in the Seventeenth Century. 9 



every magnet attracts the south-seeking pole of every other 

 magnet, and repels its north-seeking pole. 



Descartes attempted* to account for magnetic phenomena 

 by his theory of vortices. A vortex of fluid matter was 

 postulated round each magnet, the matter of the vortex entering 

 by one pole and leaving by the other : this matter was supposed 

 to act on iron and steel by virtue of a special resistance to its 

 motion afforded by the molecules of those substances. 



Crude though the Cartesian system was in this and many 

 other features, there is no doubt that by presenting definite 

 conceptions of molecular activity, and applying them to so wide 

 a range of phenomena, it stimulated the spirit of inquiry, and 

 prepared the way for the more accurate theories that came after. 

 In its own day it met with great acceptance: the confusion which 

 had resulted from the destruction of the old order was now, as 

 it seemed, ended by a reconstruction of knowledge in a system 

 at once credible and complete. Nor did its influence quickly 

 wane ; for even at Cambridge it was studied long after Newton 

 had published his theory of gravitation ;f and in the middle of 

 the eighteenth century Euler and two of the Bernoullis based 

 the explanation of magnetism on the hypothesis of vertices.* 



Descartes' theory of light rapidly displaced the conceptions 

 which had held sway in the Middle Ages. The validity 

 of his explanation of refraction was, however, called in 

 question by his fellow-countryman Pierre de Ferinat (b. 1601, 

 d. 1665), and a controversy ensued, which was kept up 

 by the Cartesians long after the death of their master. Fermat 



* Principia, Part iv, 133 sqq. 



f Winston has recorded that, having returned to Cambridge after his 

 ordination in 1693, he resumed his studies there, " particularly the Mathematicks, 

 and the Cartesian Philosophy : which was alone in Vogue with us at that Time. 

 But it was not long before I, with immense Pains, but no Assistance, set myself 

 with the utmost Zeal to the study of Sir Isaac Newton's M-onderful Discoveries." 

 \Vhiston's Memoirs (1749), i, p. 36. 



J Their memoirs shared a prize of the French Academy in 1743, and were 

 printed in 1752 in the Heciieil des pieces qui ontremporte les prix de VAcad., tome v. 

 Renati Descartes Epistolae, Pars tertia ; Amstelodami, 1683. The Fennat 

 correspondence is comprised in letters xxix to XLVI. 



