Large color-mixer for four disks, two upon each spindle. After Wundt, by Krille, Leipzig. $35 [acc. to No. 71 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))
Maybe the third wheel on the right is the drive mechanism for this device. See the same device on another picture from the Harvard photographies and some more comments on its identification.