514 INDUCTION. 



balance a column of the atmosphere of equal diameter ; 

 because, otherwise, equilibrium would not exist. 



By such ratiocinations from the separate laws of the 

 causes, we may, to a certain extent, succeed in answering 

 either of the following questions : Given a certain combina 

 tion of causes, what effect will follow ? and, What combi 

 nation of causes, if it existed, would produce a given effect ? 

 In the one case, we determine the effect to be expected in any 

 complex circumstances of which the different elements are 

 known : in the other case we learn, according to what law 

 under what antecedent conditions a given complex effect 

 will occur. 



3. But (it may here be asked) are not the same argu 

 ments by which the methods of direct observation and expe 

 riment were set aside as illusory when applied to the laws 

 of complex phenomena, applicable with equal force against 

 the Method of Deduction ? When in every single instance a 

 multitude, often an unknown multitude, of agencies, are 

 clashing and combining, what security have we that in our 

 computation a priori we have taken all these into our reck 

 oning ? How many must we not generally be ignorant of? 

 Among those which we know, how probable that some have 

 been overlooked ; and, even were all included, how vain the 

 pretence of summing up the effects of many causes, unless we 

 know accurately the numerical law of each, a condition in 

 most cases not to be fulfilled; and even when fulfilled, to 

 make the calculation transcends, in any but very simple cases, 

 the utmost power of mathematical science with all its most 

 modern improvements. 



These objections have real weight, and would be altogether 

 unanswerable, if there were no test by which, when we employ 

 the Deductive Method, we might judge whether an error 

 of any of the above descriptions had been committed or not. 

 Such a test however there is : and its application forms, under 

 the name of Verification, the third essential component part of 

 the Deductive Method ; without which all the results it can 

 give have little other value than that of conjecture. To 



