In 1801 Thomas Young demonstrated that light produces interference patterns when passing through two slits — the same phenomenon as waves in water. The experiment was a direct refutation of Newton's corpuscular theory and revived the wave theory Huygens had proposed a century earlier without managing to prevail. Young also proposed that the human eye detects color via three types of receptors sensitive to red, green, and violet — the basis of the trichromatic theory Helmholtz would develop decades later. The double-slit experiment would become, in the 20th century, the central conceptual milestone of quantum mechanics.