TIME GIVEN TO INVESTIGATIONS. 8 1 



much. Some of the most important explana- 

 tions under his theories did not occur to him 

 until years after he had begun their study. It 

 will be pointed out later that after he once got 

 possession of a working hypothesis his work 

 was largely deductive; and it will be shown 

 how extremely difficult it is to work out all the 

 important consequences of such a hypothesis 

 even in many years. After it is once done the 

 task seems so easy that the wonder is that it 

 was not done sooner. But the contemplation 

 of the development of a great theory soon re- 

 veals the enormous difficulties in the way of 

 one or many who seek to work out its conse- 

 quences. Darwin did in each of his investiga- 

 tions what is usually done for a subject by a 

 number of successive workers ; each makes an 

 important contribution to the subject, removes 

 a serious objection to a theory, explains a sec- 

 tion of the evidence, points out an important 

 consequence, or modifies the statement of it 

 to bring it more clearly in harmony with the 

 greater knowledge on the subject. By succes- 

 sive approximations many men, working toward 

 the same end, originate, build up, and improve 

 a theory until it takes its place among perma- 

 nently established truths. As far as it was 

 possible for one man to do so Darwin did all 



