We talked about an Industrial Revolution that wasn’t really about epistemic,
or what’s-really-going-on questions, but about how to make stuff work in the real world.
Now it’s time to come back to all that cool technology from the early 1800s.
How does steam work?
How can we quantify “hot air,” or mathematically describe the motion of a piston—or the heat
from the barrel of a cannon?
[Intro Music Plays]
Thermodynamics—or the physics of heat, temperature,
energy, and work—doesn’t really have a
Darwin and Wallace.
It’s a lot messier.
Scientists were confused about the basic concepts of heat transfer, or how stuff heats up or
cools down, and temperature.
And for most of human history, they didn’t even have a good way to measure temperature.
Galileo and Newton made attempts.
But it wasn’t until the early 1700s that Gabriel Fahrenheit finally nailed it.
But that still didn’t explain how and why things heat up.
A lot of people tried to crack the physics behind these phenomena.
Like chemist Antoine Lavoisier—remember him from Episode 18?
He used the caloric theory, which explained heat transfer as an ether, or colorless fluid,
that migrated from a body at a higher temperature to one at a lower.
This made sense to Lavoisier when he was upending chemistry.
Buuuuut it was wrong.
In fact, ether was the explanation for many unknown phenomenon in the eighteenth century.
And there were a lot of conflicting ether theories.
Throughout the entire 1800s, a large number
of chemists, physicists, engineers, and mathematicians
across the world worked out the not-wrong physics of heat and motion.
One of the first was American physicist Benjamin Thompson—better known as Count Rumford.
We’ve actually met Rumford before: he married Lavoisier’s scientifically inclined widow, Marie.
So, yes, Marie Lavoisier helped develop the
modern sciences of both chemistry and the physics of heat and energy!
Rumford conducted a lot of experiments in the barrels of cannons,
like how to measure and insulate against heat.
He noticed that certain materials insulated better than others, and that air seemed to
be involved in the transfer of heat… and concluded that air is a great insulator.
Then he moved on to liquids and concluded that they… are also great insulators.
All of them.
Which, you know, water boils, so…
Kinda problematic science.
But he kept going.
In his experiments, Rumford noticed that something other than the caloric ether was heating up
various substances.
So he devised an experiment which showed that the boring of a cannon released heat.
Basically he just created a cannon barrel by drilling a hole in a long piece of metal
for over two hours.
But—this was the twist—Rummy did this underwater, which eventually caused the water
to boil.
Heat wasn’t the invisible fluid part of a chemical reaction—but simple mechanical
motion.
In some ways, this result should have been obvious to anyone who observed friction, but
Rumford brought it back to scientific attention: how is heat created and transferred?
Epistēmē needed to catch up with technē.
And ether needed to be replaced by a new science.
This science picked up steam with the invention of, well, the steam engine.
After engineers like James Watt designed ways of producing steam and directing it to move
machines, scientists tried to improve the efficiency of these systems.
Steam engines were not an example of basic research applied to the real world.
The cool new tech came first, later propelling a lot of useful research into how
heat and energy function.
French physicist and engineer Nicolas Sadi Carnot grew up during the Napoleonic Wars.
He believed that steam engine efficiency was
the key to helping France become a glorious empire.
Carnot’s work with steam engines led him to think a lot about thermodynamics.
In an engine cycle, the parts of the system move through different states of energy, and
finally return to the initial state.
Inventors were thinking up all sorts of great applications for engines, like locomotives,
but no one could mathematically explain what was going on.
Carnot figured out what became known as the Carnot cycle, or the science of what happens
inside heat-producing engines.
The Carnot cycle describes the upper limit of the efficiency of a model thermodynamic
system, or system where heat moves around within set boundaries.
In 1824, Carnot published the paper “Reflections on the Motive Power of Fire, and on Machines
Fitted to Develop that Power.”
This contained, although not in the same terms we’d use today, the second law of thermodynamics,
which states that the total entropy in a closed system can never decrease,
only stay steady or increase: heat can’t randomly flow from a colder point to a hotter one.
This is just one way to express the universal principle of entropy,
or the state of disorder in a system.
But don’t get too philosophical about chaos: entropy is just a variable that you can calculate
with the right math.
Carnot didn’t quite know what he had going.
He presented his findings in terms of the reigning caloric theory.
And then he died of cholera at the tragically young age of 36.
Many other physicists around Carnot’s time realized that heat, light, chemical reactions,
and motion aren’t merely very complex phenomena on their own.
They are all part of a larger, more complex system.
And they interact with each other.
In the 1840s, several scientists independently discovered what we now confusingly call the
first law of thermodynamics, or the conservation
of energy: energy can change from one form to another.
But energy is not lost. It has to go somewhere.
Energy in coal, for example, is released into heat and light, as fire.
And the first law is not just a metaphysical idea. It can be quantified.
The whole point of thermodynamics is to put numbers to all of the complex motions and
reactions that move energy from one form to another.
To find the fixed exchange rates between states of energy.
In the 1840s, English physicist James Joule
and German doctor Julius von Mayer independently figured out
that heat transfer and mechanical work were different forms of the same thing,
which we now call energy transfer.
