text: In 1802, William Hyde Wollaston built a spectrometer, improving on Newtons model, that included a lens to focus the Suns spectrum on a screen. Upon use, Wollaston realized that the colors were not spread uniformly, but instead had missing patches of colors, which appeared as dark bands in the suns spectrum.  At the time, Wollaston believed these lines to be natural boundaries between the colors, but this hypothesis was later ruled out in 1815 by Fraunhofers work.
  Joseph von Fraunhofer made a significant experimental leap forward by replacing a prism with a diffraction grating as the source of wavelength dispersion. Fraunhofer built off the theories of light interference developed by Thomas Young, François Arago and Augustin-Jean Fresnel. He conducted his own experiments to demonstrate the effect of passing light through a single rectangular slit, two slits, and so forth, eventually developing a means of closely spacing thousands of slits to form a diffraction grating. The interference achieved by a diffraction grating both improves the spectral resolution over a prism and allows for the dispersed wavelengths to be quantified. Fraunhofer's establishment of a quantified wavelength scale paved the way for matching spectra observed in multiple laboratories, from multiple sources (flames and the sun) and with different instruments. Fraunhofer made and published systematic observations of the solar spectrum, and the dark bands he observed and specified the wavelengths of are still known as Fraunhofer lines.
  Throughout the early 1800s, a number of scientists pushed the techniques and understanding of spectroscopy forward. In the 1820s, both John Herschel and William H. F. Talbot made systematic observations of salts using flame spectroscopy.