516 INDUCTION. 



would happen. Further, even if we could have ascer- 

 tained, by the Method of Agreement, that oxygen and 

 hydrogen were both present when water is produced, 

 no experimentation on oxygen and hydrogen sepa- 

 rately, no knowledge of their laws, could have enabled 

 us deductively to infer that they would produce water. 

 We require a specific experiment on the two com- 

 bined. 



Under these difficulties, we should generally have 

 been indebted for our knowledge of the causes of this 

 class of effects, not to any inquiry directed specifically 

 towards that end, but either to accident, or to the 

 gradual progress of experimentation on the different 

 combinations of which the producing agents are sus- 

 ceptible ; if it were not for a peculiarity belonging to 

 effects of this description, that they often, under some 

 particular combination of circumstances, re-produce 

 their causes. If water results from the juxta- position 

 of hydrogen and oxygen whenever this can be made 

 sufficiently close and intimate, so, on the other hand, 

 if water itself be placed in certain situations, hydrogen 

 and oxygen are re-produced from it : an abrupt termi- 

 nation is put to the new laws, and the agents re- 

 appear separately with their own properties as at 

 first. What is called chemical analysis is the process 

 of searching for the causes of a phenomenon among 

 its effects, or rather among the effects produced by the 

 action of some other causes upon it. 



Lavoisier, by heating mercury to a high tempera- 

 ture in a close vessel containing air, found that the 

 mercury increased in weight and became what was 

 then called red precipitate, while the air, on being 

 examined after the experiment, proved to have lost 

 weight, and to have become incapable of supporting 

 life or combustion. When red precipitate was exposed 



