vi PREFACE 



hardly impair, Descartes possessed, in addition, 

 a rare mastery of the art of literary expression. 

 If the " Discours de la Methode " had no other 

 merits, it would be worth study for the sake of 

 the luminous simplicity and sincerity of its style. 



A mathematician of the very first rank, 

 Descartes knew all that was to be known of 

 mechanical and optical science in his day; he was 

 a skilled and zealous practical anatomist; he was 

 one of the first to recognise the prodigious im- 

 portance of the discovery of his contemporary 

 Harvey; and he penetrated more deeply into 

 the physiology of the nervous system than any 

 specialist in that science, for a century, or more, 

 after his time. To this encyclopaedic and yet 

 first-hand acquaintance with the nature of things, 

 he added an acquaintance with the nature of 

 men (which is a much more valuable chapter of 

 experience to philosophers than is commonly 

 imagined), gathered in the opening campaigns of 

 the Thirty Years' War, in wide travels, and amidst 

 that brilliant French society in which Pascal was 

 his worthy peer. Even a " Traite des Passions," to 

 be worth anything, must be based upon observation 

 and experiment; and, in this subject, facilities for 

 laboratory practice of the most varied and ex- 

 tensive character were offered by the Paris of 

 Mazarin and the Duchesses; the Paris, in which 

 Descartes' great friend and ally, Father Mersenne, 

 reckoned atheists by the thousand; and in which 



