By the start of the eighteenth century, however, things were changing, and changing fast. Artisans like Thomas Newcomen and itinerant experimentalists like Denis Papin were both corresponding with Robert Hooke. Engineers like Thomas Savery were demonstrating inventions in front of the physicists and astronomers of the Royal Society. Most important, mechanics, artisans, and millwrights, who had been taught not only to read but to measure and calculate, started to apply the mathematical and experimental techniques of the sciences to their crafts. Useful knowledge (the historian Ian Inkster calls it useful and reliable knowledge, or URK) became, in Mokyr’s words, “the buzzword of the eighteenth century.”4
The same mechanisms that spread the discoveries of the Scientific Revolution throughout Europe—correspondence between researchers, and publications like the Royal Society’s Philosophical Transactions—proved just as useful in the diffusion of applied knowledge. But because Europe generally, and Britain specifically, had a lot more artisans than scientists, the demand for commercially promising applications was far greater than those with a purely scientific bent. New ways of buying and selling applied knowledge emerged to meet the demand. J. T. Desaguliers, the same critic5 who had sniffed at Thomas Newcomen’s mathematical training, spent decades giving a hugely popular series of lectures all across rural England and later collected them in his 1724 Course of Mechanical and Experimental Philosophy. By the 1730s, millwrights, carpenters, and blacksmiths were able to purchase what we would today call a continuing education in pubs and coffeehouses in the craft they had learned as apprentices. By 1754, the drawing master William Shipley could found the Royal Society of Arts (at a time that made no distinction between fine, decorative, or applied arts) on a manifesto that argued, “the Riches, Honour, Strength,6 and Prosperity of a Nation depend in a great Measure on Knowledge and Improvement of useful Arts [and] that due Encouragement and Rewards are greatly conducive to excite a Spirit of Emulation and Industry….” Britain’s artisans were now buyers at their own knowledge market, and they were doing so to fatten not their reputations, but their wallets.
One of the criticisms often made of economists is that they see all of human behavior as a kind of market. But neither steam engines in general, nor Rocket in particular, makes much sense without referring to an entire series of markets: one for transportation of Manchester cotton, another for the iron on which the engine ran, still another for the coal it burned, and so on. The most important of all, however, was the Industrial Enlightenment’s de facto market in what would one day be called “best practices” from the craft world. By the first decades of the eighteenth century, a market had emerged in which an English ironmonger could learn German forging techniques, and a surveyor could acquire the tools of descriptive geometry.
But markets do more than bring buyers and sellers together. They also reduce transaction costs. One of those costs, in the early decades of the eighteenth century, was incurred due to the fact that an awful lot of the newest bits of useful knowledge were hard to compare, one with the other, because they described the same phenomenon using different words (and different symbols). As the metaphorical shelves of the knowledge market filled with innovations, buyers demanded that they be comparable, which led directly to standardization of everything from mathematical notation to temperature scales. In this way, the Industrial Enlightenment’s knowledge economy lowered the barriers to communication between the creators of theoretical models and masters of prescriptive knowledge, for which the classic example is Robert Hooke’s 1703 letter to Thomas Newcomen advising him to drive his piston by means of vacuum alone.
The dominoes look something like this: A new enthusiasm for creating knowledge led to the public sharing of experimental methods and results; demand for those results built a network of communication channels among theoretical scientists; those channels eventually carried not just theoretical results but their real-world applications, which spread into the coffeehouses and inns where artisans could purchase access to the new knowledge.
Put another way, those dominoes knocked down walls between theory and practice that had stood for centuries. The emergence of a market in which knowledge could be acquired for application in the world of commerce had also increased the population capable of producing that knowledge. It would occur in the study of medicine, of chemistry, and even of mathematics, but nowhere was it more relevant to the future of industrialization than in the study of the science of heat.
