6 INTRODUCTION 



actually presented to King Louis, but Leibniz in 1672 

 went by invitation to Paris to explain his project. His 

 advice was not taken ; but he remained in Paris for 

 four years, during which he devoted himself to the study 

 of the higher mathematics l and to the discussion of the 

 Cartesian philosophy. He had already corresponded with 

 Arnauld, and he now met also Huygens and Male- 

 branche. At this time, says Leibniz himself, 'law and 

 history were my forte V But intercourse with Huygens 

 and the study of the mathematical works of Pascal intro- 

 duced him to the problems of modern mathematics. 

 Huygens, he tells us 3 , 'had no taste for metaphysics,' 

 but Leibniz learned from him mathematical methods 

 and principles which influenced the growth of his philo- 

 sophy, and which set him on the way to the discovery of 

 the Differential Calculus. At this time also Leibniz in- 

 vented a calculating machine, superior to that of Pascal, 

 which could only add and subtract, while his own machine 

 could also multiply, divide, and extract roots. And in 

 other ways the residence of Leibniz in Paris greatly 

 affected his life-work. For instance, it probably led to 

 his writing so much in French. He had already, in his 

 essay on the philosophical style of Nizolius (1670), advo- 

 cated the use of the German language for philosophical 

 and other works. But in the time of Louis XIV Paris 

 was the intellectual centre of Europe, and to write for 

 the world was to write in French. While, therefore, 



plans which it suggests that Napoleon was at one time supposed 

 to have borrowed its ideas for his campaign. Though this has 

 been shown to be a mistake, the coincidence between the suggested 

 expedition of Louis XIV and the actual expedition of Napoleon is 

 sufficiently noteworthy. 



1 * The merit of an author in mathematics cannot be disputed, as 

 it can in other subjects. This is the reason why I remained some 

 time in France, in order to perfect myself .in mathematics, and 

 I gave my time to these sciences not on their own account, but in 

 order to make them contribute to the advancement of piety.' Lettre 

 au Due Jean Frederic (undated) (Klopp, iv. 450). 



2 Lettre a la Comtesse de Kilmansegg (1716) (Dutens, iii. 456). 

 * E. 702 b ; G. iii. 607. 



