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 in the early 17th century.
They were holding it up to the light trying to see
what it revealed about the nature of things. Nature
demonstrated her abhorrence clearly enough when you
used a drinking straw. Nature tried 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 32 feet. We see that atmospheric
pressure couldn't push it any further; but
17th-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 32 feet.
Actually, Galileo himself was trying to understand
air pressure and vacuum. Three months before he
died, in 1641, he'd hired a young assistant named
Evangelista Torricelli to help him. Two years
later, in 1643, Torricelli invented the barometer,
and he estimated atmospheric pressure. We honor him
today by naming the Torr, a unit of pressure, after
him.
In the meantime, Otto von Guericke, an influential
citizen of Magdeburg in Saxony, had become
interested in the atmosphere. He'd studied the work
of Galileo and Torricelli, but he was also involved
in the administration of Magdeburg. In fact, he was
elected mayor of the city in 1647. About this time
he invented a vacuum pump, and what he did with it
was pretty spectacular. In 1654 he gave the
citizens of Magdeburg a remarkable lesson in the
force of the atmosphere. He made two hollow
hemispheres, 20 inches in diameter, that fit
tightly together into a sphere. Then he pumped the
air out of the sphere and let 16 horses -- eight on
each side -- try to pull them apart. They couldn't,
of course. It would have taken over two tons of
force to separate the halves.
This was more showmanship than science; but it
served its purpose. He'd shown the world that
seemingly insubstantial gases could exert
astonishing forces -- forces that could probably be
harnessed. During the rest of the 17th century, all
kinds of people struggled to find a way to make use
of these forces. In 1698, Thomas Savery finally
made a workable pump that used the vacuum created
by condensing steam. Just a few years later, Thomas
Newcomen showed us how to make a steam engine on
the same principle, and -- suddenly -- the
power-generation game was afoot.
Our big power plants generate 3,500,000 HP today.
But they owe a debt to Guericke's 16-horse
experiment.
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 episode has been revised as Episode 1553.
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
(Theme Music)
The Engines of Our Ingenuity is
Copyright © 1988-1997 by John H.
Lienhard.
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