The Most Powerful Idea in the World

by William Rosen

  The key was the boiler. Low-pressure engines, from Newcomen to Watt, had boiled water in chambers whose basic design wasn’t much different from that of an oversized teakettle: a pot, or “haycock” shape, in which the furnace was placed below the water. Despite a number of improvements, it had remained essentially unchanged ever since.

  Evans’s stroke of brilliance was to place his furnace inside a water-filled chamber: more surface area for the heated gas, more heat transfer to the liquid. With nowhere to go, the boiling water turned to steam whose pressure, now about fifty pounds per square inch, drove the piston, first in one direction, then in another.

  In 1804, Evans applied for and received a federal patent for a high pressure “vibrating steam engine” that incorporated a “Boiler with the furnace in the center17 of the water enclosed in brick work.” To Evans, like every other inventor of the steam age, heat meant fuel, so increasing the first meant adding more of the second. But he also realized “the more the steam is confined18 … the greater will be the power obtained by the fuel. For every addition of 30 degrees of heat to the water doubles the power [and] doubling the heat of the water increases the power 100 times. Thus, the power of my engine rises in geometrical proportion, while the consumption of fuel has only an arithmetical ratio” (emphasis added). Evans had discovered how to produce the same power from a 500-pounder that Watt was getting from a two-ton monster; and as a bonus, it burned less fuel for every increase in horsepower—a huge advantage in an engine that needed not only to be mobile but also to carry its fuel with it. It was, by any definition, an act of genius.

  It was not, however, a success. The value of high-pressure steam was greatest where its attractive power-to-weight ratio mattered most—steam locomotion—and America was still several decades away from railroad building. Evans was, like most inventors, forced to invest his time where he could find customers. In 1805, he built a thirty-foot-long fifteen-ton steam dredge for the Philadelphia Board of Health, which was the first steam land vehicle built in the United States; the same year, he created the first significant improvement over Watt’s linkage,19 using an isosceles triangle to connect two bars at a single pivot point, a design later known as the Russell linkage.*

  However, also in 1805, he was the litigant in no fewer than four different suits, brought on both philosophical and technical grounds. One result was that his income was slashed, leaving Evans, in his own words, “in poverty at the age of 50,20 with a large family of children and an amiable wife to support.” Despite his many triumphs, Evans’s life seemed, to him at least, a succession of unsatisfying successes and paranoia-reinforcing failures. In 1795, he had published The Young Mill-wright and Miller’s Guide, which was effectively an entire millwright’s education between hard covers, went through dozens of printings, and was probably the bestselling “professional” book in the young republic. But he ran out of money before completing its sequel for steam engineers, and he published it, rather petulantly, under the title The Abortion of the Young Steam Engineer’s Guide.

  Fig. 7: America’s first working steam “locomotive”: not only the first practical high-pressure steam-powered vehicle of any sort, but the first amphibious vehicle as well, though this was largely an accident. Evans’s workshop was more than a mile inland and fifteen miles from the dredging site on the Schuylkill River, so he added wheels to his paddle-driven dredge, which he had named Orukter Amphibolos, a drawing of which is in the upper right corner, and drove it proudly down Philadelphia’s Market Street. Image by permission of the Library of Congress

  Sometimes his petulance verged on a persecution complex: “And it shall come to pass21 that the memory of those sordid and wicked wretches who opposed [my] improvements, will be execrated, by every good man, as they ought to be now….”

  In 1806, however, Evans had opened the factory he called the Mars Works, where he built more than a hundred steam engines and boilers and thousands of components for mill machinery, enough that he ended up dying a rich man in 1819.

  Evans was a visionary and a pioneer. But despite his prediction that “the time will come,22 when people will travel in stages moved by steam engines from one city to another almost as fast as birds can fly,” his greatest contribution to the history of steam locomotion was almost incidental: his decision to share the design of his boiler and high-pressure steam engine with his compatriots in Britain. As he wrote in the 1805 Abortion of the Young Steam Engineer’s Guide:

  In 1794–95, I sent drawings,23 specifications, and explanations, to England to be shown to the steam engineers there, to induce them to put the principles into practice and take out a joint patent for the improvement, in their names … Mr. Joseph Stacey Sampson, of Boston [the same one who received the second patent issued in the U.S.] who carried the papers to England, died there, but the papers may have survived.