Thought Bubble, give us an introduction:
This was such a big deal!
Heat is just motion and vice versa, just like Rummy’s cannon experiment showed!
In fact, today, the Joule is the unit of energy.
But alas, neither of their “mechanical theories of heat” was accepted at the time.
Joule experimented with batteries and electromagnets,
trying to determine the relationship between heat and motion.
He concluded that the heat needed to increase the temperature of a pound of water by
“one degree of Fahrenheit’s scale” was equal to “a mechanical force capable of raising
838 pounds to the perpendicular height of one foot.”
Today we would say that’s about four joules per calorie of work.
Joule told this to the other members of British
Association for the Advancement of Science in 1843.
Who were just like, “Congrats, brah! You’ve just invented… warm water, I guess.”
Undaunted, Joule set out to prove his theory.
Conducting experiments on his honeymoon, Joule put a dynamo in water and measured it,
experimentally confirming his mechanical theory.
He forced water through a perforated cylinder, measuring the very slight degree to which
the water heated up… and found that his mechanical heating-up energy was the same
as his electrical heating-up, about four joules.
Or, as he said: “Wherever mechanical force
is expended, an exact equivalent of heat is always obtained.”
BAM!
And then, in 1845, Joule dropped “On the Mechanical Equivalent of Heat,” in which
he detailed his experiments using a falling weight,
that is, gravity, to move a paddle wheel inside
an insulated barrel of water, in order to heat it up.
Again, he measured the energy involved and found… around four joules!
Joule finally began to get his peers’ attention, but caloric theory still reigned.
Thanks, Thought Bubble.
Julius von Mayer, on the other hand, tried to publish his ideas, but he was rejected.
So he attempted suicide…
But only broke his legs.
He was declared insane and locked up in an asylum.
For a long time, Mayer was overlooked as the independent co-discoverer of the mechanical
equivalence of heat energy.
Joule got all the credit, although Joule did give Mayer a shoutout in a paper in 1850.
Mayer also hypothesized that plants convert light into chemical energy, or photosynthesize.
Way ahead of his time!
Meanwhile, Scottish physicist William Thomson, better known as Lord Kelvin, heard Joule talk
at the British Association in 1847 and wanted more evidence.
Lord Kelvin was also a big fan of Carnot’s, but wanted to push his theories farther.
So he tried to reconcile Carnot’s work, as explained by caloric ether, with Joule’s.
Lord Kelvin is usually credited with coining the term “thermodynamics” in 1854.
Here’s his definition: “Thermo-dynamics is the subject of the relation of heat to
forces acting between contiguous parts of
bodies, and the relation of heat to electrical agency.”
Ultimately, Lord Kelvin rejected caloric theory and he teamed up with Joule.
Lord Kelvin worked on many aspects of physics and other sciences.
Today, he’s probably best remembered as the dude who worked out the science of absolute
temperatures, which are now measured in the unit called the “Kelvin.”
In the 1850s and 60s, German physicist Rudolf Clausius figured out that there were actually
two distinct laws at work in Carnot’s most famous paper…
and that they contradict each other.
Clausius restated the first and second laws of thermodynamics, removing contradiction.
His version of the second law: “Heat can never pass from a colder to a warmer body
without some other change,
connected therewith, occurring at the same time.”
In 1865, Clausius also gave the first mathematical description of entropy and named it.
And this paper ended with a brilliantly simple
summary of the first and second laws of thermodynamics:
“The energy of the universe is constant.
The entropy of the universe tends to a maximum.”
Thermodynamics deeply united chemistry and physics in the way that Newton’s Principia
had united mathematics and astronomy.
Suddenly, experiments and theories that looked
very different on the surface were joined at a basic level.
Thermodynamic concepts from the studies of heat engines were applied to chemical reactions.
Entropy proved a very useful idea, in many disciplines, including statistics.
So, at the end of the nineteenth century, if you were a fan of thermodynamics, you might
say that the question of “what is stuff” was close to being solved.
But you’d be wrong, because of Einstein—wait for him!—and because the history of thermodynamics
was a hot mess.
Pun DEFINITELY intended.
This history is often presented as an orderly progression of ideas, each building on the
foundation of laws created by earlier investigators.
But that’s not quite true.
After all, what we now call the second law of thermodynamics preceded the first
by more than twenty-five years!
So, not super orderly.
And there were long periods when invalid ideas were tenaciously held in the face of decisive
evidence of their falsity.
In other cases, as with genetics, lots of scientists simultaneously adopted a whole
new block of theory and built upon it.
Next time—sparks will fly as we meet another gang of nineteenth-century physicists and
engineers: the pioneers of electricity!
Crash Course History of Science is filmed in the Dr. Cheryl C. Kinney Studio in Missoula,
Montana and it’s made with the help of all this nice people and our animation team is
Thought Cafe.
Crash Course is a Complexly production.
If you wanna keep imagining the world complexly with us, you can check out some of our other
channels like Scishow, Nature League, and The Financial Diet.
And, if you’d like to keep Crash Course free for everybody, forever, you can support
the series at Patreon; a crowdfunding platform that allows you to support the content you love.
Thank you to all of our patrons for making
Crash Course possible with their continued support.