DREAMS; those fancies or imaginations which occur to the minds of people when asleep.

The subject of dreaming hath been investigated by several philosophers, but hitherto with very little suc- cess.—Wolfius supposes that dreams take their rise en- tirely from the sensations; and that no dream arises in the human mind without a previous sensation, though perhaps such a slight one that it cannot easily be tra- ced. This hypothesis is expressly adopted by Mr For- ney, in an essay on dreams, in the Memoirs of the Academy of Sciences at Berlin.—Mr Baxter, in his treatise of the Immateriality of the human Soul, attri- butes dreams to the action of some immaterial beings upon our soul.—Lastly, some modern physiologists reckon dreaming to be a species of delirium. Their ac- count of the matter is as follows. The brain and nervous system, which are the only organs of sensation, are gen- erally in two states, exceedingly different from one ano- ther, which may be expressed by the words excitement and collapse. The first of these denotes that state in which the nervous system is easily made sensible of the impressions of external objects, and then we are said to be awake. The second is, when external objects do not easily make these impressions; and of this state there are various degrees; drowsiness, sleep, fainting, and death. These do not indeed proceed in the order in which we have placed them. Sleep is of a quite different nature from fainting, or from that stupor and insensibility produced by a compression of the brain. But, whatever be the nature of sleep, it is certain that this state is attended with what we call a collapse of the brain; as external objects do not make the same im- pressions on the organs of sense when people are asleep, that they do when awake. Between the two states of sleeping and waking, a state of delirium always occurs; and this is most probably occasioned by the excite- ment of one part of the brain, and the collapse of ano- ther.—That one part of the brain is capable of being excited, while the other suffers a collapse, will be evi- dent from considering what happens when we are just falling asleep. Every one must be sensible, that at that time we do not lose our senses all at once. The hear- ing will continue after the sight is lost; and, even while we are yet conscious of the place we are in, false ima- ginations of a nature similar to that of dreaming will occur to our minds. But when the brain is perfectly collapsed, sensation or imagination of every kind totally vanishes, and we are altogether unconscious of existence.

On a subject so obscure, and so much out of the reach of investigation, as that of dreaming, it is diffi- cult to advance anything satisfactory. All the above- mentioned hypotheses, however, seem to be exceed- ingly imperfect.—It may be granted Wolfius and Formey, that dreams will arise from certain impres- sions made either on the external or internal parts of the body. But these impressions by no means pro- duce any thing like the sensations we have from simi- lar ones made upon us while we are awake. Thus, if a person whose digestion is not very good, goes soon to bed after eating a large supper, it is not improbable that he will dream of being oppressed with a great weight, by a monster, being suffocated, &c. These dreams. dreams undoubtedly arise from the uneasy sensations produced in the stomach from too great a quantity of food; but if the person was awake, such sensations would produce only a sickness and uneasiness at stomach.

If dreams, therefore, in all cases, proceed from sensations, we must also say, that in sleep the laws of sensation itself are altered; that those connections which we look upon to be the most constant and invariable, are not so in reality; and thus we are led into a greater difficulty than before. For example, there is no sensation more invariable than that, when a man's stomach is oppressed, he should feel what we call sickness. This sensation happening in the time of sleep, according to Wolfius, produces a dream. Very true, it will do so; but why does not the man dream that he is sick? What connection is there between sickness, the waking sensation, and being oppressed by a weight, suffocated by a monster, &c., the sleeping ones?—This difficulty seems insurmountable on the hypothesis of Wolfius and Formey.

Mr Baxter's supposition is, in its very nature, incapable of proof. We are by no means ascertained of the existence of any immaterial beings, created ones at least, that can have access to our souls; and though we were, the ridiculous fancies that sometimes occur in dreams are too absurd to be supposed the work of any rational being; much less of those who possess an higher rank in the creation than ourselves.—It must also be observed, that the method which this author takes to prove his hypothesis can never be conclusive, even though every thing he contends for should be granted. He infers that the phantasm, or what is properly called the vision, in dreams, is not the work of the soul itself, and cannot be the effect of mechanical causes; therefore, according to him, it must be the effect of immaterial, or immaterial agents operating upon the soul.—That it is not the work of the soul itself, may readily be granted; and likewise that it is not the effect of such mechanical causes as we are acquainted with; but from thence it will not follow, that it must necessarily be the effect of immaterial causes, unless we were perfectly well acquainted with the extent of all mechanical powers whatever. Nay, in many instances, such as that above-mentioned, we are certain that dreams not only may be, but actually are, the effects of mechanical causes, though we should never be able to investigate them.

