CHAPTER IX. 



UNIVERSAL GRAVITATION. 



' Nature and Nature's laws lay hid in night ; 

 God said 'Let Newton be!' and all was light." 



POPE. 



164. NEWTON'S life may be conveniently divided into three 

 portions. First came 22 years (1643-1665) of boyhood 

 and undergraduate life ; then followed his great productive 

 period, of almost exactly the same length, culminating in 

 the publication of the Principia in 1687 ; while the rest of 

 his life (1687-1727), which lasted nearly as long as the 

 other two periods put together, was largely occupied with 

 official work and studies of a non-scientific character, and 

 was marked by no discoveries ranking with those made 

 in his middle period, though some of his earlier work 

 received important developments and several new results 

 of decided interest were obtained. 



165. Isaac Newton was born at Woolsthorpe, near 

 Grantham, in Lincolnshire, on January 4th, 1643;* this 

 was very nearly a year after the death of Galilei, and a 

 few months after the beginning of our Civil Wars. His 

 taste for study does not appear to have developed very 

 earlv in life, but ultimately became so marked that, after 



* According to the unreformed calendar (O.S.) then in use in 

 England, the date was Christmas Day, 1642. To facilitate comparison 

 with events occurring out of England, I have used throughout this 

 and the following chapters the Gregorian Calendar (N.S.), which was 

 at this time adopted in a large part of the Continent (cf. chapter u 

 22). 



