Kirschmann’s instrument

Kirschmann's colour mixing apparatus as it appeared on pp. 4-5 of a 1903 E. Zimmermann catalogue pf psychological instruments. Image provided by the Max Planck Virtual Laboratory library of instrument catalogues.

Image source: http://vlp.mpiwg-berlin.mpg.de/library/data/lit26/index_html?pn=12&ws=1.5