METHOD OF DISCOVERY. 67 



probably composed of materials very similar to those of 

 which our own earth is made up : and that is also only 

 an hypothesis. But I need not tell you that there is an 

 enormous difference in the value of the two hypotheses. 

 That one which is based on sound scientific knowledge 

 is sure to have a corresponding value ; and that which 

 is a mere hasty random guess is likely to have but 

 little value. Every great step in our progress in dis- 

 covering causes has been made in exactly the same 

 way as that which I have detailed to you. A person 

 observing the occurrence of certain facts and pheno- 

 mena asks, naturally enough, what process, what kind 

 of operation known to occur in nature applied to the 

 particular case, will unravel and explain the mystery? 

 Hence you have the scientific hypothesis; and its value 

 will be proportionate to the care and completeness with 

 which its basis had been tested and verified. It is 

 in these matters as in the commonest affairs of prac- 

 tical life : the guess of the fool will be folly, while 

 the guess of the wise man will contain wisdom. In 

 all cases, you see that the value of the result depends 

 on the patience and faithfulness with which the in- 

 vestigator applies to his hypothesis every possible kind 

 of verification. 



I dare sav I mav have to return to this point by- 

 and-b.y ; but having dealt thus far with our logical 

 methods, I must now turn to something which, per- 

 haps, you may consider more interesting, or, at any 

 rate, more tangible. But in reality there are but few 

 things that can be more important for you tc under- 

 stand than the mental processes and the means by 



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