OBSERVATION AND EXPERIMENT. 445 



We have thus already come within sight of a 

 conclusion, which the progress of the inquiry will, I 

 think, bring before us with the clearest evidence : 

 namely, that in the sciences which deal with pheno- 

 mena in which artificial experiments are impossible 

 (as in the case of astronomy) , or in which they have a 

 very limited range (as in physiology, mental philo- 

 sophy, and the social science,) induction from direct 

 experience is practised at a disadvantage generally 

 equivalent to impracticability : from which it follows 

 that the methods of those sciences, in order to accom- 

 plish anything worthy of attainment, must be to a 

 great extent, if not principally, deductive. This is 

 already known to be the case with the first of the 

 sciences we have mentioned, astronomy ; that it is 

 not generally recognised as true of the others, is 

 probably one of the reasons why they are still in 

 their infancy. But any further notice of this topic 

 would at present be premature. 



4. If what is called pure Observation is at so 

 great a disadvantage compared with artificial expe- 

 rimentation, in one department of the direct explora- 

 tion of phenomena, there is another branch in which 

 the advantage is all on the side of the former. 



Inductive inquiry having for its object to ascertain 

 what causes are connected with what effects, we may 

 begin this search at either end of the road which 

 leads from the one point to the other : we may either 

 inquire into the effects of a given cause, or into the 

 causes of a given effect. The fact that light blackens 

 chloride of silver might have been discovered, either 

 by experiments upon light, trying what effect it would 

 produce on various substances, or by observing that 

 portions of the chloride had repeatedly become black, 



