Today, a story about theory and practice. 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 invention of the steam
engine began in the mid-1600s, and it didn't find
solid footing until just after 1850. James Watt's
huge contributions to its development came fairly
late in the game. They began in the 1760s.
Thermodynamics, the modern science of heat, was
largely driven into being by the steam engine. It
began taking its modern form just before 1700, and
it finally found solid footing after 1850. The
story of thermodynamics and the steam engine is
really a story about theory and practice finally
making peace with one another.
Historian Richard Hills helps us understand the
situation. Suppose you lived two hundred years ago,
and you came upon an early steam engine. What would
you see? A connecting rod moving up and down in a
big piston, driving a rocker arm. The far end of
the arm would drive a pump or turn a wheel.
You'd see the effects of pressure. You'd see forces
exerted. You'd see the effects of flowing steam. As
your mind reached for analogies, you'd see
something that reminded you of the familiar
waterwheel. The burning coal, heating the boiler,
was out of your line of sight. Heat flow was not
what would catch your attention. This machine
appeared to be all about pressure and flow.
So scientists struggled to see what made these
strange machines work, while practical people
struggled to build better engines. Most early
steam-engine builders had also worked with
waterwheels. Like steam engines, waterwheels turn
and turn and do useful work. Waterwheels led our
minds away from heat and temperature.
One inventor did take a scientific
interest in heat. James Watt began as a machinist
at the University of Glasgow. He experimented with
heat while he talked to thermodynamic pioneer
Joseph Black. Watt's greatest steam-engine
invention was the separate condenser. What
it did was greatly reduce wasted heat.
In 1824, the young French engineer Sadi Carnot
formulated the second law of thermodynamics. It
says that engines can never approach a
hundred-percent efficiency. But Carnot
misunderstood heat. He thought that heat flowed
through an engine, degrading its potential for
doing work, the same way water flows through a
waterwheel. He thought that just as much heat left
the engine as entered it. He didn't see that a
large portion of the heat passing through was being
converted to create the mechanical power
output of the engine.
So the engine was our teacher, but a confusing
teacher -- maybe the best kind of teacher: Remember
that instructor who never told you directly what
you wanted to know? The one who teased your mind
with conflicting facts? The one who made you do the
As the steam engine taught us thermodynamics, it
also offered a lesson to teachers everywhere.
Learning is not preparing for multiple-choice
tests. Learning is sifting through ambiguity. True
learning is finding our own way to the other
side of the obvious.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
Hills, R. L., Power from Steam: A History of the
Stationary Steam Engines. Cambridge: Cambridge
University Press, Chapter 9. My thanks to Lewis
Wheeler, UH Mechanical Engineering Department, for
providing this source.