A method of painting in which colour effects are obtained by applying small areas or dots of pure, unmixed colours on the canvas in such a way that to a spectator standing at an appropriate distance they appear to react together, producing greater luminosity and brilliance than would have resulted if the same colours had been physically mixed together. The method was employed empirically by the Impressionists, but it was not developed systematically and scientifically until Seurat and the Neo-Impressionists. Seurat (in common with other contemporaries) spoke of an ‘optical mixture’, but (contrary to what is usually stated) the dots do not really fuse in the viewer's eye to make different colours, for they remain visible as dots. Rather, they seem to vibrate, creating something of the shimmering effect experienced in strong sunlight. The effect is noted in Ogden Rood's Modern Chromatics (1879), a treatise on colour theory well known to Seurat. Camille Pissarro, who was closely associated with Seurat at this time, said that the optimum viewing distance for a picture painted by the divisionist method was three times the diagonal measurement. The terms divisionism and pointillism are not always clearly differentiated, but whereas divisionism refers mainly to the underlying theory, pointillism describes the actual painting technique associated with Seurat and his followers. ‘Divisionism’ (usually with a capital D) was also the name of an Italian movement, a version of Neo-Impressionism, that flourished in the last decade of the 19th century and the first decade of the 20th century. It was one of the sources of Futurism.