The third hypothesis seems also inadequate to solve the phenomena of dreaming. If this depended on a partial excitement of the brain, our ideas ought to be just, as far as that excitement could reach. Thus, supposing that part of the brain on which sight depends, to be quite collapsed; and that on which hearing depends, to be in some measure excited; the person, tho' deprived of sight, would hear sounds confusedly; but still they would only be such sounds as were actually produced by external objects; and no reason can be assigned why he should imagine he heard sounds which never existed.

Besides, in dreaming, it is very manifest, that the excitement of the brain is not partial, but false. No person in his dreams imagines himself deaf, dumb, or blind. He imagines that he sees, hears, walks, reasons; nay, sometimes that he sleeps and dreams; which a partial excitation of the brain can never account for.

Before any thing can be conjectured with probability concerning the phenomena of dreaming, it is necessary to investigate in some measure the nature of sleep.—On this subject it may be observed, that by whatever means sleep is produced, whether naturally by fatigue, artificially by compressing the brain, &c.; and however different these kinds of sleep may be from one another, one general effect still remains the same; namely, that the external senses are abolished, and the person becomes totally unconscious of whatever passes around him. From this general effect, which in all cases is constant and invariable, sleep may be defined, "a state in which all communication is cut off between our sentient principle and this visible world."—That the sentient and vital principle hath its residence in the brain, is an opinion which in all ages hath been deemed very probable. If the comparison can be allowed, it might here be said, that the brain, with regard to sensation, hath the same relation to the nerves, that a pond or reservoir of water hath to a number of small streams that flow into it and out from it.—In the brain there seems to be a kind of general repository of some part of those sensations we have formerly felt; but in what manner this repository is formed, we know not. Certain it is, that there the ideas are treasured up in such a manner as to be at times, and indeed most commonly, imperceptible to ourselves. Thus, there are many things we have done, many people we have been acquainted with, and many places we have been in, of which we are just now quite insensible, and will remain till some circumstance or other brings them to our remembrance. For example: Suppose a man has been intimately acquainted with two others who were companions, and lodged in the same house; he goes into another country, and being engaged in new pursuits, forgets both completely, that for a considerable time he hath perhaps never thought of them at all. But if he should unexpectedly meet with one of these friends in the street, he will instantly remember the other who is at a distance; and this very circumstance will bring a train of thoughts into his mind, which produces the remembrance of many things that otherwise perhaps would never have been thought of. Now, if we consider what passes with regard to our own minds and intellectual faculties, we shall readily be convinced, that every thing we do remember, occurs only in consequence of some external circumstance. If a person gave us a slight offence yesterday, today perhaps we do not think of it, even though we see the person; but if he offends again, though in another manner, the offence of yesterday instantly occurs to our minds. A thousand other instances of the like kind might be adduced; so many indeed, that some have doubted whether we ever do forget any thing so completely that it could not be brought to our remembrance by a proper combination of external circumstances.

The only things we can think of, are the present and the past. When we think of what is to come, we must combine ideas from the present and the past. If, therefore, our memory depends on a certain combination of external circumstances immediately present to our view, it must necessarily follow, that the more a person is kept in perfect solitude, or removed from everything that can affect his senses, the more he will be inclined to sleep. And, indeed, as far as this experiment can be be tried, it will most commonly be found successful.

For, let a person who has slept his usual time through the night be put to bed at noon-day, in a dark room, where there is nothing either to amuse or disturb him, and he will almost certainly fall asleep in a short time. Hence it would seem, that by whatever means our sensations of what is present, or our external senses, are suspended; by the same, our memory must also be extinguished, and we become absolutely unconscious of existence, or fall asleep.

