Today, we find out why it's useless to take coals to Newcastle. 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.

Coal found its way into the European economy in the 13th century. Isolated reports tell of coal-burning by the ancients. But Marco Polo was still suprised by Chinese coal-burning in the late 13th century. He'd also have been suprised if he'd travelled to Northern Europe and England. By then the English were already using coal for smithing, brewing, dyeing, and smelting. They were even exporting some of it to France.

13th-century millwrights had spent 200 years eating up European forests to make windmills and waterwheels. Wood was becoming too precious to use as a fuel. Wood was first replaced by surface coal -- often called sea-coal because the more obvious outcroppings were found on the coast. By far the largest sea-coal deposits were English ones.

The reason we don't bring coals to Newcastle is that Newcastle, in particular, was surrounded by huge fields of sea-coal. It was mined in open cuts 30 feet deep. And Newcastle was soon girdled by a dangerous maze of water-filled trenches.

Sea-coal was filthy stuff -- loaded with bitumen and sulfur. It created environmental problems from the start. An anonymous 14th-century balladeer vented his anger at its use:

Swart smutted smiths, smattered with smoke,
Drive me to death with din of their dints; ...
The crooked caitiffs cryen after col! col!
And blowen their bellows that all their brain bursteth.

But the medieval population explosion drove people to use this foul fossil fuel anyway. For a hundred years medieval environmentalists fought with medieval industrialists over its use. Then famine and plague ended their argument until the middle of the 15th century. When the repopulation of Europe drove people back to coal, they were armed with the new techniques of metal mining.

Metals demanded a lot of charcoal for smelting. So wood shortages reappeared, magnified by rising populations and even greater demands for metal. But now people followed the coal seams into the earth -- mining it the way they mined metal. That led them to the much cleaner hard coals we use today. These deep coals also served to replace wood in the smelting process.

So coal and metal drove one another deeper into the earth -- until 17th-century miners were stopped by the underground water table. With their whetted appetite for fuel and metal, our 17th-century forbears became desperate to keep that appetite fed.

But by now our story sounds all too familiar. Human ingenuity creates new human appetites which are eventually met by new ingenuity. It's as frightening as it is heartening to see how we can always find 11th-hour ways to keep those appetites fed.

I'm John Lienhard, at the University of Houston, where we're interested in the way inventive minds work.

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Gimpel, J., The Medieval Machine. New York: Penguin Books, 1976.