sanctioned by the learned, and in his _Natural History_ Bacon lays it down as credible that "precious stones may work by consent upon the spirits of men to comfort and exhilarate them." The learned lawyer and philosopher, indeed, was not in this much superior to the plain and simple folk who still imagined that every precious stone had some mystic value communicable to the wearer. About the same time De Boot, or Boethius, the learned physician to the Emperor Rudolf II, published his famous Lapidary, which Mr. C. W. King recommends as a work worthy of especial study for the properties of stones, and mentions how it "draws a distinction that curiously illustrates the struggle then going on between traditional superstition and common sense."[43] [41] Paton (J.), _Scottish national memorials_, p. 337. [42] The foremost interpreter of their mysteries in the Middle Ages was Marbode, Bishop of Rennes (1095-1123), in his _De Lapidibus Pretiosis Enchiridion_. [43] King, _Precious stones_, p. 12. Treatises on precious stones frequently find a place in sixteenth-century Herbals, and are often accompanied by very spirited woodcuts representing the working of precious stones and the process of adapting them to personal ornaments, together with designs of actual articles of jewellery in which they are set. Two of the finest books of the kind are--an _Ortus Sanitatis_ (Strasburg, _circa_ 1497), and a _Kreuterbuch_ printed at Frankfort in 1536. With the advance of Christianity the representation of the subjects of pagan mythology was forbidden by law; but the old ideas were retained for many years, and small objects like cameos or intaglios were carried about concealed upon the person. Later on, when all knowledge of classical art had sunk into oblivion, such stones became prized not only for the subjects engraved on them, which their mediæval owner seldom understood, but also for the fact that they were supposed to possess special talismanic virtues. The majority of these gems were mounted as rings or as seals of secular and ecclesiastical personages of rank.