DREAMS are all those thoughts which pass through the mind, and those imaginary transactions in which we often fancy ourselves engaged when in the state of sleep. Scarcely any part of nature is less open to our observation than the human mind in this state. The dreamer himself cannot well observe the manner in which dreams arise or disappear in his own mind. When he awakes, he cannot recollect the circumstances of his dreams with sufficient accuracy. Were we to watch over him with the most vigilant attention, we could not perceive with certainty what emotions were excited in his mind, or what thoughts passed through it, during his sleep. But though we could ascertain these phenomena, many other difficulties would still remain. What parts of a human being are active, and what dormant, when he dreams? Why does he not always dream while asleep? Or why dreams he at all? Do any circumstances in our constitution, situation, and peculiar character, determine the nature of our dreams?

In treating of this subject, we shall endeavour to lay before our readers such facts as have been ascertained concerning dreaming, together with the most plausible conjectures which have been offered to explain the phenomena of dreams.

In dreaming we are not conscious of being asleep. This is well known from a great variety of circumstances. When awake, we often recollect our dreams; and we remember, on such occasions, that whilst those dreams were passing through our minds, it never occurred to us that we were separated by sleep from the active world. Persons are often observed to act and talk in dreaming as if they were busily engaged in the intercourse of social life.

In dreaming we do not consider ourselves as witnessing or bearing a part in a fictitious scene. We seem not to be in a similar situation with the actors in a dramatic performance, or the spectators before whom they exhibit, but engaged in the business of real life. All the varieties of thought that pass through our minds when awake may also occur in dreams; all the images which imagination presents in the former state may be called up in the latter; the same emotions may be excited, and we are often actuated by equal violence of passion; none of the transactions in which we are capable of engaging whilst awake is impossible in dreams; in short, our range of action and observation is as wide in the one state as in the other; and whilst dreaming, we are not sensible of any distinction between our dreams and the events and transactions in which we are actually concerned in our intercourse with the world.

It is said that all men are not liable to dream. Dr Beattie, in a very pleasing essay on this subject, relates that he knew a gentleman who never dreamed except when his health was in a disordered state; and Locke mentions that a certain person of his acquaintance was almost a stranger to dreaming until the twenty-sixth year of his age, when he began to dream in consequence of having had a fever. These instances, however, are too few, and we have not been able to obtain more; and, besides, it does not appear that those persons had always attended, with the care of a philosopher making an experiment, to the circumstances of their sleep. They might dream, but not recollect their dreams on waking; and they might both dream and recollect their dreams immediately upon awaking, yet afterwards suffer the remembrance of them to slip out of their memory. We do not advance this, therefore, as a certain fact concerning dreaming; we are rather inclined to consider it as a mistake. But though it appears to be by no means certain that any of the human race are throughout the whole of life absolute strangers to dreaming; yet it is well known that all men are not equally liable to dream. The same person dreams more or less at different times; and as one person may be more exposed than another to those circumstances which promote this exercise of fancy, one person may therefore dream more than another. The same diversity will naturally take place in this as in other accidents to which mankind are in general liable.

Though in dreams imagination appears to be free from all restraint, and indulges in the most wanton freaks, yet it is generally agreed that the imaginary transactions of the dreamer bear always some relation to his particular character in the world, his habits of action, and the circumstances of his life. The lover, we are told, dreams of his mistress, the miser of his money; the philosopher reviews his researches in sleep often with the same pain and fatigue as when awake; and even the merchant at times returns to balance his books, and computes the profits of an adventure, when slumbering on his pillow. And not only do the more general circumstances of a person's life influence one's dreams; the passions and habits are nearly the same when asleep as when awake. A person whose habits of life are virtuous, does not in his dreams plunge into a series of crimes; nor are the vicious reformed when they pass into this imaginary world. The choleric man finds himself offended by slight provocations in his dreams as well as in his ordinary intercourse with the world; and a mild temper continues pacific even in sleep.

The character of a person's dreams is influenced by his circumstances when awake in a still more unaccountable manner. Certain dreams usually arise in the mind after a person has been in certain situations. Dr Beattie relates that once, after riding thirty miles in a high wind, he passed a part of the succeeding night in dreams beyond description terrible. The state of a person's health, and the manner in which the vital functions are carried on, have a considerable influence in determining the character of dreams. After too full a meal, or after eating of an unusual sort of food, a person is very apt to be harassed with uncomfortable dreams.

In dreaming, the mind for the most part carries on no intercourse through the senses with surrounding objects. Touch a person gently who is asleep, and he feels not the impression. You may awake him by a smart blow; but when the stroke is not sufficiently violent to awake him, he remains insensible of it. We speak softly beside a person asleep, without fearing that he will overhear us. His eyelids are shut; and even though light should fall upon the eyeball, yet still his powers of vision are not awakened to active exertion, unless the light be strong enough to rouse him from sleep. He is insensible both to sweet and to disagreeable smells. It is not easy to try whether his organs of taste retain their activity, without awakening him; yet from analogy it may be presumed that these too are inactive. With respect to the circumstances here enumerated, it is indifferent whether a person be dreaming or buried in deep sleep.

Yet there is one remarkable fact concerning dreaming, which may appear contradictory of what has been here asserted. In dreams we are liable not only to speak aloud in consequence of the suggestions of imagination, but even to get up and walk about, and engage in little enterprises, without awaking. Now, as we are in this instance so active, it seems that we cannot be then insensible of the presence of surrounding objects. The sleep-walker is really sensible in a certain degree of the presence of the objects around him; but he does not attend to them with all their circumstances, nor do they excite in him the same sensations as if he were awake. He feels no terror on the brink of a precipice, and in consequence of being free from fear, he is also without danger in such a situation, unless suddenly awaked. This is one of the most inexplicable phenomena of dreaming.

There is also another fact not quite consonant with what has been above mentioned. It is said that in sleep a person will continue to hear the noise of a cataract in the neighbourhood, or regular strokes with a hammer, or any similar sound sufficiently loud, and continued uninterruptedly from before the time of his falling asleep. We know not whether he awakes on the sudden cessation of the noise; but the fact is asserted, on apparently sufficient evidence, and it is curious. Even when awake, if very deeply intent on any piece of study, or closely occupied in business, the sound of a clock striking in the neighbourhood, or the beating of a drum, will escape us unnoticed; and it is therefore the more surprising that we should thus continue sensible to sounds when asleep.

Not only do a person's general character, habits of life, and state of health, influence his dreams; but those concerns in which he has been most deeply interested during the preceding day, and the views which have arisen most frequently to his imagination, very often afford the subjects of his dreams. When we look forward with anxious expectation towards any future event, we are likely to dream either of the disappointment or the gratification of our wishes. If we have been engaged throughout the day either in business or amusements which we have found exceedingly agreeable, or in a way in which we have been extremely unhappy, either our happiness or our misery is likely to be renewed in our dreams.

Though dreams have been regarded amongst almost all nations of the world, at some periods of their history, as prophetic of future events, yet it does not appear that this popular opinion has ever been established on any good grounds. Christianity, indeed, teaches us to believe that the Supreme Being may, and actually does, operate on our minds, and influence at times the determinations of our will, without making us sensible of the restraint to which we are thus subjected; and, in the same manner, no doubt, the suggestions which arise to us in dreams may be produced. The imaginary transactions in which we are then engaged may be such as are actually to occupy us in life; the strange and seemingly incoherent appearances which are presented to the mind's eye in our dreams, may allude to some events which are to befall ourselves or others. It is therefore by no means impossible, or inconsistent with the general analogy of nature, that dreams should have a respect to futurity. We have no reason to regard the dreams related in the Holy Scriptures as not inspired by Heaven, nor to laugh at the idea of a prophetic dream as absurd or ridiculous. At the same time, a mind which, during its waking hours, is filled with anxious thoughts and presentiments of the future, may reproduce these forebodings in its dreams, when the imagination acts over again the scenes of the past day, embellished and diversified with its own peculiar colouring; and as, from the mere law of probabilities, the actual result must sometimes correspond with the anticipative vision; and the dream be realised by the event, the apparent prophetic intimation is thus as much the consequence of natural causes and of the ordinary workings of the mind, as any of the phenomena which it exhibits. To accident alone is to be ascribed that correspondence which, among the uneducated or the unreflecting portion of mankind, passes for divination by means of supernatural agency; and though the cases where it occurs are necessarily few, compared with those in which the event falsifies the prognostications of the dreamer, yet being calculated to make a much stronger impression on the mind, they are remembered, whilst the others are forgotten; and hence the exception is, by a natural transition, converted into the rule.

