Gustav Robert Kirchhoff (; 12 March 1824 – 17 October 1887) was a German

physicist A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

who contributed to the fundamental understanding of electrical circuits, spectroscopy, and the emission of

black-body A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The name "black body" is given because it absorbs all colors of light. A black body ...

radiation by heated objects. He coined the term black-body radiation in 1862. Several different sets of concepts are named "Kirchhoff's laws" after him, concerning such diverse subjects as black-body radiation and spectroscopy, electrical circuits, and thermochemistry. The Bunsen–Kirchhoff Award for spectroscopy is named after him and his colleague,

Robert Bunsen Robert Wilhelm Eberhard Bunsen (; 30 March 1811 – 16 August 1899) was a German chemist. He investigated emission spectra of heated elements, and discovered caesium (in 1860) and rubidium (in 1861) with the physicist Gustav Kirchhoff. The Bu ...

Life and work

Gustav Kirchhoff was born on 12 March 1824 in Königsberg,

Prussia Prussia, , Old Prussian: ''Prūsa'' or ''Prūsija'' was a German state on the southeast coast of the Baltic Sea. It formed the German Empire under Prussian rule when it united the German states in 1871. It was ''de facto'' dissolved by an ...

, the son of Friedrich Kirchhoff, a lawyer, and Johanna Henriette Wittke. His family were

Lutherans Lutheranism is one of the largest branches of Protestantism, identifying primarily with the theology of Martin Luther, the 16th-century German monk and reformer whose efforts to reform the theology and practice of the Catholic Church launched ...

in the Evangelical Church of Prussia. He graduated from the Albertus

University of Königsberg The University of Königsberg (german: Albertus-Universität Königsberg) was the university of Königsberg in East Prussia. It was founded in 1544 as the world's second Protestant academy (after the University of Marburg) by Duke Albert of Pruss ...

in 1847 where he attended the mathematico-physical seminar directed by

Carl Gustav Jacob Jacobi Carl Gustav Jacob Jacobi (; ; 10 December 1804 – 18 February 1851) was a German mathematician who made fundamental contributions to elliptic functions, dynamics, differential equations, determinants, and number theory. His name is occasiona ...

, Franz Ernst Neumann and Friedrich Julius Richelot. In the same year, he moved to

Berlin Berlin ( , ) is the capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's List of cities in the European Union by population within ci ...

, where he stayed until he received a professorship at Breslau. Later, in 1857, he married Clara Richelot, the daughter of his mathematics professor Richelot. The couple had five children. Clara died in 1869. He married Luise Brömmel in 1872. Bunsen-Kirchhoff

Kirchhoff formulated his circuit laws, which are now ubiquitous in electrical engineering, in 1845, while still a student. He completed this study as a seminar exercise; it later became his doctoral dissertation. He was called to the University of Heidelberg in 1854, where he collaborated in spectroscopic work with

. In 1857, he calculated that an electric signal in a resistanceless wire travels along the wire at the speed of light. He proposed his law of thermal radiation in 1859, and gave a proof in 1861. Together Kirchhoff and Bunsen invented the

spectroscope An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...

, which Kirchhoff used to pioneer the identification of the elements in the Sun, showing in 1859 that the Sun contains

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...

. He and Bunsen discovered caesium and rubidium in 1861. At Heidelberg he ran a mathematico-physical seminar, modelled on Franz Ernst Neumann's, with the mathematician Leo Koenigsberger. Among those who attended this seminar were

Arthur Schuster Sir Franz Arthur Friedrich Schuster (12 September 1851 – 14 October 1934) was a German-born British physicist known for his work in spectroscopy, electrochemistry, optics, X-radiography and the application of harmonic analysis to physics. ...

and

Sofia Kovalevskaya Sofya Vasilyevna Kovalevskaya (russian: link=no, Софья Васильевна Ковалевская), born Korvin-Krukovskaya ( – 10 February 1891), was a Russian mathematician who made noteworthy contributions to analysis, partial differen ...

. He contributed greatly to the field of spectroscopy by formalizing three laws that describe the spectral composition of light emitted by incandescent objects, building substantially on the discoveries of David Alter and

Anders Jonas Ångström Anders Jonas Ångström (; 13 August 181421 June 1874) was a Swedish physicist and one of the founders of the science of spectroscopy.P.Murdin (2000): "Angstrom" chapter in ''Encyclopedia of Astronomy and Astrophysics''. Ångström is also wel ...

. In 1862, he was awarded the Rumford Medal for his researches on the fixed lines of the solar spectrum, and on the inversion of the bright lines in the spectra of artificial light. In 1875 Kirchhoff accepted the first chair dedicated specifically to

theoretical physics Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experim ...

at Berlin. He also contributed to

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultrav ...

, carefully solving the

wave equation The (two-way) wave equation is a second-order linear partial differential equation for the description of waves or standing wave fields — as they occur in classical physics — such as mechanical waves (e.g. water waves, sound waves and seism ...

to provide a solid foundation for Huygens' principle (and correct it in the process).D. Miller, "Huygens’s wave propagation principle corrected", Opt. Lett. 16, 1370–1372 (1991) In 1864, he was elected as a member of the

American Philosophical Society The American Philosophical Society (APS), founded in 1743 in Philadelphia, is a scholarly organization that promotes knowledge in the sciences and humanities through research, professional meetings, publications, library resources, and communit ...

