Today, another look at the invention of the wheel.
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.
It's fairly common knowledge
that the wheel was invented around 5500 years ago.
But what was really invented at that time? V.
Gordon Childe offers an interesting slant on the
question. What we should be looking at, he says, is
not the wheel itself, but rather the use of rotary
motion.
The human wrist/arm configuration allows 360-degree
rotation. That's why hand drills using back and
forth hand motions are among the oldest tools. Late
stone age artisans extended that rotation with
various pivoted devices. A primitive spinning
spindle plays out wool or flax fibers while the
operator keeps it moving with thumb and forefinger.
Early doors, with a vertical shaft on one side,
were anchored in sockets that let them swing open
and shut.
The next step in sophistication was using
bowstrings to drive back-and-forth rotary motions of
drills and fire starters. These devices all ran one
way to a limit, and then had to unwind. Continuous
rotation was the conceptual hurdle. Two primary
examples, the vehicle wheel and the potter's wheel, arose
about the same time.
A potter's wheel is a horizontal turntable that
holds a lump of clay and turns at least 100 rpm.
Childe finds one potter's wheel from the region of
the Tigris and Euphrates rivers (or present-day
Iraq) from as early as 3300 BC. The earliest
vehicle wheel turns up in a cuneiform document from
same region in 3500 BC.
Those dates don't differ much, and examples are too
rare to fix dates accurately. So, to the best of
our knowledge, not just the wheel, but continuous
rotation itself, dates from five and a half
millennia ago in the Fertile Crescent of the
ancient world. Another invention, closely kin to
the wheel, was the compass for making circles. The
first hinged compasses also trace to that same
region, 5500 years ago.
Early wheels show a progression of understanding.
The first wheels were cut from huge wooden slabs,
built up of boards. In other words, the lay of the
wood seems to fight the rotary motion it's meant to
accomplish. It's not 'til 2000 BC that we find wheels with
spokes. The spoke itself introduces a new subtlety since
it's loaded in tension, not compression. A vehicle
hangs on the wheel's upper spokes; it doesn't ride
on the lower ones.
Other questions of rotation had to be answered:
Wheels are best left free to rotate on a fixed
axis. If they're anchored to a rotating axle, then
they can't turn at different speeds going around a
corner. The idea of a swiveled front axle, that can
turn into a curve, is barely 2000 years old.
And so it is not the wheel itself, but the problem
of rotation, that has dogged our minds for thousands
of years. What the ancient Sumerians did was to
recognize the problem. And we have (if I may) spun
out the subtle ramifications ever since.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
Childe, V. G., Rotary Motion. A History of
Technology, Vol 1, From Early Times to Fall of
Ancient Empires (S. Singer, E. J. Holmyard,
and A. R. Hall, eds.). New York: Oxford University
Press, 1954, Chapter 9.
Williams, T. I., The History of
Invention. New York: Facts On File
Publications, 1987, Chapter 4.
The oldest extant wheel is to be found in the City Museum of Ljubluana. See:
The Kolo Wheel.
An early Engines program, Episode 24, also deals with the
invention of the wheel and the crank.
In Jan, 2000, when this program reran, listener
Leslie R. Denham took issue with my too-hasty
remark about spokes being loaded in tension. He
pointed out that that tensioned spokes didn't come
into general use until much later. I include his
full statement below since it is of great interest
in its own right.
My
grandfather was a wheelwright, so I have always
had an interest in traditional wooden spoked
wheels. The spokes are mortised into the wooden
hub, and into the felloes or fellies which make
up the wooden rim, without any kind of fastener.
The whole assembly is held together by the iron
tire which is heated and then dropped over the
wooden parts, shrinking as it cools to tighten
the wooden parts.
A
lot of my grandfather's business in the dying
days of his profession was "cutting and
shutting": cutting an iron tire which had become
loose as the wooden parts had shrunk and worn,
welding it back with a slightly smaller diameter
(hammer welding in the forge, of course) and
shrinking it back onto the wooden
wheel.
With this type of
construction, which remained the same from the
early days of the Iron Age until the early 20th
century, the spokes did not function as tensional
members. I have always thought that the first
tension wheels were bicycle wheels, which were
invented in the 19th century. These wheels
clearly have the load taken by the upper spokes.
The spokes are fastened to the rim in a way which
will not take any compressional loading, by a nut
on the outside of the rim.
The spoked wooden wheel was
improvement over the built-up wheel in that it
separated the load-carrying function from the
road-smoothing function of the rim, but its upper
spokes did not yet carry any of the
load.
Sketches by John
Lienhard
The Engines of Our Ingenuity is
Copyright © 1988-1997 by John H.
Lienhard.
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