Yet it would be too much to allow to dreams all that importance which has been ascribed to them by the priesthood among heathens, or by the vulgar among ourselves. We know how easily ignorance imposes on itself, and what arts imposture adopts to impose upon others. We cannot trace any certain connection between our dreams and those events to which the simplicity of the vulgar pretends that they refer. And we cannot, therefore, if disposed to confine our belief to certain or probable truths, join with the vulgar in believing them really referrible to futurity.

It appears that the brutes are also capable of dreaming. The dog is often observed to start suddenly up in his sleep, in a manner which cannot be accounted for in any other way than by supposing that he is roused by some impulse received in a dream. The same thing is observable of others of the inferior animals. That they should dream, is not an idea inconsistent with what we know of their economy and manners in general. We may therefore consider it as a pretty certain truth, that many, if not all, of the lower species are liable to dream, as well as human beings.

It appears, then, that in dreaming we are not conscious of being asleep; that to a person dreaming, his dreams seem realities; that although it be uncertain whether mankind are all liable to dream, yet it is well known that they are not all equally liable to dream; that the nature of a person's dreams depends in some measure on his habits of action, and on the circumstances of his life; that the state of the health, too, and the manner in which the vital functions are carried on, have a powerful influence in determining the character of a person's dreams; that in sleep and in dreaming, the senses are either absolutely inactive, or nearly so; that such concerns as we have been very deeply interested in during the preceding day, are very likely to return upon our minds in dreams in the hours of rest; that dreams may be rendered prophetic of future events; that therefore, wherever we have such evidence of their having been prophetic as we would accept on any other occasion, we cannot reasonably reject the fact on account of its absurdity; that, however, they do not appear to have been actually such, in those instances in which the superstition of nations ignorant of true religion has represented them as referring to futurity, nor in those instances in which they are viewed in the same light by the vulgar among ourselves; and, lastly, that dreaming is not a phenomenon peculiar to human nature, but common to mankind with the brutes.

We scarcely know of any other facts that have been fully ascertained concerning dreaming. But we are by no means sufficiently acquainted with this important phenomenon in the history of mind. We cannot tell by what laws of our constitution we are thus liable to be so frequently engaged in imaginary transactions, nor what are the particular means by which the delusion is accomplished. The delusion is indeed remarkably strong. One will sometimes have a book presented to him in a dream, and fancy that he reads; and actually enter into the nature of the imaginary composition before him, and even remember, after he awakes, what he knows that he only fancied himself reading. Can this be delusion? If delusion, how or for what purposes is it produced? The mind, it would appear, does not, in sleep, become inactive like the body, or at least is not always inactive while we are asleep. When we do not dream, the mind must either be inactive, or the connection between the mind and the body. Dreams must be considered as in some manner suspended; and, when we dream, the mind, though it probably acts in concert with the body, yet does not act in the same manner as when we are awake. It seems to be clouded or bewildered, in consequence of being deprived for a time of the service of the senses. Imagination becomes more active and more capricious; and all the other powers, especially judgment and memory, get disordered and irregular in their operation.

Various theories have been proposed to explain what appears here most inexplicable. Mr Baxter, in his treatise on the immateriality of the human soul, endeavours to prove that dreams are produced by the agency of some spiritual beings, who either amuse or employ themselves seriously in engaging mankind in all those imaginary transactions with which they are employed in dreaming. This theory, however, is far from being plausible. It leads us entirely beyond the limits of our knowledge; it requires us to believe without evidence; it is unsupported by any analogy; and it creates difficulties still more inexplicable than those which it has been proposed to remove. Until it be made to appear that our dreams cannot possibly be produced without the interference of spiritual agents, possessing such influence over our minds as to deceive us with fancied joys, and to involve us in imaginary afflictions, we cannot reasonably refer them to such a cause. Besides, from the facts which have been stated as well known concerning dreams, it appears that their nature depends both on the state of the human body and on that of the mind. But were they owing to the agency of other spiritual beings, how could they be influenced by the state of the body with reference to health or sickness, fasting or repletion? They must be a curious set of spiritual beings who depend in such a manner on the state of our corporeal frame. Better not to allow them existence at all, than to place them in such a dependence.

Wolffius, and after him Formey, have supposed that dreams never arise in the mind, except in consequence of some of the organs of sensation having been previously excited. Either the ear or the eye, or the organs of touching, tasting, or smelling, communicate information in a tacit and secret manner, and thus partly rouse its faculties from the lethargy in which they are buried in sleep, and engage them in a series of confused and imperfect exertions. But what passes in dreams is so very different from all that we do when awake, that it is impossible for the dreamer himself to distinguish whether his powers of sensation perform any part on the occasion. It is not necessary that imagination should be always excited by immediate sensation. Fancy, even when we are awake, often wanders from the present scene. Absence of mind is incident to the studious; the poet and the mathematician many times forget where they are. We cannot discover from any thing that a person in dreaming displays to the observation of others, that his organs of sensation take part in the imaginary transactions in which he is employed. In those instances, indeed, in which persons asleep are said to hear sounds, the sounds which they hear are said also to influence in some manner the nature of their dreams. But such instances are singular. Since then it appears that the person who dreams is himself incapable of distinguishing, either during his dreams, or by recollection when awake, whether any new impressions are communicated to him in that state by his organs of sensation; that even by watching over him, and comparing our observations of his circumstances and emotions in his dreams with what he recollects of them after awaking, we cannot, except in one or two singular instances, ascertain this fact; and that the mind is not wholly incapable of acting while the organs of sensation are at rest, and on many occasions refuses to listen to the information which they convey; we may without hesitation conclude that the theory of Wolffius and Formey has been too hastily and incautiously advanced.

Other physiologists tell us that the mind when we dream is in a state of delirium. Sleep, they say, is attended with what is called a collapse of the brain; during which either the whole or a part of the nerves of which it consists are in a state in which they cannot carry on the usual intercourse between the mind and the organs of sensation. When the whole of the brain is in this state, we become entirely unconscious of existence, and the mind sinks into inactivity; when only a part of the brain is collapsed, as they term it, we are then neither asleep nor awake, but in a sort of delirium between the two. This theory, like that last mentioned, supposes the mind incapable of acting without the help of sensation; it supposes that we know the nature of a state of which we cannot ascertain the phenomena; and it contradicts a well-known fact, in representing dreams as confused images of things around us, instead of fanciful combinations of things not existing together in nature or in human life. For these reasons it must be held as wholly inadmissible.

