Sometime in the late spring of 1771, Priestley decided to try a new twist on his childhood experiment. If animals died swiftly in a sealed jar, how long would it take a plant to suffer the same fate? It was obvious that living things couldn’t survive in such an environment for long—the question was, how long? Could a plant outlast a mouse or a frog? Or would it prove more feeble in the contained environment of the jar? He went out into the garden and pulled a small mint plant from the ground. (Priestley always referred to it as a “sprig” of mint, but it appears to have been an entire plant, given his references to its stalk and roots.) He placed the mint in a glass jar that he had inverted over the pneumatic trough. And he waited, patiently, for the plant to expire.
Benjamin Franklin had paid the Priestleys a visit on May 23, within a matter of days of Priestley’s decision to isolate a sprig of mint in a glass. Franklin had been traveling through northern England, enjoying a bit of industrial tourism with a few acquaintances. They had inspected the water-driven saws and polishers at the marble mills of Blakewell, floated down the Duke of Bridgewater’s canal in Manchester, and descended into the cramped coal mines that lay at the canal’s far end. They saw Matthew Boulton’s famous Soho ironworks in Birmingham, an overwhelming glimpse of a bizarrely mechanized future: “The work of a button,” Franklin’s companion Jonathan Williams noted in his journal, “has 5 or 6 branches in it each of which is performed in a second of Time. He likewise works plated Goods—Watch Rings and all manner of hard ware all of which is performed by Machinery in such a Manner that Children and Women perform the greatest part of it.”
In the midst of this dizzying new world of furnaces and factory floors and canals blasted through the sides of mountains, Priestley’s home lab in Leeds must have seemed like an idyll. We do not know if Priestley shared his curiosity about the mint with Franklin. Williams merely notes that Priestley “made some very pretty Electrical Experiments and some on the different properties of different kinds of Air.”
In the years to come, as Priestley’s network of friends started to include many of the industrial magnates that Franklin had visited on his northern expedition, Priestley’s lab became increasingly populated by tools that had been explicitly designed and manufactured for the needs of his research. But in his early years in Leeds there is a wonderful sense of improvisation and bricolage to Priestley’s equipment, what we would now call “hacking”: taking tools designed by other people for other purposes, and creatively repurposing them for your own needs.
We know so much about Priestley’s gear because he compulsively shared the details of his contrivances, first with fellow Royal Society members and Honest Whigs, and then in his published works. When Priestley eventually wrapped all of his chemistry experiments into a six-volume opus, he devoted a hundred pages at the beginning to an exhaustive inventory of the tools he had used to revolutionize chemistry. Volume one began with a foldout illustration that captured the kit in loving detail, the vials, jars, and beakers lined up as if for a family portrait.
What’s so striking in this image is the spirit of total openness that pervades it. There is no magician’s reserve in Priestley’s cabinet of wonders. He truly wants you to see everything, in mind-numbing detail, to the extent that some passages begin to sound more like self-assembly instructions for some impossibly complicated household appliance:
When I want to admit a particular kind of air to any thing that will not bear wetting, and yet cannot be conveniently put into a phial, and especially if it be in the form of a powder, and must be placed upon a stand (as in those experiments in which the focus of a burning mirror is to be thrown upon it) I first exhaust a receiver, in which it is previously placed; and having a glass tube, bended for the purpose, as in Pl. II. Fig. 14, I screw it to the item of a transfer of the air-pump on which the receiver had been exhausted.
