THE RENAISSANCE 145 



elaborate theories of the immortality of the soul, 

 accepted some form of reincarnation, and believed 

 in the possibility of communication between spirits 

 existing in the aethereal, aerial and terrestrial states. 



Human progress does not hold on its way in a steady 

 line. The general trend of the curve may be upwards, 

 as it certainly has been, in the matter of 

 scientific thought, for the past four cen- 

 turies. But superposed on the general curve are 

 oscillations, often violent, which disturb its course. 



At the Renaissance, the movement towards ration- 

 alism in science became appreciable ; the triumphs of 

 that spirit mark the years we have surveyed. The 

 ideas of the French Encyclopaedists, and the other 

 tendencies of thought for the half-century preceding 

 the Revolution, show the swing of the pendulum, 

 which, as always, overshot its point of equilibrium, 

 and, a century later, reached an extreme from which 

 retreat was necessary by another path. 



At the close of the Middle Ages, Thomas Aquinas 

 gives the great example of a complete scheme of uni- 

 versal knowledge, including science, framed in accord- 

 ance with orthodox Roman theology. From his day 

 onwards we see a change. Duns Scotus and Occam 

 at once began the separation between faith and reason 

 necessary for the development of natural knowledge 

 at that time. Yet the liberation of science from theo- 

 logical preconceptions was long delayed. The works 

 of Descartes and Leibniz contain theological reasoning 

 inextricably interwoven with physical facts. Even 

 Euler (1744) based the principle of least action on 

 the ground that the construction of the Universe is 



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