Look at the pattern of the paper-hanging of a room, a picture, or
almost any other object in it; then, without altering your position,
call to mind the magnificent dome of St. Paul’s Cathedral; the pattern
of the paper-hanging, or the subject of the picture, though actually
impressed on the retina of the eye, will be momentarily lost sight of
by the mind; and, during the instant, the recollected image of the dome
rising from the dingy roofs of London, will be distinctly seen, but in
indistinct colouring and outline. When the object of the recollection
is answered, the dome will quickly disappear, and the paper-hanging
pattern, or the picture, again resume the ascendancy.