LIFE AND WOEKS 5 



of poor Germany left almost without inhabitant V The 

 treaty of Westphalia had secured peace and some measure 

 of political unity, but it pointed also to an ecclesiastical 

 reunion, yet to be realized, which to men like the Elector 

 of Mainz and Boineburg seemed the best means of re- 

 storing power and happiness to the country. Negotiations 

 for the reunion of Eoman Catholics and Protestants had 

 already been begun, and thus early in his diplomatic 

 career Leibniz took part in the work of conciliation 

 which in various ways he continued throughout his life. 

 At the suggestion of Boineburg he made a special study 

 of the doctrine of transubstantiation, with the result 

 (expressed in a letter to Arnauld in 1671) that he found 

 it impossible to reconcile the Cartesian view of material 

 substance as pure extension either with the Roman 

 Catholic or with the Lutheran doctrine. He accord- 

 ingly formed the purpose of discovering a theory of 

 substance which should satisfy both, and should thus 

 become a philosophical basis for the reconciliation of the 

 Churches. 



Paris and London. 



Presently events occurred which led him away from 

 Mainz and gave him new opportunities of study and of 

 intercourse with learned men. Leibniz and his friends 

 felt strongly the necessity of drawing into safe channels 

 the military ambitions of Louis XIV, and accordingly 

 Leibniz prepared a most elaborate work in which he 

 suggested to the King of France the advantages that 

 would arise from a conquest of Egypt, and tried to con- 

 vince him that it was more worthy of a Christian king 

 to fight the unchristian Turks than to harass a poor 

 little people like the Dutch 2 . This book was never 



1 From a letter of Leibniz, quoted by Foucher de Careil, vol. iv. 

 Introduction, p. xx. 



2 This Projet de Conquete de I'figypte was published by Foucher de 

 Careil, vol. v. It shows a most remarkable knowledge regarding 

 the state of the country and its possibilities, and so clever are the 



