Today, let's play with questions. 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.

Why Do Clocks run Clockwise? asks the title of a book by David Feldman. Why indeed! This odd book looks at 239 such questions. First they look innocent -- even trivial. Then we start to see how great is our willingness to accept things without raising enough questions.

For example: "What about those warning labels on mattresses? What would happen if I cut one off?" I tried that on one person who grinned and said, "I always figured I'd be thrown in jail if I did." Actually, the label tells you who made the mattress and what he filled it with. It also warns the retailer that he's required to give you that information.

The book goes on: "What's the difference between flotsam and jetsam?" Flotsam comes from the Latin word flottare -- to float. It's the stuff that floats all the way up to the high-tide water line. Jetsam is from jactare -- to throw. It's what you'd throw overboard if you had to lighten the ship. Jetsam refers to the heavier junk that hardly gets beyond the low-tide line.

Here's an odd one: "Why do we say royalty has blue blood?" The answer comes from renaissance Spain. Royalty got little exercise. Royal blood didn't take on much oxygen. It kept a darker color. Royal veins stood out blue on pale royal skin.

"So many birds die, why don't we see more of them on the ground?" That's easy. Animals eat 'em. "What does M & M stand for?" It stands for Mars and Murrie, who once ran the company. "Why are we more comfortable at 72 degrees than at 98?" That's because our bodies have to be warmer than our surroundings to shed the energy we burn all the time.

The questions tumble forth: Why are flush toilet handles all on the left? Why does the moon seem larger on the horizon than overhead? Why do horses sleep standing up? Why do we have white half-moons on our fingernails?

This strange little book is embarrassing -- not because of the things we don't know. We're all guilty of ignorance. The crime is failing to fight our ignorance -- failing to raise questions. Any inventor knows that invention flows from the offbeat question that no one else thinks to ask. Questions and creativity go hand in hand. The book embarrasses us by reminding us of all the questions we never asked.

So why do clocks rotate clockwise? It's because the first clocks were made to imitate sundials. Sundial shadows -- at least the ones north of the equator -- rotate from west to north to east. And that's what clocks are still imitating, even today.

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

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Feldman, D., Why Do Clocks Run Clockwise? New York: Perennial Library, Harper & Row, 1988.