INTERMIXTURE OF EFFECTS. 489 



with which the four only possible methods of directly induc- 

 tive investigation by observation and experiment, are for the 

 most part, as will appear presently, quite unequal to cope. 

 The instrument of Deduction alone is adequate to unravel the 

 complexities proceeding from this source ; and the four 

 methods have little more in their power than to supply pre- 

 mises for, and a verification of, our deductions. 



4. A concurrence of two or more causes, not separately 

 producing each its own effect, but interfering with or modify- 

 ing the effects of one another, takes place, as has already 

 been explained, in two different ways. In the one, which is 

 exemplified by the joint operation of different forces in 

 mechanics, the separate effects of all the causes continue to 

 be produced, but are compounded with one another, and dis- 

 appear in one total. In the other, 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 frequent, 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 heterogeneous ; 

 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 experiment as the effects 

 of any other cause. But to discover the cause of it, that is, 

 the particular conjunction of agents from which it results, is 

 often difficult enough. In the first place, the origin and 