Part of this compulsive sharing no doubt comes from the fact that one of Priestley’s great skills as a scientist was his inventiveness with tools. He was a hacker, not a theoretician, and so it made sense to showcase his technical innovations alongside the scientific ideas they generated. But there was a higher purpose that drove Priestley to document his techniques in such meticulous detail: the information network. Priestley’s whole model of progress was built on the premise that ideas had to move, to circulate, for them to turn into better ideas. This is what led him to expose his technological apparatus in such detail, and what led him, on numerous occasions, to publish experimental data without fully vetting it first. It was a sensibility that he shared with Franklin, who, in a letter to Collinson in 1753, ended a long summary of his electricity experiments with the lines:
These Thoughts, my dear Friend, are many of them crude and hasty, and if I were merely ambitious of acquiring some Reputation in Philosophy, I ought to keep them by me, ’till corrected and improved by Time and farther Experience. But since even short Hints, and imperfect Experiments in any new Branch of Science, being communicated, have oftentimes a good Effect, in exciting the attention of the Ingenious to the Subject, and so becoming the Occasion of more exact disquisitions (as I before observed) and more compleat Discoveries, you are at Liberty to communicate this Paper to whom you please; it being of more Importance that Knowledge should increase, than that your Friend should be thought an accurate Philosopher.
“Exciting the attentions of the ingenious”—this was Priestley’s mission in a nutshell. It defeated the whole point of the enterprise to write a book about a scientific advance, without sharing all the paths followed—and all the gear assembled—to reach that vista.
Sometimes, the false turns along those paths proved to be the most productive ones. When Priestley decided to seal up his mint in a confined jar, he fully expected it to wilt and die in a matter of days or weeks. But when he returned to the plant in June, something strange and unexpected happened. The plant had stubbornly refused to die.
The plant was not affected any otherwise than was the necessary consequence of its continued situation; for plants growing in several other kinds of air, were all affected in the very same manner. Every succession of leaves was more diminished in size than the preceding. . . . The root decayed, and the stalk also, beginning from the root; and yet the plant continued to grow upward, drawing its nourishment through a black and rotten stem.
Priestley’s expectations had been entirely incorrect: in fact, the determined sprig of mint continued growing all summer long. And there were other mysteries. A candle would readily burn in the jar alongside the mint. A mouse placed inside the jar with the plant could survive happily for ten minutes, while a mouse placed in a plant-free jar in which another mouse had previously expired would begin to convulse within seconds. Somehow the plant was disabling whatever it was that snuffed out the candle and suffocated the mouse.
And here we find ourselves at the fault line of the classic Kuhnian paradigm shift, an older continent of understanding colliding with some unknown landmass. Data emerge that somehow challenge that the dominant model, either by producing results that defy the expectations of the model, or by producing results that are so strange that the dominant model no longer seems relevant. It is not entirely clear from the historical record how conscious Priestley was of the full implications of what he had observed. He wrote Franklin in late summer with an account of a new discovery—but the original letter has been lost, and so we don’t know with certainty that Priestley was reporting on his mint experiments. All we know is that Franklin forwarded Priestley’s news along to Canton with a brief note:
I have just received the enclos’d from Dr. Priestly. And as it contains an Account of a new Discovery of his, which is very curious, and, if it holds, will open a new Field of Knowledge, I send it to you immediately. Please to communicate it to Dr. Price when he returns.
It would have been difficult for Priestley, contemplating that tenacious sprig of mint in the lab on Bansinghall Street, to perceive that a Kuhnian revolution was at hand, not just because the concept did
n’t exist yet, but more important because there was no “dominant paradigm” for him to overturn. The study of air itself had only begun to blossom as a science in the past century, with Robert Boyle’s work on the compression and expansion of air in the late 1600s, and Black’s more recent work on carbon dioxide. Before Boyle and Black, there was little reason to think there was anything to investigate: the world was filled with stuff—people, animals, planets, sprigs of mint—and then there was the nothingness between all the stuff. Why would you study nothingness when there was such a vast supply of stuff to explain? There wasn’t a problem in the nothingness that needed explaining. A cycle of negative reinforcement arose: the lack of a clear problem kept the questions at bay, and the lack of questions left the problems as invisible as the air itself. As Priestley once wrote of Newton, “[he] had very little knowledge of air, so he had few doubts concerning it.”