  The timing is suggestive. In fact, it is a powerful bit of circumstantial evidence for the notion that the papers not only survived, but were read by a Cornish mine engineer named Richard Trevithick.

  TREVITHICK’S ANCESTRY, ON BOTH sides, is dotted with members of Cornwall’s mining aristocracy. His father and uncle were both captains in some of the region’s largest and most profitable copper mines, including the legendary Dolcoath mine, where Richard Sr. built the deep adit in 1765 and constructed a Newcomen engine in 1775. Richard Jr.’s early life, partly in consequence, was slightly atypical, as he was neither the product of a formal apprenticeship, nor was he schooled to be a scientist or engineer; instead, by 1784, he was already working in a relatively senior position at Dolcoath, reporting to his father, and over the next ten years, he practiced his somewhat nomadic craft at half a dozen different mines all across Cornwall, including the Tincroft and Wheal Treasury (“wheal” is a Cornish term simply meaning “mine”).

  By the 1790s, he was a local hero, partly because he was seen as an adversary of Boulton & Watt. The steam engines provided by the Birmingham firm had improved productivity, but their royalty system generated mostly resentment, since the more copper the mines produced, the more gold their owners owed to Boulton & Watt. So when Trevithick testified on behalf of Hornblower during the lawsuit, he endeared himself to most of Cornwall. Trevithick’s appearance didn’t hurt. He had grown to be a huge man, at least six feet two, and “Cap’n Dick,” as Trevithick was widely known, became the subject of Paul Bunyan–like mythmaking; one story has him throwing a sixteen-pound sledgehammer over the top of a twenty-foot-tall Newcomen engine.

  Trevithick was his country’s champion not only because of his strength, but his cleverness; in 1797, he invented and built a system that improved upon, and so replaced, the chain of buckets that had been used since Newcomen to pump water out of mines. But the engines that drove them were still built by Boulton & Watt, or under license from them—at least until 1800, when Watt’s original patent finally expired. The immediate consequence of the expiration was a dramatic increase in the appeal of the Boulton & Watt designs now that they were available without the Boulton & Watt royalties.

  Trevithick, however, wasn’t trying to imitate the Boulton & Watt engine, but to replace it. Most especially, like Evans, he wanted to dispense with Watt’s separate condenser, but unlike Evans, he didn’t know whether it was feasible. This was a basic scientific question, for which Trevithick, an indifferent student (his teachers, though they noted his intelligence, also called him “disobedient, slow, obstinate24 … frequently absent and very inattentive”), had no answer. However, he wasn’t shy about using the skills of those with more formal education, and during the Hornblower trial, he had struck up what became a lifelong friendship with Davies Gilbert, the future president of the Royal Society. In 1797, Trevithick asked him to calculate how much power would be lost if instead of capturing the steam in a separate condenser, the engine simply exhausted it into the air.

  The answer was Trevithick’s real eureka moment. Gilbert explained that with each stroke,25 the cylinder would lose exactly as much pressure in
side as the pressure outside: 14.7 pounds per square inch at sea level. This would obviously be disastrous for a Boulton & Watt separate-condensing engine, which generated only a little more than ten pounds per square inch inside the cylinder; exhausting the condensation would leave it with no pressure at all.

  But what if the pressure inside the cylinder could be increased?

