Two color-wheels, with disks. By Milton Bradley Co., Springfield. $20 [acc. to No. 74 in Münsterberg, 1893, Psychological Laboratory at Harvard University]
Source
Anonymous. 1892. Harvard Psychological Laboratory in Dane Hall: Interior of a Laboratory Room (Students studying the effect of attention on color perception). Photograph. (Harvard University Archives - HUPSF Psychological Laboratories (2))
See the same device on another photograph from the collection of Harvard photographs. The Disk on the color mixer is probably from Ernst Brücke. It produces subjective color effects when rotated.
