Diadochus
According to Marbodaeus, this gem resembles the beryl in its properties, and was most valuable in divination. It serves for the invocation of spirits, and oracular responses could be discovered in it. Albertus Magnus writes it Diacodos, and it is possibly to this stone that Braithwaite alludes in his English Gentleman : "For as the precious stone Diacletes, though it have many rare and excellent sovereignties in it, yet loseth them all if put in a dead man's mouth." Marbodaeus mentions this in his verses as a property of the diadochus. The words of Leonardus are too curious to omit: "It disturbs devils beyond all other stones, for, if it be thrown in water, with the words of its charm sung, it shows various images of devils, and gives answer to those that question it. Being held in the mouth, a man may call any devil out of hell, and receive satisfaction to such questions as he may ask." He names it Diacodas or Diacodus.
The Devil attempting to seize a magician who had formed a pact with him, is prevented by a Lay Brother. Facsimile of a miniature in the Chroniques de Saint- Denis (13th cent. MS., Bibl. Nat., Paris) 2 angsafthede dracone ugauna en i abiliuzy The Prince of Darkness. After a miniature of the Holy Grail (15th cent. MS., Bibl. Nat., Paris) The Angel, holding the keys of Hell, enchains the Devil, in the shape of a dragon, in the Pit. Miniature from a Commentary on the Apocalypse (12th cent. MS., in the library of M. Ambrose Firmin-Didot) MEDIÆVAL CONCEPTIONS OF THE DEVIL [face p. 124 Diagrams, Magical: (See Magic.)