TWO YEARS BEFORE HIS death in 1704,7 John Locke collaborated with William Grigg, the son of one of Locke’s oldest friends, to produce an interlineary translation—that is, alternating lines of Latin and English—of Aesop’s fables. One of those fables, “De sole et vento,” or “The Sun and the Wind,” famously recounts the contest between the two title characters over which could successfully cause a traveler to remove his coat. It is among the earliest, and is certainly one of the best known, accounts of the debate between heat and cold. Or, as we would call it today, thermodynamics.
Though the equations of thermodynamics are obviously essential to understanding the machine that Newcomen and Calley demonstrated in front of Dudley Castle, they were just as obviously unnecessary for building it. What the ironmonger and glazier didn’t know about the physics of the relationship between water and steam would fill libraries, while what they did know was mostly wrong. This is in no way a criticism of the inventors; what everyone knew, at the time, was mostly wrong.
Even the seventeenth century’s newfound affinity for experimental science hadn’t done much to correct misapprehensions about the nature of heat. When Francis Bacon (to be fair, more a philosopher of science than a scientist) attempted, in 1620, an exhaustive description of the sources of heat, he included not only obvious candidates like the sun, lightning, and the “the violent percussion of flint and steel,” but also vinegar, ethanol (“spirits of wine”), and even intense cold. He also failed to produce anything like a testable theory; while he did nod toward equating heat with motion, he failed to realize that heat was a measurable quantity—the first thermometers that used any sort of scale date from the early eighteenth century; imagine, if you can, drawing a map without knowing the number of inches to the mile, and you can see the obstacle this presented. Galileo, Descartes, and especially Robert Boyle also tried explain how motion was related to heat, particularly friction. They each failed, which is not surprising; nearly three centuries later, Lord Kelvin himself was still unsure whether heat energy could be equated with mechanical energy.
The reason is that seventeenth-century heat theorists were hamstrung by the two existing models from the world of natural philosophy. The first was the notion that heat8 was an “elastic fluid” or gas; the other, that it was a consequence of exciting the motion of an object’s constituent parts, which were known as “atoms,” though those who used the term didn’t mean the same thing as a modern chemistry textbook. Isaac Newton had demonstrated that the best escape from the prison of Aristotelian ideas about motion was an entirely new set of invariant laws, but Newton, curious though he was, showed only small interest in the scientific nature of heat. As a result, the first really useful theory of heat and combustion was being articulated elsewhere.
In 1678, less than a decade before Newton introduced the world to the laws of motion and universal gravitation in the first edition of Principia Mathematica (and two decades before Savery received patent number 376), the alchemist Johann Joachim Becher departed the patchwork quilt of grand duchies, principalities, and free cities that the Thirty Years War had made of Germany. By then, he had already served as a court physician to the Elector of Bavaria; as a secret agent in the pay of the Austrian Emperor; and as a special emissary for Prince Rupert, the onetime commander of royalist cavalry during the English Civil War. It was in the last capacity that he journeyed to Scotland and Cornwall, to examine and report on the coal and tin mines of Britain. He also had a personal motive: to discuss his discovery with the new Royal Society.
Becher called the substance he had “discovered” terra pingua, which confusingly translates as “fatty [by which he meant inflammable] earth.” This was a thoroughly respectable attempt to reconcile the established belief that the world was made up of the ancient four elements—fire, water, earth, and air—with the observation that the phenomenon of combustion seems to involve them all; that in some way, the process that burns wood is similar to the one that causes iron to rust, if only because the absence of air prevents both. Becher’s discovery, renamed in 1718 as phlogiston, replaced the Aristotelian elements with a different foursome: water; terra mercuralis, or fluid earth (i.e. mercury, and similar substances); inert earth, or terra lapida (that is, salts); and Becher’s terra pingua, thus covering all possible forms of matter, and demoting fire from an element to a phenomenon. The theory that explained the behavior of Becher’s inflammable earth still has, in some circles, the flavor of charlatanism, and to be sure, Becher wasn’t completely free of the taint; he had spent years trying to sell a method for turning sand into gold. However tempting it is to poke fun at the scientific ignorance of our ancestors, though, in the case of the phlogiston theory, it is a temptation that should be resisted. Though phlogiston theory is wrong, it is considerably more scientific than is generally understood, and it was an early and necessary step on the way to a proper understanding of thermodynamics, and of the way in which Rocket transformed heat into movement.
