s: it is very much quicker done than to
see the thing itself. Besides, there are many interesting observations
to be made upon the conduct and attitude of the memory images during
this operation. It is not necessary to suppose that they are in our
memory in a state of inert impressions. They are like the steam in a
boiler, under more or less tension.

At the moment when the perceived sketch calls them forth, it is as if
they were then grouped in families according to their relationship and
resemblances. There are experiments of Muensterberg, earlier than those
of Goldscheider and Mueller, which appear to me to confirm this
hypothesis, although they were made for a very different purpose.
Muensterberg wrote the words correctly; they were, besides, not common
phrases; they were isolated words taken by chance. Here again the word
was exposed during the time too short for it to be entirely perceived.
Now, while the observer was looking at the written word, some one spoke
in his ear another word of a very different significance. This is what
happened: the observer declared that he had seen a word which was not
the written word, but which resembled it in its general form, and which
besides recalled, by its meaning, the word which was spoken in his ear.
For example, the word written was "tumult" and the word spoken was
"railroad." The observer read "tunnel." The written word was "Trieste"
and the spoken word was the German "Verzweiflung" (despair). The
observer read "Trost," which signifies "consolation." It is as if the
word "railroad," pronounced in the ear, wakened, without our knowing it,
hopes of conscious realization in a crowd of memories which have some
relationship with the idea of "railroad" (car, rail, trip, etc.). But
this is only a hope, and the memory which succeeds in coming into
consciousness is that which the actually present sensation had already
begun to realize.

Such is the mechanism of true perception, and such is that of the dream.
In both cases there are, on one hand, real impressions made upon the
organs of sense, and upon the other memories which encase themselves in
the impression and profit by its vitality to return again to life.

But, then, what is the essential difference between perceiving and
dreaming? What is sleep? I do not ask, of course, how sleep can be
explained physiologically. That is a special question, and besides is
far from being settled. I ask what is sleep psychologically; for o