GENERAL CONCLUSIONS. 



What I have attempted to explain in the foregoing 

 pages is how the scientist is to set about making a 

 selection of the innumerable facts that are offered to 

 his curiosity, since he is compelled to make a selection, 

 if only by the natural infirmity of his mind, though a 

 selection is always a sacrifice. To begin with, I ex- 

 plained it by general considerations, recalling, on the 

 one hand, the nature of the problem to be solved, and 

 on the other, seeking a better understanding of the 

 nature of the human mind, the principal instrument in 

 the solution. Then I explained it by examples, but 

 not an infinity of examples, for I too had to make 

 a selection, and I naturally selected the questions 

 I had studied most carefully. Others would no 

 doubt have made a different selection, but this matters 

 little, for I think they would have reached the same 

 conclusions. 



There is a hierarchy of facts. Some are without 

 any positive bearing, and teach us nothing but them- 

 selves. The scientist who ascertains them learns 

 nothing but facts, and becomes no better able to 

 foresee new facts. Such facts, it seems, occur but 

 once, and are not destined to be repeated. 



There are, on the other hand, facts that give a large 



