**Kirchhoff** was a mathematical physicist best known for his laws on the flow of electric current.

- University professors were civil servants in Prussia at this time and so to be a university professor, Gustav's parents believed, represented the right position where someone of high academic abilities could serve Prussia.
- Given Gustav's academic abilities at school, his future career followed naturally.
- Kirchhoff was educated in Königsberg where he entered the Albertus University of Königsberg which had been founded in 1544 by Albert, the first duke of Prussia.
- Kirchhoff attended the Neumann-Jacobi seminar from 1843 to 1846.
- Now 1843 was the year in which Jacobi became unwell, so it was Neumann who influenced Kirchhoff in a very positive way.
- Neumann's interests were at this time firmly in mathematical physics and, at the time Kirchhoff began to study at Königsberg, Neumann had become interested in electrical induction.
- Neumann published the first of his two major papers on electrical induction in 1845 while Kirchhoff was studying with him.
- Kirchhoff was taught mathematics at the University of Königsberg by Friedrich Jules Richelot.
- It was while he was studying with Neumann that Kirchhoff made his first outstanding research contribution which related to electrical currents.
- Kirchhoff's laws, which he announced in 1845, allowed calculation of currents, voltages and resistances in electrical circuits with multiple loops, extending the work of Ohm.
- Kirchhoff considered an electrical network consisting of circuits joined at nodes of the network and gave laws which reduce the calculation of the currents in each loop to the solution of algebraic equations.
- Kirchhoff's laws followed from applying Ohm's law but the way in which he was able to generalise the results showed great mathematical skills.
- At this stage Kirchhoff was unaware that Ohm's analogy between the flow of heat and the flow of electricity, which formed the accepted understanding of electrical currents at that time, led to an incorrect understanding of electrical currents.
- Kirchhoff's work would, a couple of years later, lead to him to realise this error and to give a correct understanding of how the theory of electric currents and electrostatics should be combined.
- The year 1847 was an eventful one for Kirchhoff.
- Republican and socialist feelings meant that the monarchy was in trouble, but Kirchhoff was in a privileged position and was unaffected by events around him as he pressed forward with his career.
- In the year that he arrived in Breslau, Kirchhoff solved a problem concerning the deformation of elastic plates.
- Problems remained, however, which Kirchhoff solved using variational calculus.
- While Kirchhoff was in Breslau he met Bunsen who spent the academic year 1851-52 there; the two becoming firm and lasting friends.
- In 1854 Bunsen, who was working at Heidelberg, encouraged and supported Kirchhoff to move there.
- Kirchhoff accepted the offer of an appointment as professor of physics and he began a fruitful collaboration with Bunsen.
- Kirchhoff was not the only one working at the time on electric currents.
- Wilhelm Weber and Rudolf Kohlrausch were also working on the nature of such currents and published similar results to that of Kirchhoff around 1857 on the velocity of a current in a highly conductive wire.
- Kirchhoff and Weber both discovered that the velocity was independent of the nature of the wire and was almost exactly equal to the velocity of light.
- Fundamental work by Kirchhoff on black body radiation (a term he introduced in 1862) was important in the development of quantum theory.
- Kirchhoff was able to make his fundamental breakthrough by producing purer forms of substances than had been previously the case.
- Kirchhoff and Bunsen went on to examine the spectrum of the sun in 1861 and were able to identify the chemical elements in the sun's atmosphere.
- Kirchhoff is perhaps best known for being the first to explain the dark lines in the sun's spectrum as caused by absorption of particular wavelengths as the light passes through gases in the sun's atmosphere.
- Kirchhoff had been made offers by other universities but he was happy in Heidelberg and turned down such offers.
- Among the leading physicists of the nineteenth century, it was Kirchhoff whose temperament was best suited to this task.

Born 12 March 1824, Königsberg, Prussia (now Kaliningrad, Russia). Died 17 October 1887, Berlin, Germany.

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Astronomy, Origin Russia, Physics

**O’Connor, John J; Robertson, Edmund F**: MacTutor History of Mathematics Archive