Upon the same principle, school-boys commit their tasks to memory by reading them over the last thing before they go to bed. It is to be remembered that during sleep the mind may not be wholly under eclipse; for, although some of its faculties--such as perception, comparison, judgment, and especially the will, may be suspended--others (for example, memory and imagination), are often more active than in the waking state. But some persons, it is said, never dream. We are assured by Locke that he knew a gentleman who had an excellent memory, yet could not recollect ever having dreamed until his twenty-sixth year. Dr. Reid, for many years before his death, had no recollection of having ever dreamed. Dr. Eliotson also relates, apparently upon good authority, the case of a man who never dreamed until after he had a fever, in his fortieth year; and we ourselves know several persons who are not conscious of ever dreaming. Nevertheless, many contend that in all such cases dreams really occur, but that they escape the recollection; for they contend that it is impossible that the mind can, being an independent principle, ever be in a state of absolute rest. This is arguing within a very narrow circle. We must not forget that the intimate alliance of the mind with the body, subjects it to its general laws; the "heat-oppressed brain" requires rest to renew its energies, and the mind, of which it is the organ, in the mean time, may, as in profound sleep, remain perfectly quiescent. The lids of the outward senses are closed; a vail is drawn over the immaterial principle of our nature; and mind and body alike, for a period, lie in a state of utter unconsciousness. Here, however, it may fairly be asked, how happens it that the same person will at one time remember, and, at another, forget his dreams? This circumstance may, we conceive, thus be explained: