A good example of Chibret’s Chromatophotometer by Giroux. A description from ‘The Eye and its Instruments’:
With this instrument persons who confused the complementary colours could easily be distinguished from persons who were really colour blind… The instrument is made of brass and consists of a tube containing a doubly refractive prism, a plate of rock crystal and a Nicol. The prism can be turned through an angle of 45 degrees, the Nicol through 15 and the rock crystal through 360 degrees. When looking through the instrument one sees two illuminated fields, produced bt the prism, each of a colour which is complementary to the selected principal colour. Rotating the prism produces a change in the degree of saturation of the fields and and a switch of the complementary colours between the right and left fields.
Ask the Dealer
Fletcher Wallis sells objects and books relating to the history of science, medicine and technology from his unit at Admiral Vernon Arcade Portobello Road. He publishes books through Vernier Press, including Antique Medicine Chests, and Corkscrew Patents from 1795. He has been dealing for thirty five years.