This state of the body, therefore, may be produced in three different ways. 1. By a removal of all such objects as by their appearance make a strong impression on the nervous system. 2. By compressing, or otherwise injuring the brain, so that the vital principle cannot receive the sensations from the nerves. 3. By injuring the extremities of the nerves in such a manner, that they cannot receive any sensation from the impression of external objects.

The first and the last of these are the common methods by which natural sleep is produced. But, before we can fully investigate our subject, another question remains to be discussed; namely, From whence are the sentient extremities of the nerves supplied with that fluid which is the immediate instrument of sensation?

Under the article Blood, it hath been shewn, that, in respiration, there is a certain quantity of a subtile fluid received from the air, which is absolutely necessary to life. Of this fluid there is undoubtedly a considerable waste somewhere or other; because respiration cannot be interrupted even for a very short time, without a total destruction of life. The arterial blood, which receives this subtile vivifying spirit, shews that it hath done so by its florid red colour, which distinguishes it from that of the veins. During the course of the circulation, that spirit, or whatever it is, which gives the arterial blood its florid colour, is dissipated, and the blood returned by the veins makes a quite different appearance. It would seem probable, therefore, that this very volatile part is absorbed by the nerves, which everywhere accompany the blood vessels.—If this is the case, we must easily see the reason why a state of sleep so readily follows immoderate fatigue, watching, &c.; namely, because these things occasion a constant drain of the vital principle from the blood, which at last becoming greater than the supply afforded by respiration, the blood becomes deprived of a part of that principle which ought to be retained in it, and which consequently cannot be bestowed on the nerves without great uneasiness and inconvenience. In such cases, therefore, unless the external impressions are very strong, the absorption of the vital principle by the nervous system will not go on; and the consequence of this must be, that the person will very soon fall asleep, for the reasons already given.—Hence we see, why anything that impedes the circulation also produces a tendency to sleep. Of this we have a remarkable instance in the effects of cold. The first symptom of death in those who are about to perish with cold, is a drowsiness, which soon increases to such a degree that it cannot be resisted. The person sits down, as he imagines, to take a short nap, but never awakes.—In the same way we may account for that kind of sleep called fainting, which usually follows excessive evacuations or fatigue of any kind. By these the circulation of the blood is disturbed, or perhaps its quantity lessened in such a manner, that the extreme parts of the nerves cannot receive a sufficient supply of vital fluid to enable them to perform their functions. The external senses therefore cease; and though former sensations remain in the memory, yet as no external circumstance can be perceived, which only can call the memory into action, a state of total insensibility generally ensues.

This hypothesis proceeds upon a principle somewhat different from those laid down by the generality of physiologists. Those who allow the nervous fluid to be secreted from the blood by the brain, generally suppose that it is sent out from thence to all parts of the body; but the idea that any quantity of the nervous or vital fluid is absorbed from the blood by the extremities of the nerves, seems not to have occurred. It is certain, however, that we have the same evidence of this absorption by the extremities of the nerves that there is of the secretion in the brain. The blood, on this supposition, contains the vital principle; but all the blood is not sent to the brain. The greater part of it is sent to other parts of the body. There doth not seem to be any essential difference between the blood brought back from the brain, and that returned by the veins from other parts of the body. Both of them have evidently suffered a loss of their most subtile part. In the first it is not disputed that the volatile part lost by the blood is received by the brain; but what becomes of that which is lost by the blood sent to all the other parts of the body? We can here give no other answer, than that in all probability it is taken up, by the extremities of the nerves, and supplies them with the powers necessary for sensation, and the regulation of the body. Hence we see the reason why depriving any part of the body, of the blood it contained, deprives it also of sensation; namely, because there is then no source whence the extremities of the nerves can be supplied with the sentient principle.

