The psychology of Epicurus and the other atomists was a simple kind of mechanical sensationalism. _Eidola_ or images from external objects enter the soul through the sense organs. The mind stores up a great multitude of these _eidola_. Whenever we call up a picture of memory or of the imagination, we turn the attention to one of these images. Thus the mind sees in the same way that the eye does, with this difference, that it perceives much thinner eidola.[30] Cicero and Quintilian both dwell upon the importance of memory; and both seem to adopt the common theory of the time, that impressions are stamped on the mind as the signets are marked on wax. They are especially concerned, however, with principles relating to the exercise of memory; and they give instructions for mnemonic aids in oratory. Cicero lays special stress upon order as an aid to memory; and as sight is the most acute of the senses, those things are best remembered which are visualized by the imagination. In accordance with the ancient mnemonic systems he would have these imagined forms localized. The advice of Quintilian in respect to memory is especially sensible. According to him, nothing can take the place of exercise and labor. Next in importance is the division and arrangement of one’s subject. He notices also the importance of good health; and says that for slow minds an interval of rest is a good thing, though he seems to be uncertain whether the advantage is due to the rest, or whether it gives reminiscence time to mature.[31] IV. The Neo-Platonic psychology of memory is represented by Plotinus.[32] He discusses the subject at considerable length, and presents a somewhat original doctrine. Memory does not belong to God nor to the divine immutable intelligence in man, which knows by direct intellectual perception. It is a function of the soul and first appears when the world soul is individualized in bodies. Memory, however, has no basis in the physical organism, nor does the soul impress the sensations upon the body. The effects of sensations are not like impressions made by a seal, nor are they reactions (ἀντερείσεις), or configurations (τυπώσεις), but in sense-perception as in thought the soul is active. In memory, too, the soul is active, not passive. The influence of the body proves nothing against this. The changeable nature of the body may cause us to forget, but it cannot condition positive recollection. The body is the river of Lethe, but memory belongs to the soul. The part of the soul to which memory belongs is the image-forming faculty. This holds sense impressions as well as thought. Two souls, the higher and the lower, are concerned in memory. When the soul leaves the body, the recollections of the lower soul are soon forgotten in proportion as the higher soul rises toward the intelligible world.[33]