named.

Arago observed that unmagnetized iron filings create a circle around a wire if it carries current, but not when the current is stopped. Biot, in collaboration with Félix Savart, formulated a law named after them which could calculate the magnetic field generated by a current-carrying wire. All these accomplishments occurred within just months of Ørsted’s discovery.

Schweigger Multiplier

The following year, a man who was to become a legend in the field made his first mark. British chemist Michael Faraday , a protégé of Humphry Davy, discovered that electricity could produce rotary motion, leading him to build the first primitive electric motor. Faraday left it to others to develop more sophisticated machines, but in the decades ahead would make unparalleled contributions to the burgeoning field of electromagnetism.

In the mid 1820s, English engineer William Sturgeon developed the first practical electromagnet, able to support 20 times its own weight. Electromagnets of increasing sophistication and strength have played a formidable role in both research and practical applications ever since.

About the same time Sturgeon was developing his magnet, German physicist Georg Simon Ohm noticed that an electrical current produced heat. The heat, he recognized, signified resistance to the flow of the current. From this he deduced that current varies in direct ratio to a wire’s resistance. Ohm formulated a law showing this relationship between volts, amps and resistance that is the basis of electricity. Both the law and the unit of electrical resistance he described were named after him.

1820 - 1829


Danish physicist and chemist Hans Christian Ørsted notices during one of his lectures that the magnetic needle of a compass aligns itself perpendicularly to a current-carrying wire. Unlike Gian Domenico Romagnosi’s discovery of the same link between electricity and magnetism almost two decades earlier, Ørsted's announcement of the event would send shockwaves through the scientific community and lead to a flurry of new experimentation.


Mathematician André-Marie Ampère, only a week after Ørsted’s discovery was published, begins to develop a theory to explain the phenomenon and demonstrates that parallel wires with currents flowing through them attract each other when the currents flow in the same direction, but repel each other if they flow in opposite directions.


Building on the work of Ørsted, French physicist François Arago finds that unmagnetized iron filings orient themselves in a circle around a copper wire through which an electric current flows as if it were a magnet, but disperse when the current is stopped.


German mathematician and physicist Johann Schweigger builds what he terms a multiplier that could greatly amplify the magnetism of an electrical circuit. Schweigger’s multiplier became the first accurate device capable of detecting and measuring very small amounts of electricity, eventually coming to be known as the galvanometer.


French physicists Jean-Baptiste Biot and Félix Savart formulate what is now known as the Biot-Savart law, which can be used to calculate the magnetic field at a given distance from the electric current that is the source of the field.


Michael Faraday, a former bookbinder who was apprenticed in science under Humphry Davy, plots the magnetic field around a conductor and repeats Ørsted’s experiments in his laboratory at the Royal Institution. He discovers that electricity can produce rotary motion, leading him to build one of the first primitive electric motors.


German physicist Thomas Johann Seebeck discovers that a current flows through a circuit of dissimilar conducting materials if there is a difference in temperature between the materials. This thermoelectric effect is now known as the Seebeck effect.


Peter Barlow, an English mathematician and engineer, demonstrates an early version of the electric motor that is commonly referred to as Barlow’s wheel.


André-Marie Ampère, a French scientist, formulates his fundamental law for the relationship between a magnetic field and the current that is its source, similar to the Biot-Savart law but presented in a more sophisticated form utilizing the language of calculus.


French scientist Siméon-Denis Poisson introduces the concept of the magnetic scalar potential.


French scientist and politician François Arago discovers magnetic rotation, that a magnetic needle suspended over a copper disk would rotate when the disc was spun.


English engineer William Sturgeon develops and exhibits the first practical electromagnet, which is strong enough to support 20 times its own weight.


In his first paper on magnetism, Joseph Henry, an American mathematics professor, describes several improvements he made to electromagnets and other devices utilized in electromagnetic demonstrations to produce more pronounced effects.


German physicist Georg Simon Ohm publishes Die galvanische Kette, mathematisch bearbeitet (The Galvanic Circuit Investigated Mathematically). The treatise contains an account of his electromagnetic theories and includes all of the components of Ohm’s law.


British mathematician and physicist George Green extends the electric and magnetic calculations of Siméon-Denis Poisson, introduces the term potential, and explicates what is now known as Green’s theorem in his Essay on the Application of Mathematical Analysis to the Theory of Electricity and Magnetism.


American entomologist Harrison Gray Dyar constructs a telegraph in which an electric signal is recorded through chemical means as a stain on moistened litmus paper caused by the decomposition of nitric acid.

Next Section Arrow1830-1839

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