The Most Powerful Idea in the World

by William Rosen

  Even in Watt’s time, the clear line between liquid and vaporized water was pretty fuzzy. A thermometer dating from the 1750s is marked with two different “boyling” temperatures;16 at 204, water “begins to boyle,” and then at 212, “boyles vehemently,” a distinction that dates back to Isaac Newton. The measurement problem was acute enough17 that in 1776 the Royal Society appointed a committee, headed by Henry Cavendish (better known as the discoverer of hydrogen) in order to establish the “fixed points” of thermometers.

  Watt began his researches on the Newcomen engine fourteen years before the Cavendish committee delivered its conclusions in 1777 and was, in consequence, working with a clunkier set of measurements. He wasn’t, however, completely in the dark. Toward the end of his life, Watt himself provided an inventory of the basic knowledge already in circulation before his first great innovation. One small example of it18 was the twenty-year-old discovery, by the physician William Cullen (Joseph Black’s teacher, and yet another member of the remarkable faculty of the University of Glasgow), that water boiled at a lower temperature in a vacuum, thus releasing steam that would degrade the cylinder’s vacuum. This turned out to be critical, because the fact that the Newcomen engine operated in a vacuum meant that cooling the steam to the point of condensation required cooling it to temperatures even lower than 100°C/212°F. In order to calculate how much lower, Watt needed to develop an exact scale showing how changes in pressure map to boiling temperatures. Most important, he needed an accurate way of measuring the volume of steam produced by vaporizing a given volume of water, and the water condensed from a measured amount of steam. Watt was a demon for measurement, and he spent months computing the volume of steam as compared to water, the quantity of steam used by a single stroke of a Newcomen engine, the quantity of water needed to condense it, and so on. As a case in point, though Samuel Moreland had estimated that boiling a given volume of water would produce steam that would fill a space 2,000 times greater, J. T. Desaguliers calculated the number as 14,000, and Watt needed to find out for himself. In one of his notebooks,19 he describes an experiment in which he boiled an ounce of water in a “Florence Flask,” forced the air and water out, and compared before and after weights, concluding that the accurate relationship between liquid and solid volumes was 1,849 times. Once deriving the critical relationship between the phases of water, as Watt later recalled,

  I mentioned it to my friend Dr. Black,20 who then explained to me his doctrine of latent heat…. I thus stumbled upon one of the material facts by which that beautiful theory is supported…. Although Dr. Black’s theory of latent heat did not suggest my improvements on the steam-engine … the correct modes of reasoning, and of making experiments of which he set me the example, certainly conduced very much to facilitate the progress of my inventions.

  Nothing is more common in the history of science than independent discovery of the same phenomenon, unless it is a fight over priority. To this day, historians debate how much prior awareness of the theory of latent heat was in Watt’s possession, but they miss Black’s real contribution, which anyone can see by examining the columns of neat script that attest to Watt’s careful recording of experimental results. Watt didn’t discover the existence of latent heat21 from Black, at least not directly; but he rediscovered it entirely through exposure to the diligent experimental habits of professors such as Black, John Robison, and Robert Dick.

  In the end, it was the habits of recording and comparing results, time after time, that proved truly indispensable for Watt’s “rediscovery” of Joseph Black’s conjecture of latent heat, one that puzzled not only Watt, but generations of physics students ever since. Boil a quart of water, turning it into steam; it takes up a bit more than 1,800 times the space it did when liquid. But an atmospheric steam engine doesn’t want steam, it wants a vacuum, so it has to condense that steam back into water. Newcomen did so by injecting a stream of water into the sealed cylinder of his engine, but he never measured the amount needed. Watt, diligent experimentalist that he was, did: It took up to six quarts of water at room temperature to condense the steam. A year into the process, Watt had not only rediscovered Black’s theory, he was finally able to quantify it. The exhaustive process of experimenting, measuring, and experimenting again had allowed him to calculate how much steam was necessary for each piston stroke, and how much the Newcomen engine was actually generating. He now had quantities he could measure.

  The measurements showed him where the problem was. The engine depended on steam’s filling the cylinder before it was ready to produce a vacuum. But every time fresh steam was admitted into the now cooled cylinder, it didn’t expand; it just continued to condense, turning back into water until the cylinder heated up to the temperature of the steam itself. Heating the cylinder walls22 wasted up to three-quarters of the steam, or even more: In one test made in 1765, Watt found that an old-style engine was boiling more than three times as much water to heat the cylinder as it was using to create a vacuum.

  The problem was exacerbated by the fact of the vacuum itself, which effectively lowered the vaporization temperature of the water, in the same way that water boils at a much lower temperature at high altitudes: lower pressure, lower boiling temperature. The water, which needed to be heated to 100°C/212°F to boil at normal pressure, needed only half that to boil in a vacuum. And if water turns to steam at relatively lukewarm temperatures, then condensing it requires either a modest amount of very cold water (obviously impractical without refrigeration) or a huge amount at room temperature, which degraded the engine’s efficiency even further.

