THE STUDY OF POLITICAL ECONOMY. 605 



chiefly in analysis, have a like certainty, although, as with all the causes 

 of which it takes cognizance are at all times acting other causes, it can 

 never predict exact results but only tendencies. 



And, although in the study of political economy we can not use that 

 potent method of experiment by artificially produced conditions which 

 is so valuable in the physical sciences, yet, not only may we find, in the 

 diversity of human society, experiments already worked out for us, 

 but there is at our command a method analogous to that of the chemist, 

 in what may be called mental experiment. You may separate, com- 

 bine, or eliminate conditions in your own imagination, and test in this 

 way the working of known principles. This, it seems to me, is the 

 great tool of political economy. It is a method with which you must 

 be familiar and doubtless use every day, though you may never have 

 analyzed the process. Let me illustrate what I mean by something 

 which has no reference to political economy. 



When I was a boy I went down to the wharf with another boy to 

 see the first iron steamship which had ever crossed the ocean to our 

 port. Now, hearing of an iron steamship seemed to us then a good 

 deal like hearing of a leaden kite or a wooden cooking-stove. But, 

 wo had not been long aboard of her, before my comrade said in a tone 

 of contemptuous disgust : " Pooh ! I see how it is. She's all lined with 

 wood ; that's the reason she floats." I could not controvert him for 

 the moment, but I was not satisfied, and, sitting down on the wharf 

 when he left me, I set to work trying mental experiments. If it was 

 the wood inside of her that made her float, then the more wood the 

 higher she would float ; and, mentally, I loaded her up with wood. 

 But, as I was familiar with the process of making boats out of blocks 

 of wood, I at once saw that, instead of floating higher, she would sink 

 deeper. Then, I mentally took all the wood out of her, as we dug out 

 our wooden boats, and saw that thus lightened she would float higher 

 Btill. Then, in imagination, I jammed a hole in her, and saw that the 

 water would run in and she would sink, as did our wooden boats when 

 ballasted with leaden keels. And, thus I saw, as clearly as though I 

 could have actually made these experiments with the steamer, that it 

 was not the wooden lining that made her float, but her hollowness, or, 

 as I would now phrase it, her displacement of water. 



Now, just such mental operations as these you doubtless perform 

 every day, and in doing so you employ the method of imaginative ex- 

 periment which is so useful in the investigations of political economy. 

 You can, in this way, turn around in your mind a proposition or phe- 

 nomenon and look on all sides of it, can isolate, analyze, recombine, or 

 subject it to the action of a mental magnifying glass which will reveal 

 incongruities as a reductlo ad ahsurdum. Let me again illustrate : 



Before I had ever read a line of political economy, I happened once 

 to hear a long and well-put argument in favor of a protective tariff. 

 Up to that time I had supposed that " protection to domestic industry " 



