1840 - 1849

The legendary Faraday forges on with his prolific research and the telegraph reaches a milestone when a message is sent between Washington, DC, and Baltimore, MD.


Joule's law

James JouleEnglish physicist James Prescott Joule publishes a paper, On the Production of Heat by Voltaic Electricity, in which he describes the amount of heat generated by an electric current (Joule’s law).

Incandescent lamp

Inventor Frederick de Moleyns of England is granted the first patent for an incandescent lamp.

Wheatstone bridge

Wheatstone bridgeEnglish physicist Charles Wheatstone popularizes an instrument for comparing resistances that came to be known as the Wheatstone bridge, although it was invented by Samuel Christie

First telegraph line

Morse telegraphThe first official electric telegraph line, constructed with funds appropriated by Congress, is completed in the United States and the initial message is sent by its inventor, Samuel Morse.

Kirchhoff's circuit laws

German physicist Gustav Kirchhoff introduces his laws of electric circuits, which have since been named in his honor.

Faraday effect

Michael FaradayBritish chemist Michael Faraday observes that the plane of polarization of light traveling through glass is affected by magnetic lines of force, a clear indication that magnetism and light are related. The phenomenon produced experimentally by Faraday is referred to as the Faraday effect or Faraday rotation.


Michael Faraday discovers a previously unrecognized form of magnetism in bismuth, glass and a number of other materials that he dubs diamagnetism.

Induction of electric currents

Physicist and mathematician Franz Neumann of Germany publishes his deductions of the mathematical laws for induction of electric currents.

Magnetism and light

Michael Faraday suggests in a short essay that light could be an electromagnetic phenomenon.

Seeking unified theory

Wilhelm WeberGerman physicist Wilhelm Weber attempts to unify the analysis and experimental results of André-Marie Ampère, Michael Faraday and others in his development of an electromagnetic theory that involves forces between charged particles in motion. Though his theory is later discounted, Weber’s work would precede many other advances in the field of electromagnetic theory.

Ideas on diamagnetism

Wilhelm Weber puts forward the idea that diamagnetism is simply an example of Faraday’s law impinging upon molecular circuits and suggests that diamagnetism exists in paramagnetic and ferromagnetic substances, but is masked due to the comparative strength of the permanent molecular currents the possess.

Conservation of energy

Hermann von Helmholtz, a German physicist and physician, reads his paper On the Conservation of Force to the Physical Society of Berlin, providing one of the earliest and clearest accounts of the principle of the conservation of energy that governs electrostatic, magnetic, chemical and all other forms of energy.
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