OUTLINE 15 



observations must represent nature exactly. He must 

 observe without a preconceived idea. His mind must be 

 passive, that is to say silent. He listens to nature and 

 writes under her dictation. 



'But once a fact is ascertained and the phenomena 

 observed, the idea comes, reasoning intervenes, and the 

 experimenter appears in order to interpret the phenomenon. 

 The experimenter is he who, in virtue of a more or 

 less probable but anticipated interpretation of observed 

 phenomena, institutes an experiment so that in the logical 

 order of his previsions it will furnish the result which 

 serves to control the hypothesis or the preconceived idea. 

 To accompUsh this, the experimenter reflects, tries, gropes, 

 compares and combines, so as to find the experimental 

 conditions which are best fitted to attain the goal which is 

 his aim. It is necessary to experiment with a preconceived 

 idea. The mind of the experimenter must be active; that 

 is, he must interrogate nature and question her in all 

 directions following the different hypotheses which are 

 suggested to him. 



'But when the conditions of the experiment have been 

 realized and the experiment itself started according to the 

 preconceived idea or anticipated view of the mind, the 

 result, as we have already said, will be a provoked or 

 premeditated observation. It will be followed by the 

 apparition of phenomena determined by the experimenter, 

 but which he must first study so as to know in which way 

 they can be used to check the experimental idea which 

 brought them to life.' 



It is clear that these lines apply to all classes of methods 

 and are not confined to the one which is the object of our 

 first paragraph. But it seemed to us that they belonged to the 

 beginning of this chapter because of their evident character 

 of generality. 



The naturalist and the zoologist can resort to a variety 

 of methods, depending on whether they study the isolated 



