Bacon, Roger (c.1214–c.1292)
Roger Bacon [A] was not personally an experimenter or mathematician but he realized the importance of experiment and mathematics of the advancement of science. His imagination enabled him to make a remarkable collection of scientific suggestions, culled from many sources and ranging from vague hints to clear diagrams. He gave substantially correct optical explanations of [B] why a spherical flask of water  acts as a burning glass  to concentrate the rays of the sun  and [C, see below] how a convex lens  produces a magnified image  of an object  beneath it.
Bacon gave substantially correct optical explanations of [B] why a spherical flask of water  acts as a burning glass  to concentrate the rays of the sun  and [C, see below] how a convex lens  produces a magnified image  of an object  beneath it.
Roger Bacon was an English philosopher and experimenter renowned in his own day for his great knowledge of science and remembered today for allegedly prophesying many of the inventions of later centuries: aircraft, telescopes, steam engines, microscopes, and so on. In fact he was a wealthy lecturer in the schools of Oxford and Paris with a passion for alchemical (see alchemy) and other experiments, whose later life was overshadowed by disputes with the Franciscan Order, of which he had become a member in 1257. His principal writings were the Opus Majus, Opus Minor, and Opus Tertium.
Bacon described the preparation of black powder sometime in the late 1240s. He also wrote in his Epistola Fratris Rog. Baconis, de secretis operibus artis et naturae et nullitate magiae (Epistle of Roger Bacon on the Secret Works of Art and of Nature and Also on the Nullity of Magic) about devices that sound like rockets:
We can, with saltpeter and other substances, compose artificially a fire that can be launched over long distances... By only using a very small quantity of this material much light can be created accompanied by a horrible fracas. It is possible with it to destroy a town or an army ... In order to produce this artificial lightning and thunder it is necessary to take saltpeter, sulfur, and Luru Vopo Vir Can Utriet.