. In 1884, he became foreign member of the Royal Netherlands Academy of Arts and Sciences. Kirchhoff died in 1887, and was buried in the St Matthäus Kirchhof Cemetery in

Schöneberg Schöneberg () is a locality of Berlin, Germany. Until Berlin's 2001 administrative reform it was a separate borough including the locality of Friedenau. Together with the former borough of Tempelhof it is now part of the new borough of Tempe ...

, Berlin (just a few meters from the graves of the Brothers Grimm).

Leopold Kronecker Leopold Kronecker (; 7 December 1823 – 29 December 1891) was a German mathematician who worked on number theory, algebra and logic. He criticized Georg Cantor's work on set theory, and was quoted by as having said, "'" ("God made the integers, ...

is buried in the same cemetery.

Kirchhoff's circuit laws

Kirchhoff's first law is that the algebraic sum of currents in a network of conductors meeting at a point (or node) is zero. The second law is that in a closed circuit, the directed sums of the voltages in the system is zero.

Kirchhoff's three laws of spectroscopy

#A solid, liquid, or dense gas excited to emit light will radiate at all wavelengths and thus produce a continuous spectrum. #A low-density gas excited to emit light will do so at specific wavelengths, and this produces an emission spectrum. # If light composing a continuous spectrum passes through a cool, low-density gas, the result will be an absorption spectrum. Kirchhoff did not know about the existence of

energy level A quantum mechanical system or particle that is bound—that is, confined spatially—can only take on certain discrete values of energy, called energy levels. This contrasts with classical particles, which can have any amount of energy. The t ...

s in atoms. The existence of discrete spectral lines was known since Fraunhofer discovered them in 1814. And that the lines formed a discrete mathematical pattern was described by

Johann Balmer Johann Jakob Balmer (1 May 1825 – 12 March 1898) was a Swiss mathematician best known for his work in physics, the Balmer series of hydrogen atom. Biography Balmer was born in Lausen, Switzerland, the son of a chief justice also named Johan ...

in 1885. Joseph Larmor explained the splitting of the spectral lines in a magnetic field known as the Zeeman Effect by the oscillation of electrons. But these discrete spectral lines were not explained as electron transitions until the

Bohr model In atomic physics, the Bohr model or Rutherford–Bohr model, presented by Niels Bohr and Ernest Rutherford in 1913, is a system consisting of a small, dense nucleus surrounded by orbiting electrons—similar to the structure of the Solar Syst ...

of the atom in 1913, which helped lead to

quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistr ...

Kirchhoff's law of thermal radiation

It was

Kirchhoff's law of thermal radiation In heat transfer, Kirchhoff's law of thermal radiation refers to wavelength-specific radiative emission and absorption by a material body in thermodynamic equilibrium, including radiative exchange equilibrium. It is a special case of Onsage ...

in which he proposed an unknown universal law for radiation that led

Max Planck Max Karl Ernst Ludwig Planck (, ; 23 April 1858 – 4 October 1947) was a German theoretical physicist whose discovery of energy quanta won him the Nobel Prize in Physics in 1918. Planck made many substantial contributions to theoretical p ...

to the discovery of the quantum of action leading to

Kirchhoff's law of thermochemistry

Kirchhoff showed in 1858 that, in

thermochemistry Thermochemistry is the study of the heat energy which is associated with chemical reactions and/or phase changes such as melting and boiling. A reaction may release or absorb energy, and a phase change may do the same. Thermochemistry focuses on ...

, the variation of the heat of a chemical reaction is given by the difference in heat capacity between products and reactants: :

\left(\frac\right)_p = \Delta C_p

. Integration of this equation permits the evaluation of the heat of reaction at one temperature from measurements at another temperature.

Works

* * * ''Vorlesungen über mathematische Physik''. 4 vols., B. G. Teubner, Leipzig 1876–1894. ** Vol. 1: ''Mechanik''. 1. Auflage, B. G. Teubner, Leipzig 1876
online
. ** Vol. 2: ''Mathematische Optik''. B. G. Teubner, Leipzig 1891 (Herausgegeben von Kurt Hensel
online
. ** Vol. 3: ''Electricität und Magnetismus''. B. G. Teubner, Leipzig 1891 (Herausgegeben von Max Planck
online
. ** Vol. 4
''Theorie der Wärme''
B. G. Teubner, Leipzig 1894, Herausgegeben von Max Planck

Notes

References

* * *
HathiTrust full text
Partial English translation available in Magie, William Francis, ''A Source Book in Physics'' (1963). Cambridge:

Harvard UP Harvard University Press (HUP) is a publishing house established on January 13, 1913, as a division of Harvard University, and focused on academic publishing. It is a member of the Association of American University Presses. After the retirem ...

. p. 354-360.

External links

* *
Open Library
{{DEFAULTSORT:Kirchhoff, Gustav 1824 births 1887 deaths Optical physicists 19th-century German inventors Discoverers of chemical elements Scientists from Königsberg Spectroscopists Fluid dynamicists University of Königsberg alumni University of Breslau faculty Heidelberg University faculty Humboldt University of Berlin faculty Honorary Fellows of the Royal Society of Edinburgh Foreign Members of the Royal Society Foreign associates of the National Academy of Sciences Members of the Royal Netherlands Academy of Arts and Sciences Recipients of the Pour le Mérite (civil class) 19th-century German physicists Rare earth scientists Fellows of the Royal Society of Edinburgh Recipients of the Matteucci Medal Members of the Göttingen Academy of Sciences and Humanities