INDUCTION. Ill 



Inductions are easily made; the test of a 

 good investigator, however, is not the number 

 of inductions he makes, but his subsequent 

 treatment of them. In his study of the amount 

 of material brought to the surface of the ground 

 by earthworms, Darwin noticed that the sur- 

 faces of old worm-castings were often studded 

 with coarse particles; and was thence led to 

 infer that a good deal of the finest part of 

 worm-castings was washed away by the rain. 

 Such an induction is so nearly self-evident that 

 it would seem superfluous to verify it. Darwin 

 .thought otherwise; he mixed fine precipitated 

 chalk with the castings, or gently stuck it on 

 to them ; the rain washed it away and proved 

 him correct. By this little induction, and a 

 verification almost childish in its simplicity 

 and apparent insignificance, he was able to show 

 that the amount of material brought to the 

 surface by earthworms is much greater than at 

 first appears. 1 It is probably safe to say that 

 the majority even of investigators would have 

 regarded the induction sufficient unto itself, 

 and would not have hesitated to use it without 

 verification as evidence in proof of their views. 

 We here get a glimpse of how sharply Darwin 

 caught the significance of the minutest indica- 



1 The Formation of Vegetable Mould, etc., p. 272. 



