THE CHEMICAL METHOD. 541 



asked in reference to some special subject of political 

 inquiry or controversy ; such as that great topic of 

 debate in the present day, the operation of restrictive 

 and prohibitory commercial legislation upon national 

 wealth. Let this, then, be the scientific question to 

 be investigated by specific experience. 



3. In order to apply to the case the most per- 

 fect of the methods of experimental inquiry, the 

 Method of Difference, we require to find two in- 

 stances, which tally in every particular except the 

 one which is the subject of inquiry. If two nations 

 can be found which are alike in all natural advantages 

 and disadvantages ; whose people resemble each other 

 in every quality, physical and moral, innate and 

 acquired; whose habits, usages, opinions, laws and 

 institutions are the same in all respects, except that 

 one of them has a more protective tariff, or in other 

 respects interferes more with the freedom of industry ; 

 and if one of these nations is found to be rich, and 

 the other poor, or one richer than the other, this will 

 be an experimentum crucis : a real proof by experience, 

 which of the two systems is most favourable to na- 

 tional riches. But the supposition that two such 

 instances can be met with is absurd on the face of it. 

 Nor is such a concurrence even abstractedly possible. 

 Two nations which agreed in everything except their | 

 commercial policy would agree also in that. Dif- 

 ferences of legislation are not inherent and ultimate 

 diversities ; are not properties of Kinds. They are 

 effects of pre-existing causes. If the two nations 

 differ in this portion of their institutions, it is from 

 some difference in their position, and thence in their 

 apparent interests, or in some portion or other of 

 their opinions, habits, and tendencies ; which opens a 



