202 MAN, THE ANIMAL 



then the one or more happenings which it initiates 

 are designated as effects. There is thus a definite 

 relationship between cause and effect which con- 

 stitutes the essence of the scientific method. It 

 implies that the results cannot take place without 

 a given cause. When this is applied to our every- 

 day knowledge, one says that the leaves appear 

 in their season and that a maple leaf does not 

 grow on an elm tree. Fruit time and harvest are 

 preceded by an orderly series of events, each 

 linked to each as in a chain. This principle is 

 not limited to organic life. The passing street 

 car, the torrential brook in spring time freshets 

 or the destructive tornado are to be understood 

 only after a close study of certain particular 

 causes. To express the same idea in a different 

 way, one may say that every happening, every 

 material thing in the universe of to-day has had 

 a continuous history. The happenings of today 

 become the history of to-morrow and it is neces- 

 sary to know the history of yesterday, if one would 

 understand the happenings of to-day. The scien- 

 tific method implies that all observations shall be 

 made in such a way that they can be repeated, 

 controlled and verified by subsequent observers. 

 The word "controlled" has a technical meaning 

 referring especially to verified, repeated experi- 

 ments. 



3. Simply to trace the relationship between 



