The shape of that idea as it forms looks nothing like the shape that intellectual history has traditionally given it. It is not the radical leap of the epiphany:
Nor is it the oppositional ladder of the dialectic:
Instead, the true shape of an idea forming looks much more like this:
That network shape is one of the reasons why external information networks (the coffeehouse, the Internet) are so crucial to the process of innovation, because those networks so often supply new connections that the solo inventor wouldn’t have stumbled across on his or her own. But the long life span of the hunch suggests another crucial dimension here: it is not just the inventor’s social network that matters, but the specific way in which the inventor networks with his own past selves, his or her ability to keep old ideas and associations alive in the mind. If great ideas usually arrive in fragments, a partial cluster of neurons, then part of the secret to having great ideas lies in creating a working environment where those fragments are nurtured and sustained over time. This obviously poses some difficulty in modern work environments, with deadlines and quarterly reports and annual job reviews. (The typical middle manager doesn’t respond favorably to news that an employee has a hunch about something that probably won’t see results for twenty years.) But Priestley had created an environment for himself where those long-term hunches could thrive with almost no pressure, and his habit of simultaneously writing multiple documents (on multiple topics) kept the fragments alive in his mind over the decades. In the final pages of his memoirs, he mentions a lifelong habit of writing down “as soon as possible, every thing I wish not to forget.” Priestley might have never made it to his golden years in Leeds without the social network of the Club of Honest Whigs. But he also had a knack for “socializing” with his own ideas.
ONE FINAL ELEMENT of Priestley’s approach gave him a distinct advantage in scaling the mountain: his research style was uniquely suited for the problem he was wrestling with. At this early stage in its development, pneumatic chemistry was a field that happened to be highly receptive to Priestley’s characteristic approach—take dozens of minerals or plants or organisms and subject them to an endless series of experimental variations: burning, heating, bottling up. If he had been attempting to solve the riddle of universal gravitation or natural selection, his methodology would have been useless. But the mystery of air turned out to be a problem that you could productively tackle with a laundry basin, a few beer glasses, and a gift for imagining new combinations. He had put mice and spiders into a glass jar and watched them die. So why not a plant?
But what happened next was Priestley’s real stroke of combinatorial genius. After he had convinced himself that the mint in the glass was surviving despite its confinement, he decided to make a simple, but essential, modification to the experiment, one that took only a matter of seconds to engineer. On August 17, 1771, after a summer of analyzing those preternaturally healthy bottled sprigs of mint, Priestley took a thin wire and attached a “small bit of candle” to the end, and twisted the wire so that the candle end was turned upward. He lit the wick, and placed the flame next to a new sprig of mint, its roots floating in a pool of water. Then he slowly lowered a glass cylinder over the plant and the flame, and waited for the candle to burn through the supply of air in the container. Priestley knew that a mouse or spider placed into such an environment would be dead in seconds, since the candle had burned through all that was life-sustaining in “good” air. But would the plant survive? When the flame died out, he pulled the wire through the water at the base of the glass, leaving the sprig alone in the glass with no wholesome air whatsoever.
On August 27, Priestley revisited the mint in the glass. Ten days before, a flame had been snuffed out by the lack of wholesome air in the vessel, and during that period, no new air had entered the glass. Priestley knew from experience that an empty glass left in that state would be completely inhospitable to flame, as well as to any organism confined there. But when he went to light a candle in the glass, he found that “it burned perfectly well in it.”
This was genuine news. His first experiment had shown that plants failed to exhaust or poison the atmosphere the way living creatures did, but that flame burning next to the sprig of mint suggested a far more radical proposition: that plants were restoring something fundamental to the air, or they were creating the air itself. He repeated the experiment “eight or ten times in the remainder of the summer . . . without the least variation in the event.” The possibilities sent Priestley into a furious run of new configurations:
Several times I divided the quantity of air in which the candle had burned out, into two parts, and putting the plant into one of them, left the other in the same exposure, contained, also, in a glass vessel immersed in water, but without any plant; and never failed to find, that a candle would burn in the former, but not in the latter. . . . I generally found that five or six days were sufficient to restore this air, when the plant was in its vigour; whereas I have kept this kind of air in glass vessels, immersed in water many months, without being able to perceive that the least alteration had been made in it. I have also tried a great variety of experiments upon it, as by condensing, rarefying, exposing to the light and heat, &c. and throwing into it the effluvia of many different substances, but without any effect.
By the fall of 1771, Priestley was confident enough in his results to begin sharing the news with the Honest Whigs. “You may depend on the account I sent you of my experiments on the restoration of air made noxious by animals breathing it or putrefying it, which I sent to Dr. Franklin,” he wrote to Price on October 3. “Air in which candles have burnt out is also restored by the same means.” (He wrote Price again three weeks later to reiterate this point.) By the summer of 1772, Priestley had cycled through a series of different plants to confirm that the restorative effect was not somehow specific to mint. He began with a sprig of balm, which performed admirably. He then began to worry that the “aromatic effluvia” of those two plants was somehow the culprit, and so he tried the experiment with the “offensive”-smelling weed groundsel. Of all the plants he put under the glass, spinach proved to be the most effective at restoring the atmosphere inside the glass. In one experiment a spinach plant was able to fill the glass with combustible air in only two days.
