Sources of failure in inventions. 49 



failed altogether in practice, but why is this ? it is 

 not that the principles of nature operated in the one 

 case and did not operate in the other, but that we 

 have imperfectly understood them, that from some 

 unforeseen circumstances we have been unable to 

 apply them ; or that we have indolently abandoned 

 them without sufficient or proper trial. In many 

 cases we are unable to obtain the same conditions 

 of success upon the large scale that we have upon 

 the small one. In other cases a process fails because 

 of its too great expense ; many attempts have been 

 made to supersede steam as a motive power by 

 means of electro-magnetism, and engines driven by 

 that force have been constructed of five or ten horse- 

 power, but the cost of driving them has been found 

 to be at least ten times the amount of that of the 

 steam-engine of equal strength. And in other cases 

 we fail because we attempt at once to carry out upon 

 a large scale that which has only been the subject of 

 limited experiment, instead of enlarging the process 

 by small degrees, and adapting the apparatus, the 

 materials and the treatment, to the size of the 

 operation. 



That also which appears very simple in the hands 

 of an experimentalist, almost invariably becomes 

 much more complex when carried into practice in a 

 .manufactory, simply because there is then a greater 

 number of conditions to be fulfilled. Electro-plating 

 a piece of steel with silver is to a chemist a very 

 simple matter, because it is of no importance to him 