If what is now advanced can be admitted with any degree of probability, the explication of the phenomena of dreaming, as far as an explanation can reasonably be expected, will not be difficult. According to this hypothesis, as long as a certain motion is communicated, by the impression of external objects, from the sentient extremities of the nerves to the brain, so long we continue sensible of the existence of the objects around us, or are said to be awake. When, from a deficiency of the vital fluid in the extremities of the nerves, from a compression of the brain, or from any other cause, the above-mentioned motion ceases, we are insensible of our existence, and are said to be asleep. In sleep therefore the nervous fluid, which lies between the extreme parts of the nerves and the brain, is either deficient in quantity, or remains at rest, or its influx into the brain is interrupted. When we are awake, the communication is free, the fluid in sufficient quantity, and liable to be set in motion by every slight impulse. Of these impulses therefore we are sensible, and our sensations are uniform and regular. When external objects cease to be perceived, still the nerves contain a quantity of the fluid we have mentioned, and which is very easily set in motion. If irregular motions hap- pen in it from any internal cause, the consequence must be a multitude of confused and irregular sensations, which we call dreaming.

This may be illustrated by the following examples. There is no sense we exercise so much as that of sight; and it is the one of which we can most easily deprive ourselves at pleasure. By means of this sense every person has it in his power to dream when he pleases; and to do so, he needs only to shut his eyes. No person can shut his eyes even for a few moments, but he will be sensible of a great number of faint confused images presenting themselves before him; and these he cannot possibly remove, till he opens his eyes, or falls asleep altogether. It can scarcely be doubted, that these images are occasioned by the great mobility and subtlety of the fluid contained in the optic nerve. Though the regular motion produced in it by the impulse of the light ceases when the eye-lids are shut, yet an irregular one continues from some internal cause, and this motion occasions the confused sensation already mentioned. The appearance of such images we do not indeed in the present instance call dreams, because our other senses are awake; but if these individual sensations were to occur while we were asleep, undoubtedly they would be called by that name; and from what is already observed, they seem plainly to be of the same nature in both cases.

With regard to the other senses, it is not in our power to hinder the operation of external objects upon them, as we can do with our sight; but there is no reason to suppose that dreams might not be produced by them in the very same manner that they are by our faculty of vision, provided we could as easily suspend the operation of external objects upon them.—We have an evidence of the truth of this supposition in the case of fainting; which is generally preceded by a noise in the ears. In many diseases also, particularly nervous ones, the tinnitus aurium, or noise in the ears, is a very troublesome symptom.

The sense of feeling is less liable to deception while we are awake than any of the rest; nevertheless there is one case which may be referred to that of dreaming, and which has been very often taken notice of. It is an imagination common to people who have lost a limb, that they still feel a pain in it, though many years after it has been separated from their body. If this imagination occurred only in the time of sleep, we would have no hesitation in calling it a dream; but as it occurs while the persons are awake, it hath been explained without thinking of any connection between it and the phenomenon of dreaming. It is certain, however, that whatever explains the one, will explain the other also. In the case of the amputated limb, the sensation arises from some injury offered to the nerve which had formerly gone to that limb. This produces a certain motion in the nervous fluid, that is propagated along the nerves to the brain, upon which the imagination that the limb still remains immediately takes place. In like manner, if, during the time of sleep, a similar motion shall occur, a similar imagination or dream will be the consequence.—It must be observed, however, that, in dreaming, our sense of feeling is much more obscure than those of seeing and hearing. We dream that we see objects and hear sounds pretty distinctly; while we scarce feel any thing we imagine ourselves to touch, or carry in our hands; and as for the senses of taste and smell, they are scarce ever exercised in dreaming.

Dreams have in all ages been reckoned by the vulgar to have something portentous in them, and to presage future events. Indeed, there are few things about which the superstition of mankind hath more exercised itself than the interpretation of dreams. If the abovementioned solution of this phenomenon is allowed, it may readily be granted, that dreams may presage diseases, or changes of the weather, because the nervous system is very apt to be influenced by alterations in our atmosphere; and no alteration in our health can possibly take place without producing some change in the nervous system. But how they can presage events entirely unconnected with our bodies, doth not appear; or rather it appears very plain that naturally they cannot; though the sacred writers give us many instances of the knowledge of future events being conveyed to mankind in dreams, by a supernatural influence. From the solution of this phenomenon we have just now given, it appears, how imaginations resembling dreams may occur as well when we are awake as when we are asleep; and that they actually do so, we have many melancholy instances in hypochondriac and mad people.