iters considers spectral
illusion a disease, in which false perceptions take place in some
of the senses; thus, when the excitement of motion is produced in a
particular organ, that organ does not vibrate with the impression
made upon it, but communicates it to another part on which a
similar impression was formerly made. Nicolai states that he made
his illusion a source of philosophical amusement. The spectres
which haunted him came in the day time as well as the night, and
frequently when he was surrounded by his friends; the ideal images
mingling with the real ones, and visible only to himself. Bernard
Barton, the celebrated Quaker poet, describes an illusion of this
nature in a manner peculiarly striking:--

"I only knew thee as thou wert,
A being not of earth!
"I marvelled much they could not see
Thou comest from above
And often to myself I said,
'How can they thus approach the dead?'

"But though all these, with fondness warm,
Said welcome o'er and o'er,
Still that expressive shade or form
Was silent, as before!
And yet its stillness never brought
To them one hesitating thought."

"I recollected that the mode of exorcism which was successfully adopted
by Nicolai of Berlin, when haunted by similar fantasies, was a resort to
the simple process of blood-letting. I accordingly made trial of it,
but without the desired effect. Fearful, from the representations of my
physicians, and from some of my own sensations, that the almost daily
recurrence of my visions might ultimately lead to insanity, I came to
the resolution of reducing my daily allowance of opium; and, confining
myself, with the most rigid pertinacity, to a quantity not exceeding one
third of what I had formerly taken, I became speedily sensible of a most
essential change in my condition. A state of comparative health, mental
and physical with calmer sleep and a more natural exercise of the organs
of vision, succeeded. I have made many attempts at a further reduction,
but have been uniformly unsuccessful, owing to the extreme and almost
unendurable agony occasioned thereby.

"The peculiar creative faculty of the eye, the fearful gift of a
diseased vision, still remains, but materially weakened and divested of
its