1840
Joule's law

1841
Incandescent lamp
Inventor Frederick de Moleyns of England is granted the first patent for an incandescent lamp.
1843
Wheatstone bridge

1844
First telegraph line

1845
Kirchhoff's circuit laws
German physicist Gustav Kirchhoff introduces his laws of electric circuits, which have since been named in his honor.
1845
Faraday effect

1845
Diamagnetism
Michael Faraday discovers a previously unrecognized form of magnetism in bismuth, glass and a number of other materials that he dubs diamagnetism.
1845
Induction of electric currents
Physicist and mathematician Franz Neumann of Germany publishes his deductions of the mathematical laws for induction of electric currents.
1846
Magnetism and light
Michael Faraday suggests in a short essay that light could be an electromagnetic phenomenon.
1846
Seeking unified theory

1847
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.
1847
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.