Today, we invent vacuum. 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 saying, nature abhors
a vacuum, had become a major contemplation
object for natural philosophers by the early 17th
century. They were holding it up to the light
trying to see what it revealed about the nature of
things. Nature demonstrates her abhorrence clearly
enough when you use a drinking straw. Nature tries
to get rid of the vacuum by driving liquid up the
straw.
The story is told about a group of Florentine
engineers trying to suck water up from a deep sump.
Try as they would, they couldn't get the water to
rise more than thirty-two feet. You and I know that
atmospheric pressure can't push water any further;
but seventeenth-century engineers had no way of
knowing that. So they went to Galileo and asked
what was going on. Galileo wryly replied that
nature's abhorrence didn't appear to extend beyond
thirty-two feet.
Actually, Galileo had, himself, been trying to
understand air pressure and vacuum by then. In
1641, three months before he died, he'd hired a
young assistant named Evangelista Torricelli to
help him. Two years later Torricelli invented the
barometer, and he gave us a good estimate of
atmospheric pressure. We honor Torricelli today by
naming the Torr, a unit of pressure, after
him.
Meantime, Otto von Guericke, an influential citizen
of Magdeburg in Saxony, had grown increasingly
interested in the atmosphere. Von Guericke had
studied both Galileo's and Torricelli's work, but
he was also involved in the administration of the
city of Magdeburg. In fact, he was elected its
mayor in 1647. About that same time he invented a
vacuum pump, and what he did with it was
spectacular.
In 1654 he gave the citizens of Magdeburg a
remarkable lesson in the force of the atmosphere.
He machined two hollow hemispheres, twenty inches
in diameter, so they fit snuggly into a sealed
sphere. He pumped the air out of it. Then he put
sixteen horses, eight on each side, to the task of
pulling the halves apart. The horses couldn't, of
course. It would've taken a force of over two tons
to separate the halves.
That may look more like showmanship than science.
But it served its purpose. Von Guericke showed the
world that seemingly insubstantial gases could
exert astonishing forces -- forces that could
probably be harnessed. Down through the rest of the
seventeenth century, people struggled to find a way
to make use of these forces. In 1698, Thomas Savery
finally made a workable pump driven by the vacuum
created when steam condensed. Just a few years
later, Thomas Newcomen made a steam engine on the
same principle, and the power-generation game was afoot.
Our big power plants today generate more than a
gigawatt -- well over a million horsepower. That's
a long way from Otto von Guericke's startling
little sixteen-horse demonstration. But that's
where the seed was sown. That's where we saw the
potential of gases, which, at first, seemed no more
real than ectoplasm.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
Lardner, the Rev. D., Hydrostatics and
Pneumatics. American ed. Philadelphia: Carey and
Lea, 1832, Pt.II, Pneumatics, Chapt. 3.
Usher, A. P., A History of Mechanical
Inventions. Cambridge: Harvard University
Press, 1970, Chapt. XIII.
This is an updated version of Episode 113.
Image courtesy of the Burndy
Library, Dibner Institute for the History of
Science and Technology
Otto von Guericke
From Steam Engines Familiarly
Explained, 1836
Savery's 1698 steam pump
The Engines of Our Ingenuity is
Copyright © 1988-2000 by John H.
Lienhard.