  In 1800, five years after Joseph Stacey Sampson had brought Oliver Evans’s drawings to Britain, and three years after Davies Gilbert had shown that an engine operating at 60 psi would lose only a quarter of its pressure at each stroke, Richard Trevithick introduced his first high-pressure steam engine at the Wheal Hope copper mine. It used almost precisely the same method Evans used for increasing the steam pressure from the boiler. It is not known whether Trevithick saw the Evans design firsthand or—more plausibly—through William Murdock, his neighbor in the town of Redruth for six months in 1797 (and who, despite his employment by the despised firm of Boulton & Watt, was friendly with Trevithick). The sequence of events, however, is persuasive: Sampson carried Evans’s drawings to Britain in 1795, to show to “the steam engineers there.” The British steam engineer best known to be working on high-pressure steam for locomotion was William Murdock, who was Trevithick’s neighbor when the Cornishman asked Davies Gilbert to give a scientist’s opinion on what was, in essence, the practicality of Evans’s engine.

  The Wheal Hope engine showed that a high-pressure engine was practical; a little more than a year later, Trevithick was ready to demonstrate that it was mobile as well. On Christmas Eve 1801, with apparently no warning, Trevithick appeared on the High Street of the town of Camborne aboard a carriage unlike anything anyone had ever seen before. No drawings survive, though a sketch dated a year later shows a four-wheeled flatbed truck with a vertical steam engine set over the front wheels, a twelve-foot-high boiler over the rear, and the driver (wearing what looks like a top hat) set behind. We do have the testimony of one of the blacksmiths who worked on the castings for the machine, “old Stephen Williams”:

  Captain Dick got up steam,26 out in the high-road, just outside the shop at the Weath. When we get see’d that Captain Dick was agoing to turn on steam, we jumped up as many as could; maybe seven or eight of us. ’Twas a stiffish hill going from the Weight up to Camborne Beacon, but she went off like a little bird….

  When she had gone about a quarter of a mile, there was a roughish piece of road covered with loose stones; she didn’t go quite so fast…. She was going faster than I could walk, and went on up the hill about a quarter or half a mile farther, when they turned her and came back again to the shop….

  To the spectators at Camborne Hill wrapped up against the cold that Christmas Eve, the vision of a wheeled vehicle moving uphill without being either pushed or pulled must have seemed something like levitation. For millennia, the force driving wheeled vehicles had always been something external to the vehicle, which meant that the primary traction against the roadway was also generated externally: by a horse’s hooves, for example. It was by no means obvious that simply turning a wheel would generate enough traction to pull itself—the first bicycles were still decades in the future—and Trevithick apparently spent the week before his experiment hand-cranking the wheels of a model along cobblestone and dirt roads.

  Just as startling to the audience lining the half-mile-long High Street, the engine on board the Camborne carriage made its journey belching smoke like something out of myth. Trevithick’s engines, having dispensed with a separate condenser, were thereafter known as “puffers” because their steam exhausted directly to the air. The distinctive clouds familiarly associated with steam engines* had finally been born.

  It didn’t survive its own infancy; the engine that Stephen Williams rode up Camborne Hill on Christmas Eve was destroyed before New Year’s. Two of Trevithick’s drivers27 celebrating the season in a local pub left the boiler unattended, the water boiled away, and the chamber became hot enough to set fire to the engine, and to the shed in which it was housed. Which didn’t, in the end, matter all that much. In March 1802, Trevithick, with help from a fellow Cornishman, the scientist Humphry Davy, applied for and received a patent on the new locomotive.

  The market for self-propelled steam engines was still a fraction of that for stationary ones, thousands of which were by then pumping water and operating machinery throughout Britain. One of the more avid users was the Coalbrookdale foundry,28 then run by the fourth generation of the Darby family, where the boiler for the Camborne Hill locomotive was built; by the end of 1802, the Darbys had hired Trevithick to build a new stationary engine operating at the seemingly impossible pressure of 145 psi.

