CHEMISTRY AND CIVILIZATION 161 



fixed mean, whether we estimate them in gold or in day's 

 work, as the tone measures of the fluctuation in mundane 

 prosperity. But if we go to over-populated China and barely- 

 settled Alaska, we note such astounding dislocations of these 

 proportions, that we realize to what extent their apparent 

 constancy is predicated upon the equilibrium between natu- 

 ral resources and man's demand thereon; or rather, upon such 

 a superabundance of these resources, that human consump- 

 tion does not noticeably affect them. During the twenty-five 

 or thirty centuries of historic times preceding the nineteenth 

 this condition was maintained. Our forefathers drew their 

 sustenance from the surface of the earth and consumed rather 

 less than was derived from the solar energy during their re- 

 spective lives. In the nineteenth century commenced that 

 wholesale exploitation, which has drawn in ever-increasing 

 quantity upon the stored-up riches of the earth's interior. So 

 that within the last thirty years we have been forced to 

 recognize that the future progress, if not existence, of the 

 human race is threatened by the gradual exhaustion of our 

 supplies of food and fuel. Even that most unreasoning opti- 

 mist, the American politician, prates of the importance of 

 conserving our natural resources. 



The great break in the continuity of dynasties and nations 

 which the historian entitles the French Revolution coincides 

 more or less closely with that still more portentous change 

 in human history, the substitution of mechanical methods of 

 manufacture for handicraft. Simultaneously began the de- 

 velopment of chemical factories to which the historian has 

 paid no attention, though its effect reached further than even 

 the political economist ordinarily can recognize. There 

 were countless revolutions before the one which dethroned 

 Louis XVI, and man had learned to harness animals, wind 

 and water to replace his own meagre forces, and had shaped 



