The pope issued an encyclic letter, entreating those who owed him obedience to reveal where Arnold's Treatise on the Practice of Medicine might be found, it having been lost or concealed. It appears that the chief offences committed by Arnold against the Church were that he had predicted that the world would come to an end A.D. 1335; that he had said the bulls of the pope were only the work of a man, and that the practice of charity is better than prayer, or even than the mass. If he was the author of the celebrated book "De Tribus Impostoribus," as was suspected by some, it is not remarkable that he was so closely watched and disciplined. Like many of his contemporaries, he mingled a great deal of mysticism with his work, recommending, during his alchemical operations, the recitation of psalms, to give force to the materials employed. Among other such things, he describes a seal, decorated with scriptural phrases, of excellent use in preserving one from sudden death. It appears, however, to have failed of its effect on the night when Arnold's ship was drifting on an Italian lee-shore, and he had most need of it. [Sidenote: Two impulses--intellectual and moral--in operation.] The two antagonistic principles--ecclesiastical and intellectual--were thus brought in presence of each other. On other occasions they had already been in partial collision, as at the iconoclastic dispute which originated in the accusations of the Mohammedans, and ended in the tearing of Christendom asunder.