Today, let's tilt at windmills. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.
Don Quixote dwelt in the twilight of the age of chivalry in the fourteenth or fifteenth century, but he was a creature of the late sixteenth-century author Cervantes. Early in the story, Quixote cries,
Look there, my friend Sancho Panza,
where thirty or more monstrous giants present themselves,
all of whom I mean to engage in battle and slay!
He points to an array of power-generating windmills that dot the Spanish landscape. Windmills had rapidly come into wide use in Europe beginning in the late twelfth century. That was two hundred years before Quixote and four hundred years before Cervantes. For years we wondered whether Crusaders brought windmills to Europe from the Holy Land or vice versa. Today we're pretty sure they originated in the Middle East. But a new form of windmill suddenly appeared in Northern Europe right around AD 1180.
European waterwheels were the primary energy source when windmills arrived. Windmills were more complex, and they were at the mercy of the sometimes fickle winds. But they delivered more power than waterwheels, and they ground grain where there were no streams -- in the Spanish plains, for example. Windmills provided the power to drain the Dutch Lowlands below the level of any streams.
By 1760 windmills had reached an astonishing level of sophistication. Automatic regulators controlled the speed of rotation; they adjusted the pitch of the fan blades for maximum power at a given wind speed, and they turned the fan so it always faced directly into the wind. When windmills were used to grind grain, controllers regulated the pressure of the millstones on the grain.
But it was also in the 1760s that Watt began developing a vastly improved steam engine. As the eighteenth century closed, engineers stopped pouring their energies into windmills, and they turned to steam. James Watt was the Quixote who really slew the windmill.
Of course windmills didn't go away. Today they're still the power supply of choice for isolated use away from commercial electricity. We use them to fill cattle-watering troughs on the prairie, for example. As railways opened the West, every whistle-stop installed a windmill-supplied water tower to refill steam-engine boilers.
Now we're seeing a new interest in wind power. Latter-day engineers are concocting a dizzying set of improvements to make windmills serve electric power generation. The modern propeller-bladed windmill is three or four times as efficient as an advanced eighteenth-century mill, and far more powerful.
But eighteenth-century windmills remain a forgotten glory. Did you know that the variable-pitch propellers used in those mills over two hundred years ago are an invention that airplane designers didn't rediscover until the 1930s?
I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.
George, B., Reaping the Wind. American Heritage of Invention & Technology, Vol. 8, No. 3, Winter 1993, pp. 8-14.
Kealey, E., Harvesting the Air: Windmill Pioneers in Twelfth-Century England. Berkeley: University of California Press, 1987, Chapter 7.
Mayr, O., The Origins of Feedback Control. Cambridge, MA: MIT Press, 1970.
Righter, R. W., A Few Words About This Picture. American Heritage of Invention & Technology, Vol. 7, No. 1, Spring/Summer 1991, pp. 28-31.
White, L., Jr., Medieval Technology and Social Change. New York: Oxford University Press, 1966, Chapter 3.
This episode is a considerably revised version of Episode 29.
Artist's sketch of an actual windmill on the Quixote's plains of La Mancha
From the October, 1896, Scribner's Magazine