INTERMIXTURE OF EFFECTS. 515 



but are compounded with one another, and disappear 

 in one totaL In the other case, illustrated by the case 

 of chemical action, the separate effects cease entirely, 

 and are succeeded by phenomena altogether different, 

 and governed by different laws. 



Of these cases the former is by far the more fre- 

 quent, and this case it is which, for the most part, 

 eludes the grasp of our experimental methods. The 

 other and exceptional case is essentially amenable to 

 them. When the laws of the original agents cease 

 entirely, and a phenomenon makes its appearance, 

 which, with reference to those laws, is quite hetero- 

 geneous ; when, for example, two gaseous substances, 

 hydrogen and oxygen, on being brought together, 

 throw off their peculiar properties, and produce the 

 substance called water ; in such cases the new fact 

 may be subjected to experimental inquiry, like any 

 other phenomenon ; and the elements which are said 

 to compose it may be considered as the mere agents 

 of its production ; the conditions on which it depends, 

 the facts which make up its cause. 



The effects of the new phenomenon, the properties 

 of water, for instance, are as easily found by experi- 

 ment as the effects of any other cause. But to 

 discover the cause of it, that is, the particular conjunc- 

 tion of agents from which it results, is often difficult 

 enough. In the first place, the origin, and actual 

 production of the phenomenon, is most frequently 

 inaccessible to our observation. If we could not have 

 learned the composition of water until we found in- 

 stances 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 



2 L 2 



