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1859
- 1859: The German physicist Gustav Robert Kirchoff (1824–1887) and chemist Robert Wilhelm Eberhard von Bunsen (1811–1899) (Figure 3) discover that spectral lines are unique to each element.
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Who discovered dark lines in the solar spectrum?
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In 1895, the German physicist Wilhelm Conrad Röntgen discovered and extensively studied X-rays, which were later used in X-ray spectroscopy. One year later, in 1896, French physicist Antoine Henri Becquerel discovered radioactivity, and Dutch physicist Pieter Zeeman observed spectral lines being split by a magnetic field.
Niels Bohr explained the line spectrum of the hydrogen atom by assuming that the electron moved in circular orbits and that orbits with only certain radii were allowed. Lines in the spectrum were due to transitions in which an electron moved from a higher-energy orbit with a larger radius to a lower-energy orbit with smaller radius.
Spectral lines are highly atom-specific, and can be used to identify the chemical composition of any medium. Several elements, including helium, thallium, and caesium, were discovered by spectroscopic means.
In 1849, Jean Foucault, investigating the spectrum of an arc between two carbon electrodes, noticed a line similar to the D line of the solar spectrum. He attempted to superimpose the two spectra by passing the sun's rays through the arc and then through the prism.
In 1802 William Wollaston discovered dark lines in the solar spectrum, but attached little significance to them. In 1814 Joseph Fraunhofer, a superb instrument maker, made a detailed examination of the solar spectrum; he made a map of 700 of the lines we now refer to as "Fraunhofer lines".
In 1926, an Austrian physicist, Erwin Schrödinger (1887–1961; Nobel Prize in Physics, 1933), developed wave mechanics, a mathematical technique that describes the relationship between the motion of a particle that exhibits wavelike properties (such as an electron) and its allowed energies.
The achievements of Joseph Fraunhofer provided the quantitative basis for spectroscopy. Fraunhofer, born near Munich in 1787, extended Newton's discovery by observing that the sun's spectrum, when sufficiently dispersed, was crossed by a large number of fine dark lines (1814), now known as Fraunhofer lines.
