286 THE 'ORIGIN OF SPECIES.' [i860. 



far as I do, yet he can give no good reason why he should 

 not. It is funny how each man draws his own imaginary line 

 at which to halt. It reminds me so vividly what I was told * 

 about you when I first commenced geology to believe a 

 little, but on no account to believe all. 



Ever yours affectionately, 



C. Darwin. 



C. Darwin to Asa Gray. 



Down, February 18th [i860]. 

 My dear Gray, I received about a week ago two sheets 

 of your Review ;f read them, and sent them to Hooker ; they 

 are now returned and re-read with care, and to-morrow I 

 send them to Lyell. Your Review seems to me admirable ; 

 by far the best which I have read. I thank you from my 

 heart both for myself, but far more for the subject's sake. 

 Your contrast between the views of Agassiz and such as mine 

 is very curious and instructive.^ By the way, if Agassiz 

 writes anything on the subject, I hope you will tell me. I am 

 charmed with your metaphor of the streamlet never running 

 against the force of gravitation. Your distinction between 

 an hypothesis and theory seems to me very ingenious ; but I 

 do not think it is ever followed. Every one now speaks of the 

 undulatory theory of light ; yet the ether is itself hypothetical, 

 and the undulations are inferred only from explaining the 

 phenomena of light. Even in the theory of gravitation is the 

 attractive power in any way known, except by explaining 

 the fall of the apple, and the movements of the Planets ? It 

 seems to me that an hypothesis is developed into a theory 

 solely by explaining an ample lot of facts. Again and again I 



* By Professor Henslow. regards the origin of species and 

 t The ' American Journal of their present general distribution 

 Science and Arts,' March i860. over the world as equally primor- 

 Reprinted in ' Darwiniana,' 1876. dial, equally supernatural ; that of 

 % The contrast is briefly summed Darwin as equally derivative, equal- 

 up thus : "The theory of Agassiz ly natural." ' Darwiniana,' p. 14. 