Of all the writers who have treated of this subject, however, Mr Dugald Stewart is perhaps the only one who, by concentrating the lights of a sound philosophy on the results of refined and accurate observation, has been enabled to classify the phenomena of dreams, and to introduce the order of science into a department of speculative inquiry where fancy had previously reigned paramount. "Dreams," says Mr Addison, "look like the relaxations and amusements of the soul when she is disencumbered of her machine; her sports and recreations when she has laid her charge asleep. The soul is clogged and retarded in her operations when she acts in conjunction with a companion that is so heavy and unwieldy in its motions; but in dreams she converses with numberless beings of her own creation, and is transported into ten thousand scenes of her own raising. She is herself the theatre, the actor, and the beholder." This description, which is not more beautiful than true, will serve to convey some idea of the difficulties of disentangling mental operations necessarily so complex, and of keeping steadily in view the threefold character or agency which the mind exhibits in dreaming; and as the only approximation which has yet been made towards the accomplishment of so interesting an object is contained in Mr Stewart's section on the application of the principles and laws of association to explain the phenomena of dreaming (Elements of the Philosophy of the Human Mind, vol. i. p. 327, sixth edition, Lond. 1818, 8vo), we conceive that we cannot do better than subjoin this exquisite specimen of philosophical acuteness and discrimination, in the author's own beautiful language.

"With respect to the phenomena of dreaming," says Mr Stewart, "three different questions may be proposed. First, what is the state of the mind in sleep? or, in other words, what faculties then continue to operate, and what faculties are then suspended? Secondly, how far do our dreams appear to be influenced by our bodily sensations; and in what respects do they vary, according to the different conditions of the body in health and in sickness? Thirdly, what is the change which sleep produces on those parts of the body with which our mental operations are more immediately connected; and how does this change operate, in diversifying, so remarkably, the phenomena which our minds then exhibit, from those of which we are conscious in our waking hours? Of these three questions, the first belongs to the philosophy of the human mind; and it is to this question that the following inquiry is almost entirely confined. The second is more particu- It will be granted, that, if we could ascertain the state of the mind in sleep, so as to be able to resolve the various phenomena of dreaming into a smaller number of general principles; and still more, if we could resolve them into one general fact; we should be advanced a very important step in our inquiries upon this subject; even although we should find it impossible to show in what manner this change in the state of the mind results from the change which sleep produces in the state of the body. Such a step would at least gratify, to a certain extent, that disposition of our nature which prompts us to ascend from particular facts to general laws, and which is the foundation of all our philosophical researches; and, in the present instance, I am inclined to think that it carries us as far as our imperfect faculties enable us to proceed.

In conducting this inquiry with respect to the state of the mind in sleep, it seems reasonable to expect, that some light may be obtained from an examination of the circumstances which accelerate or retard its approach; for when we are disposed to rest, it is natural to imagine that the state of the mind approaches to its state in sleep more nearly than when we feel ourselves alive and active, and capable of applying all our various faculties to their proper purposes.

In general, it may be remarked, that the approach of sleep is accelerated by every circumstance which diminishes or suspends the exercise of the mental powers, and is retarded by every thing which has a contrary tendency. When we wish for sleep, we naturally endeavour to withhold, as much as possible, all the active exertions of the mind, by disengaging our attention from every interesting subject of thought. When we are disposed to keep awake, we naturally fix our attention on some subject which is calculated to afford employment to our intellectual powers, or to rouse and exercise the active principles of our nature.

It is well known that there is a particular class of sounds which compose us to sleep. The hum of bees, the murmur of a fountain, the reading of an uninteresting discourse, have this tendency in a remarkable degree. If we examine this class of sounds, we shall find that it consists wholly of such as are fitted to withdraw the attention of the mind from its own thoughts; and are, at the same time, not sufficiently interesting to engage its attention to themselves.

It is also matter of common observation, that children, and persons of little reflexion, who are chiefly occupied about sensible objects, and whose mental activity is in a great measure suspended as soon as their perceptive powers are unemployed, find it extremely difficult to continue awake when they are deprived of their usual engagements. The same thing has been remarked of savages, whose time, like that of the lower animals, is almost completely divided between sleep and their bodily exertions.

From a consideration of these facts, it seems reasonable to conclude, that in sleep those operations of the mind are suspended which depend on our volition; for if it be certain, that before we fall asleep, we must withhold, as much as we are able, the exercise of all our different powers, it is scarcely to be imagined that, as soon as sleep commences, these powers should again begin to be exerted. The more probable conclusion is, that when we are desirous to procure sleep, we bring both mind and body as nearly as we can into that state in which they are to continue after sleep commences. The difference, therefore, between the state of mind when we are inviting sleep, and when we are actually asleep, is this, that in the former case, although its active exertions be suspended, we can renew them if we please. In the other case, the will loses its influence over all our powers both of mind and body, in consequence of some physical alteration in the system, which we shall never probably be able to explain.

In order to illustrate this conclusion a little farther, it may be proper to remark, that if the suspension of our voluntary operations in sleep be admitted as a fact, there are only two suppositions which can be formed concerning its cause. The one is, that the power of volition is suspended; the other, that the will loses its influence over those faculties of the mind, and those members of the body, which, during our waking hours, are subjected to its authority. If it can be shown then that the former supposition is not agreeable to fact, the truth of the latter seems to follow as a necessary consequence.

1. That the power of volition is not suspended during sleep, appears from the efforts which we are conscious of making while in that situation. We dream, for example, that we are in danger, and we attempt to call out for assistance. The attempt indeed is in general unsuccessful, and the sounds which we emit are feeble and indistinct; but this only confirms, or rather is a necessary consequence of the supposition that, in sleep, the connexion between the will and our voluntary operations is disturbed or interrupted. The continuance of the power of volition is demonstrated by the effort, however ineffectual.

In like manner, in the course of an alarming dream, we are sometimes conscious of making an exertion to save ourselves, by flight, from an apprehended danger; but in spite of all our efforts we continue in bed. In such cases we commonly dream that we are attempting to escape, and are prevented by some external obstacle; but the fact seems to be, that the body is at that time not subject to the will. During the disturbed rest which we sometimes have when the body is indisposed, the mind appears to retain some power over it; but as, even in these cases, the motions which are made consist rather of a general agitation of the whole system, than of the regular exertion of a particular member of it, with a view to produce a certain effect, it is reasonable to conclude that, in perfectly sound sleep, the mind, although it retains the power of volition, retains no influence whatever over the bodily organs.

In that particular condition of the system which is known by the name of incubus, we are conscious of a total want of power over the body; and I believe the common opinion is, that it is this want of power which distinguishes the incubus from all the other modifications of sleep. But the more probable supposition seems to be, that every species of sleep is accompanied with a suspension of the faculty of voluntary motion; and that the incubus has nothing peculiar in it but this, that the uneasy sensations which are produced by the accidental posture of the body, and which we find it impossible to remove by our own efforts, render us distinctly conscious of our incapacity to move. One thing is certain, that the instant of our waking, and of our recovering the command of our bodily organs, is one and the same.

2. The same conclusion is confirmed by a different view of the subject. It is probable, as was already observed, that when we are anxious to procure sleep, the state into which we naturally bring the mind approaches to its state after sleep commences. Now it is manifest that the means which nature directs us to employ on such occasions, is not to suspend the power of volition, but to suspend the exertion of those powers whose exercise depends on volition. If it were necessary that volition should be suspended before we fall asleep, it would be impossible for us by our own efforts to hasten the moment of rest. The very supposition of such efforts is absurd, for it implies a continued will to suspend the acts of the will.

According to the foregoing doctrine with respect to the state of the mind in sleep, the effect which is produced on our mental operations is strikingly analogous to that which is produced on our bodily powers. From the observations which have been already made, it is manifest that in sleep the body is, in a very inconsiderable degree, if at all, subject to our command. The vital and involuntary motions, however, suffer no interruption, but go on as when we are awake, in consequence of the operation of some cause unknown to us. In like manner, it would appear that those operations of the mind which depend on our volition are suspended, while certain other operations are at least occasionally carried on. This analogy naturally suggests the idea that all our mental operations which are independent of our will may continue during sleep, and that the phenomena of dreaming may perhaps be produced by these, diversified in their apparent effects, in consequence of the suspension of our voluntary powers.

