Color-wheel, with disks. By Milton Bradley Co., Springfield
Source
Anonymous. 1892. Harvard Psychological Laboratory in Dane Hall: Instruments for Experiments on Sight. Photograph. (Harvard University Archives - HUPSF Psychological Laboratories (7))
See another Milton Bradley color mixer on the same photograph. See also the same device on another photograph from the Harvard collection. The History of Psychology Collection at Banard College refers to this device as Milton Bradley color mixing apparatus and provides a color photograph. See a paper by Edmund C. Sanford (1892) with a figure of the disc. It was used to demonstrate the Talbot-Plateau law.