1900-1909

Albert Einstein publishes his special theory of relativity and his theory on the quantum nature of light, which he identified as both a particle and a wave. With ever new appliances, electricity begins to transform everyday life.

1900

The Curies and beta rays

French husband-and-wife physicists Pierre and Marie Curie produce evidence that beta rays are a form of radiation identical to cathode rays.
1900

Planck constant

German physicist Max Planck introduces his radiation law, the fundamental physical constant that bears his name, and his concept of energy quanta. German physicist Max Planck introduces his radiation law, the fundamental physical constant that bears his name, and his concept of energy quanta.
1901

Nickel-alkaline battery

After thousands of experiments, American inventor Thomas Edison successfully develops the nickel-alkaline storage battery.
1902

Ionosphere

Following reports of Guglielmo Marconi’s transmission of radio signals across the Atlantic Ocean (1901), Oliver Heaviside of Britain conjectures that an electrically conductive layer located in the upper atmosphere of the earth enables such waves to propagate over expansive distances despite the curvature of the planet. In the United States, electrical engineer Arthur Kennelly independently arrives at the same conclusion and the hypothetical atmospheric stratum comes to be referred to as the Kennelly-Heaviside layer or the ionosphere.
1903

Finding an atom's mass

German physicist Philipp Lenard suggests that the majority of an atom’s mass is confined to only a small portion of the atom's volume based on the results of electron scattering experiments he carried out with a Crookes tube and thin metal foils.
1903

Einthoven galvanometer

Willem Einthoven, a Dutch physiologist, invents a device known as the Einthoven galvanometer that allows him to produce the first electrocardiogram, a graphical record of the electrical activity of the heart.
1903

Magnetic storms

Kristian Birkeland of Norway introduces the concept of polar magnetic storms, a form of intense, localized magnetic disturbance associated with auroras.
1903

Gas turbine

First successful gas turbine is built in France.
1904

The Lorentz transformations

Hendrik Lorentz develops a set of equations known as the Lorentz transformations in his attempt to explain the results of the Michelson-Morley experiment searching for evidence of the ether thought to pervade the atmosphere. The Dutch physicist's equations would serve as the foundation upon which Albert Einstein would build his special theory of relativity.
1904

Naming body founded

The International Electrotechnical Commission is founded and assumes responsibility for the standardization of nomenclature relating to electricity and magnetism.
1904

Fleming oscillation valve

English physicist and engineer John Ambrose Fleming harnesses the Edison effect to develop the Fleming oscillation valve, a thermionic tube with two electrodes (diode) that functioned as a signal detector and rectifier.
1905

Special theory of relativity

German physicist Albert Einstein formulates his special theory of relativity and indicates that electricity and magnetism are two aspects of a single phenomenon.
1905

Paramagnetism and temperature

French physicist Paul Langevin utilizes statistics to explain the correlation between paramagnetism and temperature.
1906

The audion

Lee De Forest, an American engineer, invents the Audion, a three-electrode thermionic tube (triode) that could detect wireless signals much better than could Fleming’s valve and which would come to play an important role in early electronic devices.
1907

Mean field theory

French physicist Pierre-Ernest Weiss develops a mean field theory to explain the behavior of iron and other ferromagnetic materials.
1908

Geiger counter

German physicist Hans Geiger develops an early version of the Geiger counter, a chamber specialized for counting particles of radiation. Significant improvements to the device would be made by Geiger and his student Walther Mueller in 1928.
1908

Sunspots and magnetic fields

George Hale, an American astronomer, publishes a report arguing that sunspots possess magnetic fields.
1909

South magnetic pole

Australian explorers Douglas Mawson and Edgeworth David complete the first successful journey to the south magnetic pole.
1909

Millikan's oil-drop experiment

American physicist Robert Millikan performs his famous oil-drop experiment and establishes the charge of an electron with greater accuracy than ever before.
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