If the appearances which the mind exhibits during sleep are found to be explicable on this general principle, it will possess all the evidence which the nature of the subject admits of.

It was formerly shown that the train of thought in the mind does not depend immediately on our will, but is regulated by certain general laws of association. At the same time it appeared, that among the various subjects which thus spontaneously present themselves to our notice, we have the power of singling out any one that we choose to consider, and of making it a particular object of attention; and that by doing so we not only can stop the train that would otherwise have succeeded, but frequently can divert the current of our thoughts into a new channel. It also appeared that we have a power (which may be much improved by exercise) of recalling past occurrences to the memory by a voluntary effort of recollection.

The indirect influence which the mind thus possesses over the train of its thoughts is so great, that during the whole time we are awake, excepting in those cases in which we fall into what is called a reverie, and suffer our thoughts to follow their natural course, the order of their succession is always regulated more or less by the will. The will, indeed, in regulating the train of thought, can operate only (as I already showed) by availing itself of the established laws of association; but still it has the power of rendering this train very different from what it would have been if these laws had taken place without its interference.

From these principles, combined with the general fact which I have endeavoured to establish with respect to the state of the mind in sleep, two obvious consequences follow. First, that when we are in this situation, the succession of our thoughts, so far as it depends on the laws of association, may be carried on by the operation of the same unknown causes by which it is produced while we are awake; and, secondly, that the order of our thoughts in these two states of the mind must be very different; inasmuch as in the one it depends solely on the laws of association; and in the other, on these laws combined with our own voluntary exertions.

In order to ascertain how far these conclusions are agreeable to truth, it is necessary to compare them with the known phenomena of dreaming; for which purpose I shall endeavour to show, first, that the succession of our thoughts in sleep is regulated by the same general laws of association to which it is subjected while we are awake; and, secondly, that the circumstances which discriminate dreaming from our waking thoughts are such as must necessarily arise from the suspension of the influence of the will.

1. That the succession of our thoughts in sleep is regulated by the same general laws of association which influence the mind while we are awake, appears from the following considerations.

Our dreams are frequently suggested to us by bodily sensations; and with these it is well known, from what we experience while awake, that particular ideas are frequently very strongly associated. I have been told by a friend, that having occasion, in consequence of an indisposition, to apply a bottle of hot water to his feet when he went to bed, he dreamed that he was making a journey to the top of Mount Etna, and that he found the heat of the ground almost insupportable. Another person, having a blister applied to his head, dreamed that he was scalped by a party of Indians. I believe every one who is in the habit of dreaming will recollect instances, in his own case, of a similar nature.

2. Our dreams are influenced by the prevailing temper of the mind, and vary in their complexion according as our habitual disposition at the time inclines us to cheerfulness or to melancholy. Not that this observation holds without exception; but it holds so generally, as must convince us that the state of our spirits has some effect on our dreams as well as on our waking thoughts. Indeed, in the latter case, no less than in the former, this effect may be counteracted or modified by various other circumstances.

After having made a narrow escape from any alarming danger, we are apt to awake in the course of our sleep with startings, imagining that we are drowning, or on the brink of a precipice. A severe misfortune, which has affected the mind deeply, influences our dreams in a similar way, and suggests to us a variety of adventures analogous in some measure to that event from which our distress arises. Such, according to Virgil, were the dreams of the forsaken Dido.

3. Our dreams are influenced by our prevailing habits of association while awake.

In a former part of this work I considered the extent of that power which the mind may acquire over the train of its thoughts; and I observed that those intellectual diversities among men, which we commonly refer to peculiarities of genius, are at least in a great measure resolvable into differences in their habits of association. One man possesses a rich and beautiful fancy, which is at all times obedient to his will. Another possesses a quickness of recollection, which enables him at a moment's warning to bring together all the results of his past experience, and of his past reflections, which can be of use for illustrating any proposed subject. A third can without effort collect his attention to the most abstract questions in philosophy; can perceive at a glance the shortest and the most effectual process for arriving at the truth; and can banish from his mind every extraneous idea which fancy or casual association may suggest to distract his thoughts or to mislead his judgment. A fourth unites all these powers in a capacity of perceiving truth with an almost intuitive rapidity, and in an eloquence which enables him to command at pleasure whatever his memory and fancy can supply to illustrate and to adorn it. The occasional exercise which such men make of their powers may undoubtedly be said, in one sense, to be unpremeditated or unstudied; but they all indicate previous habits of meditation or study, as unquestionably as the dexterity of the expert accountant, or the rapid execution of the professional musician.

From what has been said, it is evident that a train of thought which in one man would require a painful effort of study, may in another be almost spontaneous; nor is it to be doubted that the reveries of studious men, even when they allow, as much as they can, their thoughts to follow their own course, are more or less connected together by those principles of association which their favourite pursuits tend more particularly to strengthen.

"The influence of the same habits may be traced distinctly in sleep. There are probably few mathematicians who have not dreamed of an interesting problem, and who have not even fancied that they were prosecuting the investigation of it with much success. They whose ambition leads them to the study of eloquence are frequently conscious, during sleep, of a renewal of their daily occupations; and sometimes feel themselves possessed of a fluency of speech which they never experienced before. The poet in his dreams is transported into Elysium, and leaves the vulgar and unsatisfactory enjoyments of humanity, to dwell in those regions of enchantment and rapture which have been created by the divine imaginations of Virgil and of Tasso.

"As a farther proof that the succession of our thoughts in dreaming is influenced by our prevailing habits of association, it may be remarked, that the scenes and occurrences which most frequently present themselves to the mind while we are asleep are the scenes and occurrences of childhood and early youth. The facility of association is then much greater than in more advanced years; and although during the day the memory of the events thus associated may be banished by the objects and pursuits which press upon our senses, it retains a more permanent hold of the mind than any of our subsequent acquisitions; and, like the knowledge which we possess of our mother tongue, is, as it were, interwoven and incorporated with all its most essential habits. Accordingly, in old men, whose thoughts are in a great measure disengaged from the world, the transactions of their middle age, which once seemed so important, are often obliterated; while the mind dwells, as in a dream, on the sports and the companions of their infancy.

"I shall only observe farther, on this head, that in our dreams, as well as when awake, we occasionally make use of words as an instrument of thought. Such dreams, however, do not affect the mind with such emotions of pleasure and of pain, as those in which the imagination is occupied with particular objects of sense. The effect of philosophical studies, in habituating the mind to the almost constant employment of this instrument; and, of consequence, its effect in weakening the imagination, was formerly remarked. If I am not mistaken, the influence of these circumstances may also be traced in the history of our dreams, which in youth commonly involve in a much greater degree the exercise of imagination, and affect the mind with much more powerful emotions, than when we begin to employ our maturer faculties in more general and abstract speculations.

"II. From these different observations we are authorized to conclude, that the same laws of association which regulate the train of our thoughts while we are awake, continue to operate during sleep. I now proceed to consider how far the circumstances which discriminate dreaming from our waking thoughts, correspond with those which might be expected to result from the suspension of the influence of the will.

"1. If the influence of the will be suspended during sleep, all our voluntary operations, such as recollection, reasoning, &c. must also be suspended.

"That this really is the case, the extravagance and inconsistency of our dreams are sufficient proofs. We frequently confound together times and places the most remote from each other; and, in the course of the same dream, conceive the same person as existing in different parts of the world. Sometimes we imagine ourselves conversing with a dead friend, without remembering the circumstance of his death, although perhaps it happened but a few days before, and affected us deeply. All this proves clearly that the subjects which then occupy our thoughts are such as present themselves to the mind spontaneously, and that we have no power of employing our reason in comparing together the different parts of our dreams, or even of exerting an act of recollection, in order to ascertain how far they are consistent and possible.

