'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)

'If a large disc be rotated and observations be made through two apertures of diameters proportionate to their distances from the centre, flicker appears and disappears at the same speed with the same luminosity at both apertures. This is only the case when the apertures are small so that their images fall entirely within the macula since the sensibility to intermittent stimuli of that part differs from the rest as shown by Exner [note: 'Pflüger's Archiv III. p. 237. 1870.'] and Bellarminow [note: Archiv f. Opthalmologie XXXV. p. 25. 1889.'].' (402) 

'On increasing the intensity of intermittent stimuli a rapid increase in frequency is necessary at first to produce fusion; after a certain frequency has been attained a further increase in intensity does not necessitate a further increase in frequency, this has been shown by Bellarminow [note: 'Archiv f. Ophthalmolgie, XXV. p. 25. 1889.'] and surmised by Haycraft [note: 'This Journal, XXI. p. 139. 1897.']: but on still further increasing the intensity of the stimuli fusion occurs with a decreased frequency.' (435)