Let a room be only lit by the feeble gleam of a fire, almost
extinguished, and the eye will see with difficulty the objects in the
apartment, from the small degree of light with which they happen to be
illuminated. The more exertion is made to ascertain what these objects
are, as by fixing the eye more steadily upon them, the greater will be
the difficulty in accomplishing it. The eye will be painfully agitated,
the object will swell and contract, and partly disappear, but will
again become visible when the eye has recovered from its delirium.