THE PATH OF EVOLUTION 



had been held in suspense so many years by the 

 error in the measurement of a degree of the earth's 

 curvature now gave himself to the renewed calcula- 

 tion with a boldness of thought never before seen, 

 and proved by the law above named how the planets 

 and comets were held in place ; determined the nature 

 of their orbits ; the weight and form of their masses ; 

 the oscillation of the tides and fluids that covered 

 them ; the precession of the equinoxes and the endless 

 number of other questions thus given birth to. In 

 1684 Newton showed to Halley who had come to 

 Cambridge to consult him in regard to the action of 

 centrifugal forces a treatise he had composed con- 

 cerning motion (de motio), and which was the basis of 

 his great work, " The Principia." 



The latter work, " Philosophia Naturalis Principia 

 Mathematica," was shown to the Royal Society in 

 1686. The work was published by Halley at his 

 own expense. Among the savants of the time there 

 were but few capable of appreciating the value thereof, 

 and of the few, Hooke and Wren disputed the orig- 

 inality of the discoveries. Huygens even only par- 

 tially accepted the doctrine of universal gravitation. 

 He applied it to the heavenly bodies, but substituted 

 theories of his own for the movements of bodies on 

 the earth. Leibnitz was led by his metaphysical 

 tendencies to undervalue it, and to suggest methods 



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