Singular Impression On The Visual Nerves By A Luminous Object
If, while sitting in a room, you look earnestly at the middle of a
window, a little while, when the day is bright, and then shut your
eyes, the figure of the window will still remain in your eye, and so
distinct that you may count the panes. A remarkable circumstance
attending this experiment is, that the impression of forms is better
retained than that of colours; for, after the eyes are shut, when you
first discern the image of the window, the panes appear dark, and the
cross-bars of the sashes, with the window frames and walls, appear
white and bright; but if you still add to the darkness of the eyes, by
covering them with your hand, the reverse instantly takes place--the
panes appear luminous, and the cross-bars dark; and by removing the
hand, they are again reversed.