Helmholtz Color Mixer (Helmholtz' electromagnetic rotator)

(Elektromagnetischer Rotations-Apparat nach Helmholtz)
An early version of a direct-current open-frame electric motor which has a constant speed when rotating and which is capable of varying speeds. The rotation speed is varied through use of a governor. This device could be used for color mixing by turning a pulley which drives a color mixer through a pulley. (Expanded caption Copyright 1998, Edward J. Haupt).

(Source:Herman Helmholtz, illustrated as plate XLIX in Cyon, E. v. (1876). Atlas zur Methodik der physiologischen Experimente und Vivisectionen: LIV Tafeln in Holzschnitt. Giessen: J. Ricker'sche Buchhandlung.)
Source of illustration: Zimmermann, E. (1903). XVIII. Preis- Liste über psychologische und physiologische Apparate (p. 6). Leipzig: Eduard Zimmermann.

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