'increase of rate of rotation needful to extinguish flicker accompanies increase of intensity of the intermittent stimuli up to only a certain pitch of intensity of stimulation. Beyond that pitch further increase of intensity diminishes the flickering of the resultant sensation even when the rate of rotation (frequency of intermittence) remains unincreased. This Bellarminow [note: 'Archiv. f. Opthalmologie, XXXV. p. 25. 1889.'] points out, and I myself have seen from experiments carried out independently in my laboratory by Mr O. Grünbaum.' (35)

'To Mr O. Grünbaum I am indebted for carrying out some measurements of the exact speeds required under certain conditions to extinguish flicker in various of the discs.' (54)