During the fourteenth, fifteenth, and sixteenth centuries the cult of alchemy attained to the dignity of a religion. Belief in transmutation and in the virtues and powers of the philosopher’s stone, in the universal medicine, the alkahest, and the elixir of life, formed its articles of faith. The position it acquired was due to some extent to the attitude towards it of the Romish Church. Many reputable bishops and fathers were professed alchemists; and chemical laboratories, as in the Egyptian temples, were to be found in monasteries throughout Christendom. Pope John XXII., who had a laboratory in his palace at Avignon, is the reputed author of a work, _Ars Transmutatoria_, published in 1557. But to a still larger extent it was due to the fact that alchemy appealed to some of the strongest of human motives—the wish for health, the fear of death, and the love of wealth. It was a cunningly devised system, which exploited the foibles and frailties of human nature. The policy of the Church, however, it should be said, was not consistently and uniformly favourable to alchemy. Its practices occasionally came under the papal ban, although at times, to suit the exigencies of Christian princes, the interdict was removed. Theosophy and mysticism were first imported into alchemy, not by Arabs, but by Christian workers. The intimate association of religion with alchemy during the Middle Ages is obvious in the writings of Lully, Albertus Magnus, Arnaud de Villeneuve, Basil Valentine, and other ecclesiastics. Invocations to divine authority are freely scattered over their pages. Even the lay alchemist professed to rule his life and conduct by the example and precepts of the good Bishop of Regensburg. He was directed to be patient, assiduous, and persevering; discreet and silent; to work alone; to shun the favour of princes and nobles, and to ask the divine blessing on each operation of trituration, sublimation, fixation, calcination, solution, distillation, and coagulation.