'drawing on the optical studies of the 1830s, the physicist Ogden Rood had in 1893 presented what he considered method by which colours might be differentiated according to their 'reflecting power.' Spinning a circular disc on which alternating bands of light and shade had been painted, Rood measured the rate of rotation required to eliminate the sense of intermingling or 'flicker' between them (Rood 1893. For context see Ramalingam 2013, 252-257).'