374 THE CAUSES OF THE xi 



daily life may be of little or no moment as 

 affecting the general correctness of the conclusions 

 at which we may arrive ; but, in a scientific in- 

 quiry, a fallacy, great or small, is always of im- 

 portance, and is sure to be in the long run 

 constantly productive of mischievous, if not fatal 

 results. 



Do not allow yourselves to be misled by the 

 common notion that an hypothesis is untrustworthy 

 simply because it is an hypothesis. It is often 

 urged, in respect to some scientific conclusion, 

 that, after all, it is only an hypothesis. But what 

 more have we to guide us in nine-tenths of the 

 most important affairs of daily life than hypotheses, 

 and often very ill-based ones ? So that in science, 

 where the evidence of an hypothesis is subjected 

 to the most rigid examination, we may rightly 

 pursue the same course. You may have hypo- 

 theses and hypotheses. A man may say, if he 

 likes, that the moon is made of green cheese : 

 that is an hypothesis. But another man, who has 

 devoted a great deal of time and attention to the 

 subject, and availed himself of the most powerful 

 telescopes and the results of the observations of 

 others, declares that in his opinion it is 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 



