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faint the conception is which we form of anything, with our eyes open, in comparison of what we can form with our eyes shut: and that in proportion as we can suspend the exercise of all our other senses, the liveliness of our conception increases. To this cause is to be ascribed, in part, the effect which the dread of spirits in the dark has on some persons, who are fully convinced in speculation that their apprehensions are groundless; and to this also is owing, the effect of any accidental perception in giving them a momentary relief from their terrors. Hence the remedy which nature points out to us, when we find ourselves overpowered by imagination. If everything around us be silent, we endeavor to create a noise by speaking aloud, or beating with our feet; that is, we strive to divert the attention from the subjects of our imagination, by presenting an object to our powers of perception. The conclusion which I draw from these observations is, that as there is no state of the body in which our perceptive powers are so totally unemployed as in sleep, it is natural to think that the objects which we conceive or imagine, must then make an impression on the mind beyond comparison greater than anything of which we can have experience while awake.

From these principles may be derived a simple, and, I think, a satisfactory explanation of what some writers have represented as the most mysterious of all the circumstances connected with dreaming; the inaccurate estimates we are apt to form of time, while we are thus employed ;-an inaccuracy which sometimes extends so far as to give to a single instant the appearance of hours, or perhaps of days. A sudden noise for example, suggests a dream connected with that perception; and, the moment afterwards, this noise has the effect of awaking us ; and yet, during that momentary interval, a long series of circumstances has passed before the imagination. The story quoted by Mr. Addison (Spectator, No. 94.) from the Turkish Tales, of the miracle wrought by a Mahometan doctor, to convince an infidel sultan, is in such cases, nearly verified.

The facts I allude to at present are generally explained by supposing, that, in our dreams, the rapidity of thought is greater than while we are awake: but there is no necessity for having recourse to such a supposition. The rapidity of thought is, at all times, such, that in the twinkling of an eye a crowd of ideas may pass before us, to which it would require a long discourse to give utterance: and transactions may be conceived, which it would require days to realize. But, in sleep, the conceptions of the mind are mistaken for realities; and therefore our estimates of time wiil be formed, not according to our experience of the rapidity of thought, but according to our experience of the time requisite for realizing what we conceive. Something perfectly analogous to this may be remarked in the perceptions we obtain by the sense of sight. When I look into a show-box, where the deception is imperfect, I see only a set of paltry daubings of a few inches diameter; but, if the representation be executed with so much skill, as to convey to me the idea of a distant prospect, every object before me swells in its dimensions, in proportion to the extent of space which I conceive it to occupy; and what seemed before to Le shut up within the limits of a small wooden frame, is magnified, in my apprehension, to an immense landscape of woods, rivers, and mountains.

The phenomena which we have hitherto explained, take place when sleep seems to be complete; that is, when the mind loses its influence over all those powers whose exercise depends on its will. There are, however, many cases in which sleep seems to be partial; that is, when the mind loses its influence over some powers, and retains it over others. In the case of the somnambuli, it retains its power over the limbs, but it possesses no influence over its own thoughts, and scarcely any over the body; excepting those particular members of it which are employed in walking. In madness, the power of the will over the body remains undiminished, while its influence in regulating the train of thought is in a great measure suspended ; either in consequence of a particular idea, which engrosses the attention, to the exclusion of everything else, and which we find it impossible to banish by our efforts; or in consequence of our thoughts succeeding each other with such rapidity, that we are unable to stop the train. In both of these kinds of madness, it is worthy of remark that the conceptions or imaginations of the mind becoming independent of our will, they are apt to be mistaken for actual perceptions, and to affect us in the same manner.

By means of this supposition of a partial sleep, any apparent exceptions which the history of dreams may afford to the general principles already stated, admit of an easy explanation.

Upon reviewing the foregoing observations, it does not occur to me that I have in any instance transgressed those rules of philosophizing which, since the time of Newton, are commonly appealed to, as the tests of sound investigation. For, in the first place, I have not supposed any causes which are not known to exist; and secondly, I have shown, that the phenomena under our consideration are necessary consequences of the causes to which I have referred them. I have not supposed that the mind acquires in sleep any new faculty of which we are not conscious while awake: but only (what we know to be a fact) that it retains some of its powers, while the exercise of others is suspended ; and I have deduced synthetically the known phenomena of dreaming, from the operation of a particular class of our faculties, uncorrected by the operation of another. I flatter myself, therefore, that this inquiry will not only throw some light on the state of the mind in sleep; but that it will have a tendency to illustrate the mutual adaptation and subserviency which exists among the different parts of our constitution, when we are in complete possession of all the faculties and principles which belong to our nature.*

* The foregoing observations on the state of the mind in sleep, and on the phe. nomena of dreaming, were written as long ago as the year 1772; and were read, nearly in the form in which they are now published, in the year 1773, in a private literary society in this university. A considerable number of years afterwards, at the time when I was occupied with very different pursuits, I happened, in turning over an old volume of the Scots Magazine, (the volume for the year, 1749,) to ineet with a short essay on the same subject, which surprised me by its coincidence with some ideas which had formerly occurred to me. I have reason to believe that this essay is very little known, as I have never seen it referred to by any of the numerous writers who have since treated of the human mind; nor have even heard it once mentioned in conversation. I had some time ago the satisfaction to learn accidentally, that the author was Mr. Thomas Melville, a gentleman who died at the early age of twenty seven ; and whose ingenious observations on light and colors (published in the essays of the Edinburgh Philosophical Society,) are well known over Europe.

