In the 1860s James Clerk Maxwell (1831-1879) showed that all colours are a mixture of red, green and blue light. This three-colour projection apparatus (Ives' proces adapted) is based on the same principle. It was used by Sir William Abney (1843-1920), the English chemist and educationalist. Abney was known for his researches in photographic chemistry and colour photography, and did important pioneering work in photographing the solar spectrum.
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