bute to complete the
composition in accordance with the nature and design of this internal
image. Sometimes the physiological conditions of hallucination are so
powerful that it is at once produced by the appearance of an object
which has some analogy with the mental image. Whatever may be the
genesis and primitive character of the idea of space, and its psychical
and physiological relations to actual space--a question which has been
the theme of so much discussion in our time--it is certain that first
habit and then hereditary influence cause us to have the sensation and
apprehension of a psychical space, which may be termed artificial and
congenital, and upon which the various impressions of the senses are
spontaneously projected. Of this there is an evident proof in the fact
that if we look at the sun or any bright object, such as the windows of
a room in the day time, and then close our eyes, so as to make the
vision of external space impossible, the image of the sun, sometimes of
a different colour, or of the window, is projected into the darkness at
some distance from us, and moves about this psychical space. This
phenomenon also occurs in the subjective sensations of hearing, since
the sounds do not appear to be close to the ear, but at a distance. We
are not here called upon to discuss the causes which generate the
appearance of this psychical space, but the fact is indisputable; so
that conversely it becomes intelligible how the internal image may be
projected in the same way, or may at least appear to be externally
projected in hallucinations. This surprising phenomenon is only a
modification of the ordinary exercise of the psychical and physiological
faculties in the projection of images; of which, after the idea of space
has been formed by primitive experience, habit and education are the
chief factors.

Hallucinations, in the cases observed above, are due to an external
impulse; and this is especially the case in madness and other nervous
disorders; since a critical observation and clear discernment of things
is wanting, some object of vision, a voice, phrases, or sounds are much
more apt to act as a stimulus to a vast field of visual hallucinations,
or to a long succession of sentences and speeches. It is not, therefore,
wonderful that in an ecstasy, for instance, in which all the faculties
are concentrated on very few ideas and images, or perhaps on one only,
every external sign, whether obvious to sight