Friedrich Engels,
Landmarks of Scientific Socialism…
“ At the threshold of human history stands the discovery of the transformation of mechanical motion in heat, the generation of fire by friction; at the close of development up to the present stands the discovery of the transformation of heat into mechanical motion, the steam engine. In spite of the tremendous revolution in the direction of freedom which the steam engine has produced in society it is not yet half complete. There is no question that the production of fire by friction still surpasses it as an agent in the liberation of humanity. ”
