INTERMIXTURE OF EFFECTS. 255 



any other phenomenon ; and the elements which arc said to compose 

 it may be considered as the mere agents of its production ; the condi- 

 tions on which it depends, tlie facts which make up its cause. 



Tlie ejects of th(> new phenomenon, the j^rojfertics of water, for in- 

 stance, are as ^easily found by experiment as the effects of any other 

 cause. But to discover the cause of it, tliat is, the particular conjunc- 

 tion of agents from which it resuUs, is often difficult enough. In the 

 first place, the origin, and actual production of the phenomenon, is 

 most freqdently inaccessible to our ol)servation. If we could not have 

 learned the composition of water until we found instances in which it 

 was actually produced from oxygen and hydrogen, we should have 

 been forced to wait until the casual thought struck some one of passing 

 an electric spark through a mixture of the two gases, or inserting a 

 lighted taper into it, merely to try what'would happen. Further, even 

 if we could have ascertained by the Method of Agreement, that oxygen 

 and hydrogen were both present when water is produced, no experi- 

 mentation on oxygen ^nd hydrogen separately, no knowledge of their 

 laws, could have enabled us deductively to infer that they would pro- 

 duce water. We require a specific experiment on the two combined. 



Under these difficulties, we should generally have been indebted for 

 our knowledge of the causes of this class of effects, not to any incjuiry 

 directed specifically towards that end, but either to accident, or to tho 

 gi'adual progress of experimentation on the different combinations ot 

 which the producing agents are susceptible ; if it were not for a pecu- 

 liarity belonging to effects of this description, tliat they often^, under 

 some particular combination of circumstances, reproduce their causes. 

 If water results from the juxtaposition of hydrogen and oxygen when- 

 ever this can be made sufficiently close and intimate, so, on the other 

 hand, if water itself be placed in certain situations, hydrogen and oxy- 

 gen are repi'oduced from it : an abrupt termhiation is put to the n6w 

 laws, and the agents reappear separately with their own properties as 

 at first. AVliat is called chemital 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 temperature in a close vessel 

 containing air, found that the mercury increased in weight and became 

 what was then called Ted precipitate, while the au:, on being examined 

 after the experiment, proved to haye lost weight, and to have become 

 incapable of supporting life or combustion. -When red precipitate was 

 exposed to a still greater heat, it became mercury again, and gave off 

 a gas which did support life and flame. Thus the agents which by 

 theit combination produced red precipitate, namely, the mercury and 

 the gas, reappear as effects resulting from that precipitate when acted 

 upon by heat. So, if we decompose water by means of irou filings, 

 we produce two effects, rust and hydrogen : now rust is already known 

 by experiments upon the component substances, to be an effect of the 

 union of iron and oxygen: tho iron we ourselves supplied, but the 

 oxygen must have been produced from the water. The result there- 

 fore is that the water has disappeared, and hydrogen and oxygen have 

 appeared in its stead : or in other words, the original laws of these 

 gaseous agents, which had been suspended by the superinduption of 

 the new-laws called the properties of water, have again started iijto 

 existence, and the causes of water are found among its effects. 



