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 endeavour 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 proportionably 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 all times such, that in the twinkling of an eye, a crowd of ideas may pass before us to which it would require a long discourse to give utterance; and transactions may be conceived which it would require days to realize. But in sleep the conceptions of the mind are mistaken for realities; and therefore our estimates of time 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.