So the question is: Where did the doubts come from? Why did the problem of air become visible at that specific point in time? Why were Priestley, Boyle, and Black able to see the question clearly enough to begin trying to answer it? There were 800 million human beings on the planet in 1770, every single one of them utterly dependent on air. Why Priestley, Boyle, and Black over everyone else?
One way to answer that question is through the lens of technological history. They were able to explore the problem because they had new tools. The air pumps designed by Otto von Guericke and Boyle (the latter in collaboration with his assistant, Robert Hooke, in the mid-1600s) were as essential to Priestley’s lab in Leeds as the electrical machines had been to his Warrington investigations. It was almost impossible to do experiments without being able to move air around in a controlled manner, just as it was impossible to explore electricity without a reliable means of generating it.
In a way, the air pump had enabled the entire field of pneumatic chemistry in the seventeenth century by showing, indirectly, that there was something to study in the first place. If air was simply the empty space between things, what was there to investigate? But the air pump allowed you to remove all the air from a confined space, and thus create a vacuum, which behaved markedly differently from common air, even though air and absence of air were visually indistinguishable. Bells wouldn’t ring in a vacuum, and candles were extinguished. Von Guericke discovered that a metal sphere composed of two parts would seal tightly shut if you evacuated the air between them. Thus the air pump not only helped justify the study of air itself, but also enabled one of the great spectacles of early Enlightenment science.
The following engraving shows the legendary demonstration of the Magdeburg Sphere, which von Guericke presented before Ferdinand III to much amazement: two eight-horse teams attempt—and, spectacularly, fail—to separate the two hemispheres that have been sealed together by the force of a vacuum.
When we think of technological advances powering scientific discovery, the image that conventionally comes to mind is a specifically visual one: tools that expand the range of our vision, that let us literally see the object of study with new clarity, or peer into new levels of the very distant, the very small. Think of the impact that the telescope had on early physics, or the microscope on bacteriology. But new ways of seeing are not always crucial to discovery. The air pump didn’t allow you to see the vacuum, because of course there was nothing to see; but it did allow you to see it indirectly, in the force that held the Magdeburg Sphere together despite all that horsepower. Priestley was two centuries too early to see the molecules bouncing off one another in his beer glasses. But he had another, equally important, technological breakthrough at his disposal: he could measure those molecules, or at least the gas they collectively formed. He had thermometers that could register changes in temperature (plus, crucially, a standard unit for describing those changes). And he had scales for measuring changes in weight that were a thousand times more accurate than the scales da Vinci built three centuries earlier.
This is a standard pattern in the history of science: when tools for measuring increase their precision by orders of magnitude, new paradigms often emerge, because the newfound accuracy reveals anomalies that had gone undetected. One of the crucial benefits of increasing the accuracy of scales is that it suddenly became possible to measure things that had almost no weight. Black’s discovery of fixed air, and its perplexing mixture with common air, would have been impossible without the state-of-the-art scales he employed in his experiments. The whole inquiry had begun when Black heated a quantity of white magnesia, and discovered that it lost a minuscule amount of weight in the process—a difference that would have been imperceptible using older scales. The shift in weight suggested that something was escaping from the magnesia into the air. By then running comparable experiments, heating a wide array of substances, Black was able to accurately determine the weight of carbon dioxide, and consequently prove the existence of the gas. It weighs, therefore it is.
ALL OF THIS helps us understand why the whole question of air was suddenly conceivable in Priestley’s era, and why Priestley and his contemporaries were able to start solving the problem the way they did. The question of air was “in the air” not for any vague, spirit-of-the-age reasons, nor because a solitary genius had experienced a heroic epiphany. Air had become an interesting problem in large part because a handful of technologies had shed light on that most invisible of substances. The mountain was lifting the explorers higher, and in part the mountain was being moved by new tools: pumps, thermometers, scales.
