Irradiation.

Irradiation. When a bright object is looked at, an image of it is formed on the retina of the eye. The receiving apparatus there consists of a number of separate stimullable elements or sets of elements; and for the maximum distinctness of vision no one of these elements should be at all affected by stimulation of its neighbours. If, however, the object be brilliant the image on the retina is very bright, and neighbouring sensitive elements participate in the excitement; a bright object thus looks larger than it is. Examples: bright white letters on a black ground look larger than they are; black letters on a bright white ground look smaller; a white-hot wire appears thickened; the new moon appears larger than the copper-coloured 'old moon' which it appears to 'nurse'; and, especially, an electric incandescent lamp often appears, on account of the extreme brilliancy of its attenuated filament, to be almost filled with light.