OCULAR SPECTRA.
One of the most curious affections of the eye is that, in virtue of which it sees what are called ocular spectra, or accidental colours. If we place a red wafer on a sheet of white paper, and, closing one eye, keep the other directed for some time to the centre of the wafer, then, if we turn the same eye to another part of the paper, we shall see a green wafer, the colour of which will continue to grow fainter and fainter, as we continue to look at it.
By using differently coloured wafers, we obtain the following results:
| WAFER. | SPECIMEN. |
| Black | White. |
| White | Black. |
| Red | Bluish Green. |
| Orange | Blue. |
| Yellow | Indigo. |
| Green | Violet, with a little Red. |
| Blue | Orange Red. |
| Indigo | Orange Yellow. |
| Violet | Bluish Green. |