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  The Honest Whigs had evolved out of a core group of Canton’s friends; most of them had been educated at Scottish universities or the dissenting schools that had cultivated Priestley. They were all, to varying degrees, convinced of the need for a “rational Christianity,” though Franklin himself was said to abstain from most of the theological debates. Their politics were libertarian, and heated political debate often accompanied the “Welsh rabbits and apple-puffs.” Boswell dryly relates one typical exchange: “Much was said this night against the parliament. I said that, as it seemed to be agreed that all Members of Parliament became corrupted, it was better to chuse men already bad, and so save good men.” But the social and physical sciences often trumped politics at the coffeehouse: Price’s breakthrough works on probability and demography (which would later influence Malthus) were rehearsed over wine and punch with the Honest Whigs. With so many prominent electricians in attendance, the conversations would invariably turn to the single-fluid theory, or a new hypothesis about conduction. A note survives in the historical record, sent from Franklin to Canton, making plans to travel together to the club, and asking, somewhat mysteriously, for “a little of his preparation for the Electrical Cushion.”

  Priestley had spent his entire life in small towns. Literally and figuratively, he lived on the periphery of the intellectual networks that consolidated in the metropolis. Given that background and his growing interests, it is easy to understand why he would have sought out an audience at the London Coffee House. These were his heroes, after all. Despite their intimidating scholarship and cosmopolitan ways, the coffeehouse group was quick to embrace Priestley. He was personally likable, with a striking mix of intellectual acuity and gentleness. At five foot eight he was tall for his era. (European men in the eighteenth century were more than two inches shorter on average.) Portraits of him from the period show a welcoming face, with sparkling gray eyes framed by a full-bottom wig. He was not as ruggedly handsome as some later hagiographic portraits would have it. But new acquaintances took to him immediately. While it is unclear exactly how much practical experimentation Priestley had done by 1765, there is little doubt that he possessed a firm understanding of the fledgling science of electricity. Speaking the lingua franca of the electricians would alone have probably warranted a warm greeting.

  But the men had an even stronger reason to embrace the young minister: he had arrived on their doorstep offering to write a book in celebration of their research. With the hindsight of two centuries, Priestley’s central idea seems an obvious one. A hundred compelling ideas and applications had spun out of the study of electricity in the past few decades. Wouldn’t it be interesting for someone to string together the extended story of all those innovations in a single book? And do so in a way that made the tale intelligible to readers who lacked any specialized expertise?

  Books about “experimental” or “natural” philosophy were not new, of course. Newton’s Philosophiæ Naturalis Principia Mathematica had almost instantly revolutionized science when it appeared a century before. As the historian of science Thomas Kuhn writes, “No other work known to the history of science has simultaneously permitted so large an increase in both the scope and precision of research.” The Principia even sold relatively well—Newton and his publisher, Edmund Halley, actually turned a small profit from it, despite its daunting content. But Newton had played by a set of genre conventions that limited the scope of his readership. Like other experimental philosophers of the age, Newton generally adopted a synthetic approach, one that, in the words of the historian Simon Shaffer, “presented discovery as a set of logically inevitable moves, and the achievement of discovery as an heroic act.” The structure of the book was that of logical argument, the building of suppositions and proofs and counterarguments, all leading to Newton’s own brilliant conceptual leap. The book form provided a model, of sorts, for the wider system he claimed to have uncovered in the physical world. The text orbited around his own genius.

  Priestley had come to London with a vision of a different kind of book. He had seen more clearly than anyone of his era the possibility of science as a narrative experience. Newton had written a dazzling and inspired brief for his view of how the world worked. But it was ultimately his interpretation of the world that mattered, not the succession of earlier interpretations that had led the way to universal gravitation, despite his protestations about standing “on the shoulders of giants.” Priestley saw the value in tracing a chain of events, turning it into a narrative of scientific progress. Newton wanted to persuade his readers to believe in a formula. Priestley wanted to tell them a story.

  Newton also wrote in Latin, like almost all scholars of the period. Priestley’s idea was to write his history in English, to ensure the widest possible reception. That popular touch would have particularly appealed to Franklin, who had built his career and public persona by publishing practical and lively essays for the eighteenth-century equivalent of the modern mass audience, and who had never bothered to embellish his scientific experiments with scholarly affectation.

  When the evening at the London Coffee House finally came to an end, Joseph Priestley walked out into the churchyard with a new band of intellectual comrades and a promise of support for the intriguing book idea that he had outlined over the porter and wine. The electricians would open their private libraries and correspondence to him. (Simply tracking down the data had been the single biggest stumbling block to Priestley’s history, given that public libraries and bookstores—not to mention Google—hadn’t taken their modern form yet.) They promised to read the book in manuscript, and to suggest additions or corrections where appropriate.

