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
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