DAVID PARKER / SCIENCE PHOTO LIBRARY DAVID PARKER / SCIENCE PHOTO LIBRARY
Glass prism and spectrum. A beam of white light strikes the prism and is dispersed onto the opposite face. At this face, some of the light is refracted again, exiting the prism and forming the spectrum. The spectrum is a result of the different amounts of refraction of the different wavelengths of light present. In Isaac Newton's time, it was believed that white light was colourless, and that the prism itself produced the colour. Newton's experiments convinced him that all the colours already existed in the light in a heterogeneous fashion, and that "corpuscles" (particles) of light were fanned out because particles with different colours travelled with different speeds through the prism. Ultimately, Young and Fresnel combined Newton's particle theory with Huygens' wave theory to explain how colour arises from the spectrum of light.
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