The passages which coincide the most remarkably with the doctrine I have stated, are the following. I quote the first with particular pleasure, on account of the support which it gives to an opinion which I formerly proposed in the essay on conception, and on which I have the misfortune to differ from some of my friends.

“ When I am walking up the High-street of Edinburgh, the objects which strike my eyes and ears give me an idea of their presence; and this idea is lively, full, and permanent, as arising from the continued operation of light and sound on the organs of sense.

“ Again, when I am absent from Edinburgh, but conceiving or imagining myself to walk up the High-street, in relating, perhaps, what befel me on such an occasion, I have likewise in my mind an idea of what is usually seen and heard in the High-street; and this idea of imagination is entirely similar to those of sen. sation, though not so strong and durable.

“ In this last instance, while the imagination lasts, be it ever so short, it is evident that I think myself in the street of Edinburgh, as truly as when I dream I am there, or even when I see and feel I am there. It is true, we cannot so well apply the word belief in this case ; because the perception is not clear or steady, being ever disturbed, and soon dissipated, by the superior strength of intruding sensation : yet nothing can be more absurd than to say, that a man may, in the same individual instani, believe he is in one place, and imagine he is in another. No man can demonstrate that the objects of sense exist without him; we are conscious of nothing but our own sensations: however, by the uniformity, regularity, consistency, and steadiness of the impression, we are led to believe, that they have a real and durable cause without us; and we observe not anything which contradicts this opinion. But the ideas of imagination, being transient and fleeting, can beget no such opinion, or habitual belief; though there is as much perceived in this case as in the former, namely, an idea of the object within the mind. It will be easily understood, that all this is intended to obviate an objection that might be brought against the similarity of dreaming and imagination, from our believing in sleep that all is real. But there is one fact, that plainly sets them both on a parallel, that in sleep we often recollect that the scenes which we behold are a mere dream, in the same manner as a person awake is habitually convinced that the representations of his imagination are fictitious."

“ In this essay we make no inquiry into the state of the body in sleep.

If the operations of the mind in sleep can be fairly deduced from the same causes as its operations when awake, we are certainly advanced one considerable step, though the causes of these latter should be still unknown. The doctrine of gravitation, which is the most wonderful and extensive discovery in the whole compass of human science, leaves the descent of heavy bodies as great a mystery as ever. In philosophy, as in geometry, the whole art of investigation lies in reducing things that are difficult, intricate, and remote, to what is simpler and easier of access, by pursuing and extending the analogies of nature.”

On looking over the same essay, I find an observation which I stated as my own in page 95 of this work. “The mere imagination of a tender scene in a romance, or drama, will draw tears from the eyes of those who know very well, when they

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Of the In fiuence of Casual Associations on our Speculative

Conclusions. The Association of ideas has a tendency to warp our speculative opinions chiefly in the three following ways:

recollect themselves, that the whole is fictitious. In the mean time they must conceive it as real; and from this supposed reality arises all its influence on the human mind”

Soon after the publication of the first edition of this work, a difficulty was started to me with respect to my conclusions concerning the state of the mind in sleep by my excellent friend M Prévost, of Geneva; a gentleman who has long held a high rank in the republic of letters, and to whose valuable correspondence I have ofien been indebted for much pleasure and instruction. The same difficulty was proposed to me, nearly about the same time, by another friend, then at a very early period of life, who has since honorably distinguished himself by his observations on Dr. Darwin's Zoonomia; the first fruits of a philosophical genius, which, I trust, is destined for yet more important undertakings.*

As M. Prevost has, in the present instance, kindly aided me in the task of removing his own objection, I shall take the liberty to borrow his words:

“ Sans l'action de la volonté point d'effort d'attention. Sans quelque effort d'attention point de souvenir. Dans le sommeil, l'action de la volonté est suspendue. Comment donc reste-t-il quelque souvenir des son ges?"

“ Je vois bien deux ou trois réponses à cette difficulté. Quant à présent, elles se réduissent à dire, ou que dans un sommeil parfait, il n'y a nul souvenir, et que là où il y a souvenir, le sommeil n'étoit pas parfait; ou que l'action de la volonté qui suffit pour le souvenir n'est pas suspendue dans le sommeil; que ce degré d'activité reste à l'âme ; que ce n'est, pour ainsi dire, qu'une volonté élémentaire et comme insensible."

