Today, let's try to drill a hole through to China. 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.

I was recently at a national teachers' convention. People had rented space to sell educational materials. One man was pushing his new book. He'd proved, he said, that Earth's center isn't molten after all. He claimed the temperature is really absolute zero.

I doubt that he had much luck in rewriting science curricula, but he makes a point. When we haven't actually been somewhere -- in this case to the center of the Earth -- it's all too easy for laymen to bend scientific inference wherever they want it to go.

But we have been drilling ever deeper to see what's there. Commercial drilling for oil and gas typically goes down a mile or so. It rarely gets as deep as three miles. Still, one commercial bore hole in Oklahoma went to a depth of six miles. Then, like a scene from Dante's Hell, it hit molten sulfur.

We've also been doing research drilling, but funding for that hasn't been lush. No American research hole has gone down more than two miles yet.

German and Russian research rigs have gone much deeper than we have. The Russians hold the record with a hole north of the Arctic Circle, near Norway. In 1984 they reached a depth of seven and a half miles. There they found hints of deep-lying mineral wealth.

Such deep holes are hard to drill. Guiding a seven-mile drill only a foot or two in diameter is like trying to steer a thread through a concrete pier. Drill bits have to carry their own guidance systems.

And we find strange things at such depths. We've brought unknown bacteria up from depths of almost two miles. The Swedes expect to locate deep natural gas that doesn't come from organic material. Researchers are trying to sort out plate tectonics. They're trying to find out more about the San Andreas fault.

And what about temperature? Well, it certainly does go up as the drill goes down. A research drill two miles under California's Salton Sea reached an environment of almost 700 degrees.

The United States leads the technology of drilling at high temperature. Drillers sent one bit straight into a subterranean lake of lava under Hawaii. Its temperature was 2000 degrees. They did it by circulating coolant to freeze the lava around the drill. Then they bored a regular hole through solidified lava.

So just when you thought Earth had run out of frontiers, we've found a new one. There are more things in Heaven and Earth -- more things just under our feet -- than we ever imagined. And we're creating some dazzling high tech to take us there.

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

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Rosen, J., Deep Drilling: Probing Beneath the Earth's Surface. Mechanical Engineering, Vol. 113, No. 6, June 1991, pp. 70-76.