  The Newcomen engine was caught between fundamentally incompatible goals: The engine should use as little water as possible to condense the steam (in order to avoid cooling the cylinder), but as much water as possible to make sure that condensation occurred rather than more vaporization. Put another way: The cylinder needed to be kept at a constant 212°F/100°C (to avoid condensation that didn’t create a vacuum) and it needed to be kept at a constant 100°F/45°C (to avoid vaporization). Watt, in Usher’s terms, had perceived an “unsatisfactory pattern.”

  Still, after two years of measurement, analysis, and experiment, the unsatisfactory pattern was all he had. Frustrating though that was, he kept at it, to satisfy not merely his curiosity, but also his wallet; in his own words, his mind “ran on making engines cheap23 as well as good.” From the beginning, Watt recognized the problem in terms of wasted fuel, which meant wasted money, and therefore an opportunity. An idea that could significantly reduce that waste was clearly going to make someone rich. That someone didn’t need to be a skilled artisan. He didn’t have to live in a culture that had only recently articulated a property right in ideas and drafted legislation protecting that right. Scientists and philosophers, as we have seen, had been paving the way for centuries before Watt, or even Newcomen. Eighteenth-century Britain wasn’t any more hospitable to their brilliant innovations than anywhere else; but it was a lot more hospitable to innovators who couldn’t afford to invest years of their lives with no hope of material gain. Watt was brilliant, unusually so. But he was also emblematic of hundreds, soon to be thousands, of men like himself, each of them searching for a “eureka” moment.

  ALFRED NORTH WHITEHEAD FAMOUSLY wrote that the most important invention of the Industrial Revolution was invention itself. A number of others compete for second place, but the insight that came to James Watt in the spring of 1765 has a lot of support. By then, he had tried dozens of different ways to find a cylinder that would both heat up and cool down rapidly, even trying different materials for the cylinder itself, experimenting with brass, cast iron, and even wood “soaked in linseed oil, and baked to dryness,” each trial repeated half a dozen times. Nothing had worked, until he had his epiphany,* one he later described as the realization that since

  steam was an elastic body24 it would rush into a vacuum, and if a communication were made between the cylinder and an exhausted vessel it would rush into it, and might be there con
densed without cooling the cylinder. I then saw that I must get rid of the condensed steam and injection-water if I used a jet as in Newcomen’s engine. Two ways of doing this occurred to me. First, the water might be run off by a descending pipe, if an outlet could be got at the depth of thirty-five or thirty-six feet, and any air might be extracted by a small pump. The second was to make the pump large enough to extract both water and air….

  What he had envisioned was simple enough: a second chamber, connected to the cylinder by a pipe, through which the steam would flow. When it arrived in the new chamber, already surrounded by cool water, the steam would condense, a vacuum would be formed, and atmospheric pressure would pull the piston down—but the cylinder in which the piston traveled could stay hot as a new jet of steam entered it. One chamber would stay cool, the other hot, each time the engine cycled.

  The separate condenser would prove not only central to the development of steam power and the entire Industrial Revolution that ran on it, but also an utterly necessary step on the way to the very different sort of engine that powered Rocket. It is also, happily, a rich test case of the mutually reinforcing relationship between abstract theorizing and rule-of-thumb engineering. Literally rule-of-thumb: As with all mechanical inventions, the insight that inspired the separate condenser could be visualized, but it wasn’t worth much of anything until it could also be handled—note the linguistic clue. The human eye can see things that don’t yet exist, but making them requires the human hand, and it was now time for Watt to return to his university workshop and let his skilled hands turn his insight into a model.

  That year training on brass compasses and quadrants in London now proved its worth. Within weeks, he had handcrafted all the components for an engine: two cylinders, one piped to a boiler and containing a piston with a valve on the bottom to vent excess water, the other a ten-inch-long brass syringe with a diameter of 1¾″ containing two ten-inch tin “straws” each about ⅙″ in diameter, and a hand-operated air pump with a ¾″ diameter.

  Fig. 3: The “stovepipe” on the left is Watt’s separate condenser. Four years after his brainstorm on Glasgow Green, this was the result: a working cylinder that didn’t need to be cooled and reheated for each stroke, thus doubling the utility of Newcomen’s design. Science Museum / Science & Society Picture Library

  The two cylinders were connected by a horizontal pipe, and the syringe immersed in a cistern of cold water. Watt lit his boiler and let the steam flow into the piston cylinder, closed the steam cock, and pumped out the air in the syringe, thus pulling in the steam, which immediately condensed around the cold tin straws. The piston in the cylinder immediately lifted a weight of 18 pounds; a cylinder holding barely a pint of water was raising a weight equivalent to more than two gallons. Watt, a perfectionist by temperament, education, and training, had finally (though briefly) satisfied himself. Thirty years later, he would describe the model as being “nearly as perfect25 … as any which have been made since that time.” He was not normally an especially confident man—perfectionists rarely are—but in April 1765 he was optimistic enough to write to his friend James Lind, “I can think of nothing else26 but this Machine. I hope to have the decisive tryal before I see you….”

  It is not known when he actually saw Lind, but by the summer of 1765, on the back of £1,000 borrowed from Joseph Black, “the invention was complete27 … a large model, with an outer cylinder and wooden case, was immediately constructed, and the experiments made with it served to verify the expectations I had formed, and to place the advantage of the invention beyond the reach of doubt.”

