THE LIFE AND WORK OF DARWIN 209 



The years between 1836 and 1842 were marked 

 by the gradual appearance of that weakness of 

 health which ultimately forced him to leave London, 

 and take up his abode for the rest of his life in a 

 quiet country-house. This greatly discouraged him, 

 and threatened thus early to become permanent. In 

 1839 he married his cousin Emma Wedgwood, and 

 lived for three years in Upper Gower Street, then 

 suffering much from illness. In 1842 he purchased 

 a house at Down, near Beckenham, where the rest 

 of his life was spent, and the greater part of his 

 work accomplished. 



The "Origin of Species" was his first and 

 greatest work, the "chief work of my life." We 

 have already sketched the history of the develop- 

 ment of the theory, and may now consider it from 

 the more personal point of view. During the 

 voyage of the Beagle, Darwin was led to think much 

 on the subject ; and on his return, as soon as he had 

 leisure, returned to it. During the voyage he 

 "believed in the permanence of species, though 

 experiencing occasionally " vague doubts." On his 

 return in ) 836, while preparing his journal, he noted 

 how many facts indicated the common descent of 

 species. 



On the 1st of July 1837 he opened his first note- 

 book to record any facts bearing on the transmuta- 

 tion of species, and "did not become convinced that 

 species were mutable until I think two or three 

 years had elapsed." 



Darwin was most impressed by the South Ameri- 

 can fossils, and by geographical distribution, especially 



o 



