'Some months [note: 'This Jourmal, xxi. p. 396. 1897.'] ago the effect of simultaneous contrast upon the frequency of alternation necessary to fuse moderate stimuli was investigated by me, the method adopted consisted in altering the ratio of the time that the eye was exposed completely to light or darkness and the transition period.

In that paper two kinds of flicker were distinguished, which more recently Schenk [note: Pflüger's Archiv, LXVIII. p. 32. 1897.'] has recognised and termed "Flackern" and "Flimmern," corresponding to ordinary or "coarse flicker " and "fine flicker" or molecular movement respectively.' (449)