Today, technology on hold. 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.

The history of technology is filled with inventions that looked good, then got put on hold until we caught up with them. Take feedback control: Hellenistic engineers invented all kinds of liquid-level controllers during the last few centuries BC. They created devices to control the level of oil in a lamp or the flow of liquid into a water clock. They invented a bowl that refilled itself automatically as guests ladled wine from it.

Then the Romans took over Egypt (where all this invention was going on), and feedback control vanished from the human scene for two millennia. It could've served all kinds of needs, but it disappeared. Imperial Rome didn't want the control of anything out of imperial hands. Not until the extraordinary epoch of 18th-century revolution could this radical idea resurface to regulate liquid levels in steam boilers and to keep windmills facing into the wind.

Another example: The eighth-century Frankish kings began breeding horses for use in war. A century later, people figured out how to harness a horse to a plow, how a nailed horseshoe could protect the horse's hooves, and how to change the planting of fields so horses could share the extra food they helped to produce. Once people put all that together, everyone would live better.

Yet it took until the 11th century to put all that in place, because it meant rearranging real estate. People resisted changes that would vastly improve their lives to avoid short-term disruption. If it'd been your life or mine that stood to be disrupted, I don't doubt that we too would join the opponents of change.

So what technologies are on hold today? I expect that, if we put a fraction of the cost of individual automobiles into city transit systems, we could make such systems so efficient that automobiles would become a bother. As a child I got around my city on electric trolleys. The automobile blew systems like that away. Yet simple economics tells us they will come back in mutated forms.

Herbal medicines are coming back after centuries on hold. Today, dubious and credible advocates alike are recommending them. Some are junk, and some are effective pharmacology. Another decade and the smoke will clear.

Nowhere is the on-hold phenomenon as clear as it is in power production. Until we began using coal in the 13th century, all energy sources were renewable. Since then fossil and nuclear power have been dominant. Economics has necessarily dictated our choices, but we haven't been paying up front. Our payments have been strung out over decades as environmental costs build up, and as we send expensive armies to fight over cheap unrenewable energy sources.

So look around you. Ask yourself what really good technologies are on hold from other ages, just waiting for us to reawaken to their value? Those technologies are waiting for us to figure out what they are, and how to take them into our lives.

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

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Mayr, O., The Origins of Feedback Control. Cambridge, MA: MIT Press, 1970.

White, L., Jr., Medieval Technology and Social Change. New York: Oxford University Press, 1966.