Name an inventor, evoke an invention. Gutenberg, moveable type. Galileo, the telescope; Samuel F.B. Morse, the telegraph; Matthew Murray, the sliding D-valve.

Matthew Murray?

Lists of history’s great inventions always include the wheel, fire, the telephone, digital computing, the printing press, television, the automobile and (surprisingly frequently) the flush toilet. Depending on the archness of the list maker, you’ll also find the likes of the transistor radio, birth-control pills, eyeglasses, the Internet, WD-40, the push-up bra and the iPhone, which came in at No. 9 in a 2010 survey.

You won’t find the D-valve on any of them. However, almost every list is likely to include the steam engine, for which the sliding D-valve was invented by Murray in 1797. That’s because the steam engine is one of the most transformative machines in history -- the power behind the Industrial Revolution.

Yet the steam engine changed the world in a different way than we usually believe. For one thing, it didn’t actually drive the machines of the Industrial Revolution, at least not at first. Though Thomas Newcomen’s first engine appeared in 1712, it wasn’t until the middle of the 19th century that steam power overtook waterwheels as Britain’s foremost power source. This is why Murray’s 10-inch-long valve does a better job of illustrating the steam engine’s historical importance than Newcomen’s 40-foot behemoth.

Power Shift

Some historical context: During the 10 millennia between the introduction of agriculture and Newcomen, all of humanity’s work -- the textbook definition: force times distance, whether to pull a plough, turn a wheel or steer a ship -- had been performed by wind, water or muscle. That’s how the pyramids were built, and Chartres Cathedral. That’s how the Polynesians crossed the Pacific, and the Norse sailed the Atlantic.

You can do a lot of work with wind, water and muscle. What you can’t do is put a price on that work.

This is the main reason why humans were on a Malthusian treadmill that kept worldwide per-capita annual gross domestic product between $400 and $650 (in 1990 U.S. dollars) for 5,000 years. Between the death of Julius Caesar and the birth of Napoleon Bonaparte, the amount increased from a little less than $500 a year to a little more than $600.

This sort of glacial growth wasn’t due to a lack of capacity for technological innovation; people who could invent the compass, gunpowder, telescopes, blast furnaces and aqueducts weren’t deficient in talent. But no matter how hard they tried, they could measure only dramatic improvements in the basic machinery of work: the transformation of windmills from horizontal to vertical, watermills turned by water passing beneath, rather than over, or the invention of a collar that allowed ploughs to be pulled by horses, instead of instead of less efficient hay burners like oxen. However, given the variability and site-specificity of wind and water, it’s not so easy to find things that improve productivity by “only” a few percentage points.

This is a problem because sustained technological innovation is incremental: Small improvements that add up over time.

So it was with steam, which was humanity’s first power source with a variable cost: the price of a fixed quantity of coal. Because the earliest steam engines were used exclusively to pump water out of mines, the most common measurement of performance was the “duty”: pounds of water that were raised 1 foot by a bushel of coal. A high-performing Newcomen-style engine typically generated a duty of 5,000 pounds to 9,000 pounds; in other words, a bushel of coal could lift that many pounds of water. Within 50 years, improved engines were achieving a duty of 18,900 pounds. By then, they were being used to run factories (and, soon enough, locomotives) and this made measuring their efficiency by the amount of water they could lift somewhat quaint.

James Watt came up with the alternative of “horsepower,” which was the standard measure of the amount of weight that one horse could lift one foot in one minute. His measure of 33,000 foot-pounds a minute or 550 a second is pretty close to the number we use today.

Which is where Matthew Murray comes in. In 1797, the journeyman mechanic patented a new steam-engine design, one that used the D-valve -- so-called for its shape -- to control the flow of steam. It was lighter than its predecessor, and absorbed less heat, which meant that steam engines could do the same work using less coal. And he didn’t just invent the valve; in order to produce it, he needed to invent a planing machine to smooth its surfaces.

Operating Costs

A few years later, another mechanic, William Murdoch, added a connecting rod, and doubled its efficiency; Murray responded by attaching the whole works to an egg-shaped gear that shaved a few more pounds of coal off the machine’s operating costs. By the end of the 18th century, because of this accumulation of small improvements, five steam engines using 6,000 tons of coal annually could do the same work as seven engines using 19,000 were doing before. The world’s first age of sustained, incremental innovation had begun.

We still live in that era today. No matter how you plot human welfare, prosperity or inventiveness on a graph -- life expectancy, GDP, calories per person, innovations -- the world was stuck in neutral until the steam engine allowed us to measure the costs and benefits of small improvements in power production. Worldwide per-capita annual GDP in 1800 -- still only about $650 in 1990 U.S. dollars -- was more than $1,200 in 1900. By 2000, it was more than $6,000. This wasn’t achieved by the wheel, the printing press, the moldboard plough or even the push-up bra. Nor is it attributable to Murray’s D-valve, at least not by itself.

That’s the point: The steam engine was the first great invention built, not to endure, but to obsolesce; to be regularly superseded by new-and-improved successors. Like every invention since, it was an object lesson in the very great value of very small improvements.

(William Rosen is the author of “Justinian’s Flea: The First Great Plague and the End of the Roman Empire,” and “The Most Powerful Idea in the World: A Story of Steam, Industry, and Invention.” The opinions expressed are his own.)

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To contact the author of this post: William Rosen at bill@justiniansflea.com

To contact the editor responsible for this post: Max Berley at mberley@bloomberg.net