Heinrich Kayser
Born	Heinrich Gustav Johannes Kayser (1853-03-16)16 March 1853 Bingen am Rhein,Grand Duchy of Hesse
Died	14 October 1940(1940-10-14) (aged 87) Bonn,Germany
Citizenship	German
Alma mater	Sophie Gymnasium (Berlin) University of Strasbourg University of Berlin
Known for	Helium in theEarth's atmosphere Kayser (unit)
Awards	ForMemRS (1911)[1]
Scientific career
Fields	Physicist,Spectroscopy
Institutions	Technische Hochschule,Hannover University of Bonn
Doctoral advisor	Wilhelm Röntgen

Heinrich Gustav Johannes KayserForMemRS^[1] (German:[ˈkaɪzɐ]; 16 March 1853 – 14 October 1940) was a Germanphysicist andspectroscopist.^[2]

Kayser was born atBingen am Rhein. Kayser's early work was concerned with the characteristics ofacoustic waves.^[3] He discovered the occurrence ofhelium in theEarth's atmosphere in 1868 during asolar eclipse when he detected a newspectral line in the solar spectrum. In 1881, Kayser coined the word "adsorption". Together withCarl Runge, he examined the spectra ofchemical elements.^[4][5][6] This included the determination of the wavelengths, brightness and sharpness of 4500 lines from the spectrum of iron, an element chosen to act as the standard, as well as 2000 lines for carbon, since iron was vaporised in a carbon arc. The work was later extended to other elements and they developed empirical formulas for the inverse of the wavelength of the type:${\displaystyle {\lambda }^{-1}=A+B{m}^{-2}+C{m}^{-4}}$, where${\displaystyle A,B,C}$ are constants and${\displaystyle m}$ is any positive integer. However, these formulas were superseded by the one byRydberg. After the conclusion of his collaboration with Runge, he seems to have mostly diverted his research from spectroscopy.^[7] In 1905, he wrote a paper onelectron theory.^[8]

Thekayser unit, associated withwavenumber, of theCGS system was named after him, with his early recognition of the importance of the inverse wavelength measurements in vacuum rather than in air cited as a reason.^[9] He died atBonn in 1940.

• Lehrbuch der Physik für Studierende . Enke, Stuttgart 3rd ed. 1900Digital edition by theUniversity and State Library Düsseldorf

• Media related toHeinrich Gustav Johannes Kayser at Wikimedia Commons

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