Franklin returned for another visit to Leeds in June of 1772, this time bringing John Pringle, the Scottish physician who would soon be elected president of the Royal Society. Priestley gave them the full tour of his experiments with restoring air, and the visit seems to have energized him all over again about the importance of what he had discovered. On July 1, he wrote to Franklin:
I presume that by this time you are arrived in London, and I am willing to take the first opportunity of informing you, that I have never been so busy, or so successful in making experiments, as since I had the pleasure of seeing you at Leeds.
I have fully satisfied myself that air rendered in the highest degree noxious by breathing is restored by sprigs of mint growing in it. You will probably remember the flourishing state in which you saw one of my plants. I put a mouse [in] the air in which it was growing on the saturday after you went, which was seven days after it was put in, and it continued in it five minutes without shewing any sign of uneasiness, and was taken out quite strong and vigorous, when a mouse died after being not two seconds in a part of the same original quantity of air, which had stood in the same exposure without a plant in it. The same mouse also that lived so well in the restored air, was barely recoverable after being not more than one second in the other. I have also had another instance of a mouse living 14 minutes, without being at all hurt, in little more than two ounce measures of another quantity of noxious air in which a plant had grown.
We know with remarkable precision the sequence of experiments that Priestley conducted in this pursuit, thanks to the flow of letters and to Priestley’s memoirs. We know the exact dates of many of the experiments, and the exact plants or animals he placed i
nto his vessels. We know which ones lived and which ones died. And we can perceive through his first-person accounts his rising sense of excitement about what he had uncovered. But what is more obscure to us, looking back two centuries later, is how quickly Priestley grasped the full consequences of his experiment. To the untrained eye, it looked like nothing: a plant growing in a glass. Even to a natural philosopher, it might have seemed little more than a local curiosity: a few cubic inches of air created by a sprig of mint. But in that small parlor trick lay a whole new way of thinking about the planet itself, and its capacity for sustaining life. There was a system lurking in the glass that was a microcosm of a vast system that had been evolving on Earth for two billion years. Did Priestley have a hunch about this broader scale, too?
What Priestley had stumbled across is now much more than a hunch. We know that the gas that Priestley was observing is dioxygen, otherwise known as “free oxygen” or O2, a molecule formed by the union of two oxygen atoms. While oxygen is the third most common element in the universe, we know that free oxygen was exceedingly rare in the Earth’s initial atmosphere, until roughly two billion years ago, when an ancestor of modern cyanobacteria hit upon a photosynthetic process that used the energy from the sun to extract hydrogen from the abundant supply of water on the planet. That metabolic strategy was spectacularly successful—the organism quickly covered the surface of the planet—but it had a pollution problem: it expelled free oxygen as a waste product. During this period, now known as the Proterozoic, the oxygen content of the atmosphere exploded from 0.0001 percent to 3 percent, beginning its long march to the current levels of 21 percent. (Even today, Earth’s atmosphere is actually dominated by nitrogen, which makes up 78 percent of its overall volume; other gases, like argon and carbon dioxide, constitute less than a single percent.) The massive increase of oxygen in the atmosphere triggered what has been called “by far the greatest pollution crisis the earth has ever endured,” destroying countless microbes for whom the cocktail of sunlight and oxygen was deadly.
In time, though, organisms evolved that thrived in an oxygen-heavy environment. We are their descendants. The invention of photosynthesis created a radically different atmosphere for Earth—an artificial bubble created by the plants, at first lethal, and then, over time, life-sustaining, as a whole new family of organisms discovered the possibilities of aerobic respiration, through the evolution of mitochondrial power plants that used oxygen to produce energy. Without those evolutionary innovations, and without the continued production of oxygen by plants and cyanobacteria, the human race would cease to exist, along with the rest of the aerobes.
Of course this immense vista—reaching back billions of years, and down to the microscopic world of bacteria and molecules—would have been almost entirely off-limits to Priestley and Franklin. But both men had a hunch that something profound was lurking in the mint’s survival. The first indication of that hunch that has survived in the archives comes in a note from Franklin to Priestley after the June visit.
That the vegetable creation should restore the air which is spoiled by the animal part of it, looks like a rational system, and seems to be of a piece with the rest. Thus fire purifies water all the world over. It purifies it by distillation, when it raises it in vapours, and lets it fall in rain; and farther still by filtration, when, keeping it fluid, it suffers that rain to percolate the earth. We knew before, that putrid animal substances were converted into sweet vegetables, when mixed with the earth, and applied as manure; and now, it seems, that the same putrid substances, mixed with the air, have a similar effect. The strong thriving state of your mint in putrid air seems to shew that the air is mended by taking something from it, and not by adding to it.