"The processes of reasoning in which we sometimes fancy ourselves to be engaged during sleep, furnish no exception to the foregoing observation; for although every process, the first time we form it, implies volition, and, in particular, implies a recollection of the premises till we arrive at the conclusion, yet when a number of truths have been often presented to us as necessarily connected with each other, this series may afterwards pass through the mind according to the laws of association, without any more activity on our part than in those trains of thought which are the most loose and incoherent. Nor is this mere theory. I may venture to appeal to the consciousness of every man accustomed to dream, whether his reasonings during sleep do not seem to be carried on without any exertion of his will, and with a degree of facility of which he was never conscious while awake. Mr Addison, in one of his Spectators, has made this observation; and his testimony, in the present instance, is of the greatest weight, that he had no particular theory on the subject to support. 'There is not,' says he, 'a more painful action of the mind than invention, yet in dreams it works with that ease and activity that we are not sensible when the faculty is employed. For instance, I believe every one, some time or other, dreams that he is reading papers, books, or letters; in which case the invention prompts so readily, that the mind is imposed on, and mistakes its own suggestions for the composition of another.' No.487.

"2. If the influence of the will during sleep be suspended, the mind will remain as passive, while its thoughts change from one subject to another, as it does during our waking hours, while different perceptible objects are presented to our senses.

"Of this passive state of the mind in our dreams it is unnecessary to multiply proofs, as it has always been considered as one of the most extraordinary circumstances with which they are accompanied. If our dreams as well as our waking thoughts were subject to the will, is it not natural to conclude, that in the one case, as well as in the other, we would endeavour to banish, as much as we could, every idea which had a tendency to disturb us, and detain those only which we found to be agreeable? So far, however, is this power over our thoughts from being exercised, that we are frequently oppressed, in spite of all our efforts to the contrary, with dreams which affect us with the most painful emotions. And, indeed, it is matter of vulgar remark, that our dreams are, in every case, involuntary on our part, and that they appear to be obtruded on us by some external cause. This fact appeared so unaccountable to the late Mr Baxter, that it gave rise to his very whimsical theory, in which he ascribes dreams to the immediate influence of separate spirits on the mind.

"3. If the influence of the will be suspended during sleep, the conceptions which we then form of sensible objects will be attended with a belief of their real existence, as much as the perception of the same objects is while we are awake.

"In treating of the power of Conception, I formerly observed, that our belief of the separate and independent existence of the objects of our perceptions, is the result of experience; which teaches us, that these perceptions do not depend on our will. If I open my eyes, I cannot prevent myself from seeing the prospect before me. The case is different with respect to our conceptions. While they occupy the mind, to the exclusion of every thing else, I endeavoured to shew that they are always accompanied with belief; but as we can banish them from the mind, during our waking hours, at pleasure, and as the momentary belief which they produce is continually checked by the surrounding objects of our perceptions, we learn to consider them as fictions of our own creation, and, excepting in some accidental cases, pay no regard to them in the conduct of life. If the doctrine, however, formerly stated with respect to conception be just, and if, at the same time, it be allowed that sleep suspends the influence of the will over the train of our thoughts, we should naturally be led to expect, that the same belief which accompanies perception while we are awake, should accompany the conceptions which occur to us in our dreams. It is scarcely necessary for me to remark, how strikingly this conclusion coincides with acknowledged facts.

"May it not be considered as some confirmation of the foregoing doctrine, that when opium fails in producing complete sleep, it commonly produces one of the effects of sleep, by suspending the activity of the mind, and throwing it into a reverie; and that while we are in this state, our conceptions frequently affect us nearly in the same manner as if the objects conceived were present to our senses?

"Another circumstance with respect to our conceptions during sleep deserves our notice. As the subjects which we then think upon occupy the mind exclusively, and as the attention is not diverted by the objects of our external senses, our conceptions must be proportionally lively and steady. Every person knows how faint the conception is which we form of any thing 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 every thing around us be silent, we endeavour 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 any thing 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 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 will 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 be 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 every thing 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."

Some very beautiful fables have been written both by ancients and moderns in the form of dreams. The Somnium Scipionis, for instance, is perhaps one of the finest of Cicero's compositions. He who shall carefully peruse this piece, with Macrobius's commentary thereupon, will undoubtedly acquire a considerable knowledge of ancient philosophy. In the periodical publications which early diffused so much elegant and useful knowledge throughout Britain, the Tatlers, Spectators, Guardians, and the like, we find a number of excellent dreams. Addison excelled in this line of writing; his Vision of Mirza is a masterpiece of its kind. But the public are now less partial to this species of composition than they formerly were; writings purely imaginative, having ceased to be relished, are no longer produced. DREDGING.

Dredging is a term used to express the important operation in the practice of the engineer, of removing deposited matters from the beds of navigable rivers, harbours, canals, and basins.

In describing the several methods by which dredging has been successfully employed, it is not our intention to enter into geological discussions regarding the ultimate tendency of the process of deposition; but we cannot allow it to pass without at least hinting at its original cause, a knowledge of which may lead the inexperienced practitioner more readily to the proper means of removing an evil so generally complained of in our most secure and sheltered harbours. If the universal tendency to waste and decay in the higher lands, from the agency of moisture, heat, and frost, be considered, we shall find that every rill of water must carry along with it a portion of separated matter. These rivulets being so many tributary streams to the great rivers which form the drainage of vast tracts of country, we need not be surprised to find that the beds and embouchures of the Scheldt, the Meuse, the Rhine, and the Elbe, or of the Thames, the Humber, the Tay, and other great tributaries to the German Ocean, should be variously silted up; and that even this great basin itself should be much encumbered by numerous banks of deposited matters. To the agency of these, combined with the effects of cross-running tides, we ascribe the existence of the Dogger Banks, the Yarmouth Sands, the Flemish Banks, and even the great platforms of Holland, and the opposite planes of the Fens of Lincoln.

There is also a marked difference to be noticed in the separation and distribution of these matters of deposition. In those rivers which flow with a very gentle current toward the sea, fine silt, or what is sometimes termed ose, is produced; while rivers of greater fall, and consequently of more velocity, carry forward the grosser particles proportionally farther from their embouchures. Another circumstance which deserves our notice is the greater specific gravity of salt water than fresh, which (as has been ascertained by the writer of this article, on the Dee at Aberdeen, and other rivers where he has made observations) preserve their course in distinct films, the salt water under the fresh. The salt water thus flows up the courses of the respective rivers to an extent corresponding to the fall of their beds and the rise of the tide. A considerable portion of the heavier matters, as gravel and sand, are arrested in their progress sea-ward, where the current is languid; while the lighter particles floating at or near the surface are either borne along with the stream into the expanse of the ocean, or settle in the eddy-waters. In this way the projecting obstacles along the margin are formed, and thus accumulate in the form of sand banks and small islets; the creeks and sinuosities are also silted up, and too often render the connecting harbours and shipping places so shallow, as to be unfit for the purposes of floating ships of burden. To such a degree has this been experienced in some situations, as, for example, Sandwich in Kent, that this ancient sea-port is left almost in the state of an inland town; while other ports have been more or less deteriorated. Importance is therefore justly attached to such means as may be instrumental in counteracting or preventing the tendency of this process of silting. We shall accordingly direct the attention of our readers to some of those means, both natural and artificial.

Where recourse can be had to natural means in keeping a navigable channel clear, they will always be found preferable to those which are artificial. The great agent laid to our hand by nature for this purpose is the judicious use and application of the drainage waters of the connecting district, and the preservation of the full and ample flow of the tide waters. But in many instances these means are tampered with, and rendered ineffectual, by the reckless thirst of acquiring land at the expense or by the exclusion of the back-waters arising from the flow of the tide. Notwithstanding all that can be said by professional men upon the subject, this practice prevails in many parts of the united kingdom to a frightful extent. With a view to put a stop to this, an act (in which the late eminent engineer Mr Rennie, and the writer of this article, had some connection) which originated with the admiralty, was passed in 1806, entitled "An act for the preservation of public harbours of the united kingdom," Geo. III. cap. 153. But this act wants amendment, and has been rarely acted upon, especially to the extent contemplated by Earl Grey, then Lord Harwich, and first lord of the admiralty.