  Franklin, Canton, and Price took one other crucial step in their support of young Priestley: they encouraged him to conduct his own experiments while writing his history. With his Rudiments of English Grammar and his pamphlets, Priestley was already well on his way to a successful writing career when he first stepped foot into the coffeehouse. But hearing his idols urging him to write about his own investigations opened up a whole new field of possibility for the young man. A few days after that first meeting, the electricians took Priestley along to a session of the Royal Society, the apogee of English natural philosophy, where Newton himself had been president sixty years before. How thrilling it must have been for Priestley to walk into that sacred space with such illustrious new friends at his side. It was a story straight out of a nineteenth-century Bildungsroman , something from Balzac or Stendhal: a young man comes to the metropolis with big dreams and makes a name for himself. Priestley had arrived in London as a dabbler in natural philosophy, tinkering in the provinces with his electrical machine and his air pump. By the time he left, he was a scientist.

  A FEW WEEKS LATER, after his return to Warrington, Priestley wrote to Canton: “The time I had the happiness to spend in your company appears in review like a pleasing dream. . . . I ardently wish a repetition of it.” He spent the next year in a feverish rush, poring through the books and letters and pamphlets that his London friends had lent him, reconstructing the history of batteries, charges, lightning rods, and electrical fluids. He launched himself into a rapid and turbulent river of experiments, developing a style of investigation that would shape the rest of his career—more exploratory than systematic, shuffling through countless variations of materials and equipment and test subjects. Priestley was never one for the grand hypothesis; he rarely designed experiments specifically to test a general theory. The closest thing to a general theory in his work would ultimately lead to his greatest intellectual mistake. His approach was far more inventive, even chaotic. While the experiments themselves were artfully designed, his higher-level plan for working through a sequence of experiments was less rigorous. Priestley’s mode was to get interested in a problem—conductivity, fire, air—and throw the kitchen sink at it. (Literally so, in that many of his experiments were conducted in a kitchen sink.) The method was closer to that of natural selection than abstract reasoning: new ideas
came out of new juxtapositions, randomness, diversity. Priestley would later credit the emerging technology of the period—air pumps and electrostatic machines—with helping him develop his distinctive approach: “By the help of these machines,” he wrote, “we are able to put an endless variety of things into an endless variety of situations, while nature herself is the agent that shows the result.”

  There is an almost comic quality to the incessant letters that Priestley sent his electrician friends in London over the spring and summer of 1766, postcards from the laboratory of a mad scientist:

  I have made an experiment which, I think proves that Glass when heated red hot is a conductor of electricity. I took a glass tube about four feet long, and by means of mercury on the inside and tinfoil on the outside, I charged about nine inches of it very strongly. . . .

  I took a cork, and stuck into the sides of it (pointing directly from the center) thirteen vanes each consisting of half a common card. Into the middle of the card I stuck a needle. . . .

  I have made a great number of experiments on animals, some of which I refer to a letter I lately wrote to Dr Watson. Since I wrote to him, I discharged 37 Square feet of coated glass through the head and tail of a CAT three or four years old. She was instantly seized with universal convulsions, then lay as dead a few seconds. . . . Thinking she would probably die a lingering death in consequence of the stroke, I gave her a second, about half an hour after the first. She was seized as before, with universal convulsions, and in the convulsive respiration which succeeded she expired. She was dissected with great care, but nothing particular was observed.

  Early in his 1766 investigations, Priestley thought he had stumbled across a crucial observation: “mephitic” air—now known as carbon dioxide—was a conductor of electricity. He wrote excitedly to Canton with the news, only to discover in the coming weeks that the results had been compromised by small molecules of condensed water in the glass that held the air. (Water was already a well-known conductor.) He wrote a sheepish letter to his electrician friends retracting his earlier claims, but the experiment ultimately led him to one of his most important contributions to the science of electricity: the addition of charcoal to the then short list of substances that were capable of conduction, alongside water and metal.

  By the end of 1766, a more fundamental pattern had emerged out of the chaos of Priestley’s electrical investigations. Building on a puzzling experiment that Franklin had devised using an “electrical cup,” Priestley surmised that the relationship between electrical charges followed the same inverse square law that Newton had observed in gravitational attraction. (In layman’s terms, the idea was that as two charges approached each other, the electrostatic force between them increased dramatically.) Two decades later, the French physicist Charles-Augustin de Coulomb would definitively prove that Priestley’s conjectures were accurate, which is why the equation now goes by the name of Coulomb’s Law, though Priestley was the first to propose it. It remains one of the bedrock principles of physics. Coulomb’s Law would ultimately be deployed to explain why atoms attach to each other in forming molecules—why the world is made up of stuff, rather than diffuse gases. It would also play a central role in the invention of semiconductors and integrated circuits, the core technology that created the electronic and digital revolutions of the late twentieth century.

  The constant flow of letters to London documenting his progress had impressed Priestley’s electrician friends so much that by June, Messrs. Price, Franklin, and Canton decided to nominate their ambitious friend from Warrington as a member of the Royal Society:

  Joseph Priestley of Warrington, Doctor of Laws, author of a chart of Biography, & several other valuable works, a gentleman of great merit & learning, & very well versed in Mathematical & philosophical enquiries, being desirous of offering himself as a candidate for election into this Society, is recommended by us on our personal knowledge, as highly deserving that honour; & we believe that he will, if elected, be a usefull & valuable member.

