I A CHAPTER IN DARWINISM 9 



which before seemed likely to remain always concealed. 

 So great is the value of hypothesis, so essential to 

 scientific discovery, that the most skilled and highly 

 trained observer may spend his life in examining and 

 scrutinising natural objects and yet fail, if he is not 

 guided by hypothesis, to observe particular facts which 

 are of the uttermost importance for the explanation of 

 the causes of the things which he is studying. Nature, 

 it has been said, gives no reply to a general inquiry — 

 she must be interrogated by questions which already 

 contain the answer she is to give ; in other words, the 

 observer can only observe that which he is led by hypo- 

 thesis to look for : the experimenter can only obtain 

 the result which his experiment is designed to obtain. 

 For a long time the knowledge of living things, of 

 plants, and of animals could hardly be said to form 

 part of the general body of science, for the causes of 

 these things were quite unknown. They were kept 

 apart as a separate region of nature, and were sup- 

 posed to have been pitched, as it were, into the midst 

 of an orderly and cause-abiding world without cause 

 or order : they were strangers to the universal har- 

 mony prevailing around them. Fact upon fact was 

 observed and recorded by students of plants and 

 animals, but having no hypothesis as to the causes of 

 what they were studying, the naturalists of twenty 

 years ago, and before that day, though they collected 

 facts, made slow progress and some strange blunders. 

 Suddenly one of those great guesses which occasion- 

 ally appear in the history of science, was given to the 

 science of biology by the imaginative insight of that 



