In our inquiry into the nature of Dreaming, the simplest, and, I think, the most philosophical course will be to ascertain, in the first instance, what the state of the mind in dreaming has in common with its waking condition, and then to proceed to consider the differences between them.

Every one, no matter how little accustomed to the analysis of his thoughts and feelings, must have noticed that a large proportion of the materials of dreams are derived from past experience; that they are the products of a kind of memory; but that they are often put together in odd combinations, not unlike the effects of a wanton or wilful imagination during the waking hours.

To pursue the proposed order of investigation, it will be necessary, even at the risk of being somewhat tedious, or of speaking of things already sufficiently familiar to my audience, to make one or two remarks upon memory and imagination.

The simplest form of memory is the mere reproduction of a sensation, or the return of a thought, or of a former emotion to the mind. When the recurrence of certain feelings and ideas is brought about by an effort of the will, such act of the mind is denominated recollection. But when the past images come unbidden, we say that they are the products of mere remembrance. So that there are two kinds of memory, - the one passive, the other actite. When the mind exists in its most listless state, past impressions and ideas, though of the faintest description, are revived in continuous succession. If the eyes are shut, and no sounds prevailing, these images may be almost unmingled with present perceptions, unless the internal organs give rise to uneasy sensations. But even when a full tide of fresh perceptions are rushing through the senses, they do not prevent the recurrence of by-gone images and emotions; on the contrary, as we shall see presently, they have a direct tendency to revive such images and emotions, and, in so doing, they often greatly enhance the pleasure or the pain of the present moment.

In active memory, we command the return of former impressions. It is true that these shadows of the past do not always come at our bidding; we may " call them from the vasty deep" of old experience, but they will not always answer. In exercising what dominion we have over them, we, however, do but subject them to the same laws as those which regulate the phenomena of passive memory, - the laws of association or suggestion. To take one of the least complex of instances. If I wish to recall the name of an absent person, I fix my mind attentively on his image; and then the place in which I last saw him, the time, the contemporary circumstances, and the conversation of other persons will also return to my mind, and very possibly bring in their train the name which was not suggested by the first presentation of his image. In a similar manner we recall a subject of discourse. In conversation we are sometimes interrupted, and, after the disturbing cause has ceased, we wish to take up the thread where it was broken off; but to find it, we may be obliged to go back to a much earlier period in the conversation, and then the subsequent topics recur by means of those links of association which first brought them together.

It would obviously be quite out of my province to enter on the wide subject of the principles of association or suggestion; it will be sufficient to remark, that ideas, meaning by this word those states of consciousness not immediately produced by outward sensations, suggest one another, sometimes from the mere fact of their having formerly coexisted; sometimes from their similarity; sometimes from their contrast, as when the idea of a dwarf suggests that of a giant; and sometimes from proximity of place. At other times the connections are of a less casual nature. Such are the relations of analogy, of proportion, of cause and effect. I am aware that most of these principles may, by a refined analysis, be resolved into mere association or proximal succession. I must not omit to remark, that not only the ideas are renewed in this manner, but also the various emotions that have been formerly associated with them ; and, likewise, that they are liable to be summoned before us not only by other ideas, but, likewise, by present sensations, whether derived from without, or from the internal organs. And here we must notice an interesting fact which bears importantly on the subject of this lecture, namely, that impressions may be made on the sentient nerves, which, although they do not give rise to perceptions, will excite in the mind ideas and emotions either painful or pleasurable. Thus, there are various forms of indigestion, which may produce the most distressing states of mind, filling it with all kinds of gloomy ideas, and yet not give rise to sensations, in the strict sense of the word.

The operations of fancy and imagination may be analysed into ideas suggested on some one of the principles of as-sociation to which I have adverted. Fancy is generally Understood as the faculty which calls up related images; though they are often connected so slightly with the first thoughts, that to many minds they never occur at all; and they are such, for the most part, as produce sentiments of the beautiful, the sublime, the ludicrous, or the terrible. Persons are said to have a quick fancy, in whom remote ideas are readily brought together. Imagination is often used synonymously with fancy; but it is a faculty of a higher description. It not only, like fancy, brings together many striking images and thoughts, and combines them in new groups which have the most agreeable or painful effect on the mind, but it so combines them as to produce images of persons and places, and things that seem to be newly created.

The products of imagination are not like those of fancy, loosely aggregated, so that they can be seen at once to be new combinations of old materials, but they are so artificially interwoven, and all in such keeping and consistency, that they seem struck out at once as new individuals. Hence, the possessors of the highest form of imagination might well be called poets, literally makers. But even in the dullest and least poetic, these so-called faculties may be at work. There is indeed the same distinction to be drawn between active and passive fancy and imagination, as between active and passive memory. In the course of our investigation, we shall find sufficient illustration of the fact to which I have last adverted.