 observed […] that shadow, or the limitation of this light, was necessary; for if we remove the dark body on NP, the colors FGH cease to appear, and if we make the opening DE large enough, the red, orange, and yellow at F extend no further because of that than do the green, blue, and violet at H—instead, all the extra space between the two at G remains white. (AT 6: 331, MOGM: 336) 