In noticing the natural means of cleaning harbours, we cannot perhaps better illustrate the subject than by reference to Montrose, in Forfarshire, where some of the continuous proprietors have from time to time proposed to make firm ground of part of the great natural basin connected with the harbour of that port. This basin is flooded every tide to the extent of about five square miles, and is estimated, especially in spring-tides, to contain about fifty-five millions of cubic yards of the back-waters of the tide, which passing four times in the twenty-four hours through this harbour, produces so powerful a current that the shifting sand-bank at the entrance, called the Annet, is prevented from being thrown across the mouth of it in gales of easterly wind. In this state of the weather the Annet-bank has a continual tendency westward, while the back-waters of this great natural basin check its progress, and not only keep the navigation open, but are sufficient to preserve a considerable depth in it during the lowest tides.

In the course of forming the bold design of opening a Lake Harbour near Lowestoft, and carrying an inland navigation to the mercantile city of Norwich, Mr Cubit the engineer projected an entrance to this harbour, with a pair of gates measuring fifty feet in width, and of a depth so considerable that their ground-sill is sunk about twelve feet under low water of spring-tides, the rise of which upon this coast is very limited: the gates are laid at this depth, so as to be capable of receiving the largest class of mercantile ships. They are also ingeniously contrived for letting off the head-waters of Lake Lothing. This extensive sheet of water, which pervades a great portion of the lower district of Suffolk, is to be used as back-water to scour and keep the entrance of the harbour open against the effects of storms from the east sea acting upon the sand bunks which so much encumber this part of the coast. This great work is only in the progress of being executed, but very sanguine expectations are entertained of its success.

In the improvement of the navigation of the river Clyde, the river means resorted to have been those of narrowing the Clyde channel and confining the current; and these have been so successful that a depth of about ten feet has been obtained, instead of only five feet as formerly, by which the trade Dredging, and commerce of the city of Glasgow derive the most decided advantages. Formerly only barges came up to the city, now sea-borne ships from all quarters of the globe are seen at its quays. But in forming a design upon the principle of narrowing the channel of a river, and thereby shutting out a portion of the tide waters, several elements connected with the local circumstances of the place require to be carefully weighed before attempting to lessen the capacity or water-way of a river. Much depends on the level or rise of the bed of the river, the perpendicular rise of the tide on the coast, the situation of its embouchure, and other circumstances which favourably and fortunately present themselves upon the Clyde. The application of the steam tug-boat, in towing vessels through narrow channels, has removed objections of the most serious nature upon this navigation.

Many other circumstances might be adduced to show the advantages of supplying the natural means in our power to the scouring of navigable tracks. The writer of this article has now (1833) under consideration the improvement of the harbour of Ballyshannon, in the county of Donegal, which possesses the natural means to an immense extent of clearing its embouchure, having almost the entire drainage waters of the county of Fermanagh collected in Lough Erne, which extend to about fifty miles in length, and in some places three miles in breadth, the entire overflow of which passes over the bar of Ballyshannon harbour.

The most eminent engineers, both of our own country and of France, have introduced scouring basins into their designs of tide harbours. Mr Smeaton constructed a tide-basin of this kind at Ramsgate in Kent, where the silt of the outer harbour is loosened by artificial means, and dredged into the tracks or courses of water issuing from the sluices of an artificial tide-basin. By this means a considerable portion of the deposited stuff is carried out of the harbour into deep water. It is, however, to be regretted that there is not a more extensive collection of back-waters here, as, from its very circumscribed position, that eminent engineer was prevented from enlarging his scouring basin to a sufficient extent to ensure the best effects of his design.

At Dover there is a good example of artificial scouring upon a small scale. This harbour is often choked up in a single tide, with the debris of the heights of Dover, and with the flinty gravel which surrounds this coast. Upon these occasions, the back-waters of an adjoining basin are conducted in great cast-iron pipes of about three feet in diameter. The water issuing from these pipes is made to act upon a system of temporary weirs, consisting of deal-boards set on edge, which are shifted about at pleasure in different directions, so as to bring the water from the sluices to bear upon the gravel; and it is astonishing with what facility the entrance to this harbour is by these means cleaned and rendered accessible to the packets, from a state of being quite shut up.

In extensive plans of docks for floating ships much use is or may be made of a system of sougs or sluices for scouring or floating away mud. By opening these sluices from one dock into another, as is done by Mr Hartley, engineer for the Liverpool docks, the advantages of such a command of head-water is attended with the most beneficial effects, both for clearing the several docks, and also the outer harbours or receiving basins of this great port.

The common plough and harrow, differing very little from their ordinary construction, and also a kind of frame of timber shod with plate iron, and provided with stilts or handles somewhat like a great shovel, are often used for loosening and dredging stuff within reach of removal by a stream of back-water, with which it is afterwards floated out of the respective harbours or navigable tracks. These and various other simple implements, suited to local circumstances, are sometimes employed by manual labour, and also with horse power, where the bottom is sufficiently firm to admit of the necessary trackage. Nor must we omit to mention the use of the common wheelbarrow and spade so much used in operations of this kind.

The spoon dredging apparatus, with its boat, as represented in Plate CCV., fig. 13, is of long standing, and was probably first used by the Dutch, who still apply it extensively. It is also much employed upon the river Thames, for lifting ballast and deepening the navigation of that greatest of all commercial rivers. Referring to fig. 13, the reader will at once comprehend the construction and application of this simple apparatus. The boats for this purpose vary in size according to the situation in which they are to be worked, say from twenty to sixty tons burden. They are built to float upon an easy draught of water, and are sometimes flush-decked, carrying their cargo wholly upon deck; but for the greater part, and especially those of the larger size, they are in the state of open boats, with a kind of inner sole or floor. When the excavated matters are not to be employed in banking on the sides of the river, or ballasting ships, the boat is formed with a kind of hopper-hold, somewhat upon the principle of the fishing smacks with wells, being convenient for getting quit of the stuff in deep water. In this case a hold of two compartments, one fore and one aft, are formed, as represented by the dark shading and dotted lines in fig. 13. Each of these hoppers has an aperture or opening in the bottom, through which the stuff is dropped by the flap-door, marked letter A, as represented in the figure. In some circumstances, also, the stuff is received into a system of sheet-iron boxes, and lifted out of the boat by a tackle, to be emptied. The spoon or shovel, marked letter B, which accompanies these boats, consists of a strong ring or hoop of malleable iron, the cutting part of which is of steel, and is about six or seven feet in circumference, properly formed for dredging upon soft mud or gravelly ground. To this ring a large bag made of bullocks' hide, but more generally of tanned leather, is strongly attached with thongs. The bag is perforated with a number of small holes for allowing the water to drain off, and its capacity may be about four or five cubic feet. A pole of from thirty to forty feet in length is fixed to the spoon, or rather two poles are so laid together with hoops and rings as to be lengthened or shortened at pleasure, to suit the depth of water in which the apparatus is required to work. A rope is also attached to the bottom of the bag, for directing its position at the commencement of each operation. This apparatus is generally worked with a chain or rope, brought from the spoon to a winch, worked with wheel and pinion, through a block suspended from a small crane used for hauling the bag and its contents along with the progress of the boat, and in lifting the spoon over the gunwale to be emptied into the hopper of the boat. The purchase-rope is led along the deck to the winch, by a snatch-block placed in a proper direction for this purpose. The boat is moored at the head and stern, and its berth may be shifted at pleasure. These boats are generally managed and worked with from two to four men, who with this simple apparatus can lift in a tide from twenty to sixty tons of stuff from the bottom, at the depth of two and a half or three fathoms, when the ground is somewhat loose, and favourable for the operation. In Holland this apparatus, and all these simple modes of dredging, are much practised upon the extensive flats at the entrance of their great navigable rivers, in connection with the sluices and natural currents issuing from their extensive basins and canals. On the British coast, dredging, when carried on to any extent, Dredging is now confined chiefly to the spoon and bucket machines; and here steam, wherever it can be applied, is the great moving power. In Holland the excavated matter is very generally of a mossy description, which, after being strongly compressed in moulds by that industrious people, is in a state to be speedily used as turf fuel. On the Thames the spoon dredging machine is conducted upon a large scale, and in the most systematic manner, under the immediate direction of the Trinity Board. The stuff brought from the bottom consists chiefly of mud and gravel. This is not only a useful operation for deepening and preserving the navigation, but the stuff itself is sold to good advantage as ballast for shipping. To such an extent is this carried, that the colliers, or shipping from London to Newcastle, have raised ballast hills in the neighbourhood of Shields, which from their vast extent have become objects of no small curiosity.