But that is only a partial answer, because to explain what brought Priestley to that lab in Leeds, what compelled him to put that sprig of mint in the jar, you also have to ask the question: Why Priestley? Why not someone else? Why not Franklin or some other Honest Whig, working within the same technological regime as Priestley and Black?
This is where we normally get to the accidents of biography, the random churn of coincidences and personal anecdote, driven by both nature and nurture: He just happened to study with an influential mentor who got him interested in the field. Or: He just happened to be born with some outlandish cognitive gift that let him see farther and deeper than his rivals. Or, more comically: He just happened to be sitting under that apple tree.
Yet there must be recognizable streams that run beneath all that surface turbulence. In trying to answer the question of how to keep climbing the mountain, are there principles we can find on the biographical scale that can potentially help us climb other peaks? Can we learn something useful from Priestley the individual, from his sensibility or temperament?
Perhaps the most important factor—and the most neglected in the modern canon of how-to books on innovation—is the simple fact that Priestley was following a long hunch, one that he’d been exploring in a casual way for thirty-odd years, ever since he’d bottled up that first spider with his brother Timothy. He’d had a hunch that there was something intriguing in the whole question of why things died when you cut off their air supply, even if he didn’t have the conceptual tools to solve the mystery, or even to explain why the problem seemed so intriguing in the first place. It was that hunch that led him to explore the Jakes and Nell Brewery, that brought him back to pneumatic chemistry after his immersion in electricity. Priestley’s memoirs and correspondence reveal that he had ruminated on the cycle of noxious and wholesome air “for a long time” before launching into a systematic study of it, after the move to Leeds.
The idea that hunches are crucial to scientific breakthrough is nothing new, of course. What’s interesting about Priestley is not that he had a hunch, but rather that he had the intelligence and the leisure time to let that hunch lurk in the background for thirty years, growing and evolving and connecting with each new milestone in Priestley’s career. We know that epiphanies are a myth of popular science, that ideas don’t just fall out of the sky, or leap out of our subconscious. But we don’t yet recognize how slow in developing most good ideas are, how they often need to remain dormant as intuitive hunches for decades before th
ey flower. Chance favors the prepared mind, and Priestley had been preparing for thirty years. We talk about great ideas using the language of flashes and instant revelation, but most great ideas happen on the scale of generations, not seconds. (Think of the almost glacial pace that characterized Darwin’s “discovery” of natural selection.) Most great ideas grow the way Priestley’s did, starting with some childhood obsession, struggling through an extended adolescence of random collisions and false starts, and finally blooming decades after they first took root.
This pattern of long cultivation holds true for Priestley’s thinking across the wide spectrum of his interests. The notes on the distortions of Christianity that he filed away in his drawer in Needham in the 1750s would emerge twenty years later as a cohesive and brilliant dismantling of contemporary Christian beliefs. His hunches about restructuring the educational system first appeared in his curriculum at Warrington, then animated the introductory chapter of The History and Present State of Electricity, and would ultimately play a key role in his friendship with Thomas Jefferson in the closing years of Priestley’s life.
That hunches so often work this way makes intuitive sense, given the biological structure of the human brain. Ideas are built out of self-exciting networks of neurons, clusters of clusters, with each group associated with some shade of a thought or memory or emotion. When we think of a certain concept, or experience some new form of stimulus, a complex network of neuronal groups switches on in synchrony. (Priestley knew nothing about neurons, of course, but he subscribed to a generalized version of this associationist theory that he learned from the British philosopher David Hartley, whose model of cognitive “vibrations” anticipated the modern theory of neuronal association.) Priestley puts a sprig of mint under a glass in a makeshift lab in Leeds, and a hundred clusters light up in his brain: the memory of his brother Timothy and the spiders; the smell of mint in the garden at Warrington; the bad air bubbling over the vats at the brewery. Each time those associations are triggered together, the connection between them strengthens, making it more likely that they fire together as an ensemble the next time around, when some new stimulus triggers part of the network.
The Invention of Air Page 6
