On the sun-baked plains of the American Midwest in 1892, a revolution was loudly sputtering to life: the tractor, an engine which signaled the end of the era of animal power and the beginning of the age of machine power. This machine was not just a piece of equipment; the tractor was a manifestation of an exponential shift in energy density, from animal metabolism to coal burning, empowered by discoveries in thermodynamics. But diffusion of the tractor, screeching across the horizon, took much l...