A correct perception by the mind is essential to healthy and natural vision, and this perception the deranged intellect can not effect. We should go farther than this for a complete elucidation of spectral illusions. At the time the spectre made its appearance, the mind may be neither altogether diseased nor altogether healthful; the perceptive powers may recognize through the eye all surrounding objects exactly as they appear, but, almost in the same instant of time, the mind may mix up an unreal object with them. How, then, is the unreal object introduced into the scene? There is the strongest ground for believing that the unreal objectthe spectre - is an idea of the mind acting on the optic nerve, and impressing a picture on the retina, just as effectually as if the object were external to the person. The mind, as it were, daguerreotypes the idea the flash of thought on the retina, or mirror of the eye, where it is recognized by the powers of perception. That spectres are mental pictures, is forcibly stated as follows by Sir David Brewster: "I propose to show that the 'mind's eye' is actually the body's eye, and that the retina is the common tablet on which both classes of impressions are painted, and by means of which they receive their visual existence according to the same optical laws. Nor is this true merely in the case of spectral illusions. It holds good of all ideas recalled by the memory, or created by the imagination, and may be regarded as a fundamental law in the science of pneumatology. "In the healthy state of the mind and body, the relative intensity of these two classes of impressions on the retina is nicely adjusted. The mental pictures are transient, and comparatively feeble, and in ordinary temperaments are never capable of disturbing or effacing the direct images of visible objects. The affairs of life could not be carried on if the memory were to intrude bright representations of the past into the domestic scene, or scatter them over the external landscape. The two opposite impressions, indeed, could not coexist. The same nervous fibre which is carrying from the brain to the retina the figures of memory, could not at the same instant be carrying back the impressions of external objects from the retina to the brain. The mind cannot perform two different functions at the same instant, and the direction of its attention to one of the two classes of impressions necessarily produces the extinction of the other. so rapid is the exercise of mental power, that the alternate appearance and disappearance of the two contending impres sions is no more recognized than the successive observations of external objects during the twinkling of the eyelids." But DREAMING is a modification of disordered mental action, arising usually from some kind of functional derangement. In sound sleep, the functions of digestion, the circulation of the blood, and all others, may be said to be duly in action, and the mind is accordingly not disturbed. If, however, any of the bodily functions be in a state of derangement; if, in particular, the digestion be incommoded, which it ordinarily is in an artificial mode of life, the senses, the nerves, the mind will probably also be affected, and an imperfect sleep, with an imperfect consciousness, is the result. According to the best writers on the subject, it has been ascertained that, in beginning to sleep, the senses do not unitedly fall into a state of slumber, but drop off one after the other. The sight ceases. in consequence of the protection of the eyelids, to receive impressions first, while all the other senses preserve their sensibility entire. The sense of taste is the next which loses its susceptibility of impressions, and then the sense of smelling. The hearing is next in order; and last of all comes the sense of touch. Furthermore, the senses are thought to sleep with different degrees of profoundness. The sense of touch sleeps the most lightly, and is the most easily awakened; the next easiest is the hearing; the next is the sight; and the taste and smelling awake the last. Another remarkable circumstance deserves notice; certain muscles and parts of the body begin to sleep before others. Sleep commences at the extremities, beginning with the feet and legs, and creeping towards the centre of nervous action. The necessity for keeping the feet warm, and perfectly still, as a preliminary of sleep, is well known. From these explanations, it will not appear surprising that, with one or more of the senses, and perhaps, also, one or more parts of the body imperfectly asleep, there should be, at the same time, an imperfect kind of mental action, which produces the phenomenon of dreaming. A dream, then, is an imperfectly formed thought. Much of the imperfection and incoherency of such thoughts is from having no immediate consciousness of surrounding objects. The imagination revels unchecked by actual circumstances, and is not under the control of the will. Ungoverned by any ordinary standards of reason, we, in dreaming, have the impression that the ideas which chase each other through the mind are actual occurrences: a mere ill-formed thought is imagined to be an action. As thought is very rapid, it thus happens that events which would take whole days, or a longer time, in performance, are dreamed in a few moments. wonderful is this compression of a multitude of transactions into the very shortest period, that when we are accidentally "awakened from a profound slumber by a loud knock at, or by the rapid opening of, the door, a train of actions which it would take hours, or days, or even weeks to accomplish, some So times passes through the mind. Time, in fact, seems to be in a great measure annihilated. An extensive period is reduced, as it were, to a single point, or rather a single point is made to embrace an extensive period. In one instant we pass through many adventures, see many strange sights, and hear many strange sounds. If we are awaked by a loud knock, we have perhaps the idea of a tumult passing before us, and know all the characters engaged in it-their aspects, and even their very names. If the door open violently, the floodgates of a canal may appear to be expanding, and we may see the individuals employed in the process, and hear their conversation, which may seem an hour in length. If a light be brought into the room, the notion of the house being in flames invades us, and we are witnesses to the whole conflagration from its commencement till it be finally extinguished. The thoughts which arise in such situations are endless, and assume an infinite variety of aspects. "One of the most remarkable phenomena attendant upon dreaming, is the almost universal absence of surprise. Scarcely any event, however incredible, impossible, or absurd, gives rise to this emotion. We see circumstances at utter variance with the laws of nature, and yet their discordancy, impracticability, and oddness, never strike us as at all out of the usual course of things. This is one of the strongest proofs that can be alleged in support of this dormant condition of the reflecting faculties. Had these powers been awake and in full activity, they would have pointed out the erroneous nature of the impressions conjured into existence by fancy, and shown us truly that the visions passing before our eyes were merely the chimeras of an excited imagination— the airy phantoms of imperfect sleep.' LESSON LXIV. Illusions of the Imagination. CHAMBERS'S MISCELLAny, PERSONS in a desponding or gloomy state of mind are exceedingly liable to be deceived by their fancies. The morbid imagination catches at every seemingly mysterious appearance, and transforms it into a spectre, or warning of approaching dissolution. "A man who is thoroughly frightened," observes a popular American writer, "can imagine almost any thing. The whistling of the wind sounds in his ears like the cry of dying men. As he walks along trembling in the dark, the friendly guide-post is a giant; the tree gently waving in the wind is a ghost; and every cow he chances to meet is some fearful apparition from the land of hobgoblins. Who is there that cannot testify, from personal experience, to some such freaks of imagination? How often does one wake up in the night and find the clothes upon the chair, or some article of furniture in the room, assuming a distinctly defined form, altogether different from that which it in reality possesses! “There is in imagination a potency far exceeding the fabled power of Aladdin's lamp. How often does one sit in wintry evening musings, and trace in the glowing embers the features of an absent friend! Imagination, with its magic wand, will there build the city with its countless spires or marshal contending armies or drive the tempest-shattered ship upon the ocean. The following story, related by Scott, affords a good illustration of this principle: - "Not long after the death of a late illustrious poet, who had filled, while living, a great station in the eye of the public, a literary friend, to whom the deceased had been well known, was engaged, during the darkening twilight of an autumn evening, in perusing one of the publications which professed to detail the habits and opinions of the distinguished individual |