_ is stirred, as it
would be by the presence of the object' (De Insomn., ii. 460, b, 23-
26).

The ghost in a haunted house is taken for a figure, say, of a monk,
or of a monthly nurse, or what not, but no monthly nurse or monk is
in the establishment. The 'percept,' is a 'percept,' for those who
perceive it; the apparition is an apparition, for _them_, but the
perception is hallucinatory.

So far, everybody is agreed: the differences begin when we ask what
causes hallucinations, and what different classes of hallucinations
exist? Taking the second question first, we find hallucinations
divided into those which the percipient (or percipients) believes,
at the moment, and perhaps later, to be real; and those which his
judgment pronounces to be _false_. Famous cases of the latter class
are the idola which beset Nicolai, who studied them, and wrote an
account of them. After a period of trouble and trial, and neglect
of blood-letting, Nicolai saw, first a dead man whom he had known,
and, later, crowds of people, dead, living, known or unknown. The
malady yielded to leeches. {183} Examples of the first sort of
apparitions taken by the judgment to be _real_, are common in
madness, in the intemperate, and in ghost stories. The maniac
believes in his visionary attendant or enemy, the drunkard in his
rats and snakes, the ghost-seer often supposes that he has actually
seen an acquaintance (where no mistaken identity is possible) and
only learns later that the person,--dead, or alive and well,--was at
a distance. Thus the writer is acquainted with the story of a
gentleman who, when at work in his study at a distance from England,
saw a colleague in his profession enter the room. 'Just wait till I
finish this business,' he said, but when he had hastily concluded
his letter, or whatever he was engaged on, his friend had
disappeared. That was the day of his friend's death, in England.
Here then the hallucination was taken for a reality; indeed, there
was nothing to suggest that it was anything else. Mr. Gurney has
defined a hallucination as 'a percept which lacks, but which can
only by distinct reflection be recognised as lacking, the objective
basis which it suggests'--and by 'objective basis,' he means 'the
possibility of being shared by all persons with normal senses'.
Nobody but the 'percipient' was present on the occasion just
described, so we cannot say whether other people would have seen the
visitor, or not.