In 1802, William Hyde Wollaston built a spectrometer, improving on Newton's model, that included a lens to focus the Sun's 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 sun's 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 Fraunhofer's work.