Before leaving the consideration of revived sensations, I may notice a peculiarity as to light and sound. We seldom, at least in healthy dreams, have visions of great brilliancy; the light is not that of the noon-day, but the sober hue of evening, or even the dim grey shade of twilight. Hence, when we speak of shadowy, ill-defined perceptions of our waking life, we are apt to call them dream-like. The same obtains of sounds, which, unless produced by out ward causes, and blended with the dream, are usually of the kind described by the poet,

" Like the faint, exquisite music of a dream."

The imperfection of the dreaming memory is remarkably illustrated when we are revisited by the forms of those who have long departed this life; for we believe them to be still living, simply because we have forgotten that they are dead. Another very important fact as to these revived impressions is, that we do not often subject them to the dominion of the will. A great difference is very observable in those processes of thought which belong to the imaginative faculty. The combinations are not, as under the active imagination of our waking hours, effected in order to fulfil some illustrative purpose, nor, as in the passive imagination, are we conscious that the scenes, however wild, and the persons, however monstrous, are mere creations of the mind. The emotions they excite are often of the most overpowering description.

"Dreams in their development have breath, And tears, and tortures, and the touch of joy. They leave a weight upon our waking thoughts, They take a weight from off our waking toils, They do divide our being. • • * • • • • They have power, The tyranny of pleasure and of pain."

But, on the other hand, it is a singular distinctive characteristic of dreaming that the emotions which we might, a priori, have expected to arise are not produced. Of these the emotion of surprize* or wonder is the most frequently wanting. The wildest incoherences, the confounding of personal identities, the mingling of material and mental properties, the most miraculous violations of the best ascertained laws of nature, excite no more admiration than the commonest events of life. I have dreamed of standing at the foot of a vast cataract, picking up shells and sand, the fall of water being suspended, as it were, in the air, while I was quietly employed at its base, and unconscious that there was any-thing extraordinary in all this. Dr. Macnish says, " on one occasion fancy so far travelled into the regions of absurdity, that I conceived myself riding upon my own back; one of the resemblances being mounted upon another, and both animated with the soul appertaining to myself, in such a manner that I knew not whether I was the carrier or the carried"

A gentleman to whom this Institution is largely indebted gave me the following experience: - "I have several times appeared to read a portion of an imaginary work as regularly as if it had been real. I have also dreamed that I was dead, and that I carried my own body in a coach to bury it, and that when I reached the place of burial a stranger said, 'I would not advise you, sir, to bury your body in this place, for they are about to build so near it, that I have no doubt the body will be disturbed by the builders.' 'That,' I replied, ' is very true ; I thank you for the information, and I will remove it to another spot;' upon which I awoke."

It is probable that the absence of surprize, on the occasions alluded to, is due to the defective exercise of the comparing faculty. A want of discernment of the true relations of things is one of the most remarkable characteristics of dreaming, and consequently the newness and strangeness of the connections of the things presented to our observation do not strike us. Defective exercise of the comparing faculty, however, is a roundabout phrase for expressing the fact, that the associated ideas are fewer in number. Dryden says, -

"Dreams are the interludes which fancy makes ; When monarch reason sleeps, this mimic wakes, Compounds a medley of disjointed things,- A court of coolers, or a mob of kings."

Now, "a mob of kings" to a person awake would be odd and surprizing enough, because with such a sight there would arise in his mind all his former ideas of those august personages. But the dreamer has the regal multitude before him, and no other idea arises in his mind, by memory or association, to shew the absurdity of the impression. The blending of the past and present, the intermingling of the events of the 17th and 19th centuries, the division of the indivisible personal consciousness, from the want of due associations, are not perceived to be incongruities, or impossibilities, and therefore we are not surprised. It is in this respect that dreaming bears so close a resemblance to insanity, so that it has been long ago remarked that delirium is dreaming awake, as dreaming is the delirium of sleep. A notable difference, however, consists in this, that the former is apt to be acted upon, while the execution of the sleeper's vagrant fancies is precluded by the thraldom in which his active powers are held; except in those morbid cases in which the nervo-muscular system does not slumber with the rest of the body, and to which I alluded in my former lecture. Some metaphysicians of high reputation have held, that the want of command over the order of our ideas is the great distinguishing mark of dreaming, - an opinion to which we cannot entirely subscribe. The suspension of volition, though a frequent, and, perhaps, a general accompaniment, is not by any means indispensable to dreaming; for we certainly do exercise it in the recollections, and in the efforts at action in our dreams. Nevertheless, as we have already observed, the principal mental phenomena are of the passive character. It must be borne in mind, however, that in sleep we do not often wish to command our thoughts. When we are awake, our sensations are constantly interfering with the order of ideas, and, therefore, we are obliged to exert efforts of the will, as it is called, to keep such and such thoughts before us. Ideas are more readily associated with ideas, when sensations are excluded. Hence many persons instinctively close their eyes when engaged in deep thought. And the vagrant ideas of a person in a reverie, or fit of abstraction, or in a brown-study, being little mingled with perceptions, are very like those of a dreamer.