'Filehne [note: 'v. Graefe's Archiv, XXXI. p. 20.'] noticed that with discs of equal alternate black and white sectors the frequency of intermittence of stimulation is not in exact agreement when discs of many sectors are compared with discs of few sectors. The discs of many sectors have, to extinguish flicker, to rotate relatively faster than theory demands. Mere linear velocity seems to assist the fusion of the sector sensations.' (37)

'That the maximum speed at which the sensation of flicker is produced depended upon other factors besides luminosity was noted by Filehne [note: v. Graefe's Archiv XXXI. p. 20. 1885.'], whose observations were made on white discs on some of which only four black sectors of 45º each were painted. Rotated at a speed to produce 25-30 alternations per second, fusion occurred, while if the number of painted sectors were great, flicker might exist at a frequency of 74 alternations per second.' (396)