In this last hypothesis, Franklin had it half right: the plant was taking and adding at the same time, producing oxygen and absorbing carbon dioxide. But his instincts about the fundamental concept were uncanny: the mint’s capacity for rejuvenating “putrid” air was part of a larger system that extended far beyond an isolated laundry sink in Leeds. Franklin saw the whole story almost immediately: this discovery of Priestley’s was a key to understanding the cycle of life on Earth.
Had Priestley made that leap before, or did he need Franklin to complete the thought? The truth is we don’t know, but there is a clear sense in the intonation of Franklin’s note that suggests he is offering a fresh analysis of his friend’s experiment, making new connections and not simply parroting something that Priestley already had told him in the Leeds laboratory. Franklin had his flaws, but obliviousness to his friends’ achievements was not among them, and everything in their correspondence suggests that Franklin had come to consider Priestley his peer, if not his superior, as a scientist. Perhaps Priestley had rushed through the cabinet of wonders, and hadn’t dwelt on the ramifications of his mint experiment as fully as one would expect. But given the prominence that it plays in the letters around this period, it seems entirely reasonable to assume that Priestley gave the mint experiment center stage during Franklin’s visit. Priestley himself saw fit to quote directly from Franklin’s musings in his initial published accounts of the experiment, which would seem to corroborate the notion that the broader, synthetic view of Priestley’s discovery originated with Franklin.
If Franklin was indeed the first to propose the wider ramifications of Priestley’s experiment, it would be a fitting continuation of their intellectual duet: Franklin created Priestley the scientist; Priestley popularized the legend of Franklin the daring electrician; and now Franklin was helping Priestley grasp the full significance of his discovery.
In his letter to Priestley, Franklin even managed to trace the implications of the restored air all the way up to an embryonic version of “green” politics:
I hope this will give some check to the rage of destroying trees that grow near houses, which has accompanied our late improvements in gardening, from an opinion of their being unwholesome. I am certain, from long observation, that there is nothing unhealthy in the air of woods; for we Americans have every where our country habitations in the midst of woods, and no people on earth enjoy better health, or are more prolific.
These surviving letters between Priestley and Franklin give us front row seats to one of history’s more elusive dramas: intellectual land-masses shifting underfoot thanks to a conversation between two people. We can see here the first stirrings of a genuinely new way of thinking about life on Earth and our role in that system. The air we breathe is not some unalienable fact of life on Earth, like gravity or magnetism, but is rather something that is specifically manufactured by plants. And that manufacture is itself part of a vast, interconnected system that links animals, plants, and invisible gases in a “rational” flow. And the choices we make as humans—destroying trees that grow near houses, for instance—can have a dangerous impact on that flow, if the core participants in the system aren’t properly appreciated and protected. In discovering how Mother Nature had invented our atmosphere, Franklin and Priestley were inventing something just as profound: the ecosystems view of the world.
In the book that he would eventually publish, Experiments and Observations on Different Kinds of Air, Priestley spelled out the global implications in clear language:
Once any quantity of air has been rendered noxious by animals breathing in it as long as they could, I do not know that any methods have been discovered of rendering it fit for breathing again. It is evident, however, that there must be some provision in nature for this purpose, as well as for that of rendering the air fit for sustaining flame; for without [it] the whole mass of the atmosphere would, in time, become unfit for the purpose of animal life; and yet there is no reason to think that it is, at present, at all less fit for respiration than it has ever been. I flatter myself, however, that I have hit upon one of the methods employed by nature for this great purpose. How many others there may be, I cannot tell.
By the fall, the Honest Whigs were abuzz with Priestley’s discovery. Negotiations ensued within
the Royal Society and by November the Society voted to award him the Copley Medal, the most prestigious scientific prize of its day, “on account of the many curious and useful Experiments contained in his observations on different kinds of Air.” In receiving the prize, Priestley was joining the ranks of his friends Canton and Franklin, who had three medals between them. Only five years after they had encouraged him to turn his experimental hobbies into a serious vocation, Priestley had reached the highest pinnacle of scientific achievement. Sir John Pringle, newly elected president of the Society, gave an unusually long address in presenting the medal, explaining why Priestley’s contributions were so valuable. He placed special emphasis on the mint in the glass, and the vast system of life it helped explain:
From these discoveries we are assured, that no vegetable grows in vain, but that from the oak of the forest to the grass of the field, every individual plant is serviceable to mankind; if not always distinguished by some private virtue, yet making a part of the whole which cleanses and purifies our atmosphere. In this the fragrant rose and deadly nightshade co-operate; nor is the herbage, nor the woods that flourish in the most remote and unpeopled regions unprofitable to us, nor we to them; considering how constantly the winds convey to them our vitiated air, for our relief, and for their nourishment.
The Invention of Air Page 7
