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is necessarily the case when we are dealing with questions 

 which relate to periods of time long past, as must be those 

 involving phylogeny. 



Moreover, it must not be forgotten that what I propose to 

 do is after all much like what is done in oven those sciences 

 which we sometimes call the exact sciences. The ether of 

 space, the undulatory theory of light, the tentative hypotheses 

 as to the nature of electricity and gravitation, the form and 

 extent of the universe, and the constitution of matter itself, 

 are a few of the familiar speculations which physicists, astron- 

 omers and chemists have made parts of the conceptions of 

 their respective sciences. To be sure, one can go but a short 

 distance indeed in any science without finding it necessary to 

 erect a speculative framework upon which to arrange his ob- 

 served facts. As Jevons has so aptly expressed it in his 

 ' Principles of Science' (2: p. 131) : 



When facts are already in our possession, we frame an hypoth- 

 esis to explain their mutual relations, and by the success or 

 non-success of this explanation is the value of the hypothesis to 

 be entirely judged. In the framing and deductive treatment of 

 such hypotheses, we must avail ourselves of the whole body of 

 scientific truth already accumulated, and when once we have 

 obtained a probable hypothesis, we must not rest until we have 

 verified it by comparison with new r facts. * * * Out of the 

 infinite number of observations and experiments which are pos- 

 sible at every moment, theory must lead us to select those few 

 critical ones which are suitable for confirming or negativing our 

 anticipations. 



A little later (p. 137) he remarks: 



"The true course of inductive procedure is that which lias 

 yielded all the more lofty and successful results of science. It 

 consists in anticipating Nature, in the sense of forming hypoth- 

 eses as to the laws which are probably in operation; and then 

 observing whether the combinations of phenomena arc such as 



would follow from the laws supposed. The investigator begins 



with facts and ends with them. He uses such fads as arc in the 

 first place known to him in suggesting probable hypotheses; de- 

 ducing other facts which would happen if a particular hypothesis 

 is true, he proceeds to test the truth of his notion by fresh obser- 

 vations or experiments. If any result prove different from what 

 he expects, it leads him either to abandon, or to modify his 

 hypothesis; but every new fact may give some new suggestion 

 as to the laws in action." 



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