On entering a room, we imagine that we see the whole side of it at
once, as the cornice, the pattern of the paper-hanging, pictures,
chairs, &c., but we are deceived; for each object is rapidly, but
singly presented to the eye, by its constant motion. If the eye were
steady, vision would be lost. For example, fix the eye on one point,
and you will find the whole scene become more and more obscure, till it
vanishes. Then, if you change the direction of the eye ever so little,
at once the whole scene will be again perfect before you.