At the core of the theory is the idea that anything that can be burned must contain a material—phlogiston—that is released by the process of burning. Once burned, the dephlogisticated substance becomes calx (an example would be wood ash), while the air surrounding it, which was known to be essential to combustion, became phlogisticated. Thus, burning wood in a sealed chamber could never result in complete combustion, because the dephlogisticated air necessary for burning became saturated with phlogiston. The reason that wood ash weighs less than wood, therefore, is because of the loss of phlogiston to the air when it is partially burned.
However, any theory of heat transfer that depended upon the swap of a substance demanded that it go somewhere. Phlogiston theory worked fine for those things that weighed less after heating something else, but it was vulnerable to an encounter with any substance that didn’t. Magnesium, for example, seems to gain weight when heated (actually, it becomes magnesium oxide). Heat can be transferred even when “condensed phlogiston” doesn’t change at all. A red-hot hunk of iron will cause water to steam even if it weighs the same after it is cooled by that same water.
By the middle of the eighteenth century, despite some truly passionate devotees, most especially the English chemist Joseph Priestley, phlogiston theory was displaced, largely by the work of the French scientist Antoine Lavoisier. Which is why phlogiston theory deserves a bit more respect than it is generally given. It is a goofy theory, to be sure, with funny-sounding names for its fundamental concepts (though no funnier-sounding than quarks, Higgs bosons, or other notions from the world of quantum physics). But it is a theory, in a way that the four elements of antiquity were not. Phlogiston was incorrect in its particulars: The relationship between fire and rust is that both are examples of what happens when oxygen, which would not be discovered for another century, reacts with another substance. But it was also testable, in the sense made famous by the philosopher of science Karl Popper. Phlogiston theory could be proved false, and eventually was. The first to do so was a pioneering physicist and chemist at the University of Glasgow, a key figure in the evolution of the steam engine, named Joseph Black.
BLACK WAS A THOROUGHGOING Scot, despite his Bordeaux birthplace, an incidental consequence of his family’s involvement in the wine trade, and his early schooling in Belfast. He matriculated at both Glasgow and Edinburgh universities, and subsequently served as professor of chemistry at first one and then the other, ending up at Edinburgh in 1766. Long before that, he had demonstrated a remarkable gift for experimental design, and what was, for the time, painstaking care in experimentation itself, particularly into the nature of heat.
The gift for designing experiments was much on display in Black’s research into the nature of what a later science of chemistry knows as carbon dioxide. He was not, by all accounts, much interested in testing phlogiston theory when he began; instead, as a physician, he was looking for a way to dissolve kidney stones. His investigations accordingly began with an investigation into the then well known process by which chalk, or calcium carbonate, turns into the caustic quicklime, which was the name then used for calcium oxide. Black chose to work with a similar substance: magnesium carbonate, then known as magnesia alba. Since the transformation required combustion, at very high heat, phlogiston theory suggested that the reason was the absorption of the fiery substance by the chalk. Black, by careful experiment, showed that the magnesia alba weighed less after heating, but regained precisely the same amount when cooled in the presence of potash, from which he reasoned that the substance that departed the original substance—CO2—had returned. He did not, of course, put it quite that way, since oxygen itself still awaited discovery some decades later. Instead, he wrote, “Quick-lime [i.e. calcium oxide] therefore does not attract air when in its most ordinary form, but is capable of being joined to one particular species only, which is dispersed thro’ the atmosphere, either in the shape of an exceedingly subtle powder, or more probably in that of an elastic fluid [which I have called] ‘fixed air.’”9 Or, as your high school chemistry teacher would explain it, calcium oxide becomes calcium carbonate in the presence of carbon dioxide.
