UNITED KINGDOM - NOVEMBER 20: 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' process 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. (Photo by SSPL/Getty Images)