  The time had come for the next step. And the next step was going to cost money—a lot more than he could borrow from colleagues at the university. Watt needed capital. Investment capital, however, wasn’t easy to find in 1765 Britain; and it was a lot harder than it had been fifty years earlier. The reason was one of the greatest financial bubbles in history, the collapse of the South Seas Company.

  THE SOUTH SEAS COMPANY had been incorporated in 1711, with a charter that granted what was potentially a far more lucrative monopoly than anything Edward Coke had contemplated a century earlier. In return for buying £10 million of government debt, the Company was given exclusive trading rights throughout Central and South America, whose bounty included wool, rum, sugar, and, most profitably, slaves. Promoted like an eighteenth-century Enron, the South Seas Company offered not only the promise of unimaginable wealth, but stock that could be purchased by virtually anyone. This was both a novel and an appealing idea in a time when the world’s largest corporation, the British East India Company, had fewer than five hundred investors. Since, however, the Company’s only real asset was the British government’s promise of access to ports that were entirely controlled by the Spaniards, making money from trading proved difficult. The Company was, even so, brilliant at promoting its own prosperity, placing newspaper stories, hosting parties, and maintaining luxurious offices in the most expensive buildings in London. In January 1720, stock was issued at a par price of £100 a share; by August, at the peak of the bubble, when the average British artisan was earning less than £100 a year, a single share of the Company traded for £1,000. And even worse, it inspired other businesses to issue stock on what might be called speculative ventures, including a company capitalized at £1 million in order to produce a perpetual motion machine. One of the more candid styled itself “A Company for carrying on an undertaking28 of great advantage, but no one to know what it is.”

  The result, once the bubble burst and the dust cleared, was that Parliament essentially barred the issuing of stock for any business purpose, which limited the potential pool of investors to what would today be called venture capitalists. In the case of Watt’s invention, this meant partnering with an entrepreneur with both ready cash and a liking for technology.

  John Roebuck was then a forty-seven-year-old serial entrepreneur who had started half a dozen different businesses, each of them intending to exploit a technological innovation, including the first industrial refinery that manufactured sulfuric acid* by combining sulfur dioxide with oxygen and the resulting compound with water, all in a lead-lined chamber. The acid refinery prompted his first patent application, but by no means his last. By the time he met Watt in 1765, he was also master of one of the world’s most innovative forges, the legendary Carron Ironworks, and holder of patent number 780—the number of patents granted annually was still, a century after the Statute on Monopolies, measured in dozens—for a new process for making bar iron.

  A correspondence between the ambitious young instrument maker and the nearly twenty years older businessman began in the summer of 1765, prompted by Joseph Black, who counted both as friends. In September, Watt wrote to Roebuck inviting an investment in his discovery that producing steam within a vacuum was dramatically more efficient than producing it in air, his excitement such that “I am going on with the Modell29 of the Machine as fast as possible and hope to have it finished in another week.”

  Rereading the letters, it is impossible to miss the tension present from the beginning. Roebuck fancied himself at least as gifted a scientist as Watt, and insisted on an extreme form of due diligence, demanding to see Watt’s drawings, notes, and models. He demanded that Watt try to create a vacuum without a jet of water condensing the steam, and even urged him to discard the separate condenser, which was, after all, the point of the entire exercise. Watt, for his part, was generally courteous, but convinced of both his own talent and of the power of the separate condenser. For months, the two engaged in the sort of epistolary courtship that puts one in mind of the way that porcupines mate. Only when Roebuck, who was nothing if not intelligent enough to recognize Watt’s gifts, satisfied himself that the separate condenser promised everything Watt believed, did he agree to a partnership. The terms of the agreement obligated Roebuck to absorb all future expenses related to building a machine that would, in Watt’s words, produce the same amount of work for half the amount of fuel. He further agre
ed to pay off Watt’s debt to Black in return for two-thirds of future profits.

  Watt’s frustrations were just beginning. Vacuum is notoriously unstable, but it needed to be kept intact in order for the engine to do its work. Newcomen’s vacuum seal had been nothing more than a leather collar with a layer of water on top, but Watt had to avoid using it on his own engine, since the water would, of necessity, cool the hot cylinder and so eliminate most of the advantage of the separate condenser. But everything else he tried was either too porous—steam escaped and air entered—or created too much friction in the cylinder, costing a huge amount of energy. As a result, he tried dozens of combinations30 of materials for both piston and cylinder: wood, tin, copper, and cast iron, in square and round shapes, sealed with leather, cloth, cork, oakum, asbestos, and numerous alloys of lead, and lubricated with mercury, graphite, tallow, manure, and vegetable oil. “Cotton was proposed31 by my friend Chaillet; I thought of trying it but was deterred first by its price, secondly, by the very thing you have found: that it could not be easily made to cohere without glue or weaving the substances. I have hopes of pasteboard … mixed with dung; I propose to separate the gall and sand from the dung by washing. I have found by experiment that for making joints steam tight, there is nothing equal to it as it is of no consequence whether the joint be naturally round or not….”