INTRODUCTORY 33 



gardeners, and by extensive reading. When I see the 

 Hst of books of all kinds which I read and abstracted, 

 including whole series of Journals and Transactions, I am 

 surprised at my own industry. I soon perceived that 

 selection was the keystone of man's success in making 

 useful races of animals and plants. But how selection 

 could be applied to organisms living in a state of nature 

 remained for some time a mystery to me." 



Here we have Darwin's scientific classification of facts, 

 what he himself terms his " systematic inquiry." Upon 

 the basis of this systematic inquiry comes the search for 

 a law. This is the work of the imagination ; the inspira- 

 tion in Darwin's case being apparently due to a perusal 

 of Malthus' Essay on Population. But Darwin's imagina- 

 tion was of the disciplined scientific sort. Like Turgot, 

 he knew that if the first thing is to invent a system, then 

 the second is to be disgusted with it. Accordingly there 

 followed the period of self-criticism, which lasted four or 

 five years, and it was no less than nineteen years before 

 he gave the world his discovery in its final form. Speak- 

 ing of his inspiration that natural selection was the key to 

 the mystery of the origin of species, he says : — 



" Here, then, I had at last got a theory by which to 

 work ; but I was so anxious to avoid prejudice, that I 

 determined not for some time to write even the briefest 

 sketch of it. In June 1842 {i.e. four years after the 

 inspiration), I first allowed myself the satisfaction of 

 writing a very brief abstract of my theory in pencil in 3 5 

 pages ; and this was enlarged during the summer of i 844 

 into one of 230 pages, which I had fairly copied out and 

 still possess." 



Finally an abstract from Darwin's manuscript was 

 published with Wallace's Essay in 1858, and the Origin 

 of Species appeared in 1859- 



In like manner, Newton's imagination was only paral- 

 leled by that power of self-criticism which led him to lay 

 aside a demonstration touching the gravitation of the 

 moon for nearly eighteen years, until he had supplied a 

 missing link in his reasoning. But our details of Newton's 