In proportion as the commerce of a country extends, its ships increase in their dimensions, and a greater depth of water is consequently required to float them; and hence greater difficulty and expense attends the construction and preservation of harbours for their accommodation. To effect these objects, and especially to obtain a greater depth of water, recourse has been had to various means, such as the extension of piers, the formation of breakwaters, and deepening by means of the process of dredging now described. These simple modes have, however, been succeeded by a still more powerful engine termed the bucket dredging machine.

Since the date of the last edition of this work, very considerable improvements have been effected in the system of dredging, both by the application of the power of steam, and the form and construction of the apparatus itself, as well as that of the vessel containing it. The machine is said to have been first worked by men only; when the principles upon which it acts were more fully ascertained, horses were employed, and worked round a covered gin-track or circular path within the boat. A machine of this description, worked by horse power, was used for some years at the port of Greenock, though it was there ultimately found more suitable and expedient to resort to manual labour, applied by crane-work with wheel and pinion. Perhaps, in all situations where fuel is very expensive, and where the work is not of sufficient extent for the full employment of steam, it will be found better, in a process of this kind, to employ manual labour than horses, which, from the circumscribed and hampered nature of the track on board of the vessel, must be very disadvantageous, as experience has shown on the Clyde. Indeed, the only question seems to be, in such cases where steam cannot be profitably employed, whether it were not better to use the spoon apparatus, as upon the Thames, where manual labour is at the highest rate.

In this article we shall give a minute detail of one of the best and latest constructed dredging machines, employed by Messrs Gibb upon the harbour works of Aberdeen. This machine was entirely constructed by Messrs John Duffus and Company of that port, both as regards the vessel and the machinery. In describing it we refer to Plates CCIV. and CCV. Fig. 1, Plate CCIV., represents a longitudinal section of the vessel, exposing to view an elevation of the steam-engine and bucket apparatus, with its framework. The ground to be dredged is also shown, with the buckets in contact, and the attendant barge astern. Fig. 2 is a plan of the vessel and machinery. Her extreme length as taken by measurement is ninety feet, and the extreme breadth twenty-two feet; the length of the ark or well which contains the bucket-frame is fifty-four feet, and its width four feet one inch in the clear. The after-part of the vessel being thus formed into two compartments, these are connected at the stern by four strong timbers, placed across the well, and immediately above the keel. Upon these, timbers are placed in sloping directions for supporting the planking. This vessel draws only four feet of water, but the bucket frame can be lowered so as to dredge in a depth of fifteen feet. The steam engine is of the usual form of marine condensing engines; the diameter of the cylinder is twenty-four inches, and the length of the stroke thirty-one inches, being equal to the power of about sixteen horses. From the nature of the process of dredging, the resistance is extremely irregular, causing violent shocks; and therefore malleable instead of cast iron is used as much as possible in the construction of the moving parts. For the same reason a heavy fly-wheel becomes necessary, to regulate the motion. As a vessel of this description, in a tide harbour, must frequently get aground in places where it is unequal, the whole machinery is liable to be strained. On this account it is necessary that all pipes connected with the engine should be of copper, and for the same reason every facility is given for disengaging the parts of the machinery, to prevent fracture or derangement. From the corrosive nature of the stagnant water in harbours, which must be used for condensing, it is necessary to line or case the air-pump with copper or brass, and also to make the buckets, air-pump, valves, and rod, of the same metal. It has been observed that cast iron wastes more rapidly when exposed to the action of this harbour-water than in the open sea.

Subjoined are the dimensions of some of the principal parts of the engine. These, to the practical engineer, may hardly seem to be necessary; but as the Aberdeen machine has been found to answer every expectation, and as it appears to the writer to be similar to those so successfully employed on the river Clyde, it may be of consequence to the general reader to know, from such data, the proper strength and size for its different parts. This engine is set upon a cast-iron cistern, measuring three feet in width, and prolonged as far as to contain the air-pump, foot-valve, and condenser. The cistern and cylinder, set on the top, are strongly bolted down through the bottom of the vessel. On the top of the cistern the columns of support for the fly-wheel shaft are set at a sufficient height to connect with the dredge-gearing, which is stayed by a circular entablature, as represented in the plan of the engine at letter a. It has also a diagonal stay, securely bolted to a bracket, cast on the side of the cylinder. The side levers of the engine are seven feet eight and a fourth inches long; between centres one and three-fourth inches thick of plate, and three and three-fourth inches thick on the back; fifteen inches broad in the middle, with forked ends one and three-fourth inches thick, for laying hold of the cross-rail and cylinder side-rods. The cylinder cross-head is seven and a half inches deep at the middle, tapering to four inches where the side-rods are attached, and five and a fourth inches in diameter at the eye, and two inches in thickness. The cross-head of the air-pump is four and a half inches diameter at the eye, five and a half inches deep, and one and three-fourth inches thick. The cylinder side-rods are two and one-eighth inches diameter at each end, and two and two-eighth inches at the middle. The side-rods of the air-pump are finished with forked ends, for embracing the side-lever centre on each side, and fitted with straps and braces. The main centres are four and five-eighth inches diameter, keyed into the side levers. The parallel motion is constructed with radius and parallel boxes, as is usual in this description of engine. The connecting-rod is of malleable iron, three inches diameter at both ends, and three and three-fourth inches at the centre, fitted into the eye of the cross-tail with a gib and cutter. The fly-wheel Dredging. is ten feet three inches in diameter, and eight inches deep by four inches broad in the rim, as represented in dotted lines upon the cross section of the vessel, fig. 3, Plate CCIV., and at fig. 1, Plate CCIV. The shaft is of cast iron, seven and three-fourth inches diameter. The engine is also provided with a governor and its necessary connections, and is driven from the fly-wheel shaft by means of a pulley and belt.

The boiler, marked e, fig. 1, Plate CCIV., is of iron, measuring ten feet four inches across the end, eight feet four inches long, and four feet eight inches in height in the middle, with two furnaces two feet three inches wide. The water-ways between the flues are four inches wide, and the flues fifteen and a half inches, making one and a half turns in the length of the boiler. The sides and tops of the furnaces, the bottoms and sides of the flues, are three eighths of an inch thick, and the top half an inch in thickness. The copper steam-pipes are of the thickness No. 10 on the wire-guage, the funnel a of the engine is two feet in diameter and twenty-five feet in height, made of plate-iron an eighth of an inch in thickness.

