SEVENTEENTH AND EIGHTEENTH CENTURIES 179 

 in Bavaria, receiving a strictly religious upbringing, which left its mark on 

 his entire life. He studied at Jena, where be became a doctor and for a time 

 gave lectures. After having been for some years court physician at Weimar, 

 he came, as mentioned above, to Halle and taught there for about twenty 

 years. At first his relations with Hoffmann were in every way friendly, but 

 gradually the good feeling between them changed, and, finding that Hoff- 

 mann's personal superiority excluded all possibility of competition, Stahl 

 resigned from his professorship and in 1716 accepted an appointment as 

 physician to the court in Berlin. He died there in 1734. Hoffmann and Stahl 

 possessed their pietistic devoutness in common, but otherwise they were 

 highly contrasted: Hoffmann, of stately build, lovable, and popular; Stahl, 

 in his appearance insignificant, in his manner austere and inaccessible, in- 

 tolerant towards his opponents, and bitter in controversy. At any rate he 

 was a sincere seeker after truth, who was honest enough — a quality other- 

 wise not very common amongst scientists — when he changed his opinion, 

 openly to admit the incorrectness of his former views, and he likewise 

 possessed that rare habit of gratefully acknowledging his predecessors' 

 contributions to the problems he dealt with, 



Reformer of chemistry 

 As a scientific writer Stahl was, like Hoffmann, extraordinarily productive 

 and he dealt with a considerable number of different medical problems. As 

 a scientist he was undeniably superior to his rival; in fact, his name is one 

 of the foremost in the history of the natural sciences — principally on ac- 

 count of his work as a chemist. At the close of the seventeenth century there 

 was still being commonly taught at the German universities the subject of 

 alchemy — belief in the transformation of metals, in the philosophers' 

 stone, and all the rest of the mediasval mysticism which in western Europe, 

 thanks to Boyle and his successors, had already been disestablished. Even 

 Stahl had begun as an alchemist, and in his earliest writings he discusses 

 the usual alchemistic problems, but by his own efforts he undeceived himself 

 and thereafter never hesitated to point to the treatises of his youth as a 

 warning. That uniform conception of the changes in nature which the 

 alchemists sought to produce by means of their mystical speculations Stahl 

 now endeavoured to attain by a comparison of those processes that take 

 place in combustion on the one hand and the calcination of metals on the 

 other. Finally he obtained a common ground of explanation for these phe- 

 nomena by postulating the existence of a fluid substance, phlogiston, in both 

 combustible substances and metals; in combustion phlogiston disappeared 

 from the burnt material, as it did also from the metal in calcination; the 

 metal calces were thus like the metal, minus phlogiston. If the metal calces 

 were heated with a substance containing phlogiston — as, for instance, 

 coal — the metal was recovered by the reintroduction of phlogiston. — 