I am abundantly sensible of the force of this objection ; and am far from being satisfied, that it is in my power to reconcile completely the apparent inconsistency. The general conclusions, at the same time, to which I have been led, seem to result so necessarily from the facts I have stated, that even although the difficulty in question should remain for the present unsolved, it would not, in my opinion, materially affect the evidence on which they rest. In all our inquiries, it is of consequence to remember, that when we have onee arrived at a general principle by a careful induction, we are not entitled to reject it, because we may find ourselves unable to explain from it, synthetically, all the phenomena in which it is concerned. The Newtonian theory of the tides is not the less certain, that some apparent exceptions occur to it, of which it is not easy (in consequence of our imperfect knowledge of the local circumstances by which, in particular cases, the effect is modified) to give a satisfactory explanation.

Of the solutions suggested by Mr. Prévost, the first coincides most nearly with my own opinion; and it approaches to what I have hinted (in page 209 of this work) concerning the seeming exceptions to my doctrine, which may occur in those cases where sleep is partial. A strong confirmation of it, undoubtedly, may be derived from the experience of those persons (several of whom I have happened to meet with) who never recollect to have dreamed, excepting when the soundness of their sleep was disturbed by some derangement in their general health, or by some accident which excited a bodily sensation.

Another solution of the difficulty might perhaps be derived from the facts

Observations on the Zoonomia of Dr. Darwin. By Thomas Brown, Esq. Edinburgh, 1798.

First, by blending together in our apprehensions things which are really distinct in their nature; so as to introduce perplexity and error into every process of reasoning in which they are involved.

(stated in pp. 68, 69 of this volume) which prove, “that a perception or an idea, - which passes through the mind, without leaving any trace in the memory, may yet serve to introduce other ideas connected with it by the laws of association."

From this principle it follows, that if any one of the more remarkable circumstances in a dream should recur to us after we awake, it might (without our exerting during sleep that attention which is essential to memory) revive the same concatenation of particulars with which it was formerly accompanied. And what is a dream, but such a concatenation of seeming events presenting itself to the imagination during our waking hours; the origin of which we learn by experience to refer to that interval which is employed in sleep; finding it impossible to connect it with any specified time or place in our past history? One thing is certain, that we cannot, by any direct acts of recollection, recover the train of our sleeping thoughts, as we can, in an evening, review the meditations of the preceding day.

Another cause, it must be owned, presents an obstacle to such efforts of recollection; and is, perhaps, adequate of itself to explain the fact. During the day, we have many aids to memory which are wanting in sleep (those, in particular, which are furnished by the objects of our external senses;) and of these aids we never fail to avail ourselves, in attempting to recollect the thoughts in which the day has been spent. We consider, in what place we were at a particular time, and what persons and things we there saw; endeavoring thus to lay hold of our intellectual processes, by means of the sensible objects with which they were associated ; and yet, with all these advantages, the account which most men are able to give of their meditations at the close of a long summer's day, will not be found to require many sentences. As in sleep, our communication with the external world is completely interrupted, it is not surprising, that the memory of our dreams should be much more imperfect than that of our waking thoughts; even supposing us to bestow, at the moment, an equal degree of attention on both.

It is of more importance to remark, in the present argument, that those persons who are subject to somnambulism, seldom, if ever, retain any recollection of the objects of their perceptions, while under the influence of this disorder. If the principles I have endeavored to establish be just, this is a necessary consequence of their inattention to what then passes around them; an inattention of which nobody can doubt, who has had an opportunity of witnessing the vacant and unconscious stare which their eyes exhibit. The same fact illustrates strongly the suspension, during sleep, of those voluntary powers, to which the operations both of mind and body are at other times subjected.

These considerations derive additional evidence from a common remark, that idle people are most apt to dream, or, at least to recollect their dreams. The thoughts of the busy and of the studious are directed by their habitual occupations into a particular channel; and the spontaneous course of their ideas is checked, and turned aside, by the unremitted activity of their minds. In the heedless and dissipated, the thoughts wander carelessly from object to object, according to the obvious relations of resemblance and of analogy, or of vicinity in place and time. As these are the prevailing principles of association in sleep, the chances that the dreams of such men shall be again presented to them in the course of the following day, are infinitely multiplied.

Which of these solutions approaches most nearly to the real state of the fact, I do not presume to decide. I think it probable, that both of them are entitled to notice, in comparing the phenomena of dreaming with the general principles to which I have endeavored to refer them. In cases where our dreams are occasioned by bodily sensations, or by bodily indisposition, it may be expected that the disturbed state of our rest will prevent that total cessation of the power of attention, which takes place when sleep is profound and complete ; anil, in such instances, the attention which is given to our passing thoughts, may enable us afterwards to retrace them by an act of recollection. On the other hand, the more general fact unquestionably is, that at the moment of our awaking, the interval spent in sleep presents a total blank to the memory; and yet, it happens not unfrequently, that, at the distance of hours, some accidental circumstance occurring

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