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No. 1363:
Man the Measure

Today, let's ask what meters measure. 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.

Twenty-five hundred years ago the Greek philospher Protagoras said, "Man is the measure of all things." In that, he was closer to literal truth than we might think. The gages and meters we use to measure things usually begin by copying our own senses. You can see that by looking at our weights and measures. They all reflect, in some way or another, what we see and feel.

A pound or a kilogram is roughly the mass of any fairly dense material (like a rock or a piece of metal) that we can comfortably hold in our hand. The inch, foot, yard, and meter all correspond with various body parts.

The mile and kilometer also have a meaning that comes clear in parts of rural America where people talk about the distance of a see. Ask someone in Eastern Kentucky how far it is into town and she might say, "Oh, 'bout two sees." She means you should look down the road as far as you can see. Where your vision runs out, you spot say, an oak tree. You walk to it and look again. There, in the distance, is the town, just two sees away. How far is a see? Of course it varies but, even in flat terrain, our ability to make things out usually ends after about a mile or a kilometer.

Degrees Fahrenheit or Celsius are about the smallest increments of temperature we can feel. (We can usually feel a one-degree fever.) We can sense about one volt with our tongue. Our ears are sensitive to about one pound per square inch of pressure change.

The kilowatt and horsepower are pretty similar -- roughly the power most people can produce in a short sprint up the stairs. By the way, when James Watt specified the unit of a horsepower he made it less than the work of a real horse so his engines would seem more powerful. Not only is the kilowatt or horsepower close to the maximum power you or I can produce in a short burst; it's also the most power we can tangle with without being hurt. It's close to the rate the sun pours energy on us when we tan ourselves on the beach. It's like the rate we consume energy when we take a hot shower.

So our meters replicate us. Like us, their accuracy runs out beyond a point. Like us, their range and scope is limited. Our instrument-based science rightly claims to be the best means we have for describing physical reality at any moment. But, as objective as science tries to be, it's a science that necessarily carries a human slant. The science we practice is a science that describes a world with us in it.

That's why our science and our science-based engineering ultimately serve us so well. They mirror human needs and nature just because they're based on measurements that have never been too far from human needs, or from our human dimensions.

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

(Theme music)

This is a substantially revised version of Episode 52.

Some more units of measurement and their human equivalents


inch thumb digit
foot human foot
yard or meter distance from nose to tip of outstretched arm
quart most liquid we could drink at one sitting
decibel least change in sound level we can hear
Btu, kcal, or Joule least energy we can sense in our coffee cup
year, month, day time needed for a natural experience to recur
month menses
second order of human reaction time
mile per hour speed of slow human locomotion