nsations are given
by Dr. Carpenter.[54] Here is one. An officer who superintended the
exhuming of a coffin rendered necessary through a suspicion of crime,
declared that he already experienced the odour of decomposition, though
it was afterwards found that the coffin was empty.[55]

It is, of course, often difficult to say, in such cases as these, how
far elements of actual sensation co-operate in the production of the
illusions. Thus, in the case just mentioned, the odour of the earth may
have been the starting-point in the illusion. In many cases, however, an
imaginative mind appears to be capable of transforming a vivid
expectation into a nascent stage of sensation. Thus, a mother thinking
of her sick child in an adjoining room, and keenly on the alert for its
voice, will now and again fancy she really hears it when others hear
nothing at all.

_Transition to Hallucination._

It is plain that in these cases illusion approaches to hallucination.
Imagination, instead of waiting on sensation, usurps its place and
imitates its appearance. Such a "subjective" sensation produced by a
powerful expectation might, perhaps, by a stretch of language, be
regarded as an illusion, in the narrow sense, in so far as it depends on
the suggestive force of a complete set of external circumstances; on the
other hand, it is clearly an hallucination in so far as it is the
production of the semblance of an external impression without any
external agency corresponding to this.

In the class of illusory expectations just considered the immediately
present environment still plays a part, though a much less direct part
than that observable in the first large group of illusions. We will now
pass to a second mode of illusory expectation, where imagination is
still more detached from the present surroundings.

A common instance of this kind of expectation is the so-called
"intuition," or presentiment; that something is going to happen, which
expectation has no basis in fact. It does not matter whether the
expectation has arisen by way of another's words or by way of personal
inclinations. A strong wish for a thing will, in an exalted state of
mind, beget a vivid anticipation of it. This subject will be touched on
again under the Illusions of Belief. Here I am concerned to point out
that such presentiments are fertile sources of sense-illusion. The
history of Church miracles, visions, and the like amply illustrates the
effect of a vivid a