Fig. 3, Plate CCIV., represents a cross section of the vessel accurately drawn to the scale, showing its outline, and the manner in which it is constructed. The machinery is supported upon the three keels ABC of the vessel by their respective keelsons, or beams placed immediately over them. The bottom of the vessel is further supported by the like means, DD. The central keel extends only to the fore part of the ark or well. This cross section also exhibits an elevation of the train of wheels for raising and lowering the bucket-frame. From the main spur-wheel on the lying shaft, marked E, fig. 3, Plate CCIV., down to the lowest wheel on the same shaft, with the chain-barrel, marked L, the connection is in the following order. The main spur-wheel is of that description called a mortise-wheel: it is eight feet in diameter, constructed in a very ingenious manner, to revolve upon a friction nave as follows: The nave is three feet seven inches in diameter, smoothly turned on the circumference, and fixed to the lying shaft with keys. The wheel is also particularly turned in the eye to coincide with the nave, and is furnished with eight pinning plates and screws marked f, for tightening it at pleasure, and made to pass with sufficient force upon the nave, in order to carry the spur-wheel round in its fair work along with it; but if overstrained, it immediately slips, and thereby any injurious consequences to the apparatus are prevented. The cogs or teeth of this wheel are made of hard wood; all the teeth of the other wheels are made of cast iron. The spur-pinion g, the half of which only is shown, is on the same shaft with the fly, as is also the small spur-wheel h. The pinion g works in the main spur-wheel, and is three feet six inches in diameter. The small spur-wheel h, the half of which only is shown, connects the engine and the other wheels for working the chain-barrel: it is three feet seven and a half inches in diameter, and works in the wheel i, measuring four feet two and three fourth inches in diameter. On the shaft of the last-mentioned wheel, which is four and an eighth inches square, there is fixed a pinion j, of one foot three inches diameter, working in the wheel K, which is three feet eleven inches in diameter; and on the same shaft there is fixed a wheel l, two feet six inches in diameter, working in another wheel L, which is four feet ten inches in diameter: it is fixed upon the shaft that carries the purchase chain-barrel, and is the last wheel of the train. The barrel of cast iron, Plate CCIV., fig. 1 and 2, measures five feet ten inches in length within the flanges, two feet in diameter, and two feet eight inches over the flanges. It makes six and one tenth revolutions in one minute, being equal to thirty-eight strokes of the piston.

This barrel is provided with an offset-clutch, for engaging and disengaging it from the engine, for the purpose of raising and lowering the bucket-frame; and as a precaution against accident, this clutch is provided with a friction-nave similar to that already described for the main spur-wheel. This becomes indispensably necessary in situations like that of Aberdeen, where tree-roots, stones, or the like, obstruct the buckets. The machinery would otherwise run great risk of being torn in pieces and destroyed. This barrel is also provided with a brake-wheel and friction-hoop, for lowering or fixing the bucket-frame to any required depth. This is effected by means of a weight constantly acting over a pulley at the extremity of the lever s, Plate CCIV., fig. 1, for pressing the friction-hoop upon the circumference of the brake-wheel with force sufficient to hold the bucket-frame in any position. But when this weight is partially removed, which is done by the hand, the bucket-frame is lowered to the intended depth at the discretion of the master of the vessel, or person who has charge of the work. The upper tumbler is square, as shown in fig. 1, Plate CCV., and in the vertical section, fig. 2, showing the flange and part of the body of the tumbler. In the original form it is cast in one piece, the body being an octagonal prism, and is afterwards brought to the square form by bolting the triangular bars a on the alternate sides. Fig. 12 represents the upper end of the bucket-frame, the shaft M which carries the tumbler N, and the great bevelled-wheel O, which is shown in section; also a view of one of the buckets P attached to the links QQ of the bucket-chain. RR are the plumber-blocks, and SS the brackets for supporting the shaft. Fig. 4 is a cross section of the under tumbler of the bucket-frame, which is five sided: a is the flange, b the strong studs to which the tumbler bars are bolted, c the tumbler bars, and d the bolts by which they are secured. Fig. 5 is a vertical section of the flange, with the same letters of reference, showing the method of fixing the tumbler bars. The lying shaft is of cast iron, in five lengths, as represented in the longitudinal section, Plate CCIV., fig. 1. It is six and a half inches in diameter; the second length of the shaft is furnished with an offset clutch at m, for disengaging the bucket-frame without stopping the engine. This clutch is put into and out of gear by the lever n; but the clutch is more particularly shown in Plate CCV., fig. 6 and 7. The coupling-boxes for the lying shaft are fifteen inches long by one and three fourth inches thick, fastened together by four screwed bolts of one and a fourth inch square.

The bucket-frame, with its train of buckets, as represented in Plate CCIV., fig. 1, is fifty-two feet in length between the centres of the lower and upper tumbler shafts. The frame is of the best oak timber, each side being of one entire piece. The buckets, one of which is represented in Plate CCV., fig. 8, are perforated in the back and bottom with small holes for draining off the water. They measure one foot nine inches in depth, one foot two inches in width from back to breast at the bottom, and one foot five inches at the mouth; the breadth from side to side is two feet two inches. The mouth-piece or cutting edge a is of tempered steel; b is a side view of the double link connected with the bucket. Fig. 9 is an edge view of this link, fig. 10 a side view of the single link, and fig. 11 an edge view of it. These links are twenty-one inches long from centre to centre, three inches in breadth by two in thickness, with a ring of steel one fourth of an inch in thickness welded into the eye of each. The bolts for the chain are two inches in diameter, coated with steel. The weight of each double link is about 84 lbs. and of each single link about 44 lbs. The trussing rod for the bucket-frame, marked u, Plate CCIV., fig. 1, is three inches in breadth. DRE DRE

nathan Hulls was of that place; he obtained a British Dredging patent for working vessels by steam in 1735, although strange to say, it was not introduced into practice till 1812, when the late Mr Henry Bell fitted out the canal steamer boat upon the Clyde. Since that period the steam dredging machine has come into very general use. On the Clyde there are now no fewer than three such vessels as we have described employed, besides a diving bell for the removal of large boulder stones, which in various parts obstruct that navigation. The engines and apparatus used on the Clyde are chiefly of the manufacture of Messrs Girdwood and Berry of Glasgow.

The dredging machine delineated in Plates CCIV. and CCV. was constructed by Messrs John Duffus and Company, Aberdeen. As before noticed, it is simple in its form, and contains the latest improvements both in the build of the vessel and the position and arrangement of the machinery. The great object to be attended to in framing these vessels is, to obtain such a degree of strength as not only to withstand the tremulous motion of the engine and dredging buckets, but also to be capable of resisting the strains to which they are continually liable in taking the ground, or in the fair way of shipping.

The cost of the vessel, engine, and bucket apparatus, complete, with her twelve lighters, may be taken at L5000. The expenditure of coal is at the rate of four cwt. per hour, and the daily expense of working her at L3. 3s. But these items of course vary in amount, according to local circumstances and the situation of the port.

The strength of the vessel, the power of the engine, fitness of the machinery, and the security of the whole against accident by fire, are circumstances connected with the application of the dredging-machine which will always meet with the attentive consideration of the engineer, whose regulation in all the parts of this apparatus will be guided by the actual operation to be performed, as more or less suitable to the peculiar situation of the works in which this apparatus is to be employed. What we have been able to bring under the professional reader's notice in this article, we trust will be sufficient to give him an idea, not only of the construction of the apparatus, and the principles upon which it acts, but also to afford such details as cannot fail to be highly useful in the construction of such an apparatus. To the general reader, who may not take much interest in the details of complicated machinery, we presume our section, elevation, and plan of the bucket dredging-machine will be sufficiently obvious. To him it will also have been interesting to know how operations of this kind are performed, the quantity of work that may be done, and the rate of its expense. We shall also be happy if our observations upon the baneful consequences of shutting out tide water by embarking shall happen to come under the eye of those possessed of legislative power, and be the means of rendering more effective the act of 1800, for the preservation of the navigable rivers of the kingdom, as noticed at page 193. (T.T.)