Ammianus Marcellinus describes a séance in 371 C.E., in The Later Roman Empire (354-378 C.E.). The instrument used was a metal disk with the alphabet inscribed around its circumference, supported on an olivewood tripod. A ring on a thread was held above it, to spell out messages and answers. Thus we have a neat combination of pendulum and proto-Ouija board.
“My lords, in an unlucky moment we put together out of laurel twigs in the shape of the Delphic tripod the hapless little table before you. We consecrated it with cryptic spells and a long series of magical rites, and at last made it work. The way in which it did so, when we wished to consult it about hidden matters, was this. It was placed in the middle of a room thoroughly fumigated with spices from Arabia, and was covered with a round dish made from the alloys of various metals. The outer rim of the dish was cunningly engraved with the twenty-four letters of the alphabet separated by accurate intervals. A man dressed in linen garments and wearing linen sandals, with a fillet around his head and green twigs from a lucky tree in his hand, officiated as priest. After uttering a set prayer to invoke the divine power which presides over prophecy, he took his place above the tripod as his knowledge of the proper ritual had taught him, and set swinging a ring suspended by a very fine cotton thread which had been consecrated by a mystic formula. The ring, moving in a series of jumps over the marked spaces, came to rest on particular letters, which made up hexameters appropriate to the questions put and in perfect scansion and rhythm, like the lines produced at Delphi or by the oracle of the Branchidae.”