The Roots of Progress

Science and steam

October 27, 2018

In a previous post, I addressed the question of the relationship between the Scientific and Industrial Revolutions. I looked at how much some of the early inventions of the Industrial Revolution, in particular the steam engine, were influenced by or dependent on scientific understanding.

The steam engine was invented before the science of thermodynamics, and did not depend on it. Thermodynamics is needed to optimize an engine, but not to invent it. To invent it, however, did depend on at least some scientific understanding of atmospheric pressure, which had been demonstrated as early as the 1600s, in particular by Denis Papin.

Further, I noted that

the inventors of the time corresponded with scientists, as a part of the “Republic of Letters.” In particular, Thomas Newcomen, inventor of the first steam engine, corresponded with the great physicist Robert Hooke. They discussed the engine in particular, and Hooke specifically advised Newcomen in 1703 to drive the piston purely by means of vacuum.

I’m now reading an excellent book titled Energy: A Human History, which gives a few more examples.

First is the influence of Dr. Joseph Black and his theory of latent heat on the inventor James Watt. During his experiments,

Watt measured how much steam it took to heat a volume of cold water to boiling. To his surprise, he discovered that “water converted into steam can heat about six times its own weight of well-water to 212°…. Being struck with this remarkable fact, and not understanding the reason of it, I mentioned it to my friend Dr. Black, who then explained to me his doctrine of latent heat.”

… Watt took from the theory the information he needed: that water absorbed a great deal of heat in changing into steam and lost a great deal of heat changing back into water. If he wanted to make a more efficient steam engine, he reasoned, one that used less coal and therefore cost less to operate, then “it was necessary that the cylinder was always as hot as the steam that entered it, and that the steam should be cooled down below 100° (Fahrenheit) [when injected with cold water to condense it to make a vacuum] to exert its full powers.”

This understanding led directly to Watt’s great breakthrough, the separate condenser.

The second example relates to high-pressure steam engines. Watt’s engine, like Newcomen’s, relied on atmospheric pressure acting against a vacuum. However, atmospheric engines are relatively large, heavy, and inefficient. They were stationary, used to drive industrial machines such as pumps, hammers, and drills. To make engines with a power-to-weight ratio that would enable locomotion, you need to increase the pressure of the steam.

Richard Trevithick was one of the first engineers to experiment with high-pressure steam. He, too, consulted on his designs with a scientific expert who applied principles of physics to his engineering problems:

Using high-pressure steam directly, Trevithick no longer needed to bleed off the steam into a separate condenser. It could be vented into the air. But he needed to know what his engine would lose and what it might gain if it did so. Who could tell him?

… In London, he met and befriended twenty-nine-year-old Davies Giddy, a mathematician and former high sheriff of Cornwall and a friend of Trevithick’s father…. Giddy remembers, “On one occasion, Trevithick came to me and inquired with great eagerness as to what I apprehended would be the loss of power in working an engine by the force of steam, raised to the pressure of several atmospheres, but instead of condensing [the steam,] to let the steam escape. I of course answered at once that the loss of power would be one atmosphere.” That is, whatever the pressure of the steam in Trevithick’s engine, the only loss from his design compared with an atmospheric engine would be the loss of the vacuum: his engine would have to work not against a vacuum but against atmospheric pressure, 14.7 pounds per square inch. And, added Giddy, such loss would be partly offset in Trevithick’s simpler direct-steam design by having eliminated some of the other inefficiencies of an atmospheric engine—no air pump with its friction, no friction or work raising the condensing water from its reservoir. “I never saw a man more delighted,” Giddy concludes.

Trevithick went on to build high-pressure steam engines and to experiment with using them for locomotion, including a steam-powered carriage that was like a strange, distant ancestor of the automobile. (Trevithick had a working prototype in the early 1800s, before the advent of railroads, but for reasons that are unclear to me, no investors wanted to fund further development and the project went nowhere.)

So it seems that almost every major innovator in steam engines had direct correspondence with a physicist or mathematician who helped them directly in their invention.

Books in this post

Energy: A Human History