These remarks conclude what I have to say on the subject of the present chapter. It would appear, that when ideas of vision are rendered unduly intense, three stages of excitement may give rise to spectral impressions.

In the first stage of excitement, nothing more than the outlines of the recollected images of the mind are rendered as vivid as external impressions.

In the second stage, ideas are vivified during darkness so as to produce phantasms of a perfect form; but these are easily expelled by a strong exposure to light.

In the third stage of excitement, the illusions incidental to it are not dispelled by light, but may subsist during the influence of sensations of an ordinary degree of intensity.

* This story I have quoted from a late work, the Edinburgh Literary Gazette. It is the report of an anecdote related by Sir Walter Scott, on the occasion when I read a paper to the Royal Society, which has given rise to the present expanded dissertation.

CHAPTER IV.

AN INQUIRY INTO THOSE LAWS OF MENTAL CONSCIOUS

NESS WHICH GIVE RISE TO THE ILLUSIONS OF
DREAMS.

I talk of dreams,

Which are the children of an idle brain,

Begot of nothing but vain phantasy,

Which is as thin of substance as the air,

And more inconstant than the wind.-SHAKSPEARE.

THERE is, perhaps, no one familiar with the various apparition-stories which have from time to time been published, who is not strongly inclined to suspect that many of them are mere dreams. Whether this conjecture be well-founded or not, it is often difficult to determine. On this account it will be necessary to investigate the phenomena of sleep with some degree of care.

In reference to this inquiry it may be observed, that the excitability of the sanguineous fluid, upon which the vividness of our mental feelings depends, has, in a healthy condition of the system, its due limits. The power possessed by the blood of augmenting the heart's systole or diastole cannot be too long kept up. After a certain degree of excitation, a tendency is shewn to an opposite state of debility, when

the feelings of the mind gradually decrease in their degree of vividness. Thus, there are periodical laws which govern our hours of slumber, and which, at the same time, are conducive to the regular exercise of the important functions of assimilation.

Some philosophers have supposed, that in sleep there is a temporary suspension of thought; others (the Cartesians in particular) have much more reasonably conceived that thought continues without any intermission. For, upon the principle inculcated by the late Dr Brown, that all our mental feelings are nothing more than the mind itself existing in different states, it is difficult to imagine in what way this relation of the mind to the body can possibly be suspended or dissolved, as long as the vitality of our frame subsists. When, likewise, it is considered, that we cannot entertain the least conception of any other states of the mind, than those which must necessarily include sensations or renovated feelings, the hypothesis becomes extremely plausible, that mental feelings of this kind, though certainly of extreme faintness, do actually occur in sleep, or even during deliquum.

This theory may be viewed in connexion with certain states of the circulating system, upon which those of the mind depend. The vividness of our mental feelings is regulated by the force and duration of each systole and diastole of the heart. Should these actions be too short and feeble, a corresponding faintness in the affections of the mind is the result, as is the case during the tremulous fluttering pulsations which are characteristic of syncope; also, if objects of

S

sensation are uniform in their impressions, the vividness of our mental states will be no less diminished. Hence the promotion of sleep by the unchanged feelings of touch, which are induced by a horizontal position of the body during rest; hence also the somniferous effect of monotonous sounds. The continuation of sleep is likewise favoured by the exclusion of all impressing objects of vision.

After these preliminary remarks, I shall attempt a strict scrutiny of the states of the mind peculiar to sleep, as they are to be distinguished from those which occur during our waking hours.

According to the definition which I have given of sensations, they are states of the mind induced by objects actually present, and acting upon the organs of sense, while ideas are the renewals of past sensations. A question then, which, as we shall soon find, is most intimately connected with this inquiry, may be asked, By what law we thus arrive at our notions of the present and the past?

When, by the repetition of any sensation, those feelings are recalled with which they were before associated, such past feelings are renovated in a less vivid state, and hence acquire the name of ideas; that is, images of prior sensations. It is, then, from nothing more than the comparative degrees of vividness which distinguish sensations and ideas, that the mind becomes intuitively susceptible of certain relative feelings of succession that subsist between them; which feelings of succession we express by such terms as the present and the past. This notion of a succession of mental states is in fact acquired by an ultimate law of

our nature. The more vivid or sensible affection is contemplated as present to the mind, while the less vivid, or ideal state, is considered as past.

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But it is essential to this knowledge of succession, that it should at the same time bear a reference to the identity of the mind; and, accordingly, this conviction is suggested, whenever we think of the present and the past. The late Dr Brown was the first to successfully explain this last-mentioned principle of the human intellect. "In all the varieties of our feelings," he remarks, we believe that it is the same mind which is thus variously affected;" or, as this metaphysician has elsewhere explained himself, "that "the mind, which is capable of existing in various states, is felt by us as one in all its varieties of feelings.”—“ The belief flows from a principle of intuition, and it is in vain to look for evidence beyond it. We have an irresistible belief in our identity as long as we think of the present and the past.”

In correspondence, then, with this view, I shall consider mental consciousness as that intellectual feeling of the mind suggested+ by a succession of sensations and renovated feelings, whereby it acquires a notion of the present and of the past, and of one and the same

* Dr Brown, in his Physiology of the Human Mind, likewise remarks, that," in accordance with the belief in our identity, we use the personal pronoun I to express the whole series of these feelings to one self as the permanent subject of them."

I

This is a very appropriate word employed by Dr Brown. am sorry, however, that a difference of views on certain subjects will not always allow me to apply the term in the exact sense in which this eminent author meant it should be used.