Today, the story of a great bridge and a mysterious
disease. 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.
James Eads, born in Indiana
in 1820, was uneducated but smart and well-read. In
his 20s he designed a diving bell and worked at
salvaging cargo from sunken river boats. During the
Civil War, Eads built ironclad gunboats. He was at
home in our inland river system.
At the age of 46, Eads, who'd never built a bridge,
was called on to bridge the Mississippi at St.
Louis. Here he flew in the face of conventional
wisdom. Instead of the usual truss bridge, he
proposed to build three huge cantilever arches, 500
feet long.
The real trick would be placing the piers right in
the middle of the largest river in the world. Eads
knew the swirling mess of moving mud and silt that
made up the river bottom. And he knew bedrock lay
100 feet deeper still. But how to solve the
problem? The answer turned up in France, where he
found a technology for setting piers in soil under
water -- the plenum pneumatic, or caisson. He'd use
caissons, but on a scale they'd never been used.
He built an 80x60-foot steel box, nine feet high
and open at the bottom like a great cookie cutter.
At first it floated on air trapped inside. Then, as
Eads built the masonry pier on top of it, it sank
down to the riverbed. He pumped pressurized air
into the caisson to keep the water and mud out.
Workers descended a stairwell through the masonry
to the caisson and entered it through an airlock.
Inside, they dug out mud while the whole structure
gradually settled downward toward bedrock. Workers
above kept piling the masonry pier on top of it.
Things went fine for a while. When the pressure in
the caisson reached twice atmospheric pressure,
workers felt pains in their joints as they left the
caisson. Since they had trouble standing straight,
they called the problem "the bends." When they
reached a depth where the pressure was three
atmospheres, Eads had to send men to the hospital.
Some suffered total paralysis. They began dying.
All the while, Eads took visitors into the
caissons. They found it exciting when they couldn't
whistle in the dense air. But none suffered any
problems. Obviously, the less time you spent below,
the less you suffered. Eads gradually reduced the
work cycle to only 45 minutes. Doctors were
baffled.
Historian David Diaz tells how autopsies revealed
swollen blood vessels and dark, tarry blood, but no
explanation. Fourteen deaths later, the bridge
finally opened. It was a remarkable accomplishment.
Even today, those piers are the deepest on record.
Meanwhile, the contractors went bankrupt. A few
years later, we saw that, if you breathe high
pressure air very long, your blood absorbs its
nitrogen. Then, when you quickly depressurize,
nitrogen bubbles come out of solution and raise
havoc with your body.
So Eads gave us a great 19th-century engineering
triumph. But he also left us painfully aware -- of
the terrible price of learning.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
