60 INTRODUCTION TO SCIENCE 



forward into those which are to come. By deduc- 

 tion Neptune was discovered before it was seen. 

 By deduction, given three good observations of 

 a passing comet, we can predict its return to a 

 night. 



As a good example, cited by Prof. Case, of the 

 abuse of the deductive method by one of the 

 greatest of all intellects, we may recall an argu- 

 ment used by Aristotle to support the old circular 

 astronomy. The stars are eternal and must have 

 eternal motion. The only eternal motion is circu- 

 lar. Therefore the stars move in circles round the 

 earth. "It is a case of two hypothetical premises 

 leading to a false conclusion. Every step is false. 

 There is nothing for it but experience. The real 

 question is how the stars move in point of fact." 



It is not within the scope of this little book to 

 enter into a detailed discussion of the various 

 scientific methods such as the mathematical, the 

 empirical, the explanatory, and the verificatory, 

 which Mill distinguished. But there are two 

 important considerations to be borne in mind, 

 first, that great conclusions seem often to be 

 reached by a flash of imaginative genius, perhaps 

 the expression of long-continued processes of sub- 

 conscious cerebration; and, second, that in actual 

 practice induction and deduction are mingled in 

 intricate ways. 



In many instances we find that experiment and 



