We have evidence of the use of crystal balls as means of divination in medieval times, and “scrying” in some of its many forms was by no means rare in the Greek and Roman periods. The essential requisite for the exercise of this species of divination is a polished surface of some sort upon which the scryer shall gaze intently; for this purpose mirrors, globules of lead or quicksilver, polished steel, the surface of water, and even pools of ink, have been employed and have been found to insure quite as satisfactory results as the crystal ball. The points of light reflected from the polished surface (_points de repère_) serve to attract the attention of the gazer and to fix the eye until, gradually, the optic nerve becomes so fatigued that it finally ceases to transmit to the sensorium the impression made from without and begins to respond to the reflex action proceeding from the brain of the gazer. In this way the impression received from within is apparently projected and seems to come from without. It is easy to understand that the results must vary according to the idiosyncrasy of the various scryers; for everything depends upon the sensitiveness of the optic nerve. In many cases the effect of prolonged gazing upon the brilliant surface will simply produce a loss of sight, the optic nerve will be temporarily paralyzed and will as little respond to stimulation from within as from without; in other cases, however, the nerve will be only deadened as regards external impressions, while retaining sufficient activity to react against a stimulus from the brain centres. It is almost invariably stated that, prior to the appearance of the desired visions, the crystal seems to disappear and a mist rises before the gazer’s eye. [Illustration: ROCK-CRYSTAL BALL PENETRATED BY CRYSTALS OF RUTILE. MADAGASCAR.] The Achaians, as Pausanius relates, frequently used a mirror to divine diseases or to learn whether there was danger of sudden death. Of the Temple of Demeter, or Ceres, at Patras, he writes:[266] In front of the temple of Demeter there is a well. A stone wall separates this well from the temple, but steps lead down to it from the outside. Here there is an infallible oracle, although it does not answer all questions, but only those touching diseases. They attach a slender cord to a mirror and let it down into the well, balancing it carefully so that the water does not cover the face, but only touches the rim. Then, after making a prayer to the goddess and burning incense to her, they look into the mirror, and it shows whether the sick person will die or recover. Such is the power of truth in this water. This sacred well with its oracle of the magic mirror must have been in Lucian’s mind when, in his description of the palace of the Moon-King, he says:[267]