Ultra Scarce 1940s Glenn Colorule for Testing Color Vision oval dish And the balls rattle around

And the balls rattle around quite nicely in their very thinly walled cage

clinical looking dark green box with silvery white print and one initial--"M" in this case

Tiny text on all of them reads "Registered" and on a few is printed them reads Copyright 1896 F

This one--labeled "G" in what surely was a whole series--makes me think he had tired of the textile designing exercise by this point

and there is a red dyed bone hook included

Ultra Scarce 1940s Glenn Colorule for Testing Color Vision oval dish And the balls rattle aroundI have found a bunch of academic papers and studies discussing the use of the Glenn Colorule, but can't find even a picture of another out there anywhere. There are records of in a few academic libraries, so I know it was produced by s explained on the box text, it was made to be used to test the color vision of observers, to test the quality of light sources, and or to demonstrate disagreement caused by "pseudo," or false, color matches. There's a