  Their faith in the Cornishman, and in high-pressure steam, was understandable, but it was controversial. The future of steam power was very clearly at stake, and the established powers of British manufacturing had everything riding on the existing Boulton & Watt low-pressure designs. The Birmingham firm’s founders had retired in 1800, but their sons were, if anything, more hostile both to high-pressure steam and to Trevithick than were their fathers. No one knew this better than Cap’n Dick; after the boiler of a high-pressure engine exploded in Greenwich in September 1803, Trevithick wrote of his belief that “Mr. B. & Watt29 is abot to do mee every engurey in their power for they have don their outemost to repoart the exploseion both in the newspapers and private letters.” But though the Boulton & Watt public relations campaign could slow the adoption of high-pressure steam engines—and infuriate Trevithick—it could not stop it. In 1803, a Welsh ironmaster named Samuel Homfray, jealous of his competitors at Coalbrookdale, invited Trevithick to bring his magic across the Bristol Channel from Cornwall to Wales.

  Industrialization in Wales, as in England, had been partly a function of geology, and the great ironworks that had grown up around the town of Merthyr Tydfil in the 1760s were testimony to the generous local supplies of hematite, limestone, coal, and water, the key ingredients for a furnace-and-forge economy. Just as rich was the supply of ironmongers—four large ironworks, each competing with one another to meet the ever increasing demands of British industry. Competing, and also cooperating: the four ironworks each used the same route to transport their goods to Cardiff and the coast: the twenty-four-mile-long Glamorganshire Canal, which they had built, owned, and, in theory, shared.

  They did not, however, share it happily. The owner of the Cyfarthfa ironworks, Richard Crawshay, was also the majority shareholder in the canal, and as a result, barges hauling Cyfarthfa iron were granted preferential treatment. His partners, the owners of the Dowlais, Plymouth, and Penydarren works, were angry enough to build a parallel route for their iron, a horse-drawn railway. One of them was Samuel Homfray of Penydarren, Richard Trevithick’s new employer.

  Homfray’s original objective in hiring the Cornishman seems a bit unformed in retrospect. It is certain that he wanted a new steam engine to run the hammer in Penydarren’s forge, but unlikely that he had already thought about replacing the horses pulling his iron-filled carts. For one thing, the existing railway was built for horses rather than locomotives; the rails were set into concrete stones set four feet apart, and had no crossties in between to trip up the horses. Also, the grade was extremely gentle;30 on the way from Merthyr to the wharf at Abercynon, the railway dropped only one foot for every forty-five traveled, putting less strain on the horses both going and returning.

  Fig. 8: The Penydarren engine, a replica of which is still on display at the National Maritime Museum at Swansea, was as important in its way as either Newcomen’s 1712 Dudley Castle pump, or Watt’s 1776 New Willey engine, or even the Stephensons’ Rocket. National Railway Museum / Science & Society Picture Library

  In the event, something provoked Crawshay to bet Homfray five hundred guineas that no steam locomotive could do the job of the horses. To win, Trevithick needed to build an engine capable of hauling ten tons of iron ore from Merthyr to the wharf, nine and a half miles away.

  The Penydarren locomotiv
e is practically an encyclopedia of innovation. As protection against explosion, it used one of Trevithick’s cleverest inventions, the so-called “fusible plug,” a small lead cylinder inserted into a predrilled hole in the wall of the engine’s boiler—a hole that, in a properly operating engine, would always be underwater. If, however, the water level in the boiler were to fall low enough to become dangerous, the heat would melt the lead plug, allowing the steam to blow out the fire. The Penydarren engine also incorporated a U-shaped fire tube, a return flue that carried the air heated by the furnace from one end of the boiler and back again, which put at least twice as much surface area in contact with the water. Even more important, it didn’t just exhaust the spent steam into the air, but used a chimney that, in Trevithick’s own words, “makes the draft much stronger”31—that is, the exhaust steam, hotter than the surrounding atmosphere, rose. By doing so, it pulled more oxygen into the furnace, raising its temperature and increasing the efficiency of the heat engine itself.

  In other respects, it was a bit of what a later generation of engineers would call a kludge. Trevithick was obliged to build an engine that would serve Homfray’s forge as a steam hammer, whether or not it worked to transport his ore, and it was therefore cobbled together from pieces intended for different functions. Its piston operated like a slide whistle, driving only the two wheels on the engine’s left side and conserving momentum with an enormous flywheel set behind them. And, on February 21, 1804, it worked—sort of: