Today, an old technology meets a new one. 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 Chinese built a machine
called a South-Pointing Chariot almost 2000 years
ago. It was a small cart with a figure on top. As
it moved down a twisting road, the figure always
pointed south. When 19th-century historians first
read about this odd machine, they assumed it used a
compass. Actually, it didn't.
Hidden in the cart was an astonishing gear train.
Its heart was a differential gear, like the one in
your car. As the wheels turned, so did the figure
on top. The gears kept the figure pointing in the
same direction it'd been pointing when the trip
began. The cart didn't use a compass at all. Its
gears simply remembered which way the figure
pointed at first. Those early Chinese had an
amazing command of gearing to make such a thing.
Now that same principle is coming out of the Orient
again. This time, the Honda company has announced a
new navigation system for its cars. It'll display a
map on a dashboard TV screen. The map is stored on
a compact disc. You can replace it when you want to
update the map. Your position and direction will
show on the screen. But how do they manage that?
Three strategies can be used to keep track of a
car's position. The most obvious is to use a
compass. But compasses need all kinds of
correction, and they're easily thrown off by any
magnetic field. The best way to track position
would be to read a radio signal the way an airplane
does. But to do that you need a network of
transmitting stations along the road. Someday we
might use that kind of system, but not yet.
So car companies come back to what we call dead
reckoning. That means keeping track of the distance
your car travels and the turns it makes. We come
back to the South-Pointing Chariot. Some companies
want to tie into the differential -- to use the old
Chinese technology directly. Honda changes that
The heart of their system is a helium jet flowing
between two wires. When the car turns, the inertia
of the jet carries it into one of the two wires and
cools it. That sends an electric signal to a
computer. The signal tells the computer how the
direction of the car has changed.
That seems wonderfully high-tech, but the old
South-Pointing Chariot rides within it. Like the
South-Pointing Chariot, the Honda system has to be
reset now and then -- the way you reset a clock.
Its purpose might be similar, too. The old Chinese
chariot was built to impress the people with the
mystic powers of the emperor. Perhaps we see some
faint echoes of that in the new Honda system, as
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds