An endeavour was made to form a series of colour equations with her eyesight by placing three slits in different parts of the spectrum, but without success, although a match with white was made in two positions. One slit was in the orange-red (52 of the scale), another at E, and the third at G; mixtures were made which she said matched the white, but they were so erratic that it was useless to measure the apertures. When the slit in the violet was covered up, a white patch being alongside as a comparison, she called the mixture of red and green “brownish-green”; when the slit in the red was covered she called the mixed light of green and violet “green”; and when the green slit was covered up she called the purple colour a “different kind of brown.” When the first slit was moved into the red near the lithium line she called the colours “green,” whenever the green slit was uncovered. A piece of red glass was placed in the white reflected beam, forming a red patch, and a patch of the blue at scale No. 30·5 (λ 4862) was placed alongside, and she matched them in luminosity and in colour. (The dominant colour of the signal glass in question was λ 6220.) She finally was tested with colour discs. To make white she required 130 G + 113 R + 117 U = 72 W + 218 B. She was then tried with the blue and green discs alone and made a match-- 258 U + 102 G = 65 W + 295 B. An attempt was made to match with the green and red discs alone, but this failed. She matched the red disc alone with black and white, and also the blue disc alone-- 360 R = 56 W + 304 B (corrected), 360 U = 60 W + 300 B (corrected). With any proportion of R and U mixed together she matched a grey of approximately the same intensity as above, as it might be supposed she would from the last two equations. Taking the intensity curve of the light reflected from the red disc, it was found to contain a great deal of the part of the spectrum which she called brownish, viz., from 33·5 to 48 on the scale, whereas the blue reflected a trifle of this portion of the spectrum, as did also the green; and this may account for her making a match to grey of U and G, and not of R and G, but it is hard to see why she matched U alone and also R with the grey. Reviewing the case, it seems that any perception of colour is very small, and that the sensations are green and much less red. From the equations it also seems that she would have matched green with white and black alone, and that 360 G = 75 W + 285 B. Perhaps the explanation of the matches and names of colours may be that a proportion of colour may be mixed with another without being perceived, but this colour so hidden has still the capability of neutralising a certain quantity of the complementary colour. CHAPTER XIII.