Clement died in 1268. The papacy remained vacant for a couple of years, but in 1271 Gregory X came in on a conservative reaction. Bacon passed most of the rest of his life in prison, perhaps through his own ungovernable temper, and ostensibly his writings seem to have had little or no effect on his contemporaries, yet it is certain that he was not an isolated specimen of a type of intelligence which suddenly bloomed during the Reformation. Bacon constantly spoke of his friends, but his friends evidently did not share his temperament. The scientific man has seldom relished martyrdom, and Galileo’s experience as late as 1633 shows what risks men of science ran who even indirectly attacked the vested interests of the Church. After the middle of the thirteenth century the danger was real enough to account for any degree of secretiveness, and a striking case of this timidity is related by Bacon himself. No one knows even the name of the man to whom Bacon referred as “Master Peter,” but according to Bacon, “Master Peter” was the greatest and most original genius of the age, only he shunned publicity. The “Dominus experimentorum,” as Bacon called him, lived in a safe retreat and devoted himself to mathematics, chemistry, and the mechanical arts with such success that, Bacon insisted, he could by his inventions have aided Saint Louis in his crusade more than his whole army. [Footnote: Émile Charles, _Roger Bacon. Sa vie et ses ouvrages_, 17.] Nor is this assertion altogether fantastic. Bacon understood the formula for gunpowder, and if Saint Louis had been provided with even a poor explosive he might have taken Cairo; not to speak of the terror which Greek fire always inspired. Saint Louis met his decisive defeat in a naval battle fought in 1250, for the command of the Nile, by which he drew supplies from Damietta, and he met it, according to Matthew Paris, because his ships could not withstand Greek fire. Gunpowder, even in a very simple form, might have changed the fate of the war.