This discovery alone, which was the first test that phlogiston theory failed, would have purchased for Professor Black a place in the history of science. But what earned him a place in the story of steam power were his subsequent experiments on the nature of heat itself. Or, more accurately, on the nature of ice.
Water, as we have seen, is a most curious substance: In both its gaseous and solid states, it occupies more volume than it does as a liquid. It is also (practically uniquely) present on earth as a solid, a liquid, and a gas. By 1760, Black had become fascinated by the properties of water in its solid version, and even more fascinated by the transition from one phase to another. He was particularly intrigued by the fact that frozen water, whether in the form of ice or snow, did not melt immediately upon coming into contact with high heat, but did so gradually. For another curious fact is that a glass with ice in it will stay the same temperature—a little above 32°F or 0°C—whether it has six unmelted ice cubes in it or one. The temperature starts to rise only when all the ice is melted. In the same way, a pot of water brought to a boil does not thereafter increase in temperature, no matter how hot the fire underneath it. These are by no means intuitive results, but Black observed them again and again, once again finding phlogiston theory insufficient to explain the phenomena. Instead, he came up with an idea of his own, called latent heat, which he defined as the amount of heat gained or lost by a particular substance before it changes from one physical state to another—gas to liquid, solid to liquid. To Black, latent heat was the best way to explain the fact that water, when it nears its boiling point, does not suddenly turn to steam with, in his words, “a violence equal to that of gunpowder.”10
The experiments that confirmed this hypothesis were simple, and ingenious. Black took a quantity of water and, using a thermometer, took its temperature. He then placed the water over heat11 and measured both the amount of time it took for the water to boil and the amount of time it took, once boiling, to boil away completely. By comparing the two, he established the amount of heat the water continued to absorb after its own temperature stopped rising. Many years later, Black described his discovery:
I, therefore, set seriously about making experiments,12 conformable to the suspicion that I entertained concerning the boiling of fluids. My conjecture, when put into form, was to this purpose. I imagined that, during the boiling, heat is absorbed by the water, and enters into the composition of the vapour produced
from it, in the same manner as it is absorbed by ice in melting, and enters into the composition of the produced water. And, as the ostensible effect of the heat, in this last case, consists, not in warming the surrounding bodies, but in rendering the ice fluid; so, in the case of boiling, the heat absorbed does not warm surrounding bodies, but converts the water into vapour. In both cases, considered as the cause of warmth, we do not perceive its presence: it is concealed, or latent, and I give it the name of LATENT HEAT …
Thus, Black calculated that a pound of liquid water had a latent heat of vaporization of 960°F; its latent heat of fusion—the amount of heat ice absorbs before completely melting—he measured at 140°F.* That is a lot of latent heat. Water absorbs nearly three times the amount of heat before vaporizing as the same quantity of ethanol, one of the many reasons that your waiter can flambé brandy, but not orange juice. Again, Black’s experimental and quantitative mind used a different sort of arithmetic: He heated a pound of gold13 to 190° and placed it in a pound of water at a temperature of 50°; when he took the temperature of the combined elements and found it to be only 55°, he concluded that water had nearly twenty times more capacity for heat than did gold.
It took a pretty big fire, therefore, to boil the water in the atmospheric engine Thomas Newcomen had erected in front of Dudley Castle that day in 1712. Joseph Black had discovered a new way of measuring how big, but the relevant metric for Newcomen and Calley wasn’t degrees Fahrenheit. It was fuel.
This simple fact was, in its way, as revolutionary as Coke’s Statute or Newton’s Laws of Motion. For millennia, advances in the design of machines to do work had been driven entirely by measures of their output: a tool that plows more furrows, or spins more wool, or even pumps more water, was ipso facto a better machine. Prior to the seventeenth century, the choices for performing such work—defined, as it would be in an introductory physics class, as the transfer of energy by means of a force—had been made from the following menu:
The Most Powerful Idea in the World Page 10