While perhaps the most extensive such timeline to date, it is surely not complete. Sources for further information have been provided.
1678: Dutch mathematician and physicist Christian Huygens (1629–1695) proposes the wave theory of light.1729: French mathematician and scientist Pierre Bougeur (1698–1758) notes that the amount of light passing through a liquid sample decreases with increasing sample thickness.
1752: Thomas Melville (1726–1753) of the University of Glasgow, Scotland, observes a bright yellow light emitted from a flame produced by burning a mixture of alcohol and sea salt. When the salt is removed, the yellow color disappears.
1760: German mathematician and scientist Johann Heinrich Lambert (1728–1777) publishes his "Law of Absorption."
1786: American astronomer and instrument maker David Rittenhouse (1732–1796) produces the first primitive diffraction grating with parallel hairs laid across two screws.
1802: English scientist William Hyde Wollaston (1766–1828) is the first to observe dark lines in the spectrum of the sun.
1814: The German optician Joseph von Frauenhofer (1787–1826) invents the transmission diffraction grating and makes a detailed study of the dark lines in the solar spectrum.
1826: Scotsman William Henry Fox Talbot (1800–1877) observes that different salts produce colors when placed in a flame.
1851: M.A. Masson produces the first spark-emission spectroscope.
1852: German scientist August Beer (1825–1863) publishes a paper showing that the amount of light absorbed was proportional to the amount of solute in aqueous solutions.
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.