The chemical investigations of the great English Franciscan have proved valuable to the science which he loved. He studied carefully the properties of saltpetre, and if he did not discover gunpowder, he contributed to its perfection by teaching the purification of saltpetre by its dissolution in water and by crystallisation. He also called attention to the chemical rôle played by the air in combustion.[J] Many of Bacon’s works still remain in manuscript, but his _Speculum Alchimiæ_ was done into French by Girard de Tourmes, and published at Lyons in duodecimo and octavo in 1557. _De Potestate Mirabili Artis et Naturæ_, which is merely a chapter of the Epistle already cited, was translated by the same hand. In another work, entitled _Radix Mundi_, the supreme secret of Hermetic philosophy is said to be hidden in the four elements. This treatise, which quotes Paracelsus, is, however, an impudent forgery. The “Mirror of Alchemy,” like other works of the philosophers, appeals to Hermes as to a master-initiate, whose authority is not only sufficient but final. The natural principles of all metals are argent vive, that is, sophic mercury, and sulphur. The various proportions in which these principles are combined, together with their degrees of purity, constitute the sole difference between the best and the basest metal. FOOTNOTES: [I] Nam quadraturam circuli se ignorasse confitetur, quod his diebus scitur veraciter. [J] Figuier, _L’Alchimie et les Alchimistes_, p. 97. ALAIN OF LISLE. An alchemical treatise, entitled _Dicta de Lapide Philosophico_, appeared in octavo at Leyden during the year 1600. It was attributed to Alanus Insulensis, and was reprinted in the _Theatrum Chimicum_, Argentorati, 1662. It is denied that this work is the production of that Alain de Lisle who was called the universal doctor, and who, after a brilliant period passed in the University of Paris, retired to a cloister as a lay brother, in order to be master of his time, and to devote himself entirely to philosophy. Migne’s _Dictionnaire des Sciences Occultes_ asserts that another Alanus flourished at the same period, but the existence of the alchemical volume is the sole ground for this statement. It cannot be shown, on the other hand, that Alain practised the Hermetic Science, but he was the author of a “Commentary on the Prophecies of Merlin.” He was made bishop of Auxerre, and died in 1278. The publishers of alchemical treatises were accustomed to trade upon brilliant reputations of the past by attributing worthless works to great authorities. The name of Alanus Insulensis appearing on the title-page of the _Dicta de Lapide Philosophico_ may perhaps be accounted for in this manner.