| Full | 24° | 32° | 21° | 27° |
| ½ | 17° | 28° | 16° | 22° |
| ¼ | 13° | 16° | 14° | 20° |
| ⅛ | 8° | 10° | 13° | 16° |
It will be evident how the field contracts as the light is diminished in brightness, and also that the blue field does not diminish equally with the yellow field, but is more persistent. Again, it will be noticed that the luminosity of the blue, for the same extent of field to be covered, has to be much lower than for the yellow.
The diminished area of the spot of light also diminishes the field, and the same order of diminution of field is obtained as with the larger spot.
Another set of experiments, made with the same aperture of slit passed through the spectrum, and the field taken at different points, give the following results:—
| Spectrum scale. (See [Fig. 41], [Page 210]. | Nasal side. | Temporal side. |
| 58·6 | 18° | 35° |
| 54·6 | 27° | 46° |
| 50·6 | 33° | 47° |
| 46·6 | 25° | 30° |
| 42·6 | 21° | 21° |
| 38·6 | 17° | 17° |
| 34·6 | 22° | 30° |
| 30·6 | 25° | 33° |
| 26·6 | 33° | 40° |
| 22·6 | 37° | 44° |
| 18·6 | 28° | 40° |
| 14·6 | 22° | 34° |
| 8·6 | 20° | 30° |
Here we see that although the luminosity of the colour spots varies at the spectrum luminosity, the fields do not vary proportionally; when the luminosities of the green, yellow and red are made equal, the fields become nearly equal on the nasal side. The field for the blue, however, then becomes vastly larger than that for the others, showing a peculiarity which is very remarkable.
Fig. 41.
Spectrum Scale.
Recently published experiments on colour fields have been so largely based on the exigencies of the Hering theory, that it is somewhat difficult to decide their significance from any other aspect.