'the method gives a ready and accurate means of obtaining measurement of quantity of contrast-effect, i.e. in terms of frequency of intermittence, that is in the same terms as of the "flicker" method of colour photometry introduced by Rood.

'Rood [note: 'American Journ. of Science, XLVI. p. 173. 1893.'] has recently re-introduced to notice a method of photometry advocated on not very convincing grounds by Schafhäutl [note: Universal Vibrations-photometer: Akad. d. Wiss. München, VII. p. 465.] forty years ago. The method is based on Plateau's [note: 'Dissert. sur quelques propriétés des impressions &c. Liège, 1829.] research, and proceeds on the well-known relation existing in light-sensations between their intensity and the rate of frequency of repetition required to fuse them.' (34)

'the delicacy of the flicker method led me to enquire whether "flicker" may be applied with success to the exarnination of the influence exerted on the intensity of light-sensations by contrast both of place and time, that is, using Hering's term "induction," by areal and by temporal induction.' (35)

'it is due to Rood showing that fusion of stimuli depended upon frequency and luminosity of colour, that flicker photometry has developed.' (396)

'Sherrington's 1897 paper [on 'flicker fusion']... dealt primarily with a... set of investigations into the 'fusion' not of light-, but of colour-sensations. Again 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).'