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from without we know that it comes from within. 

 As Mr Benn puts it, we have extended the atomistic 

 method from " matter " to motion. Harvey's con- 

 temporary, Francis Bacon, sagaciously guessed that 

 heat is an expansive motion of particles ; but he 

 regarded heat and cold as two contrary principles. 

 Almost in the same generation the brilliant John 

 Mayow perceived a substance in the air "allied 

 to saltpetre," which passed in and out of the blood 

 by the way of the lungs or placenta. " Innate heat " 

 then gave way to phlogiston ; but it was not till 

 the discovery of oxygen and of the conservation 

 of energy that we attained a theory of energy, and 

 finally got rid of " matter and form," and of all the 

 thicket of metaphysics, relating thereto ; through 

 which in the day of Harvey no mind, however 

 mighty, could have made its way. 



In the history of medieval thought we must 

 always bear in mind that in neither of its two periods 

 were theology, logic, metaphysics, psychology, or 

 even physics, fully differentiated ; and before the 

 Arabian literature they were not differentiated at 

 all 1 . Logic, which for us is but a drill, and, like all 



1 The word "philosophy" in the Middle Ages signified the 

 pursuit of knowledge of things human and divine, and of the 

 causes of them. It was often divided into Physics, Ethics and 



