108 THE METHOD OF DARWIN. 



as unsatisfactory. As a deduction from his 

 general theory, he believed that the habit of 

 expressing our feelings by certain movements 

 had been somehow gradually acquired. This 

 view required that the whole subject of expres- 

 sion should be studied under a new aspect, and 

 each expression be given a rational explana- 

 tion. 1 This led him to undertake his work on 

 the " Expression of the Emotions in Man and 

 the Lower Animals." Deduction pointed out 

 that expression must fall under the general 

 explanation; but it was impossible to foresee 

 the principles which governed the develop- 

 ment of the various expressions. From 1838 

 to 1872 he toiled away at the mass of complex 

 facts, and slowly overcame the difficulty of 

 bringing the different expressions together 

 under one or a few points of view. At last' he 

 was able to educe three principles of expres- 

 sion, which seemed to him to account for most 

 of the expressions and gestures involuntarily 

 used by man and animals under the influence 

 of various emotions and sensations. These 

 principles he arrived at, as he himself says, 

 only at the close of his observations. 2 They 



1 Expression of the Emotions in Man and the Lower 

 Animals, p. 19. 



2 Ibid., p. 27. 



