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164. Author:Isaac Newton 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 early in life, but ultimately became so marked that, after