'before making use of rotating discs for contrast phenomena it is needful, as a control, to see whether differences of mere radial distance influence the results. Marbe [note: 'Wundt's Philosophienstudien, XII. 280.'] and Schenk [note: 'Pflüger's Archiv, LXIV. p. 165. 1896.'] (with Schmidt) have examined this point on discs with alternate equal black and white sectors. The former finds fusion rather more easy along arcs further from than nearer to the centre of the disc; the latter that with increasing speed of rotation "flickering" persists longer in the peripheral zone than in the central.' (35-36)

'My results in this matter - as far as I have, in the above manner, studied it - agree with Marbe when the luminosity is low, with Schenk when the luminosity is high. To the question for which I particularly desired an answer I obtained the reply that in regard to the influence of radial distance upon "flicker" it is but small.' (37)

'Marbe [note: 'Wundt Philosoph. Stud. XII. p. 279. 1896 and IX. p. 384. 1893.'] has stated several theoretical reasons for considering the Talbot-Plateau law inaccurate but has not made any direct observations.' (439)