In the following chapters we shall see that a great variety of objects are used to promote the externalisation of subliminal images. Not only is the plain crystal, or its congener the black stone, used, together with its first cousin the mirror, and the primitive substitute of water, but almost any bright object seems to have been employed at one time or another. Thus we find the sword among the Romans ; and in mediaeval Europe polished iron is suggested in Faust's Höllenzwang ; lamp-black is sometimes smeared on the hand, or, as we shall see later, a pool of ink poured into it ; visions are seen in smoke and flame, in black boxes, in jugs, and on white paper; in more than one place we find that diviners gaze at the livers of slain animals to provoke hallucinations ; and a classical and mediaeval method, which has lasted until our own day, consisted in blindfolding the seer, and suggesting to him that he should scry in a mirror with the top of his head.