  As the year progressed, Priestley’s letters were increasingly accompanied by chapters (Priestley called them “numbers,” in the parlance of the day) from his growing manuscript. Somehow in the stretch of about fifteen months, Priestley had managed to write seven hundred pages on electricity and its pioneers, while exploring an “endless variety of situations” with his own experiments.

  When The History and Present State of Electricity, with Original Experiments was published in 1767, the book instantly landed Priestley in that upper echelon of electricians that had welcomed him so warmly at the London Coffee House. A forty-page review in the Monthly Review called it “excellent . . . judicious, and well-informed.” It sold well enough to support five English editions, and was subsequently translated into both French and German. Copies circulated around the globe: the Italian electrician Alessandro Volta read it; Franklin sent multiple copies back to the colonies. (By 1788, it was part of the standard natural philosophy curriculum at Yale.) The book would remain the principal text on electricity for nearly a hundred years.

  The History began with a stirring argument for why electricity was so interesting in the first place:

  Hitherto philosophy has been chiefly conversant about the more sensible properties of bodies; electricity, together with chemistry, and the doctrine of light and colours, seems to be giving us an inlet into their internal structure, on which all their sensible properties depend. By pursuing this new light, therefore, the bounds of natural science may possibly be extended, beyond what we can now form an idea of. New worlds may open to our view, and the glory of the great Sir Isaac Newton himself, and all his contemporaries, be eclipsed, by a new set of philosophers, in quite a new field of speculation. Could that great man revisit the earth, and view the experiments of the present race of electricians, he would be no less amazed than Roger Bacon, or Sir Francis, would have been at his.

  Priestley condensed all of his own discoveries into the closing two hundred pages of the book, leaving the first five hundred to an exhaustive narrative of scientific progress, relating each innovation in careful detail.

  He even included a few sections in the middle of the book that offered guidance for the aspiring scientists and showmen in his audience: “Practical maxims for the use of young electricians” and “A description of the most ENTERTAINING EXPERIMENTS performed by electricity.” Those sections may not sound all that scholarly to the modern ear, but they were crucial to the underlying objectives of the book. Priestley aimed to popularize not simply by helping ordinary readers understand the new science of electricity, but also by encouraging them to become scientists themselves. While he wanted to celebrate the electricians’ discoveries, he deliberately avoided establishing an aura of otherworldly genius around them:

  Were it possible to trace the succession of ideas in the mind of Sir Isaac Newton, during the time he made his greatest discoveries, I make no doubt but our amazement at the extent of his genius would a little subside. . . . [T]he interests of science have suffered by the excessive admiration and wonder with which several first rate philosophers are considered; and . . . an opinion of the greater equality of mankind in point of genius would be of real service in the present age.

  The History was a seminal achievement in Enlightenment science for two distinct reasons. First, there were Priestley’s original contributions to the science, the ideas that had won him admiration in London and landed him in the Royal Society. (In the style of Newton, Priestley had also included a number of unanswered questions and potential avenues for exploration that his successors would fruitfully investigate in the coming years.) But his History was as much a breakthrough for its form as for its content. He had invented a whole new way of imagining science; instead of a unified, Newtonian pronouncement, Priestley recast natural philosophy as a story of progress, a rising staircase of enlightenment, with each new innovation building on the last. In his prologue to the History, he contrasts his method favorably with the existing genres of civ
il history and natural history: the epic stories of kings and wars and famines, or the meticulous inventories of nature—insects, rock formations, flowers—that had become commonplace over the preceding century. There were great lessons and pleasures to be found in those other forms of writing, Priestley argued, but they lacked the definitive movement toward clarity and understanding that could be found in his own philosophical history:

  The History of Electricity is a field full of pleasing objects, according to all the genuine and universal principles of taste, deduced from a knowledge of human nature. Scenes like these, in which we see a gradual rise and progress in things, always exhibit a pleasing spectacle to the human mind. . . . This pleasure, likewise, bears a considerable resemblance to that of the sublime, which is one of the most exquisite of all those that affect the human imagination. For an object in which we see a perpetual progress and improvement is, as it were, continually rising in its magnitude; and moreover, when we see an actual increase, in a long period of time past, we cannot help forming an idea of an unlimited increase in futurity; which is a prospect really boundless, and sublime.

  In one sense, we can see Priestley inventing in these passages an entire genre of popular science: tales of discovery and exploration designed to captivate and engage the mind of a generalist reader. (Priestley would publish an even more accessible, and shorter, version of his History the following year, which he called A Familiar Introduction to the Study of Electricity.) But he is also building a specific way of connecting past and future that would animate his writing and thinking for the rest of his life, and that would profoundly shape the worldview of the American founders as well. Looking backward over the history of electricity enabled him both to appreciate how science had become an engine of progress and improvement and to project forward into the future, to imagine that ascending line, its trajectory continuing through the coming centuries. This is one of the origin points for a distinctly modern view of the world—call it progressive futurism. Countless other cultures had imagined themselves living at the apex of history and human understanding. Priestley took that assumption, grounded it in an empirical story of scientific discovery, and then added the crucial caveat: This is only the beginning!