there was the secret of eventually manageable energy for transportation purposes. Succeeding centuries were not as fruitful in great scientists as the thirteenth, and yet at the beginning of the fourteenth there was a pope, three of whose scientific treatises--one on the transmutation of metals, which he considers an impossibility, at least as far as the manufacture of gold and silver was concerned; a treatise on diseases of the eyes, of which Professor Allbutt [Footnote 4] says that it was not without its distinctive practical value, though compiled so early in the history of eye surgery; and, finally, his treatise on the preservation of the health, written when he was himself over eighty years of age--are all considered by good authorities as worthy of the best scientific spirit of the time. This pope was John XXII, of whom it has been said over and over again by Protestant historians that he issued a bull forbidding chemistry, though he was himself one of the enthusiastic students of chemistry {55} in his younger years and always retained his interest in the science. [Footnote 5] [Footnote 4: Address cited] [Footnote 5: For the refutation of this calumny with regard to John XXII, see "Pope John XXII and the supposed Bull forbidding Chemistry," by James J. Walsh, Ph. D., LL. D., in the _Medical Library and Historical Journal_, October, 1905.] During the fourteenth century Arnold of Villanova, the inventor of nitric acid, and the two Hollanduses kept up the tradition of original investigation in chemistry. Altogether there are some dozen treatises from these three men on chemical subjects. The Hollanduses particularly did their work in a spirit of thoroughly frank, original investigation. They were more interested in minerals than in any other class of substances, but did not waste much time on the question of transmutation of metals. Professor Thompson, the professor of chemistry at Edinburgh, said in his history of chemistry many years ago that the Hollanduses have very clear descriptions of their processes of treating minerals in investigating their composition, which serve to show that their knowledge was by no means entirely theoretical or acquired only from books or by argumentation. Before the end of this fourteenth century, according to the best authorities on this subject, Basil Valentine, the more particular subject of our essay, was born.