INTERMIXTURE OF EFFECTS. 315 



tect in these any common element, we may be able to ascend from them 

 to some one cause which is the really operative circumstance in them all. 

 Thus it is now thought that in the production of heat by friction, percus- 

 sion, chemical action, etc., the ultimate source is one and the same. But if 

 (as continually happens) we can not take this ulterior step, the different 

 antecedents must be set down provisionally as distinct causes, each suffi- 

 cient of itself to produce the effect. 



We here close our remarks on the Plurality of Causes, and proceed to 

 the still more peculiar and more complex case of the Intermixture of Ef- 

 fects, and the interference of causes with one another : a case constituting 

 the principal part of the complication and difficulty of the study of nature; 

 and with which the four only possible methods of directly inductive inves- 

 tigation by observation and experiment, are, for the most part, as will ap- 

 pear 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 premises 

 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 modifying the effects of one anoth- 

 er, 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 corapouiuled with one another, and disappear 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 govern- 

 ed 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 be- 

 ing brought together, throw oft" 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 pro- 

 duction — the conditions on which it depends, the facts which make up its 

 cause. 



The effects of the new phenomenon, the ^yroperties 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 ori- 

 gin and actual production of the phenomenon are most frequently inacces- 

 sible to our observation. 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 foi'ced 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. Besides, many substances, though they can be analyzed, 

 can not by any known artificial means be recorapounded. Further, even 

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

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



