-----+-------+----------+----------+-----+--------------------+---------------- I. | II. | III. | IV. | V. | | Spectrum -----+-------+----------+----------+-----+ | colour to Scale|Wave- |Luminosity|Luminosity| IV. | Colours to X. | normal No. |length.|to the |to X. | -- | | eye. | |normal eye| | III.| | -----+-------+----------+----------+-----+--------------------+---------------- 60 | 6730 | 7·3 | 0 | 0 |Sees only the white |Red. | | | | |stripe | 57 | 6423 | 32 | 10 | 0·31|Calls red yellowish,|Scarlet. | | | | |and white bluish | 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|Greenish-yellow. | | | | |blue; white he | | | | | |sees as white | 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, |Greenish-blue. | | | | |and white yellowish | 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.