The focus of Marat's work was the study of how light bends around objects, and his main argument was that while Newton held that white light was broken down into colours by refraction, the colours were actually caused by diffraction. When a beam of sunlight shone through an aperture, passed through a prism and projected colour onto a wall, the splitting of the light into colours took place not in the prism, as Newton maintained, but at the edges of the aperture itself. Marat sought to demonstrate that there are only three primary colours, rather than seven as Newton had argued.