Fifty years ago, science took for granted that the rate of acceleration could not last. The world forgets quickly, but even today the habit remains of founding statistics on the faith that consumption will continue nearly stationary. Two generations, with John Stuart Mill, talked of this stationary period, which was to follow the explosion of new power. All the men who were elderly in the forties died in this faith, and other men grew old nursing the same conviction, and happy in it; while science, for fifty years, permitted, or encouraged, society to think that force would prove to be limited in supply. This mental inertia of science lasted through the eighties before showing signs of breaking up; and nothing short of radium fairly wakened men to the fact, long since evident, that force was inexhaustible.