He passed the test of the Holmgren wools satisfactorily, proving that the usual vision was normal for colour, but failed at once with the pellet test.
Fig. 36.
The objects in view were to test his perception of the spectrum colours, and then the extent of his retinal field for colour. This last is not recorded here. The spectrum colours were reduced to uniform luminosity between λ 4600 and λ 6600. Diaphragms containing holes of different sizes were placed in front of the last prism, and thus a round spot of monochromatic light of the same luminosity was produced upon the screen when a slit was passed through the spectrum. From the red end to λ 5270 he called the whole of the colours white, and from that point he began to see blue, called the colours bluish and blue. When the full illumination for all the colours was used, the same results were obtained. From this examination it would appear that he was totally deprived of the sensation of any colour except of blue. A subsequent examination of his perception of the luminosity of different rays, however, has to be taken into account, for in the first examination he had no light of pure white with which to compare the colours. In the next experiments, a strip of white light was placed in juxtaposition to the colour, and the results were slightly different. The table below gives his luminosity measures ([Fig. 36]). Col. I. is the empyric scale number, II. is the wave-length, III. the luminosity of the colour to the normal eye, IV. the luminosity to X., and V. the ratios of III. to IV.
In the diagram, his luminosity curve X. is shown, its area being 1400 against 1650 for the normal eye. His central perception of light, as arrived at by the extinction method, was only two-thirds of that of the normal eye; hence his area of luminosity should be 1100. As it is 1400, the ordinates of the above curve should be multiplied by 0·8, to compare with that of the normal eye.
| I. | II. | III. | IV. | V. | Colours to X. | Spectrum colour to normal eye. |
| Scale No. | Wave- length. | Luminosity to the normal eye | Luminosity to X. | IV. — III. | ||
| 60 | 6730 | 7·3 | 0 | 0 | Sees only the white stripe | Red. |
| 57 | 6423 | 32 | 10 | 0·31 | Calls red yellowish, and white bluish | Scarlet. |
| 55 | 6242 | 65 | 38 | 0·65 | „ „ | |
| 53 | 6074 | 96 | 86 | 0·89 | Both one colour | Red-orange. |
| 51 | 5920 | 99 | 90 | 0·91 | „ „ | Orange-yellow. |
| 47 | 5660 | 92 | 83 | 0·90 | Calls green a little blue; white he sees as white | Greenish-yellow. |
| 43 | 5430 | 69 | 625 | 0·90 | „ „ | Yellowish-green. |
| 40 | 5270 | 50 | 46 | 0·92 | „ „ | Green. |
| 32 | 4910 | 8·5 | 9 | 1·06 | Sees blue as blue, and white yellowish | Greenish-blue. |
| 31 | 4960 | 7 | 8 | 1·14 | „ „ | Blue. |
| 26 | 4680 | 3 | 3 | 1·00 | „ „ | Blue. |
His readings of luminosity were made without any hesitation, and were concordant for each observation, which is not to be wondered at, as the matches, except at the blue end, were practically matches of different mixtures of black and white.
It appears that the white which X. sees as white is the same as the orange sodium light, and that the red he sees is yellowish. The mixture of this yellowish-white with the blue makes white. He sees a little blue in the spectrum colour at λ 5720, so it must be taken that at that point of the spectrum he begins to see colour—a point which is considerably lower than that given by his preliminary examination of the spectrum colour, and due, no doubt, to the fact that in this experiment he had the white light of the positive pole of the electric light to compare with it. It seems probable that what X. called yellowish was really a sensation of white mixed with a very small quantity of red sensation, for he saw no yellow in the orange, in which that colour would be most easily distinguished on account of its luminosity. Red light, when strongly diluted with white light, to the normal eye is often called orange.
As, practically speaking, the colour vision of X. is confined to blue and white, it is of interest to note the difference in luminosity at the different parts of the spectrum that is registered by him and by P., who had blue (violet) monochromatic vision. To facilitate the comparison, the luminosity curve of the latter is shown in the diagram.
Fig. 37.