Hitherto the discussion of spirit has been considered impracticable by scientific methods, and theology and metaphysics have occupied the field. In this border-land between the known and the unknown, ignorance and charlatanry have held high carnival, and those who love scientific accuracy perhaps are excusable in regarding the belief in spiritual beings as a superstition; yet there has accumulated as folk lore, as myths, as an outside, out-of-the-way literature, a vast mass of material, some of which, it is true, is mere rubbish, through which gleams bright veins of truth, showing the close relations between the seen and the unseen universes. Here and there a sensitive mind has received the light in clearer effulgence, and made the surrounding gloom more densely impenetrable. At remote intervals the oriflamme of the spiritual conception of nature has flashed athwart the intervals of gross materialism, but religion, moral conduct, not knowledge, has been the motive. This age demands knowledge for its own sweet sake, assured that the highest morality will flow therefrom. In the study of the conditions of the mind, the various states of sleep, clairvoyance, somnambulism, etc., will be defined and illustrated. SLEEP.--Sleep is the “twin sister of death” only in appearance, for aside from poetic fancy, sleep is the negative condition of activity. In perfect sleep all the faculties of the mind are in repose, and the bodily functions go on with the least waste. It is essentially restful and recuperative. The waste of the body, its wear and tear of muscle and nerve is repaired; new cells take the place of those broken down, and the debris moves slowly forward to the excretory organs and is eliminated. In this state of negative repose there is no manifestation of thought, and it is as unlike the clairvoyant or sensitive state as that of wakefulness; but shaded into this state of sleep, as into that of wakefulness, are various degrees of sensitiveness. The conditions of sleep are provocative of this impressibleness. Night is negative; the silence and the vail of darkness shutting out external objects conduce to make the mind negative and susceptible. At midnight is the culmination of this negativeness, and hence the ghastly dread of that hour has a foundation in fact, and is not an idle superstition. Ghosts may never appear, yet if they were to appear the midnight hour, of all others, would be assigned by the student cognizant of this fact for them to come like shafts of frozen moonshine, into the walks of men.