It will not surprise us, therefore, to find that this activity of the mind, deprived of the usual means of making itself known to others by gesture, sound, or action, seeks frequently a symbolical utterance, and this is the grain of truth here also hid under the vast amount of rubbish, known as the interpretation of dreams. Troubles and difficulties may thus appear as storms; sorrow and grief as tears; troubled waters may represent pain, and smooth ice impending danger; a dry river-bed an approaching famine, and pretty flowers great joy to come, provided, always, we are disposed to admit a higher class of prophetic dreams. Such a view is supported by high authority, for since the days of Aristotle, great writers, divines as well as philosophers, have endeavored to classify dreams according to their nature and importance. The great reformer, Melanchthon, in his work on the soul, divided them into common dreams, void of importance; prophetic dreams, arising from the individual gifts of the sleeper; divine dreams, inspired by God either directly or through the agency of angels, and finally, demoniac dreams, such as the witches' sabbath. One great difficulty attending all such classification arises, however, from the well-known fact, already alluded to, that external sensations are by far the most frequent causes of dreams. Even these have been systematically arranged by some writers, most successfully, perhaps, in the work of Maine de Biran, but he overlooks again the numerous cases in which external noises and similar accidents produce a whole train of thoughts. Thus Pope dreamed of a Spaniard who impudently entered his library, ransacked the books on the shelves, and turned a deaf ear to all his remonstrances. The impression was so forcible that he questioned all his servants, and investigated the matter thoroughly, till he was finally forced to acknowledge that the whole transaction was a dream caused by the fall of a book in his library, which he heard in his sleep. A still more remarkable case occurred once in a hotel in Dantzic, where not one person only, but all the guests, without exception, dreamed of the sudden arrival of a number of travelers, who disturbed the whole house, and took possession of their rooms with unusual clatter and noise. Not one had arrived, but during the night a violent storm had arisen, causing doors to slam and window-shutters to flap against the house, noises which had aroused in more than fifty people precisely the same impressions. IV. VISIONS. Concipiendis visionibus quas phantasias vocant. --QUINTILIAN.