ENERGETICS 3 g 



used in representing experimental results in a graphic form. The fact should also be 

 remembered that Descartes realised the import of his method as the commencement of "the 

 expression by means of algebraical formula} of continuously varying quantities " (Playfair) 



FIG. 26. PORTRAIT OF JOHN NAPIER OF MERCHISTON. 



(From portrait in possession of the University of Edinburgh. 

 From The Merchistonian, 1912-13.) 



In other words, the history of the differential calculus may be said to begin with him. His 

 portrait will be found in Fig. 25. 



If the reader attempts to follow the reasoning given by Descartes himself, he will find 

 it a difficult task. It seems as if the philosopher did not wish that his opponents, of whose 

 mental capacity he had a very small opinion, should understand him too easily. Accessible 

 editions of Descartes' works will be found given in the Bibliography at the end of the 

 present work. 



